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An Old Crystallization Technique as a Fast, Facile, and Adaptable Method for Obtaining Single Crystals of Unstable “Li2TCNQF4” and New Compounds of TCNQ or TCNQF4: Syntheses, Crystal Structures, and Magnetic Properties
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An Old Crystallization Technique as a Fast, Facile, and Adaptable Method for Obtaining Single Crystals of Unstable “Li2TCNQF4” and New Compounds of TCNQ or TCNQF4: Syntheses, Crystal Structures, and Magnetic Properties
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  • Slavomíra Šterbinská
    Slavomíra Šterbinská
    Faculty of Sciences, Institute of Chemistry, Department of Inorganic Chemistry, P. J. Šafárik University in Košice, Moyzesova 11, 041 54 Košice, Slovakia
    Instituto de Nanociencia y Materiales de Aragón (INMA) and Departamento de Química Inorgánica, CSIC-Universidad de Zaragoza, Zaragoza 50009, Spain
    More by Slavomíra Šterbinská
  • Mariia Holub*
    Mariia Holub
    Faculty of Sciences, Institute of Physics, P. J. Šafárik University in Košice, Park Angelinum 9, 041 54 Košice, Slovakia
    *Email: [email protected]
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  • Erik Čižmár
    Erik Čižmár
    Faculty of Sciences, Institute of Physics, P. J. Šafárik University in Košice, Park Angelinum 9, 041 54 Košice, Slovakia
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  • Juraj Černák
    Juraj Černák
    Faculty of Sciences, Institute of Chemistry, Department of Inorganic Chemistry, P. J. Šafárik University in Košice, Moyzesova 11, 041 54 Košice, Slovakia
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    Orcidhttps://orcid.org/0000-0002-8143-1368
  • Lawrence Rocco Falvello*
    Lawrence Rocco Falvello
    Instituto de Nanociencia y Materiales de Aragón (INMA) and Departamento de Química Inorgánica, CSIC-Universidad de Zaragoza, Zaragoza 50009, Spain
    *Email: [email protected]
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    Orcidhttps://orcid.org/0000-0002-0444-996X
  • Milagros Tomás
    Milagros Tomás
    Instituto de Síntesis Quimica y Catálisis Homogénea (ISQCH), Departamento de Química Inorgánica, Pedro Cerbuna 12, University of Zaragoza−CSIC, E-50009 Zaragoza, Spain
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Crystal Growth & Design

Cite this: Cryst. Growth Des. 2023, 23, 6, 4357–4369
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https://doi.org/10.1021/acs.cgd.3c00160
Published May 26, 2023

Copyright © 2023 The Authors. Published by American Chemical Society. This publication is licensed under

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Abstract

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Detailed structural information is essential for understanding the properties of TCNQ and TCNQF4 compounds (TCNQ = 7,7,8,8-tetracyanoquinodimethane; TCNQF4 = 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane). The ineludible requirement of obtaining crystals of a size and quality sufficient to yield a successful X-ray diffraction analysis has been challenging to satisfy because of the instability of many of these compounds in solution. Crystals of two new complexes of TCNQ, [trans-M(2ampy)2(TCNQ)2] [M = Ni (1), Zn (2); 2ampy = 2-aminomethylpyridine], as well as unstable [Li2(TCNQF4)(CH3CN)4]·CH3CN (3), can be prepared in minutes by a horizontal diffusion technique and can be harvested easily for X-ray structural studies. Compound 3, previously described as “Li2TCNQF4,” forms a one-dimensional (1D) ribbon. Compounds 1 and 2 can also be obtained as microcrystalline solids from methanolic solutions of MCl2/LiTCNQ/2ampy. Their variable-temperature magnetic studies confirmed a contribution of strongly antiferromagnetically coupled pairs of TCNQ•─ anion radicals at higher temperatures with exchange coupling J/kB = −1206 K and J/kB = −1369 K for 1 and 2, respectively, estimated using a spin dimer model. The presence of magnetically active anisotropic Ni(II) atoms with S = 1 in 1 was confirmed, and the magnetic behavior of 1, representing an infinite chain of alternating S = 1 sites and S = 1/2 dimers, was described by a spin-ring model suggesting ferromagnetic exchange coupling between Ni(II) sites and anion radicals.

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Synopsis

A horizontal diffusion technique facilitates the crystallization of three compounds with the TCNQ radical anion or diamagnetic TCNQF4. The magnetism of the heterospin Ni(II) complex and that of the isostructural Zn(II) analogue are compared. The same procedure permits the capture of the ephemeral lithium cation-containing polymer [Li2TCNQF4(CH3CN)4]n·nCH3CN.

Introduction

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Compounds based on TCNQ [TCNQ = 7,7,8,8-tetracyanoquinodimethane; IUPAC 2,2′-(cyclohexa-2,5-diene-1,4-diylidene)dipropanedinitrile] and its derivatives manifest an ample variety of physical properties, with their electronic and magnetic behavior having been the subject of innumerable studies. Key to understanding the properties of TCNQ derivatives, particularly in solids, is the determination of their structures, with accurate information on bonding and intermolecular interactions involving TCNQn– (n = 0, 1, 2, and intermediate between 0 and 2), which in turn requires the preparation of crystals adequate for structure determination, usually by in-house X-ray diffraction.
Some of the widely used procedures for the preparation of crystals such as solvent evaporation, solvent exchange, and vertical diffusion of different solutions require the compound to be in solution for hours to days, or even months because a slow evaporation or diffusion process favors the formation of fewer nuclei with more crystal growth. (1)
TCNQ (Scheme 1) as a diamagnetic solid can be reduced easily, yielding the TCNQ•– anion radical (AR), and by further reduction, a diamagnetic dianion TCNQ2– can be formed. (2) TCNQ in the form of the AR is interesting from a magnetic point of view since the presence of an unpaired electron makes it magnetically active (S = 1/2). The magnetic properties of numerous compounds based on the TCNQ AR have been studied in detail. (3−12) Besides magnetic properties, TCNQ-containing compounds were studied as promising semiconducting materials, (13,14) materials for quantum computing, (15) electric capacitors, (16) and gas sensors, (17) and as porous materials for gas storage and separation. (18)

Scheme 1

Scheme 1. Chemical Structures of TCNQ and 2ampy
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The TCNQ AR can act as a simple counter anion, or due to the presence of four cyanide groups, it can act as a ligand in coordination complexes; in the latter case, the TCNQ AR can be bound as a terminal ligand via an N atom from one of the cyanide groups, or it can act as a μ2-, μ3-, or μ4-bridging ligand. (2)
From a magnetic point of view, complexes containing magnetically active 3d or 4f central atoms and TCNQ AR are heterospin systems in which the overall magnetic properties are determined by the magnetic properties of both constituents and by their interaction. In addition, the magnetic properties will also be affected by the arrangement of the TCNQ ARs; in the case of the frequently occurring π-dimerization of TCNQ units, their strong antiferromagnetic (AFM) coupling leads to a singlet ground state of the π-dimerized unit. (19) Heterospin complexes with Ni(II) possess the combination of spins S = 1 and S = 1/2, which can be considered as analogues to Ni(II)/Cu(II) heterobimetallic complexes (S = 1, S = 1/2). (20)
The Cambridge Structural Database (21) records more than 30 complexes of Ni(II) with TCNQ. Among these complexes, monodentate coordination of TCNQ AR to the Ni(II) central atom is infrequent, having been observed to date only in the complexes [NiLR(TCNQ)2] (LR = 1,8-(C2H4OH)2-1,3,6,8,10,13-hexaazacyclotetradecane), (22) [Ni(cyclam)(TCNQ)2] (cyclam = 1,4,8,11-tetraazacyclotetradecane), (23) and [Ni(L2)(TCNQ)2](TCNQ)·CH3COCH3 (L2 = pentaazamacrocyclic ligand containing the 1-hexadecyl alkyl chain). (24) In all of these complexes, the TCNQ ARs occupy relative trans-positions in the octahedral coordination sphere of the central Ni(II) atom, while a cis-arrangement of TCNQ ARs was observed only in [Ni(trien)(TCNQ)2] (trien = 1,4,7,10-tetraazadecane), (23) as forced by the character of the blocking ligand trien.
It was observed some time ago (25) that recrystallization of these compounds frequently produces their degradation, and thus for structure analysis, it is important to obtain the compounds directly as single crystals to avoid the necessity of recrystallization. For instance, Li+ salts of TCNQ or TCNQF4 (TCNQF4 = 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane) can be used as reactants for the preparation of TCNQ/TCNQF4 compounds; however, there have been few reports of structures of Li+ with TCNQ or TCNQF4. Besides some organic salts in which Li+ is bonded to crown ethers, (26−28) there are just two structures; in one of them, TCNQ is bonded to Zn, (29) and in the other one, (30) each Li+ cation is coordinated by four TCNQF42– groups forming a two-dimensional (2D) metal–organic framework.
Within our broader interest in the crystal structures and magnetic properties of heterospin Ni(II) complexes with the TCNQ AR, (12,31) we have prepared a novel heterospin complex [Ni(2ampy)2(TCNQ)2] (1; 2ampy = 2-aminomethyl-pyridine) with two TCNQ ARs coordinated to the Ni(II) central atom. This compound has been prepared in two different ways, as microcrystals from a methanol solution of NiCl2·6H2O and 2ampy with LiTCNQ and as single crystals of sufficient quality for X-ray structure determination from the reaction in methanol of crystals of an insoluble 2ampy coordination compound, [Ni(2ampy)2(NO3)2], with soluble LiTCNQ, in a fast, facile procedure designed to avoid decomposition. The phase identity of the compounds obtained through the two different procedures was established using X-ray powder diffraction. We have further tested this procedure with the preparation and structure analysis of single crystals of [Li2(TCNQF4)(CH3CN)4]·CH3CN (3). The preparation of this compound in acetonitrile and its instability were described some ten years ago, (32) at which time it was reported that attempts to grow crystals suitable for diffraction analysis were unsuccessful.
We also report the crystal structure at three temperatures (100, 170, and 293 K) of the new Ni(II) compound (1), along with its magnetic properties. For the sake of comparison, especially with the aim of elucidating the contribution of the TCNQ AR to the magnetic properties, we have also synthesized and structurally and magnetically characterized the isostructural Zn(II) complex [Zn(2ampy)2(TCNQ)2] (2).

Experimental Section

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Materials

NiCl2·6H2O, ZnCl2, TCNQ, TCNQF4, LiI, methanol, 2ampy, and FomblinY oil (d: 1.92 g/mol at 25 °C, average M.W. 6500) were purchased from commercial sources and used as received. LiTCNQ, [Ni(2ampy)2(NO3)2], and [Zn(2ampy)2(NO3)2] were prepared according to published procedures. (25,33,34)

Synthesis and Crystallization of [trans-Ni(2ampy)2(TCNQ)2]

To a methanolic solution of NiCl2·6H2O (5 mL, 0.3 mmol; 0.079 g) were added consecutively with vigorous stirring, a methanolic solution (3 mL) of 2ampy (0.6 mmol; 0.07 mL) and a methanolic solution (10 mL) of LiTCNQ (0.72 mmol; 0.168 g). After 10 min, the resulting solid was separated by filtration and washed with methanol and diethyl ether. Yield: 71%.
CHN analysis (exp./calc. in %) for C36H24N12Ni (M = 683.38 g/mol): C, 62.50/63.27; H, 3.80/3.54; N, 24.31/24.60.
FT-IR (ATR, cm–1): 3315m, 3260m, 3028w, 2178vs, 2159m, 1606w, 1572vs, 1501vs, 1433m, 1337vs, 1286w, 1253w, 1216w, 1185vs, 1123s, 1103m, 1021s, 984s, 954w, 929w, 878w, 825vs, 755vs, 718vs, 643s, 543m, 511w, 482vs, 449w.
Single crystals for the X-ray study were prepared by a horizontal diffusion method as follows:
A few light purple crystals of [Ni(2ampy)2(NO3)2] of approximate dimensions 0.7 mm × 0.7 mm × 0.7 mm were added to 3 mL of MeOH in a Petri dish of 30 mm diameter. Then, 3.5 mg of solid LiTCNQ was added about 15 mm away from the purple crystals. A green/blue color developed instantaneously in the solution, and within 10 min, shiny dark crystals of compound 1 appeared on the surface of the purple crystals (Figure 1).

Figure 1

Figure 1. Dark crystals of 1 grown on the surface of blue/purple crystals of [Ni(2ampy)2(NO3)2].

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Synthesis and Crystallization of [trans-Zn(2ampy)2(TCNQ)2] (2)

The synthesis of 2 was performed by the same procedure as for 1, using ZnCl2 (0.3 mmol; 0.045 g) instead of nickel chloride hexahydrate. Yield: 68%. CHN analysis (exp./calc., in %) for C36H24N12Zn (M = 690.04 g/mol): C, 62.24/62.66; H, 3.55/3.51; N, 24.27/24.36. FT-IR (ATR, cm–1): 3306m, 3251m, 3052w, 3031w, 2642w, 2173w, 2158vs, 2123w, 1571vs, 1502vs, 1433m, 1382w, 1334vs, 1286w, 1254w, 1212w, 1180vs, 1121s, 1098m, 1016s, 982s, 955w, 930w, 880w, 825vs, 756vs, 718vs, 638s, 541s, 510w, 482vs, 438w.
Single crystals of 2 for the X-ray study were prepared by a similar procedure to that used for the single crystals of 1, by horizontal diffusion using the complex [Zn(2ampy)2(NO3)2] prepared according to Tandon. (34) Within an hour, dark violet prisms of 2 had formed in the space near the insoluble Zn-containing starting material. These were harvested from the solution and analyzed.

Synthesis and Crystallization of [Li2(TCNQF4)(CH3CN)4]·CH3CN (3)

Single crystals of appropriate size and quality for the X-ray study were prepared by the horizontal diffusion method. In a crystallization dish with a radius of 30 mm were placed 2 mL of acetonitrile, 45 mg (0.36 mmol) of solid LiI, and 2 mg (7.24 × 10–3 mmol) of solid TCNQF4, with LiI and TCNQF4 separated by approximately 15 mm. Within 10 min, transparent needle-like crystals of 3 were formed near the original location of TCNQF4. The acetonitrile solution was withdrawn, and FomblinY oil was added immediately in order to cover the crystals and prevent decomposition. The crystals are stable under the oil for a time span of 10–30 min (Figures 2 and S1).

Figure 2

Figure 2. Preparation of single crystals of 3. In this test, the crystals are visible under the microscope for 1 min after the addition of the reactants, and they begin to disappear about 7 min later. (a–f). Time-stamped progression of crystal growth and disappearance. (g, h) Further magnified views from panels (c, d), respectively.

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Instrumental Methods

C, H, and N elemental analyses for 1 and 2 were performed on a PerkinElmer 2400 Series II CHNS/O Analyzer. The infrared spectra for 1 and 2 in the range of 4000–300 cm–1 were recorded on a Jasco FT-IR 4600 spectrophotometer using the attenuated total reflectance (ATR) method. The X-ray powder diffraction patterns of bulk samples of 1 and 2 were measured on a RIGAKU D-Max/2500 diffractometer with a rotating anode and an RINT2000 vertical goniometer in the 2θ range 3.0–40° using Cu Kα radiation (λ = 1.5406 Å) and a 2θ step size of 0.02°; the model powder diffraction pattern was calculated using the program MERCURY. (35)

X-ray Structural Analysis of [M(2ampy)2(TCNQ)2] (M = Ni, Zn)

Single-crystal X-ray data for [Ni(2ampy)2(TCNQ)2] (1) were collected using the same crystal at 100, 173, and 296 K, and data for [Zn(2ampy)2(TCNQ)2] (2) were collected at 100 K on an Oxford Diffraction Xcalibur diffractometer equipped with a Sapphire3 CCD detector and a graphite monochromator utilizing MoKα radiation (λ = 0.71073 Å). The CrysAlis software package (36) was used for data collection and reduction. Absorption correction was done using ABSPACK (multiscan method). (37) The structures were solved using SHELXT (38) and refined against F2 using the full-matrix least-squares method with the program SHELXL-2018/3 (39) incorporated in the WinGX program package. (40) Anisotropic displacement parameters were refined for all non-hydrogen atoms. The hydrogen atoms bonded to carbon atoms were included at idealized positions and refined as riders with isotropic displacement parameters assigned as 1.2 times the Ueq values of their corresponding bonding partners.
The crystal that was used for all three analyses of the Ni(II) complex was found to be an aggregate of two components related by a rotation calculated to be 2.88° about the real-space vector (0.8498, –0.4396, 0.2909) at T = 100 K, with a similar relationship holding at the other two temperatures. For the data at 100 K, the refined volume fraction for the second component was 0.369(2). In addition, because of the nature of the twinning, with the accompanying difficulty of separating the intensities of partially overlapped low-angle reflections, and in view of the presence of outliers, after examination of the data and results, it was decided to exclude reflections outside the resolution range of 0.82–5.00 Å (8.15–51.36° 2θ, ShelxL instruction “SHEL 5 0.82”). The low-angle limit excluded 12 reflections in addition to the 11 reflections that were rejected on the grounds of having been, in our judgment, affected by the beamstop. The high-angle cutoff was chosen on the basis of the inspection of quality indicators, including the CC(1/2) statistic. (41) It was hoped that the refinement of 1 under these conditions would give a result less affected by bias caused by the twinning. Other refinement conditions were also tested, including refinement with no exclusion based on resolution alone; the latter gives R1 = 0.0697 and wR2 = 0.1779, so any benefit from fine-tuning the data set in this manner is not reflected in the residuals. For the refinement of 1 at T = 296 K, the same resolution limits were used, while for T = 173 K, the high-angle limit was not used.
Structure graphics were drawn using the program Diamond. (42) The crystal data and final parameters of the structure refinements are summarized in Table 1, while selected geometric parameters are given in Table 2. Possible hydrogen bonds are gathered in Table 3.
Table 1. Crystal Data and Structure Refinement for [M(2ampy)2(TCNQ)2] [M = Ni (1), Zn (2)] and [Li2(TCNQF4)(CH3CN)4]·CH3CN (3)a
 1–1001–1731–29623
CSD number22060252206024220602622060272239060
empirical formulaC36 H24 N12 NiC36 H24 N12 NiC36 H24 N12 NiC36 H24 N12 ZnC22 H15 N9 F4 Li2
molecular weight683.38683.38683.38690.04495.31
crystal systemtriclinictriclinictriclinictriclinicmonoclinic
space groupP1̅P1̅P1̅P1̅P21/n
unit-cell dimensions     
a (Å)9.0246(8)9.0239(9)9.0243(7)9.0137(3)14.8097(6)
b (Å)9.6591(7)9.6857(9)9.7506(7)9.6468(2)8.4555(3)
c (Å)10.0936(8)10.1231(11)10.2192(9)10.1775(3)21.9080(9)
α (°)89.456(6)89.085(8)88.426(7)90.858(2)90
β (°)70.683(7)70.632(9)70.606(8)70.728(3)109.735(4)
γ (°)71.792(7)71.652(9)71.382(7)72.056(3)90
V (Å3)784.41(12)788.41(15)800.68(12)788.01(4)2582.23(18)
Z11114
Dcalc (Mg/m3)1.4771.4391.4171.4541.274
T (K)100(2)173(2)296(2)100(2)103(2)
θ range (°)4.30–25.674.16–28.604.13–25.682.68–30.911.46–25.99
reflections collected566511414105551964024832
independent reflections5665114141055543545153
goodness-of-fit on F20.9490.8241.0351.0621.052
R indices (I > 2σI)R1 = 0.0685R1 = 0.0764R1 = 0.0696R1 = 0.0368R1 = 0.0618
wR2 = 0.1689wR2 = 0.1727wR2 = 0.1320wR2 = 0.0811wR2 = 0.1541
R indices (all data)R1 = 0.1022R1 = 0.1640R1 = 0.1490R1 = 0.0469R1 = 0.0777
wR2 = 0.1815wR2 = 0.1937wR2 = 0.1439wR2 = 0.0868wR2 = 0.1663
diff. peak/hole (e/Å3)1.619; −0.5031.287; −0.6071.016; −0.6180.375; −0.6040.790; −0.354
a

MoKα radiation [λ(α̅) = 0.71073 Å] was used for all measurements.

Table 2. Selected Geometric Parameters for Complexes 1–100 and 2 [Å (°)]
 M = Ni, 1M = Zn, 2 M = Ni, 1M = Zn, 2
M-N12.102(5)2.1447(13)C15-N41.151(6)1.153(2)
M-N22.076(5)2.0797(14)C17-N51.150(6)1.153(2)
M-N32.128(4)2.2892(14)C18-N61.152(6)1.154(2)
C14-N31.137(5)1.152(2)N1-M-N280.6(2)80.09(5)
Table 3. Possible Hydrogen Bonds in 1 (M = Ni) and 2 (M = Zn) at 100 K [Å (°)]a
D–H···AD–H (1/2)H···A (1/2)D···A (1/2)D–H···A (1/2)
N2-H2A···N6ii0.91/0.862.16/2.182.962(6)/2.981(2)147/155
N2-H2B···N4iii0.91/0.862.36/2.353.198(6)/3.166(2)154/157
a

Symmetry codes: (ii) x, y – 1, z + 1; (iii) 1 – x, 2 – y, 1 – z.

X-ray Structural Analysis of [Li2(TCNQF4)(CH3CN)4]·CH3CN (3)

A freshly harvested crystal of [Li2(TCNQF4)(CH3CN)4]·CH3CN (3), covered with a thin layer of perfluorinated oil (FomblinY) and mounted on a MiTeGen micromount, was placed in the nitrogen cold stream of the diffractometer with as little exposure to the ambient atmosphere as was practically possible during the transfer. The cold-stream temperature was maintained at 103 K for the entirety of the diffraction measurements, and the sample showed no signs of decomposition.
Indexing by routine procedures yielded a C-centered orthorhombic cell with preliminary dimensions a = 14.8027(6), b = 41.2186(13), c = 8.4409(2) Å, and V = 5150.2(3) Å3. Data reduction yielded a full data set with Rint = 0.0517 for the Laue group mmm. Rint is _diffrn_reflns_av-R-equivalents as defined in the Core CIF Dictionary (https://www.iucr.org/resources/cif/dictionaries/cif_core viewed on 10 April, 2023). Systematic absences corresponded to the orthorhombic space group C2221, which has a unique set of absences within the orthorhombic system.
We were unable to derive a recognizable structure solution using orthorhombic symmetry [and not limiting the space group choice to C2221]; the analysis thereupon proceeded under the hypothesis that the sample was a twin by pseudo-merohedry. (43,44) In this stage of the analysis, the problem was treated as a case of monoclinic symmetry with pseudo-orthorhombic metrics in the twin. The structure solution and refinement proceeded routinely from that point. For the structure solution, the cell was reduced from the initial C-centered orthorhombic (oC) setting to primitive monoclinic (mP), with the cell parameters given in Table 1. The transformation from oC to the mP setting, by rows and based on unit-cell axes, is (−1 0 0/0 0 1/0.5 0.5 0), and the twin law for the monoclinic setting, also by rows, is (−1 0 0 / 0 –1 0 / 1 0 1). Both of these matrices can be derived using the program Platon. (45) On this basis, the original pseudo-orthorhombic c-axis of 8.4555(3) Å (final refined value) corresponds to the monoclinic symmetry direction. The first space group choice for the monoclinic setting was P21/n, based upon “systematically weak” groups of reflections. The twin law for this system obscures systematic absences for putative n- or c-glide planes since it produces an overlap of absent reflections from one twin individual with nonabsences from the other.
The structure was solved using ShelxD (46) with space group P21/n and with the twin information incorporated into the peak list optimization stage of the calculations. The program revealed all 37 non-H atomic sites of the asymmetric unit, and where needed, those sites were assigned their correct element types manually. For the sake of curiosity, we also used ShelxT, which assigned the correct space group, P21/n, and also revealed all 37 unique atomic sites with their correct elements assigned.
The solution from ShelxD was used to commence the refinement. The first test consisted of isotropic refinement of the 37 non-H atoms, with no twin law applied. This gave R1 = 0.2345 and wR2 = 0.6071, with a significant number of systematic absence violations (356 out of 1132) and with all of the 50 worst-fit reflections having Fo2 significantly larger than Fc2. This preliminary refinement was repeated with the twin law included, giving R1 = 0.1166 and wR2 = 0.3599 and with 18 of the 50 worst-fit reflections having Fo2 < Fc2. The population parameter for the second individual refined to a value near one-half. These and other considerations indicate a strong possibility of twinning, as has been expounded by Herbst-Irmer and Sheldrick. (47)
In the final refinement, the non-hydrogen atoms were refined anisotropically, and no restraints or constraints were used for them. H atoms, all of which are in the methyl groups of five acetonitrile fragments, were placed with an idealized geometry about their carrier carbon atoms but with the initial torsion angle about the neighboring C–C bond established by a local difference Fourier calculation. During refinement, the H atoms were treated as riders and also allowed to rotate about the C–C bond but not to tilt.
The refinement converged with the residuals given in Table 1. The final refined value of the population parameter for the second individual was 0.480(2). Selected geometric parameters and possible hydrogen bonds are given in Tables 4 and 5.
Table 4. Selected Geometric Parameters for 3 [Å (°)]
C5-N11.171(5)Li1-N11.987(7)N1-Li1-N4108.3(2)
C6-N21.142(5)Li1-N42.001(8)C2-C1-C3113.7(2)
C11-N31.170(5)Li1-N52.046(6)C8-C7-C9113.6(2)
C12-N41.150(5)Li1-N62.037(6)  
Table 5. Possible Hydrogen Bonds in 3 [Å (°)]a
D–H···AD–HH···AD···AD–H···A
C16-H16A···F1v0.982.393.245(4)145
C20-H20C···N3vi0.982.683.602(5)157
C22-H22A···F3vii0.982.533.287(5)133
a

Symmetry codes: (v) x, y + 1, z; (vi) 3/2 – x, −1/2 + y, 1/2 – z; (vii) 1 – x, 1 – y, −z.

Magnetic Studies

Magnetic properties were investigated using a Quantum Design MPMS-XL5. Measurements of the temperature dependence of the magnetic moment were performed in a magnetic field of 1 kOe in zero-field-cooled (ZFC) and field-cooled (FC) regimes at temperatures from 1.8 to 300 K. The field dependence of magnetization was measured in magnetic fields up to 5 kOe at temperatures of 1.8 and 4.5 K. The diamagnetic contribution of the gelatin capsule, the sample itself (estimated using Pascal’s constants), and the typical value of the temperature-independent paramagnetic susceptibility of Ni2+ ions (100 × 10–6 emu/mol) for complex 1 were subtracted from the raw data.

Results and Discussion

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Syntheses, Crystal Formation, and Identification of trans-[M(2ampy)2(TCNQ)2] [M = Ni (1), Zn (2)]

The reaction of LiTCNQ with nickel chloride hexahydrate in the presence of 2ampy in a methanolic solution yielded the complex [Ni(2ampy)2(TCNQ)2] (1) in a microcrystalline form. With the aim of better understanding the magnetic contribution from the TCNQ ARs, we also synthesized the analogous Zn(II) complex (2) (S = 0). None of our attempts to recrystallize the microcrystalline solids in order to obtain samples of acceptable size and quality for X-ray diffraction was successful, including using different solvents or diffusion of different combinations of solvents. Moreover, not even the compounds themselves were recovered from these attempts, an indication that once the compounds are in solution, they decompose. This apparently is not unusual in this kind of chemistry, as similar behavior was observed long ago. (25)
A different strategy was designed with the aim of producing the compounds directly in the form of crystals large enough and of sufficient quality for single-crystal X-ray diffraction analysis, thus avoiding recrystallization. However, one of the possible strategies, using a fast reaction, can produce microcrystals unsuitable for single-crystal X-ray diffraction; that is the case for the preparation using MCl2, 2ampy, and LiTCNQ in MeOH, as described above.
We found that a sufficiently fast reaction that produces single crystals of 1 and 2 that yield successful X-ray diffraction analysis occurs in methanol at room temperature when LiTCNQ is added in close proximity to insoluble crystals of [M(2ampy)2(NO3)2] (M = Ni, Zn). (33,34) The process can be followed under a microscope. Figure 1 shows crystals of 1 grown in about 10 min on the surface of insoluble purple crystals of [Ni(2ampy)2(NO3)2].
This is an easy, simple, and, importantly, fast procedure for obtaining crystals, which is often the most challenging step in preparing and characterizing a new product. As it involves a time frame of 10 min as opposed to several hours or even days, we were able to forestall decomposition. This process is not adequate, however, for producing a bulk sample because the relative insolubility of the Ni-containing starting material slows the production of larger quantities of product, once again permitting decomposition or the formation of a mixture of products. Thus, the two procedures, one for synthesizing the bulk product and the other for obtaining single crystals for structure analysis, must both be used. The former is a fast solution-based reaction with soluble reagents, and the latter has soluble LiTCNQ placed in close proximity to crystals of an insoluble precursor. The insolubility of one of the precursors seems to impede the formation of a large number of crystallization nuclei and therefore favors the growth of fewer crystals, as can be seen in Figure 1. To summarize, the method consists of using the reactants in close proximity, with one of them quite insoluble. Obviously, the new compound also has to be insoluble in the solvent used.
The identity of the bulk solids was confirmed by comparing their X-ray powder diffractograms to the calculated patterns based on the single-crystal X-ray structure analyses (see the Supporting Information, Figures S2 and S3). The purity and chemical identity of 1 and 2 were also corroborated by C, N, and H elemental analyses. We note that Ballester et al. (23) reported the synthesis and characterization of analogous Ni(II) complexes with TCNQ and tetra N-donor ligands (cyclam = 1,4,8,11-tetraazacyclotetradecane, trien = 1,4,7,10-tetraazadecane).
The infrared spectra of compounds 1 and 2 (Figures S4 and S5) are dominated by absorption bands located around 2200 cm–1 assigned to ν(C≡N) stretching vibrations from TCNQ units. In the case of 1, two absorption bands at 2178 and 2159 cm–1 were observed, while in the case of compound 2, one additional weaker band was located (2173, 2158, and 2123 cm–1). Similar values (2186, 2182, and 2161 cm–1) were observed in the IR spectrum of [Ni(cyclam)(TCNQ)2] with monodentate N-coordinated TCNQ ARs. (23) Also, in the spectra of both 1 and 2, other strong absorption bands originating from vibrations of ν(C═C), δ(CH), ω(C(CN)2), and ν(C–C) were observed at around 1570, 825, 480, and 1330 cm–1; their tentative assignment was done with reference to the literature. (19,48)

Synthesis and Crystal Formation of [Li2TCNQF4(CH3CN)4]·CH3CN (3)

In order to test the applicability of the simple horizontal diffusion procedure for obtaining crystals of some unstable compounds for which speed can be key, we tested the method with the Li/TCNQF4 system. The synthesis of pure bulk “Li2TCNQF4” in acetonitrile at 50–60 °C has been reported; (32) however, attempts to obtain crystals were unsuccessful.
Crystals of [Li2TCNQF4(CH3CN)4]·CH3CN (3) can be prepared by the addition of LiI and TCNQF4 to acetonitrile under normal laboratory conditions. Figure 2 shows selected photos of the process as viewed under a microscope. The full process is recorded in the Supporting Information (Figure S1). Initially (Figure 2a), the yellow solid TCNQF4 is added to acetonitrile in a Petri dish (30 mm diameter); (Figure 2b), after LiI (white cream color, left superior part of the photo of the Petri dish) is added, very quickly (less than 30 s), a dark color appears in the TCNQF4 zone. This color is typical of the TCNQF4•– radical, which is the first reduction step. In addition, a part of the methanol solution is now green (yellow + dark blue). In less than 1 min, some needles of compound 3 can be observed in the lower right part of the photo in Figure 2c,g. These needles continue appearing, now over the whole Petri dish, for some minutes (Figure 2d,h) and then disappear in approximately 10 min (Figure 2e). Finally, most of the dark blue solid disappears (Figure 2f).
A time span of around 10 min transpires from when the first crystals appear to the disappearance of the last one. We estimate that the “lifespan” of a given crystal, from when it visually appears under the microscope until it disappears, can be from 3 to 6 min. This agrees with the already described instability of “Li2TCNQF4” in acetonitrile. However, the elimination of the acetonitrile solution (removal by a pipette is sufficient) and the immediate addition of FomblinY oil serves to preserve the crystals long enough to select a single crystal and transfer it to the cold stream of a diffractometer for structure analysis. This simple procedure enables the identification even of species that disappear in a matter of minutes, as in the present case.
Horizontal diffusion techniques are not new, (49,50) although they do not seem subject to as much use as other methods, except for high-temperature applications. (51) For the present study, the application of a simple variant of this family of techniques has proved capable of producing direct crystallization with the limited nucleation needed to permit sufficient crystal growth. The method is also easily adaptable in terms of controlling diffusion speed, and importantly, in its simplest form, enabling facile crystal harvesting and mounting.

Crystal Structures of [M(2ampy)2(TCNQ)2] [M = Ni(1), Zn(2)]

As the two crystal structures, [Ni(2ampy)2(TCNQ)2] (1) (Figure 3 for T = 100 K and Supporting Figures S6 and S7 for T = 173 and 296 K, respectively) and [Zn(2ampy)2(TCNQ)2] (2) (Figure S8), are isostructural, we will describe the crystal structure of 1 and the relevant information for 2 will be given in parentheses. The structure of 1 is formed by molecules of the complex [Ni(2ampy)2(TCNQ)2], which reside on crystallographic centers of symmetry. The central Ni(II) [Zn(II)] atom is coordinated by a distorted octahedron consisting of two chelating 2ampy ligands in the equatorial plane and monodentate TCNQ•– ARs in the axial positions. Each axial ligand is coordinated via one N atom yielding an {N6} donor set. As of this writing, as has been mentioned the CSD (21) holds three analogous Ni(II) complexes with terminal TCNQ•– ligands trans- to each other, namely, [Ni(bhe[14]aneN6)(TCNQ)2], (22) [Ni(cyclam)(TCNQ)2], (23) and [Ni((hd)-[14]aneN5)(TCNQ)2]·TCNQ·(CH3)2CO. (24) In contrast, we do not find any entries in the CSD for an analogous Zn(II) complex with an {N6} donor set and two monodentate TCNQ ARs. The nearest similarity to 2 is displayed by the dinuclear complex [Zn2(bpy)4(TCNQ)2(TCNQ-TCNQ)] (CUMMOO), in which each Zn(II) atom is coordinated by two chelating 2,2′-bipyridine (bpy) ligands and one terminal TCNQ AR with a σ-dimerized (TCNQ)22– dianion bridging the two metals. (52) We note that in this compound, the nitrogen donor atoms from TCNQ are in cis-positions. The Ni–N bond distances in 1 fall in the range 2.076(5)–2.128(4) Å [2.0797(14)–2.2892(14) Å for Zn] (Table 2). These bond distances, as well as other geometric parameters, are in line with those reported for the above-mentioned [Ni(cyclam)(TCNQ)2] complex at 295 K (23) and [Zn(TCNQ)(nicotinamide)2]·DMF at 100 K, (53) respectively.

Figure 3

Figure 3. Molecular structure of 1 at 100 K showing the atom numbering scheme. The thermal ellipsoids are drawn at the 50% probability level. Symmetry code: (i) 1 – x, 1 – y, 1 – z.

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It was reported that KTCNQ exists in two polymorphic phases with a first-order phase transition at 122 °C; the low- and high-temperature phases are both monoclinic, but they differ in cell parameters. (54−56) We explored the possibility of a temperature-dependent phase transition in 1, which, if present, could be expected to have interesting consequences for the magnetic properties. To this end, we analyzed the structure of 1 at T = 100, 173, and 296 K; no qualitative structural change was observed. Selected geometric parameters for 1 at T = 173 and 296 K are given in Table S1. We also note that the twinned nature of the crystal did not change with temperature. Selected crystallographic data for these measurements are listed in Table 1, where we observe that the changes are those that are expected with varying temperatures, an example being the unit-cell volume.
The extended structures of 1 and 2 are consolidated by N–H···N hydrogen bonds (Figures 4 and S9 and Table 3); these mediate the formation of 2D supramolecular aggregates dominated by hydrogen-bonded ring systems with a graph-set symbol R42 (26) (Figure 4, R1).

Figure 4

Figure 4. Hydrogen bonding system in 1. H-bonds are represented as yellow dashed lines. For the sake of clarity, the chelate rings and hydrogen atoms not participating in hydrogen bonds are omitted. Symmetry codes: (ii) x, y – 1, z + 1; (iii) 1 – x, 2 – y, 1 – z; (v) 1 – x, 1 – y, 2 – z.

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The π-dimerization and consequent spin pairing of the quinoid rings of TCNQ ARs have implications for the magnetic properties of 1 and 2. The neighboring quinoide rings are coplanar and eclipsed, and the interplanar distances are 3.1236(2) Å for 1 and 3.1266(2) Å for 2. These short distances reflect strong π-dimerization. In the analogous complex [Ni(cyclam)(TCNQ)2], (23) a similar distance between planes was observed [3.18(1) Å]. Even shorter distances were found in the compounds [Ni(trans-dieneN4)](TCNQ)2 (trans-dieneN4 = 5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradeca-4,14-diene) [3.16(1) Å] (57) and [Ni(dieneN4)](TCNQ)3 [3.13(1) Å]. (58)

Crystal Structure of [Li2TCNQF4(CH3CN)4]·CH3CN (3)

The crystal structure of compound 3 is formed by ribbons of “Li2TCNQF4” (Figure 5) in which the Li cations form the periphery of the chain and TCNQF42– are the internal part in such a way that the Li cations act as bridges between two TCNQF42– and each TCNQF42– fragment is bonded to four Li cations. The ribbon is thus formed by Li+ and TCNQF42– in a 2:1 ratio. The Li cations are also contacted by two terminal CH3CN groups, which complete a tetrahedral environment about Li+ (Figure 5). There is also one interstitial acetonitrile molecule per TCNQF42–. The main distances and angles are collected in Table 4, and the possible hydrogen bonds are in Table 5.

Figure 5

Figure 5. Ribbons of “Li2TCNQF4” in the crystal structure of [Li2TCNQF4(CH3CN)4]·CH3CN, (3). Symmetry codes: (ii) −x, −y, −z; (iv) 1 – x, −y, −z.

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Successive C6F4 fragments along the ribbon are not coplanar, forming a dihedral angle of 35.02(11)°, as can be seen in Figure 6. The chains run parallel to the crystallographic a-axis with the interstitial acetonitrile molecules between the chains (Figure 7).

Figure 6

Figure 6. Inclination of the C6F4 rings in 3.

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Figure 7

Figure 7. View of the chains in 3.

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As was mentioned before, there are very few structures with Li and TCNQ or TCNQF4, and of those, only in the following cases is TCNQ or TCNQF4 bonded to the Li cation. TCNQ•– is bonded to Li[15]crown-5 in the Li+([15]crown-5)(TCNQ)2 (26) and (15-crown-5)LiTCNQ crystals, (27) forming discrete aggregations. On the other hand, Li+ and TCNQF42– form a 2D aggregate in [Cp2Co]Li(TCNQF4), (30) in which Li+ is bonded to 4 TCNQF42– groups. Compound 3, to our knowledge, is the first structurally characterized 1D ribbon formed by Li+ and TCNQ-/2- or TCNQF4-/2-. A related chain can be found in some Cu(I)2TCNQ or Cu(I)2TCNQF4 compounds. (59,60) In fact, “Cu(I)2TCNQF4” with acetonitrile has been described; (60) however, its X-ray single-crystal structure could not be determined, and its structure was related to that of Cu(I)2TCNQF4(EtCN)2, which has CH3CH2CN instead CH3CN. The “Cu(I)2TCNQF4” chain in the propionitrile compound is similar to the one in compound 3, although with two interesting differences: (a) the Cu(I) centers have a coordination index of just 3, and (b) the TCNQF4 groups in the ribbons are coplanar.

Magnetic Properties

The magnetic properties of 1 and 2 were studied in the temperature range of 1.8–300 K. No difference between ZFC and FC responses was observed, suggesting no magnetic ordering in both complexes. The value of χT = 0.04 emuK/mol of 2 at 300 K (Figure 8, inset), corresponding to the effective magnetic moment μeff = 0.57μB (μB is the Bohr magneton), is evidence of the greatly reduced magnetic moment originating from two TCNQ ARs in a molecule of 2, each carrying spin 1/2. This reduction is expected due to the presence of strong π-dimerization between TCNQ ARs from neighboring molecules, as shown in Figure S9. The appropriate magnetic model to describe magnetic properties represents an AFM spin dimer with a strong exchange coupling J, defined by a Hamiltonian
H^dimer=−JS^1S^2
(1)
which allows only a small population of magnetic spin-triplet states to be accessible at ambient temperatures. A small, almost constant value of χT below 200 K can be related to the presence of a minor concentration of nondimerized paramagnetic TCNQ ARs. As a result, the temperature dependence of the susceptibility was described by a model consisting of a paramagnetic contribution described by the Curie law and the Bleaney–Bowers formula (61) for AFM spin dimers.
χ=2(1−c)χCurie+cχdimer
(2)
where parameter c represents the reduced concentration of dimers. The best fit to the experimental data was obtained for exchange coupling J/kB = −1369 K and c = 0.995 (only 0.5% of TCNQ AR pairs are noninteracting, contributing to the paramagnetic susceptibility), with the g-factor fixed to gTCNQ = 2 in all presented calculations. The exchange coupling strength falls between the ones suggested in similar complexes with central Ni(II) ions by Ballester et al., (23,57) following the trend in distances between TCNQ ARs from neighboring molecules forming π-dimers. The low-temperature magnetization of 2 shown in Figure 9 can be described by the Brillouin function for the paramagnetic contribution of 0.7% of noninteracting (broken) TCNQ AR pairs (c = 0.993).

Figure 8

Figure 8. Temperature dependence of susceptibility and χT (inset) of 2 (open symbols) measured in the applied field of 1 kOe, including the model χ = 2(1 – c)χCurie + cχdimer proposed in the text.

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Figure 9

Figure 9. Field dependence of the magnetization of 2 at 1.8 and 4.5 K (open symbols), including the fit of the Brillouin function representing the paramagnetic contribution of nondimerized paramagnetic TCNQ species.

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Regarding complex 1, one has to include the contribution of the Ni(II) ion (3d8, spin S = 1) present in the molecular unit, yielding χT = 1.262 emuK/mol at 300 K (Figure 10, inset), corresponding to the effective magnetic moment μeff = 3.178 μB. A small increase in χT above 200 K is expected due to the strong π-dimerization between TCNQ ARs from neighboring molecules forming AFM spin dimers. At low temperatures, a drop in χT can be the consequence of zero-field splitting of Ni(II) ions and/or the effective AFM exchange interaction between them. Since at low temperatures, the magnetic moment of Ni(II) ions dominates, a negligible contribution of paramagnetic TCNQ ARs (expected to be similar to 2) will be omitted in the further analysis. In the first step, we neglected a possible interaction between Ni(II) ions and TCNQ ARs within a molecule, similar to refs (24,57) but an effective coupling could be transmitted between Ni(II) in neighboring molecules through coordinated TCNQ ARs (π-dimerized TCNQ ARs) and total susceptibility was defined by a simplified model.
χ=χNi+χdimer+χ0
(3)
A possible correction to the estimation of the diamagnetic contribution using Pascal’s constants and temperature-independent paramagnetism is included using χ0. The contribution of Ni(II) ions, χNi, is represented by the formula
χNi=χZFS/(1−zJ′NAg2μB2χZFS)
(4)
where NA is the Avogadro constant, g is the average g-factor, J′ is an exchange interaction with neighboring z ions introduced in the frame of mean-field theory (62) (in our case, z = 2 is assumed), and χZFS is the susceptibility of isolated Ni(II) ions described by the effective spin Hamiltonian, taking into account the zero-field splitting (ZFS) with parameters D and E.
H^ZFS=D[S^z2−S(S+1)/3]+E[S^x2−S^y2]
(5)
Since the correct determination of the sign of a small D parameter from the analysis of the magnetic response of a polycrystalline sample may be ambiguous, we have used a simple approach to predict its sign and magnitude from the deformation of the coordination octahedron as proposed in ref (63). Using the structural data obtained at 296, 173, and 100 K, one can find that the sign of the D parameter changes between 296 and 173 K from positive to negative. Moderate values of D/kB = 4.9 K at 296 K, D/kB = −5.4 K at 173 K, and D/kB = −4.3 K at 100 K were obtained, and a strong rhombicity E/D is expected. Since the susceptibility is affected by such values of ZFS parameters only at low temperatures, we assumed a single negative D parameter as the starting value for our analysis.

Figure 10

Figure 10. Temperature dependence of the susceptibility and χT (inset) of 1 (open symbols) measured in the applied field of 1 kOe, including the fit of the simplified model χ = χNi + χdimer + χ0 (solid line) and a spin-ring model (dashed line) proposed in the text.

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The calculation of temperature dependence of the susceptibility χZFS and corresponding field dependence of magnetization MZFS based on eq 5 was performed using the EasySpin (64) toolbox in the MATLAB environment. The average magnetic response was calculated from the distribution of the magnetic-field vector over the orientational grid to account for the polycrystalline characteristics of the sample. The χT was then calculated using eq 3. The contribution of AFM spin dimers in low-temperature magnetization is negligible and was omitted. The calculation of MZFS was performed, also neglecting effective interactions between Ni(II) ions since the inclusion of both the rhombic E parameter and effective interaction in the framework of the mean-field theory for the magnetization of a polycrystalline sample is not trivial. The simultaneous fit of χT and magnetization shown in Figures 10 and 11 by solid lines yielded D/kB = −8.5 K, E/D = 0.28, average g-factor gNi = 2.11, J′/kB = −0.6 K, J/kB = −1206 K, and χ0 = 3.3 × 10–4 emu/mol. A lower value of exchange coupling J in 1 in comparison with 2 might suggest some influence of the interaction with neighboring Ni(II) ions on the exchange coupling within the dimerized TCNQ ARs. With the aim of estimating the exchange coupling between Ni(II) ions and TCNQ ARs in the molecule, one would have to define a model Hamiltonian describing an infinite chain of alternating S = 1 sites and S = 1/2 dimers in the following scheme
−12···1···12−12···1···12−12···1···12−
with two exchange couplings, J (−) and J1–1/2 (···). The calculations of magnetic properties for such a model are not available in the literature to our knowledge. We have applied a spin-ring model, taking a fragment of the chain with 2 molecular units 12···1···12−12···1···12 and applying periodic boundary conditions (exchange coupling J between the end-chain spins). The Hamiltonian of such a spin ring can be defined in the EasySpin toolbox, including the ZFS parameters for S = 1 sites, energy eigenvalues found by the exact diagonalization method, and the susceptibility and magnetization, can be calculated. The best agreement with the experimental data, as shown in Figures 10 and 11 by dashed lines, was then obtained for the set of parameters D/kB = −6.5 K, E/D = 0.2, average g-factor gNi = 2.12, J/kB = −1105 K, J1–1/2/kB = 22 K, and χ0 = 2 × 10–4 emu/mol. A strong ferromagnetic (FM) exchange interaction J1–1/2 between Ni(II) and ARs was also observed in Ni(TCNQ)2 (65) or a Ni(II)-verdazyl radical complex. (66) It is interesting that the ground state of such a model results in an effective antiparallel orientation of S = 1 spins for both possible FM and AFM coupling J1–1/2, which is in accordance with negative J′ obtained from a simplified model of weakly interacting Ni(II) ions and AFM spin dimers.

Figure 11

Figure 11. Field dependence of the magnetization of 1 at 1.8 and 4.5 K (open symbols), including the fit of the simplified (solid lines) and spin-ring model (dashed lines) proposed in the text.

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Conclusions

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A fast and facile variation of well-traveled diffusion methods, consisting of adding the reactants in close proximity in a Petri dish with a solvent in which one of the reactants and the final product are insoluble or only slightly soluble, can produce suitable crystals for X-ray diffraction studies of TCNQ or TCNQF4 compounds. This method can be extended to other compounds and can be useful when any of the chemicals is unstable in solution. In addition, intermediate compounds can be identified and isolated when following the reaction under a microscope.
Using this method, the following compounds have been prepared and identified crystallographically: (a) unstable [Li2TCNQF4(CH3CN)4]·CH3CN (3) was prepared and analyzed structurally for the first time showing that Li+ and TCNQF42– form a 1D ribbon with two acetonitriles coordinated to each Li+ and (b) two new isostructural complexes with TCNQ•– ARs, namely, [Ni(2ampy)2(TCNQ)2] (1) and [Zn(2ampy)2(TCNQ)2] (2). Both compounds are neutral and formed by a central atom of Ni(II) or Zn(II) coordinated equatorially by two chelating 2ampy ligands and in the axial positions by monodentate TCNQ•– ARs.
Measurements of the magnetic susceptibility and magnetization of compounds 1 and 2 were performed. A strong AFM exchange coupling within the pairs of TCNQ•─ ARs from neighboring molecules was obtained, J/kB = −1206 K and J/kB = −1369 K for 1 and 2, respectively, from the spin dimer model. The presence of magnetically active anisotropic Ni(II) atoms with S = 1 in 1 was included in the model of an infinite chain of alternating S = 1 sites and S = 1/2 dimers; its simple version, a spin-ring model, was used to estimate the exchange coupling between Ni(II) and TCNQ•– ARs.

Supporting Information

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The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.cgd.3c00160.

  • Full process of preparation of single crystals; powder patterns; IR spectra; molecular structures; hydrogen bonding system; and geometric parameters (PDF).

Accession Codes

CCDC 2206024–2206027 and 2239060 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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Author Information

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  • Corresponding Authors
    • Mariia Holub - Faculty of Sciences, Institute of Physics, P. J. Šafárik University in Košice, Park Angelinum 9, 041 54 Košice, Slovakia;  Email: [email protected]
    • Lawrence Rocco Falvello - Instituto de Nanociencia y Materiales de Aragón (INMA) and Departamento de Química Inorgánica, CSIC-Universidad de Zaragoza, Zaragoza 50009, Spain;  Orcidhttps://orcid.org/0000-0002-0444-996X;  Email: [email protected]
  • Authors
    • Slavomíra Šterbinská - Faculty of Sciences, Institute of Chemistry, Department of Inorganic Chemistry, P. J. Šafárik University in Košice, Moyzesova 11, 041 54 Košice, Slovakia;  Instituto de Nanociencia y Materiales de Aragón (INMA) and Departamento de Química Inorgánica, CSIC-Universidad de Zaragoza, Zaragoza 50009, Spain
    • Erik Čižmár - Faculty of Sciences, Institute of Physics, P. J. Šafárik University in Košice, Park Angelinum 9, 041 54 Košice, Slovakia
    • Juraj Černák - Faculty of Sciences, Institute of Chemistry, Department of Inorganic Chemistry, P. J. Šafárik University in Košice, Moyzesova 11, 041 54 Košice, Slovakia;  Orcidhttps://orcid.org/0000-0002-8143-1368
    • Milagros Tomás - Instituto de Síntesis Quimica y Catálisis Homogénea (ISQCH), Departamento de Química Inorgánica, Pedro Cerbuna 12, University of Zaragoza−CSIC, E-50009 Zaragoza, Spain
  • Author Contributions

    All authors contributed to the preparation of the manuscript.

  • Notes
    The authors declare no competing financial interest.

Acknowledgments

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This work was supported by the Slovak Grants (APVV-18-0016, VEGA 1/0189/22) and by the Spanish Ministerio de Ciencia e Innovación (Grant PID2021–124880NB-I00), the European Union Regional Development Fund, (FEDER), and the Diputación General de Aragón, Project M4, E11_20R. We acknowledge the use of the Servicios de Apoyo a la Investigación of the University of Zaragoza.

Abbreviations

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2ampy

2-aminomethylpyridine

TCNQ

7,7,8,8-tetracyanoquinodimethane

IUPAC

2,2′-(cyclohexa-2,5-diene-1,4-diylidene)dipropanedinitrile

TCNQF4

2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane.

References

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    Coordination Chemistry Reviews (1994), 129 (1-2), 157-93CODEN: CCHRAM; ISSN:0010-8545.
    In a review with 153 refs. is presented a survey of the structural and electronic features of metal complexes with TCNE, TCNQ and some related mols. Other topics discussed include: ligand properties, reactivity, and phys. properties. Interesting phys. properties resulting from the extended π conjugation in metal complexes of the polynitrile ligands are briefly referred to by example of elec. cond., magnetic coupling and long-wavelength optical absorption.
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  3. 3
    Miller, J. S.; Zhang, J. H.; Reiff, W. M.; Dixon, D. A.; Preston, L. D.; Reis, A. H., Jr.; Gebert, E.; Extine, M.; Troup, J. Characterization of the charge-transfer reaction between decamethylferrocene and 7,7,8,8,-tetracyano-p-quinodimethane (1:1). The iron-57 Moessbauer spectra and structures of the paramagnetic dimeric and the metamagnetic one-dimensional salts and the molecular and electronic structures of (TCNQ)n(n = 0, −1, −2). Phys. Chem. 1987, 91, 4344– 4360,  DOI: 10.1021/j100300a028
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    3
    Characterization of the charge-transfer reaction between decamethylferrocene and 7,7,8,8,-tetracyano-p-quinodimethane (1:1). The iron-57 Moessbauer spectra and structures of the paramagnetic dimeric and the metamagnetic one-dimensional salts and the molecular and electronic structures of (TCNQ)n(n = 0, -1, -2)
    Miller, Joel S.; Zhang, Jian H.; Reiff, William M.; Dixon, David A.; Preston, L. D.; Reis, Arthur H., Jr.; Gebert, Elizabeth; Extine, Michael; Troup, Jan; et al.
    Journal of Physical Chemistry (1987), 91 (16), 4344-60CODEN: JPCHAX; ISSN:0022-3654.
    The charge-transfer reaction of decamethylferrocene, Fe(C5Me5)2 (Fc1) and 7,7,8,8-tetracyano-p-quinodimethane (TCNQ) have been characterized. Three major reaction products of varying stoichiometry, cond., and magnetism are formed: a 1-D metamagnetic 1:1 salt, [Fc1]+ [TCNO]•- (I); a paramagnetic 1:1 dimeric salt, [Fc1]2+ [TCNQ]22- (II); and a conducting 1:2 salt of [Fc1]+ [TCNQ]2- compn. The crystal and mol. structures of I and II were detd. The structure of II consists of discrete stacks of DAAD dimeric (D = Fc1; A = TCNQ) units. One-dimensional stacking of ions is not obsd. The decamethylferrocenium cations have av. Fe-C distances of 2.096 (7) Å, longer than the 2.050 Å reported for neutral decamethylferrocene. The C5Me5 rings appear eclipsed; however, as a result of the disorder only one ring was partially resolvable. The C5Me5 rings are essentially parallel to the TCNQ moieties and sepd. by 3.554 Å. The TCNQ anions form a tight a1g dimer (sepd. by a short distance of 3.147 Å) and are slipped along the short TCNQ axis. Bonding arises through filling of the bonding a1% dimer orbital. The structure of I consists of discrete one-dimensional chains comprised of alternating radical cation donors, D, and anion acceptors, A, i.e., ...DADA.... The decamethylferrocenium cation has a staggered conformation with an av. Fe-C distance of 2.090 Å. The C5Me5 rings are staggered and are canted with respect to the [TCNQ]•- moieties by 3.9°. The distance between the TCNQ and the C5Me5 rings is 3.43 Å. The [TCNQ]•- anion represents the first structural characterization of an isolated [TCNQ]•- in the solid state. Ab initio MO calcns. with the STO-3G basis set were carried out for [TCNQ]n (n = 0, -1, -2). To confirm the results of the MO calcns., [TCNQ]2- [as the [Co(C5Me5)2]+ (2:1) salt] was structurally characterized for the first time. The structures of C5 and D5d decamethylcobaltocenium cations have been reported for the 1st time. The structure of [TCNQ]2- has also been detd. for the first time. The dianion is planar within the exptl. error and possesses D2h local symmetry. The C6 ring is benzene-like with an av. ring C-C distance of 1.41 Å.
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  4. 4
    O’Hare, D.; Miller, J. S. One-Dimensional Solids Containing Bis(η-Arene)Chromium Cations. Mol. Cryst. Liq. Cryst. 1989, 176, 381– 389,  DOI: 10.1080/00268948908037496
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    4
    One-dimensional solids containing bis[η-arene)chromium cations
    O'Hare, Dermot; Miller, Joel S.
    Molecular Crystals and Liquid Crystals (1989), 176 (), 381-90CODEN: MCLCA5; ISSN:0026-8941.
    Charge transfer salts based on bis(η-arene)chromium cations and TCNE (TCNE = tetracyanoethylene) exhibit both para and ferromagnetic behavior depending on their structural motif. In contrast, magnetic susceptibility measurements on the thermodn. phase of [Cr(η-C6H3Me3)2]•+[TCNQ]•- (TCNQ = 7,7',8,8'-tetracyano-p-quinodimethane) indicate that the material does not obey the Curie-Weiss law. However, the magnetic susceptibility can be fitted over all temps. by considering a paramagnetic component from [Cr(η-C6H3Me3)2]•+ and [TCNQ]22- S = 0 dimers with a thermally accessible S = 1 excited state.
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  5. 5
    Clérac, R.; O’Kane, S.; Cowen, J.; Ouyang, X.; Heintz, R.; Zhao, H.; Bazile, M. J.; Dunbar, K. R. Glassy Magnets Composed of Metals Coordinated to 7,7,8,8-tetracyanoquinodimethane: M(TCNQ)2 (M = Mn, Fe, Co, Ni). Chem. Mater. 2003, 15, 1840– 1850,  DOI: 10.1021/cm021053d
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    5
    Glassy Magnets Composed of Metals Coordinated to 7,7,8,8-tetracyanoquinodimethane: M(TCNQ)2 (M = Mn, Fe, Co, Ni)
    Clerac, Rodolphe; O'Kane, Shannon; Cowen, Jerry; Ouyang, Xiang; Heintz, Robert; Zhao, Hanhua; Bazile, Mervin J., Jr.; Dunbar, Kim R.
    Chemistry of Materials (2003), 15 (9), 1840-1850CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
    The homologous series M(TCNQ)2 (M = Mn(II), Fe(II), Co(II), and Ni(II); TCNQ = 7,7,8,8-tetracyanoquinodimethane) prepd. from reactions of [M(MeCN)6][BF4]2 and [Bu4N][BF4] in MeCN was carefully analyzed from the perspective of synthetic issues and phys. characterization, including complete magnetic analyses by the tools of d.c. and a.c. magnetometry. The preparative method was optimized to definitively establish the reproducibility of the chem. as judged by IR spectroscopy, TGA, powder x-ray crystallog., and elemental anal. Scanning electron microscopic (SEM) and transmission electron microscopic (TEM) studies results are also in accord with the conclusion that these materials are pure, isostructural phases. The d.c. magnetic measurements reveal a spontaneous magnetization for the four materials at low temps. with a weak field coercivity of 20, 750, 190, and 270 G at 2 K for Mn(TCNQ)2, Fe(TCNQ)2, Co(TCNQ)2, and Ni(TCNQ)2, resp. At low temps., a.c. susceptibility measurements confirm the presence of a magnetic phase at 44, 28, 7, and 24 K for Mn(TCNQ)2, Fe(TCNQ)2, Co(TCNQ)2, and Ni(TCNQ)2, resp., but do not support the description of this system as a typical magnet. In the absence of the a.c. magnetic data, the behavior is indicative of ferri- or ferromagnetic ordering (depending on the metal), but in fact a complete study of their phys. properties revealed their true nature to be a glassy magnet. The glassiness, which is a high magnetic viscosity known to originate from randomness and frustration, is revealed by a frequency dependence of the a.c. susceptibility data and is further supported by a lack of a lambda peak in the heat capacity data. These results clearly demonstrate that mol.-based materials with a presumed magnetic ordering may not always be exhibiting truly cooperative behavior.
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  6. 6
    Zhao, H.; Bazile, M. J., Jr.; Galán-Mascarós, J. R.; Dunbar, K. R. A Rare-Earth Metal TCNQ Magnet: Synthesis, Structure, and Magnetic Properties of {[Gd2(TCNQ)5(H2O)9][Gd(TCNQ)4(H2O)3]}·4 H2O. Angew. Chem., Int. Ed. 2003, 42, 1015– 1018,  DOI: 10.1002/ange.200390234
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    6
    A rare-earth metal TCNQ magnet: synthesis, structure, and magnetic properties of {[Gd2(TCNQ)5(H2O)9][Gd(TCNQ)4-(H2O)3]}·4H2O
    Zhao, Hanhua; Bazile, Mervin J., Jr.; Galan-Mascaros, Jose R.; Dunbar, Kim R.
    Angewandte Chemie, International Edition (2003), 42 (9), 1015-1018CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
    The crystn. of the polymeric salt, {[Gd2(TCNQ)5(H2O)9][Gd(TCNQ)4(H2O)3]}·4H2O, is described, and was shown to consist of both cationic and anionic layers that exhibit different ratios of GdIII and TCNQ- radicals. This material is an example of a lanthanide/org. radical based magnet and is the first lanthanide-TCNQ magnet.
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  7. 7
    Alonso, C.; Ballester, L.; Gutiérrez, A.; Perpiñán, M. F.; Sánchez, A. E.; Azcondo, M. T. Tetracyanoquinodimethanido Derivatives of (Terpyridine)- and (Phenanthroline)metal Complexes – Structural and Magnetic Studies of Radical-Ion Salts. Eur. J. Inorg. Chem. 2005, 3, 486– 495,  DOI: 10.1002/ejic.200400540
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  8. 8
    Jain, R.; Kabir, K.; Gilroy, J. B.; Mitchell, K. A. R.; Wong, K.-Ch.; Hicks, R. G. High-temperature metal-organic magnets. Nature 2007, 445, 291– 294,  DOI: 10.1038/nature05439
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    8
    High-temperature metal-organic magnets
    Jain, Rajsapan; Kabir, Khayrul; Gilroy, Joe B.; Mitchell, Keith A. R.; Wong, Kin-chung; Hicks, Robin G.
    Nature (London, United Kingdom) (2007), 445 (7125), 291-294CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)
    For over two decades there were intense efforts aimed at the development of alternatives to conventional magnets, particularly materials comprised in part or wholly of mol. components. Such alternatives offer the prospect of realizing magnets fabricated through controlled, low-temp., soln.-based chem., as opposed to high-temp. metallurgical routes, and also the possibility of tuning magnetic properties through synthesis. However, examples of magnetically ordered mol. materials at or near room temp. are extremely rare, and the properties of these materials are often capricious and difficult to reproduce. Here the authors present a versatile soln.-based route to a new class of metal-org. materials exhibiting magnetic order well above room temp. Reactions of the metal (M) precursor complex bis(1,5-cyclooctadiene)nickel with three different orgs. A-TCNE (tetracyanoethylene), TCNQ (7,7,8,8-tetracyanoquinodimethane) or DDQ (2,3-dichloro-5,6-dicyano-1,4-benzoquinone)-proceed via electron transfer from nickel to A and lead to materials contg. Ni(II) ions and reduced forms of A in a 2:1 Ni:A ratio-i.e., opposite to that of conventional (low Curie temp.) MA2-type magnets. These materials also contain oxygen-based species within their architectures. Magnetic characterization of the three compds. reveals spontaneous field-dependent magnetization and hysteresis at room temp., with ordering temps. well above ambient. The unusual stoichiometry and striking magnetic properties highlight these three compds. as members of a class of stable magnets that are at the interface between conventional inorg. magnets and genuine mol.-based magnets.
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  9. 9
    Berlie, A.; Terry, I.; Giblin, S.; Lancaster, T.; Szablewski, M. A muon spin relaxation study of the metal-organic magnet Ni(TCNQ)2. J. Appl. Phys. 2013, 113, 17E304  DOI: 10.1063/1.4798616
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  10. 10
    Vasylets, G. Y.; Khotkevich, A. V.; Bukrinev, A. S.; Krasnyi, A. S.; Starodub, V. A.; Kravchenko, A. A.; Medviediev, V. V. Electroconductivity of anion-radical TCNQ salts containing cations [M(bipy)3]2+ (M - Fe, Ni or Zn). Funct. Mater. 2015, 22, 338– 341,  DOI: 10.15407/fm22.03.338
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    10
    Electroconductivity of anion-radical TCNQ salts containing cations [M(bipy)3]2+ (M-Fe, Ni or Zn)
    Vasylets, G. Y.; Khotkevich, A. V.; Bukrinev, A. S.; Krasnyi, A. S.; Starodub, V. A.; Kravchenko, A. A.; Medviediev, V. V.
    Functional Materials (2015), 22 (3), 338-341CODEN: FMUAB4; ISSN:2218-2993. (National Academy of Sciences of Ukraine, Institute for Single Crystals)
    Elec. resistance temp. dependence of three TCNQ anion-radical salts of complex compn. contg. cations [MII(bipy)3]2+ (M - Fe, Ni or Zn, bipy - 2,2'-dipyridil) have been studied. Measurements have been performed in the range 180-300 K on tableted samples. The compd. exhibit semiconducting properties and undergo the Peierls transition. Specific resistance at room temp. is of 7.7 Ω·cm-1 for Fe contg. salt and 2.3·10-2 Ω·cm-1 and 2.5·10-2 Ω·cm-1 for salts contg. Ni and Zn, resp.
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  11. 11
    Šoltésová, D.; Vasylets, G.; Čižmár, E.; Botko, M.; Cheranovskii, V.; Starodub, V.; Feher, A. Exchange interaction between TCNQ and transition metal ion mediated by hydrogen bonds in [Mn(phen)3](TCNQ)2·H2O and [Co(phen)3](TCNQ)2·H2O. J. Phys. Chem. Solids 2016, 99, 182– 188,  DOI: 10.1016/j.jpcs.2016.08.022
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    11
    Exchange interaction between TCNQ and transition metal ion mediated by hydrogen bonds in [Mn(phen)3](TCNQ)2·H2O and [Co(phen)3](TCNQ)2·H2O
    Soltesova, D.; Vasylets, G.; Cizmar, E.; Botko, M.; Cheranovskii, V.; Starodub, V.; Feher, A.
    Journal of Physics and Chemistry of Solids (2016), 99 (), 182-188CODEN: JPCSAW; ISSN:0022-3697. (Elsevier Ltd.)
    The magnetic properties, sp. heat and EPR spectra of anion-radical salts [Mn(phen)3](TCNQ)2·H2O and [Co(phen)3](TCNQ)2·H2O, in which TCNQ mols. and transition metal ions are not connected by covalent bonds and magnetic interactions are mediated via hydrogen bonds, were investigated. Measurements of the magnetic response were performed down to 1.8 K in magnetic fields up to 7 T. The heat capacity of investigated compds. was measured in temp. range from 0.38 K to 35 K in magnetic fields up to 9 T for [Mn(phen)3](TCNQ)2·H2O and up to 3 T for [Co(phen)3](TCNQ)2·H2O. The EPR spectra of studied samples were investigated for both samples in the temp. range from 2 K to 300 K. Theor. model of weakly-coupled magnetic units composed of four TCNQ anion radicals and of two transition metal ions was proposed for interpretation of obtained data. The energy of exchange interactions between TCNQ mols. and transition metal ion is important for the description of low-temp. behavior of studied anion-radical salts and was estd. to be in the range of 1.3-1.5 K.
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  12. 12
    Šterbinská, S.; Holub, M.; Hegedüs, M.; Titiš, J.; Čižmár, E.; Falvello, L. R.; Černák, J. Temperature-dependent dimerization of TCNQ anion-radical in [Ni(bpy)3]2(TCNQ–TCNQ)(TCNQ)2·6H2O: Single-crystal structure, magnetic and quantum chemical study. Solid State Sci. 2022, 131, 106959  DOI: 10.1016/j.solidstatesciences.2022.106959
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    12
    Temperature-dependent dimerization of TCNQ anion-radical in [Ni(bpy)3]2(TCNQ-TCNQ)(TCNQ)2·6H2O: Single-crystal structure, magnetic and quantum chemical study
    Sterbinska, Slavomira; Holub, Mariia; Hegedus, Michal; Titis, Jan; Cizmar, Erik; Falvello, Larry R.; Cernak, Juraj
    Solid State Sciences (2022), 131 (), 106959CODEN: SSSCFJ; ISSN:1293-2558. (Elsevier Masson SAS)
    The crystal structure of [Ni(bpy)3]2(TCNQ-TCNQ)(TCNQ)2·6H2O (1) was studied by X-ray single-crystal structure anal. at 145 K and 100 K. The crystal structures of 1 at these two temps. are essentially the same as the crystal structure studied previously at 200 K: the structure is built up of [Ni(bpy)3]2+ complex cations, two centrosym. crystallog. independent TCNQ·- anion-radicals, disordered σ- and π-dimerized (TCNQ)2 units, and water mols. of crystn. Lowering the temp. from 200 K, via 145 K-100 K has shown that at lower temps. the proportions of σ- and π-dimerization in the disordered (TCNQ)2 unit are shifted in favor of σ-dimerization; moreover, variation of the weaker C-C σ-bond formed upon dimerization was obsd. In addn., lowering the temp. led to a shortening of the distance between the two crystallog. independent anion-radicals which are stacked along the b-axis with overlapped exo groups. The σ- and π-dimerization in the disordered (TCNQ)2 unit was studied by quantum chem. calcns. which showed smallest energy difference for σ and π-dimer at 200 K with respect to 145 K and 100 K in line with a lowest proportion of the dimerization obsd. exptl. Temp.-dependent (1.8-270 K) magnetic study of 1 has shown the contribution of Ni(II) ions (S = 1) and the contribution of four S = 1/2 species carried by TCNQ radicals at higher temps., strongly coupled by antiferromagnetic (AFM) exchange interaction at 270 K while at low temp. a negligible contribution of TNCQ radical spins was obsd.
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  13. 13
    Nafady, A.; O′Mullane, A. P.; Bond, A. M. Electrochemical and photochemical routes to semiconducting transition metal-tetracyanoquinodimethane coordination polymers. Coord. Chem. Rev. 2014, 268, 101– 142,  DOI: 10.1016/j.ccr.2014.01.017
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    13
    Electrochemical and photochemical routes to semiconducting transition metal-tetracyanoquinodimethane coordination polymers
    Nafady, Ayman; O'Mullane, Anthony P.; Bond, Alan M.
    Coordination Chemistry Reviews (2014), 268 (), 101-142CODEN: CCHRAM; ISSN:0010-8545. (Elsevier B.V.)
    A review. TCNQ·- radical anions (TCNQ = 7,7,8,8,-tetracyanoquinodimethane) form a wide range of semiconducting coordination polymers when coordinated to transition metals. Some materials such as CuTCNQ and AgTCNQ exhibit mol. switching and memory storage properties; others have intriguing magnetic properties and for example may behave as mol. magnets at low temp. In this review, the electro- and photo-chem. synthesis and characterization of this important class of material is reviewed. In particular, the electrochem. and the redox properties of TCNQ derivs. of coordination polymers based on Cu, Ag, Mn, Fe, Co, Ni, Zn and Cd transition metals are surveyed, with an emphasis on the mechanistic aspects of their electrochem. formation via nucleation-growth processes. Given that TCNQ is an extremely good electron acceptor, readily forming TCNQ·- and TCNQ2-, electrochem. redn. of TCNQ in the presence of a transition metal ion provides an ideal method for synthesis of metal-TCNQ materials by electrocrystn. from org. solvents and ionic liqs. or solid-solid transformation using TCNQ modified electrodes from aq. media contg. transition metal electrolytes. The significance of the reversible formal potential (E0f) in these studies is discussed. The coupling of electrocrystn. on electrode surfaces and microscopic characterization of the electrodeposited materials reveals a wide range of morphologies and phases which strongly influence their properties and applications. Since TCNQ can also be photo-reduced in the presence of suitable electron donors, analogous photochem. approaches to the synthesis of TCNQ-transition metal derivs. are available. The advantages of electrochem. and photochem. methods of synthesis relative to chem. synthesis are outlined.
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  14. 14
    Goldberg, S. Z.; Spivack, B.; Stanley, G.; Eisenberg, R.; Braitsch, D. M.; Miller, J. S.; Abkowitz, M. Synthesis, structure, and physical properties of the bis(7,7,8,8-tetracyano-p-quinodimethane) salt of the paramagnetic cluster tris[(di-μ-chloro)(hexamethylbenzene)niobium], [Nb3(μ-Cl)6(C6Me6)3]2+(TCNQ)22-. J. Am. Chem. Soc. 1977, 99, 110– 117,  DOI: 10.1021/ja00443a021
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    14
    Synthesis, structure, and physical properties of the bis(7,7,8,8-tetracyano-p-quinodimethane) salt of the paramagnetic cluster tris[(di-μ-chloro)(hexamethylbenzene)niobium], [Nb3(μ-Cl)6(C6Me6)3]2+(TCNQ)22-
    Goldberg, Stephen Z.; Spivack, Bruce; Stanley, George; Eisenberg, Richard; Braitsch, David M.; Miller, Joel S.; Abkowitz, Martin
    Journal of the American Chemical Society (1977), 99 (1), 110-17CODEN: JACSAT; ISSN:0002-7863.
    The title complex was synthesized from Nb3Cl6(C6Me6)3+PF6-, Li+TCNQ-, and TCNQ in MeCN. Its crystal and mol. structures were detd. The crystal structure consists of zigzag chains of alternating di-μ-chloro-(hexamethylbenzene)niobium trimer cations and TCNQ anion dimers. The trinuclear cluster has m symmetry with two crystallog. independent Nb-Nb distances of 3.327 (2) and 3.344 (3) Å. There is one crystallog. independent TCNQ anion which forms a dimeric unit with its centrosymmetrically related form. The interplanar spacing between TCNQ moieties is 3.10 Å and the overlap between them is of an exo double bond ring type. The mea sepn. of 3.65 Å between the slightly bent hexamethylbenzene and TCNQ units suggests little interaction. The room temp. ESR spectrum consists of a nearly isotropic [g = 1.996 (2)] and relatively broad absorption [peak to peak deriv. line width of 36.95 (3) Oc]. This is consistent with the unpaired electron residing on the niobium cluster. Thus, the mol. is [Nb3Cl6(C6Me6)3]2+(TCNQ)22- and represents the solid-state stabilization of the previously postulated S = 1/2 cluster by TCNQ. The single-crystal and polycrystalline cond. data indicate a semiconductor behavior with a room temp. cond. of 0.001 ohm-1 cm-1 and an activation energy of 0.35 eV (2800 cm-1).
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  15. 15
    Bertaina, S.; Dutoit, C.-E.; van Tol, J.; Dressel, M.; Barbara, B.; Stepanov, A. Rabi oscillations of pinned solitons in spin chains: A route to quantum computation and communication. Phys. Rev. 2014, 90, 060404(R)  DOI: 10.1103/PhysRevB.90.060404
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  16. 16
    Leo, K.; Schneider, O. US20050179399A1, 2005.
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  17. 17
    Pyshkin, O.; Kamarchuk, G.; Yeremenko, A.; Kravchenko, A.; Pospelov, A.; Alexandrov, Y.; Faulques, E. Evidence for sensory effects of a 1D organic conductor under gas exposure. J. Breath Res. 2011, 5, 016005  DOI: 10.1088/1752-7155/5/1/016005
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    17
    Evidence for sensory effects of a 1D organic conductor under gas exposure
    Pyshkin, O.; Kamarchuk, G.; Yeremenko, A.; Kravchenko, A.; Pospelov, A.; Alexandrov, Yu; Faulques, E.
    Journal of Breath Research (2011), 5 (1), 016005/1-016005/9CODEN: JBROBW; ISSN:1752-7155. (Institute of Physics Publishing)
    This work describes the gas-sensitive properties of a one-dimensional org. conductor before and after exposure to carbon monoxide and human breath. A sensitive material, an anion-radical salt of tetracyanoquinodimethane, has been investigated by IR spectroscopy and elec. resistivity measurements. Drastic spectral and elec. changes are found after gas exposure showing that the compd. interacts strongly with human breath, carbon monoxide, and ammonia. Under breath action the resistance changes by more than three orders of magnitude while the adsorption of CO, one of the components of breath, results in a decrease in both IR absorption and elec. cond. The intensity of the IR absorption spectrum of the material in the CO medium decreases down to 30% in the 2180-2500 cm-1 range. This absorption varies by about 10% between 750 and 2500 cm-1 after breath action. Direct elec. measurements show that actions of donor or acceptor gas result in opposite changes of elec. resistance. The elec. resistance of the sample can drop down to 0.4 MΩ due to the pulse action of ammonia at 4 ppm concn., while it increases upon exposure to carbon monoxide media at concns. of 6-25 ppm. The response signal of the investigated samples changes proportionally to the concn. of the acting gas. The results substantiate prominent gas sensitivity of the investigated material, which might find applications for breath anal., in particular, for the development of noninvasive diagnosis of gastric diseases.
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  18. 18
    Matsuda, R. Design and Synthesis of Porous Coordination Polymers Showing Unique Guest Adsorption Behaviors. Bull. Chem. Soc. Jpn. 2013, 86, 1117– 1131,  DOI: 10.1246/bcsj.20130157
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    Design and synthesis of porous coordination polymers showing unique guest adsorption behaviors
    Matsuda, Ryotaro
    Bulletin of the Chemical Society of Japan (2013), 86 (10), 1117-1131CODEN: BCSJA8; ISSN:0009-2673. (Chemical Society of Japan)
    A review. Methods for design and synthesis of porous coordination polymers showing unique adsorption properties are discussed. Gas storage and sepn. are becoming a high priority area of research due to economic, industrial, and environmental reasons. The last two decades have therefore witnessed dramatic growth in the search for more efficient and adaptable nanoporous materials. In particular, much attention has been focused on porous coordination polymers (PCPs) or metal org. frameworks (MOFs) as new nanoporous materials. Based on the unlimited combination of metal ions and org. ligands, PCPs can provide infinite variety of nanospace in their pores. As mol. adsorption is dependent on the size, shape, and surface nature of nanospace, many unique mol. adsorption or trapping phenomena have been reported in this class of compds. Examples include selective adsorption of acetylene over carbon dioxide in the CPL series of PCPs, using charge-transfer to induce selective adsorption of nitric oxide and oxygen in TCNQ (7,7,8,8-tetracyano-p-quinodimethane) based PCP and light-induced on-demand adsorption and structural transformations in CID-based PCPs. The guidelines underpinning such unique, highly selective guest adsorption are discussed.
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  19. 19
    Ballester, L.; Gutiérrez, A.; Perpiñán, M. F.; Azcondo, M. T. Supramolecular architectures in low dimensional TCNQ compounds containing nickel and copper polyamine fragments. Coord. Chem. Rev. 1999, 190–192, 447– 470,  DOI: 10.1016/S0010-8545(99)00098-3
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    Supramolecular architectures in low dimensional TCNQ compounds containing nickel and copper polyamine fragments
    Ballester, L.; Gutierrez, A.; Perpina, M. F.; Azcondo, M. T.
    Coordination Chemistry Reviews (1999), 190-192 (), 447-470CODEN: CCHRAM; ISSN:0010-8545. (Elsevier Science S.A.)
    A review, with 57 refs., discusses Ni(II) and Cu(II) polyamine derivs. which are adequate fragments to interact with the org. acceptor TCNQ, favoring the formation of σ bonds between the metal atom and the TCNQ nitrile groups. In its radical anion form, this mol. tends to form dimeric dianions (TCNQ)2 2- by overlapping of the π cloud with a neighboring radical. When the metal has a stable and coordinatively satd. environment these dianions remain uncoordinated, but if the metal has vacant positions or labile ligands formation of two M-TCNQ bonds is obsd. In these cases the dianions are bridging two metal units forming infinite chains. In the dimers, the radicals are strongly antiferromagnetically coupled behaving as diamagnetic units. These compds. with localized electrons behave as insulators, or poor semiconductors. In its neutral form the TCNQ has a low coordinative ability, but its presence favors the overlap of the dianionic dimers to form infinite stacks. When both neutral and radical-anionic TCNQ are present in the reaction mixt. the derivs. obtained usually have three TCNQ mols. per metal atom. Depending on the interactions between the TCNQ and the metal two situations are found: if all the TCNQ mols. are uncoordinated the electronic charge on the org. stack is delocalized, but if direct bonding to the metal is present, the bonded mols. show radical anion characteristics, while the uncoordinated TCNQ behave as neutral mols. The presence of this neutral TCNQ weakens the coupling in the (TCNQ)2 2- dimers and a temp. dependent contribution from the TCNQ to the magnetic susceptibility is found. These compds. having mixed valence TCNQ units show a greater electronic delocalization and behave as good semiconductors with higher cond. values and lower activation energies in the derivs. that do not show direct bonding between the metal and the TCNQ.
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  20. 20
    Černák, J.; Kočanová, I.; Orendáč, M. Copper-Nickel Heterobimetallic Compounds. Comments Inorg. Chem. 2012, 33, 2– 54,  DOI: 10.1080/02603594.2012.700970
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    Copper-Nickel Heterobimetallic Compounds
    Cernak, J.; Kocanova, I.; Orendac, M.
    Comments on Inorganic Chemistry (2012), 33 (1-2), 2-54CODEN: COICDZ; ISSN:0260-3594. (Taylor & Francis, Inc.)
    A review. Motivated by the theor. prediction of the existence of alternate chains in the case of one-dimensional Cu-Ni compds. the current state of these heterobimetallic compds. is described. A classification of Cu-Ni heterobimetallic compds. based on the magnetic properties of the resp. metal is considered, namely, and classes (is for diamagnetic and for paramagnetic). These four classes of Cu-Ni compds. are further classified by structure and compn. Based on these classifications representative examples for each group are described from a structural perspective as well as magnetic properties. Addnl. information is given on the typical preparative methods.
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  21. 21
    Groom, C. R.; Bruno, I. J.; Lightfoot, M. P.; Ward, S. C. The Cambridge Structural Database. Acta Crystallogr., Sect. B: Struct. Sci., Cryst. Eng. Mater. 2016, 72, 171– 179,  DOI: 10.1107/S2052520616003954
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    The Cambridge Structural Database
    Groom, Colin R.; Bruno, Ian J.; Lightfoot, Matthew P.; Ward, Suzanna C.
    Acta Crystallographica, Section B: Structural Science, Crystal Engineering and Materials (2016), 72 (2), 171-179CODEN: ACSBDA; ISSN:2052-5206. (International Union of Crystallography)
    The Cambridge Structural Database (CSD) contains a complete record of all published org. and metal-org. small-mol. crystal structures. The database has been in operation for over 50 years and continues to be the primary means of sharing structural chem. data and knowledge across disciplines. As well as structures that are made public to support scientific articles, it includes many structures published directly as CSD Communications. All structures are processed both computationally and by expert structural chem. editors prior to entering the database. A key component of this processing is the reliable assocn. of the chem. identity of the structure studied with the exptl. data. This important step helps ensure that data is widely discoverable and readily reusable. Content is further enriched through selective inclusion of addnl. exptl. data. Entries are available to anyone through free CSD community web services. Linking services developed and maintained by the CCDC, combined with the use of std. identifiers, facilitate discovery from other resources. Data can also be accessed through CCDC and third party software applications and through an application programming interface.
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  22. 22
    Ballester, L.; Barral, M. C.; Gutiérrez, A.; Monge, A.; Perpiñán, M. F.; Ruiz-Valero, C.; Sánchez-Pélaez, A. E. Tetracyanoquinodimethane Derivatives of Macrocyclic Nickel(II) Complexes. Synthesis and Crystal Structure of Bis(7,7,8,8-tetracyanoquinodimethanido)(1,8-bis(2-hydroxyethyl)-1,3,6,8,10,13-hexaazacyclotetradecane)nickel(II). Inorg. Chem. 1994, 33, 2142– 2146,  DOI: 10.1021/ic00088a015
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    Tetracyanoquinodimethane Derivatives of Macrocyclic Nickel(II) Complexes. Synthesis and Crystal Structure of Bis(7,7,8,8-tetracyanoquinodimethanido)(1,8-bis(2-hydroxyethyl)-1,3,6,8,10,13-hexaazacyclotetradecane)nickel(II)
    Ballester, Loreto; Barral, M. Carmen; Gutierrez, Angel; Monge, Angeles; Perpinan, Maria Felisa; Ruiz-Valero, Caridad; Sanchez-Pelaez, Ana E.
    Inorganic Chemistry (1994), 33 (10), 2142-6CODEN: INOCAJ; ISSN:0020-1669.
    The reactivity of the dichloro(1,8-disubstituted-1,3,6,8,10,13-hexaazacyclotetradecane)nickel(II) complex [NiCl2LR] (R = C2H4OH, Et, CH2Ph) toward LiTCNQ leads to a complete replacement of the chloride groups by the anionic TCNQ•- with formation of [NiLR(TCNQ)2]. The crystal structure of the hydroxyethyl deriv. was solved. The Ni atom is hexacoordinated surrounded by 4 nitrogens of the macrocyclic ligand and 2 axial monodentate TCNQ•- ligands, being the 1st Ni-TCNQ complex showing σ-bonds between the org. acceptor and the metal atom. Intermol. interactions between TCNQ groups from adjacent mols. forming dimeric units and H bonds involving the hydroxo groups and 1 of the N atoms of a neighboring TCNQ unit are the most significant features of the crystal structure. These compds. behave virtually as insulators at room temp.
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  23. 23
    Ballester, L.; Gutiérrez, A.; Perpiñán, M. F.; Amador, U.; Azcondo, M. T.; Sánchez, A. E.; Bellitto, C. Supramolecular Architecture in Nickel(II) Polyamine Tetracyanoquinodimethanido Systems. Inorg. Chem. 1997, 36, 6390– 6396,  DOI: 10.1021/ic970851g
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    Supramolecular Architecture in Nickel(II) Polyamine Tetracyanoquinodimethanido Systems
    Ballester, Loreto; Gutierrez, Angel; Perpinan, M. Felisa; Amador, Ulises; Azcondo, M. Teresa; Sanchez, Ana E.; Bellitto, Carlo
    Inorganic Chemistry (1997), 36 (27), 6390-6396CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
    Three different supramol. architectures corresponding to [Ni(dien)2](TCNQ)2 (dien = 1,4,7-triazaheptane; TCNQ = 7,7,8,8-tetracyanoquinodimethane), [Ni(trien)(TCNQ)2] (trien = 1,4,7,10-tetraazadecane), and [Ni(cyclam)(TCNQ)2] (cyclam = 1,4,8,11-tetraazacyclotetradecane) were prepd. and crystallog. characterized: [Ni(dien)2](TCNQ)2, triclinic, space group P‾1, a 8.319(2), b 9.074(2), c 11.145(3) Å, α 80.91(2), β 74.10(2), γ 82.12(2)°, Z = 1; [Ni(trien)(TCNQ)2], orthorhombic, space group Pccn, a 22.677(7), b 7.888(5), c 15.801(3) Å, Z = 4; [Ni(cyclam)(TCNQ)2], triclinic, P‾1, a 8.699(2), b 9.752(3), c 10.138(2) Å, α 87.29(2), β 77.14(2), γ 75.00(2)°, Z = 1. All of them are built by dimeric units (TCNQ)22- which are out of the coordination sphere in [Ni(dien)2](TCNQ)2 and σ-coordinated to the metal in cis and trans positions in [Ni(trien)(TCNQ)2] and [Ni(cyclam)(TCNQ)2], resp. In the two latter compds. the bonded dimeric units (TCNQ)22-, formed by intermol. interactions, give rise to infinite chains consisting of alternating [Ni(N4)]2+ and (TCNQ)22- moieties in the crystal. The existence of hydrogen bonds between the TCNQ nitriles and amine groups belonging to the metal fragments stabilizes the supramol. architecture, increasing the dimensionality of the interactions. The spectroscopic and magnetic properties are discussed according to the structural models.
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    Choi, H. J.; Suh, M. P. Nickel(II) Macrocyclic Complexes with Long Alkyl Pendant Chain: Synthesis, X-ray Structure, and Anion Exchange Property in the Solid State. Inorg. Chem. 2003, 42, 1151– 1157,  DOI: 10.1021/ic025971p
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    24
    Nickel(II) Macrocyclic Complexes with Long Alkyl Pendant Chain: Synthesis, X-ray Structure, and Anion Exchange Property in the Solid State
    Choi, Hye Jin; Suh, Myunghyun Paik
    Inorganic Chemistry (2003), 42 (4), 1151-1157CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
    A nickel(II) pentaaza macrocyclic complex contg. a 1-hexadecyl pendant chain, [Ni(L)](ClO4)2·H2O (1; L = I), was synthesized by a 1-pot metal-template condensation reaction. Crystal data for 1: triclinic, space group P‾1, a 8.333(4), b 8.356(3), c 28.374(9) Å, α 81.865(19), β 86.242(18), γ 63.871(17), Z = 2. Solid 1 forms hydrophobic layers that are constructed by the long alkyl chains of the macrocycles. Solid 1 exchanges ClO4- with NCS-, PF6-, C2O42-, NO3-, and CF3SO3- that are dissolved in water. From the reaction of [Ni(C25H55N5)Cl2] with Et3NH(TCNQ)2 in EtOH/DMF/acetone soln., [Ni(C25H55N5)(TCNQ)2](TCNQ)·(CH3COCH3) (2) (TCNQ = 7,7,8,8-tetracyano-p-quinodimethane) was prepd. Crystal data for 2: triclinic, space group P‾1, a 8.459(0), b 13.945(1) Å, c 26.833(2) Å, α 88.744(2), β 84.536(2), γ 80.089(4), Z = 2. In 2, TCNQ anions coordinate nickel(II) at the axial sites, which form π-stacked TCNQ- dimers to give rise to 1-dimensional chains. The neutral TCNQ mols. are included between the dimerized TCNQ- species, which construct a π-stacked group of six TCNQ units as blocked by the long alkyl chains. Compd. 2 is an elec. insulator. It shows a weak signal in the EPR spectrum. The magnetic susceptibility data of 2 measured at 5-300 K exhibit a simple paramagnetism at low temps. (<100 K) but an increase in the magnetic moment at higher temps. due to the contribution of a thermally accessible triplet state for the antiferromagnetically coupled [TCNQ]22-.
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  25. 25
    Melby, L. R.; Harder, R. J.; Hetler, W. R.; Mahler, W.; Benson, R. E.; Mochel, W. E. Substituted Quinodimethans. II. Anion-radical Derivatives and Complexes of 7,7,8,8-Tetracyanoquinodimethan. J. Am. Chem. Soc. 1962, 84, 3374– 3387,  DOI: 10.1021/ja00876a029
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    Substituted quinodimethans. II. Anion-radical derivatives and complexes of 7,7,8,8-tetracyanoquinodimethan
    Melby, L. R.; Harder, R. J.; Hertler, W. R.; Mahler, W.; Benson, R. E.; Mochel, W. E.
    Journal of the American Chemical Society (1962), 84 (), 3374-87CODEN: JACSAT; ISSN:0002-7863.
    V is a strong Lewis acid and forms charge-transfer complexes with π-bases. Thus, 0.18 g. V in 50 ml. boiling CHCl3 was added to 0.10 g. Cu 8-quinolinate (XIV) in 50 ml. boiling CHCl3 and the soln. concd. to 50 ml. and left overnight to give 48% V-XIV π-complex, black plates, decompg. 195° resistivity (ρ) 3 × 107 ohm-cm. (unless otherwise stated ρ was detd. on mech. compacted microcryst. samples at room temp.). Similarly were prepd. (donor, solvent, appearance of complex, mole ratio of donor to V in complex, % yield, decompn. range, and ρ ohm-cm. given): p-C6H4(NH2)2, CHCl3, purple-black microcrystals, 1:1, 83, 162 to above 300°, 3 × 103 [activation energy for conductivity (Εa) 0.28 e.v.; electron paramagnetic resonance (e.p.r.) shows 4 × 1020 ± 25% unpaired electrons per mole]; 2-methyl-p-phenylenediamine, CHCl3, black microcrystals, 1:1, 44, 150-5°, 3 × 105; p-Me2NC6H4NH2, CHCl3, black leaflets, 1:1, 38, 112-17°, 2 × 109 (e.p.r. shows 4 × 1021 ± 25% unpaired electrons per mole); p-C6H4(NHMe)2, CH2Cl2, black needles, 1:1, 50, 111-14°, 2 × 104; p-C6H4(NMe2)2, CHCl3, blue-black platelets, 1:1, 71,128-9°, 106; diaminodurene, VII, purple micro-crystals, 1:1, 86,190 to above 300°, 109; 2,3-diaminonaphthalene, CHCl3, black microcrystals, 1:1, 27, 165 to above 300°, 1010; 1,5-diaminonaphthalene, CHCl3, black needles, 1:1, 59, 197°, 109 (e.p.r. shows 2 × 1019 ± 25% unpaired electrons per mole); 2-aminofluorene, MeCN, brown-black needles, 1:1, 80, 207-42°, 109; 2-aminochrysene, CH2Cl2, brown needles, 1:1, 51, 211-17° 1010; p-C6-H4(OH)2, VII, black microcrystals, 1:2, low, 180-5°, --; 1,2,3-C6H3(OH)3, CH2Cl2, --, 2:1, low, 105°, --; VIII, VII, black needles, 1:1, 42, 282-3°, 1011; pyrene, VII, purple needles, 1:1, 52, 260°, 1012; 4,6,8-trimethylazulene, VII, black crystals, 1:1, 85, 160-7°, 109; pyrrole-2-aldehydeimine (XV) Cu chelate, CHCl3, purple needles, 1:1,69,170 to above 300°, 5 × 1010; XV Ni chelate, CH2Cl2, blue-black needles, 1:1, --, 210-20°, 1011. Most of the π-complexes cannot be crystd. without some decompn., although the solids are quite thermally stable, and are best prepd. from highly purified starters. V (Q) undergoes one-electron redn. with Cu, Ag, or other metal iodides to give simple salts of the anion-radical (Q•-). Thus, 40 g. LiI (an excess is used to scavenge liberated iodine as I3-) in 100 ml. boiling MeCN added to 20.4 g. V in 2 1. boiling MeCN gave 98% Li+Q•- (XVI), purple microcrystals, decompd. above 300°, ρ 2 × 105 ohm-cm. Similarly were prepd. (cation source, salt, appearance, % yield, decompn. range, and ρ ohm-cm. given): NaI, Na+Q•-, purple microcrystals, 59, above 300° 3 × 104; KI, K+Q•-, red needles, 70, above 300°, 5 × 103; BaI2, Ba++, (Q•-)2, purple crystals, 70, --, 8 × 105; NH4I (in VII-MeOH)-NH4+•-, maroon needles, 60, 210-15°, 6 × 104; (NCCH2CH2)-Me3N+I-, (NCCH2CH2)Me3N+Q•-, blue-black crystals, --, --, 106. CsI is exceptional in that it gives a complex salt (contg. formally neutral V). A filtered soln. of 2.9 g. CsI in 50 ml. boiling MeOH added to 2.0 g. V in 200 ml. boiling MeCN gave 1.64 g. (Cs+)2(Q•-)2Q, purple prisms, ρ 9 × 104 ohm-cm. (Ea 0.36 e.v.; single crystal detns. of ρ along the 3 major axes gave 500, 6 × 104, and 6 × 104 ohm-cm.; ρ for complex salts is anisotropic). The soly. of XVI in H2O and EtOH (∼l% by wt.) allows the prepn. of simple salts by metathesis. Thus, 12 g. CuSO4.5H2O in 70 ml. H2O added to a filtered soln. of 2.2 g. XVI in 200 ml. H2O gave 2.2 g. Cu++(Q•-)2, green powder, ρ 200 ohm-cm. (Ea 0.12 e.v.). Boiling solns. of 0.84 g. XVI in 200 ml. alc. and 1.1 g. N-methylquinolinium iodide in 10 ml. alc. were mixed, the mixt. was left 2 hrs. at room temp., the product washed with cold alc. and Et2O, and recrystd. to give 76% (N-methylquinolinium)++Q•-, purple microcrystals, decompg. 240-4° (MeCN),ρ 107 ohm-cm. Similarly, the following simple salts were prepd. by metathesis in aq. soln. (cation source, product, appearance, % yield, decompn. range, and ρ ohm-cm. given): CsCl, Cs++Q•-, purple crystals, 67, --, 3 × 104 (Ea 0.15 e.v.); MnCl2, Mn++-(Q•-)2.3H2O, blue powder, 98, ∼170°, 9 × 104; FeSO4, Fe++-(Q•-)2.3H2O, blue powder, 95, ∼170°, 5 × 104; CoSO4, Co++-(Q•-)2.3H2O, blue powder, 91, ∼170°, 9 × 104; NiCl2, Ni++-(Q•-)2.3H2O, blue powder, 95, 170°, 9 × 104; CuI, Cu+Q•-, blue-black needles, 54, --, 200 (Ea 0.13 e.v.); AgNO3, Ag+Q•-(gives free V in light). blue powder, 98, --, 8 × 105; Ce(NO3)3, Ce+++(Q•-)3.6H2O (gives free V in light), blue powder, 98, --, --; Sm(NO3)3, Sm+++(Q•-)3.6H2O, blue powder, 92, --, 2 × 104; Pb(NO3)2, Pb++(Q•-)2.1.5H2O, blue powder, 99, --, 2 × 105; Cu(NH3)4SO4, Cu(NH3)2++(Q•-)2, green powder, 94, --, 700; Cu(H2NCH2CH2NH2)2SO4, Cu(H2NCH2CH2NH2)2++(Q•-)2, blue powder, 97, --, 4 × 104; CuCl2 + 2,2'-dipyridylamine, Cu-(2,2'-dipyridylamine)++(Q•-)2, --, 80, --, 40 (Ea 0.06 e.v.); FeSO4 + 1,10-phenanthroline (phen), Fe(phen)3++(Q•-)2.-6H2O, --, 95, 260°, 106; NiCl2 + phen, Ni(phen)3++(Q•-)2.-6H2O, green powder, 98, --, 108; Ni(phen)2Cl2, Ni(phen)2++-(Q•-)2.6H2O, green powder, 96, --, 2 × 108; Cr(OAc)3, (Cr+++)2-(AcO-)4(HO-)(Q•-).6H2O, blue powder, 30, --, 109; Et3N.HCl or Et3N.HBr, Et3NH+Q•- (XVIII), blue powder, 81, ∼180°, 109; Bu4NI, Bu4N+Q•-, blue powder, --, 135%, 1012; Et2Me-(NCCH2)NI, Et2Me(NCCH2)N+Q•-, blue powder, --, ∼193°,109, Ph3MePI, Ph3MeP+Q•-, purple crystals, 99, ∼170°, 4 × 1010; (Me2N)3SCl or (Me2N)3SBr, (Me2N)3S+Q•-, purple solid, 88, ∼155°, 2 × 1010; N-methylpyridinium iodide (XVIII) (in MeCN-alc.), (N-methylpyridinium)+Q•-, purple needles, trace, ∼235°, 105; 4-cyano deriv. of XVIII (in MeCN-alc.), (4-cyano-N-methylpyridinium)+Q•-, purple needles, 52, 224-6° 106; 4-cyano-N-methylquinolinium iodide (in MeCN-alc.), (4-cyano-N-methylquinolinium)+Q•-, purple needles, 51, 196-8% 105; 2-(4-dimethylaminophenylazo) deriv. of XVIII (in MeCN-alc.), [N-methyl-2-(4-dimethylaminophenylazo)pyridinium]+Q•-, metallic-green plates, 77, 237-77° 106. Some simple salts were prepd. by treatment of the free base with V (the source of the proton in the cation of the salt thus formed is unknown but is probably the amine; a possible mechanism is discussed or with a mixt. of V and VI. Thus were prepd. (reactants, solvent, product, appearance, % yield, decompn. range, and ρ ohm-cm. given): base + V, CH2Cl2, (4-hydroxy-2,3,5,6-tetramethylanilinium)+-Q•-, black microcrystals, 60, 168-74°, 160 (Εa 0.10 e.v.); base + V, CHCl3, (5,8-dihydroxyquinolinium)+Q•-, black micro-crystals, 72, 168-9°, 15 (Ea 0.07 e.v.); IV + V + VI, MeCN, (pyridinium)+Q•-, purple prisms, 59, 158-95°, 106; base + V + VI, MeCN, [2-(4-dimethylaminophenylazo)pyridinium]+Q•-, metallic-green plates, 88, 230-45°, 106. Aq. solns. of the simple salts rapidly decomp. The blue color of concd. aq. solns. is due to the presence of a dimeric species; dil. aq. solns. and solns. in org. solvents are green due to absorption by Q•-, λ (MeCN) 420 (ε 24,300), 842 (ε 43,300), 744, 760, 680, 665 mμ. Infrared spectra of the simple salts show broad bands at 4.55-4.60 and 1-1.5 μ. Tropylium iodide (XIX) reacts abnormally with XVI: a filtered soln. of 1.20 g. XVI in 120 ml. H2O was added dropwise to 1.00 g. XIX in 15 ml. H2O until the blue color persisted, the ppt. was collected, washed with H2O (1.07 g., 99%, Agl was pptd. from the filtrate and washings on addn. of 1.5 g. AgNO3in 10 ml. H2O), dissolved in CH2Cl2, and the soln. concd. to ppt. 0.39 g. V. Further concn. gave 0.09 g. solid material and finally evapn. to dryness gave 0.80 g. α,α'-ditropyl-α,α,α',α'-tetracyano-p-xylene (XX), yellow prisms, m. 200-6°. Recrystn. from C6H6 gave material, m. 201-2° (dried 1 hr. at 110°). A mechanism is proposed for the formation of XX. Complex salts can be prepd. by addn. of V to solns. of the simple salts. Thus, 0.50 g. V in 30 ml. boiling MeCN was added to a filtered soln. of 0.61 g. XVII in 25 ml. boiling MeCN and the mixt. left 20 min. at room temp. to give 0.24 g. Et3NH+(Q•-)Q (XXI), black needles, decompg. above 195°, ρ 20 ohm-cm. (Εa 0.13 e.v.; single crystal detns. of ρ gave 0.5, 40, and 1000 ohm-cm. for the 3 major axes). Similarly were prepd. (salt, % yield, decompn. range, and ρ ohm-cm. given): (2,4,6-triphenylpyrylium)+(Q•-)Q (simple salt prepd. by metathesis from 2,4,6-triphenylpyrylium fluoborate), 21, 270° 16 (Ea 0.04 e.v.); (Me2N)3S+(Q•-)Q, 89, 229°, 30 (Εa 0.11 e.v.). The iodides of org. cations give complex salts with V, although the product from morpholine hydriodide (XXII) depends on the proportions of the reactants. Thus, near boiling solns. of 0.4 g. V and 1.1 g. XXII, each in 30 ml. MeCN, were mixed and left overnight at room temp. to give 0.15 g. (morpholinium)+(Q•-), red prisms, decompg. ∼220°, ρ 109 ohm-cm. (single crystal detns. of ρ gave 6 × 108 ohm-cm. for the 3 major axes). With 0.4 g. V in 25 ml. MeCN and 0.54 g. XXII in 20 ml. MeCN the sole product was 40% (morpholinium)2+-(Q•-)2Q, black plates, decompg. 210°, ρ105 ohm-cm. (single crystal detn. of ρ gave 5 × 103 ohm-cm.). A boiling soln. of 1.0 g. V in 100 ml. VII treated with 0.57 g. Et2N.HI in 7 ml. boiling MeCN and the mixt. left 30 min. at 0° gave 0.42 g. XXI. Similarly were prepd. (cation in the salt M+Q•-Q, appearance, % yield, decompn. range, and ρ ohm-cm. given): Et3-MeN, black rods, 65, 265-74°, 6 × 103; Et4N, black crystals, 79, 255-68°, 2 × 104; (4-amino-2,3,5,6-tetramethylanilinium) (prepd. in CHCl3-alc.), blue-black needles, 75, 180-220°, 8 (Εa 0.08 e.v.); (4-cyano-N-methylpyridinium), blue-black needles, 26, 258-60°, 48; (N-methylquinolinium), blue-black needles, 22, 245-50°, 3; (4-cyano-N-methylquinolinium), blue-black needles, 39, 223-39° 58; (N-ethylquinolinium), blue-black needles, 57, 237-9°, 8; (N-propylquinolinium), black rods, 92, 226-8°, 2 (single crystal detn. of ρ gave 0.5, 6, and 450 for the 3 major axes); [N-(2-phenylethyl)quinolinium,], black needles, 78, 248-50°, 3; [N-methyl-2-(4-dimethylaminophenylazo)pyridinium], purple-black microcrystals, 74, 248-9°, 12; Ph3MeP,. --, 60, 231-3°, -- (single crystal detn. of ρ gave 60, 600, and 105 for the 3 major axes; Εa 0.25 e.v.); Ph3EtP, --, 41, 223-5°, -- (single crystal detn. of ρ gave <10, 10, and 400 for the 3 major axes); Ph4P, --, 33, 228-37°, -- (single crystal detn. of ρ gave 103, 106, and 2 × 106 for the 3 major axes); Ph3MeAs, --.56, 224-7°, -- (single crystal detn. of ρ gave 57, 900, and 105 for the 3 major axes; Εa 0.22-0.23 e.v.); Ph3EtAs, --, 44, 212-19° -- (single crystal detn. of ρ gave 2 and 6600 for 2 of the major axes); Ph4Sb, --, 42, 219-20° -- (single crystal detn. of ρ gave 13 and 1.5 × 104 for 2 of the major axes); Ph3S, --, 65, 235-40°, -- (single crystal detn. of ρ gave 1.0 for the long axis); Ph3Se, --, 71, 240-5% 400. Et3N (0.75 ml.) in VII was added to a near boiling soln. of 2.8 g. V in 250 ml. VII then left 21 hrs. at room temp. to give 1.18 g. XXI. Similarly were prepd. (solvent, cation in the salt M+Q•-Q, appearance, % yield, decompn. range, and ρ ohm-cm. given): VII, Me3NH, black crystals, 90, >215° 5 × 106; VII, (triethylenediamine-H) (in [M+]2-[Q•-]Q), black microcrystals, 26, 270°, 10; CH2Cl2, (4-hydroxy-N-benzylanilinium), black microcrystals, 36,175 to above 300° 55 (Εa 0.075 e.v.); CHCl3, (4-amino-N,N-diethylanilinium), black rods, 55, 144 to above 300°, 175 (Εa 0.09 e.v.); MeCN (10 moles ferrocene/mole V), (ferricinium), black needles, low, --, 0.24 (single crystal); MeCN, (dimethylferricinium), black needles, 60, 170° 31. (Cobalticinium)Q•-Q, ρ 6.5 ohm-cm. (Εa 0.034 e.v.), was prepd. in 20% yield by mixing aq. solns. of cobalticinium chloride and XVI. Et3N (1.5 ml.) in 15 ml. MeCN was added to a soln. prepd. by addn. of 1.0 g. VI in 50 ml. hot MeCN to 3.0 g. V in 350 ml. gently boiling MeCN and the mixt. left overnight at room temp. to give 3.16 g. (62%) XXI. Similarly were prepd. (cation in the salt M+Q•-Q, appearance, % yield, decompn. range, and ρ ohm-cm. given): tert-BuMe2NH, black crystals, 82, 214°, 9; pyridinium, blue-black needles, 42, 168-85°, 37; (2,2'-bipyridinium), --, 100, 235-68°, 0.5. The mixed complex salt Ph3MeP+Ph3MeAs+(Q•-)2Q2 was prepd. from Ph3MePI, Ph3MeAsI, and V in MeCN. (Quinolinium)+•-Q (XXIII), blue-black needles, decompg. ∼250°, has the lowest ρ of any org. compd. (0.01 ohm-cm. for the long axis of a single crystal; compaction ρ 0.5 ohm-cm.). XXIII was prepd. in 91% yield from quinoline (XXIV) hydriodide (XXV) and XVI in MeCN, in 44% yield from XXV and XVI in CH2Cl2, in 87% yield from XXIV, V, and VI in MeCN, in 71% yield from XXIV, V, and durohydroquinone in MeCN, and from XXV and V in MeCN or CH2Cl2. Spectroscopic, polarographic, and conductivity data show that in soln. the complex salts are dissocd. into cation, Q•-, and V but they can be crystd. without change in compn. In the solid state there is probably complete electron delocalization between Q•- and Q. The complex salts are characterized by low ρ which shows exponential temp. dependence typical of intrinsic semiconductors. Both simple and complex salts are decompd. by mineral acids, e.g. 2.10 g. powd. XXI was added to 30ml. 2.4N HCl, the mixt. stirred 16 hrs. at room temp., the ppt. collected, washed with 2 ml. 2.4N HCl (0.27 g. Et3N was recovered from the filtrate and washings), then with H2O, and dried to give 1.66 g. V-VI mixt. (3:1). Q•- is oxidized to V by iodine; thus, 1.0 g. iodine added to 0.2 g. XXI in 10 ml. MeCN and the mixt. warmed on a steam-bath gave 0.12 g. (79%) V. Spectroscopic, polarographic, e.p.r., and elec. data are briefly discussed. 31 references.
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  26. 26
    Sambe, K.; Hoshino, N.; Takeda, T.; Nakamura, T.; Akutagawa, T. Dynamics and Structural Diversity of Li+(Crown Ether). Supramolecular Cations in Electrically Conducting Salts. J. Phys. Chem. C 2020, 124, 13560– 13571,  DOI: 10.1021/acs.jpcc.0c02686
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    Dynamics and Structural Diversity of Li+(Crown Ether) Supramolecular Cations in Electrically Conducting Salts
    Sambe, Kohei; Hoshino, Norihisa; Takeda, Takashi; Nakamura, Takayoshi; Akutagawa, Tomoyuki
    Journal of Physical Chemistry C (2020), 124 (25), 13560-13571CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
    Li+([12]crown-4)2(TCNQ)2 (1), Li+([15]crown-5)(TCNQ)2 (2a and 2b), and Li+([18]crown-6)(TCNQ)2·(H2O)2 (3) salts (TCNQ = 7,7,8,8-tetracyano-p-quinodimethane) were prepd. and examd. in terms of crystal structures, dielec. consts., magnetic susceptibilities, and elec. conductivities. The dynamic behavior of the small Li+ was easily activated inside the cavities of [15]crown-5 and [18]crown-6. In salt 2a, a structural phase transition at 160 K is thermally activated by a change in the -CN···Li+···NC- coordination from an asym. to a sym. environment. The phase-transition temp. for salt 2a is ∼25 K lower than that for the isostructural Na+([15]crown-5)(TCNQ)2, indicating that the behavior of Li+ inside the [15]crown-5 cavity is considerably more dynamic than that of Na+ in the same situation. Crystal polymorphs 2a and 2b are obsd. for Li+([15]crown-5) supramol. cations, where the two-dimensional intermol. interactions of TCNQs in salts 2a and 2b are constructed by the spanning-overlap mode of the π-dimers and π-tetramers, resp. The packing periodicity in the latter salt is twice that in the former, and this structural difference prevents the structural phase transition for salt 2b. In salt 3, the orientational disorder of Li+ inside the cavity of the [18]crown-6 is a combination of the dynamic behavior of Li+ itself and that of Li+-coordinated polar H2O mols., which are evidenced by two types of dielec. relaxation. Li+ is considerably smaller than Na+, allowing it to form a dynamic Li+···O coordination environment.
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    Yan, B.; Horton, P. N.; Russell, A. E.; Wedge, Ch. J.; Weston, S. C.; Grossel, M. C. Crown ether alkali metal TCNQ complexes revisited – the impact of smaller cation complexes on their solid-state architecture and properties. CrystEngComm 2019, 21, 3273– 3279,  DOI: 10.1039/C9CE00234K
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    Crown ether alkali metal TCNQ complexes revisited - the impact of smaller cation complexes on their solid-state architecture and properties
    Yan, Bingjia; Horton, Peter N.; Russell, Andrea E.; Wedge, Christopher J.; Weston, Simon C.; Grossel, Martin C.
    CrystEngComm (2019), 21 (21), 3273-3279CODEN: CRECF4; ISSN:1466-8033. (Royal Society of Chemistry)
    The solid-state behavior of four alkali metal TCNQ complexes: (15-crown-5)LiTCNQ (1), (15-crown-5)NaTCNQ (2), (15-crown-5)Li(TCNQ)2·H2O (3·H2O) and (15-crown-5)Na(TCNQ)2·H2O (4·H2O) has been explored by single crystal X-ray diffraction, IR (IR), Raman and ESR (EPR) measurements. The presence of a small cation and ionophore leads to subtle changes in behavior compared with their larger alkali metal analogs and in the hydrated salts water bridges form links between the crown-encapsulated cations and neighboring TCNQ stacks.
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    Yan, B.; Horton, P. N.; Weston, S. C.; Russell, A. E.; Grossel, M. C. Novel TCNQ-stacking motifs in (12-crown-4)-complexes of alkali metal TCNQ salts. CrystEngComm 2021, 23, 6755– 6760,  DOI: 10.1039/D1CE01075A
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    Novel TCNQ-stacking motifs in (12-crown-4)-complexes of alkali metal TCNQ salts
    Yan, Bingjia; Horton, Peter N.; Weston, Simon C.; Russell, Andrea E.; Grossel, Martin C.
    CrystEngComm (2021), 23 (38), 6755-6760CODEN: CRECF4; ISSN:1466-8033. (Royal Society of Chemistry)
    An investigation of the solid-state behavior of five 12-crown-4 alkali metal TCNQ complexes, (12-crown-4)2LiTCNQ (1), (12-crown-4)2NaTCNQ (2), (12-crown-4)2Li(TCNQ)2 (3), (12-crown-4)2Na(TCNQ)2 (4), and (12-crown-4)2K(TCNQ)2 (5), reveals an unusual "cross-stitch" packing motif with the extended face-to-face π-stacked TCNQ̇ - columns present in complexes 1 and 2. The effect of the presence of addnl. neutral TCNQ0 has also been explored.
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    Li, Q.; Wang, Y.; Yan, P.; Hou, G.; Li, G. Two 7,7,8,8-tetracyanoquinodimethane lead and zinc complexes featuring 3D and 0D structure: Synthesis, structure and electrochemical properties. Inorg. Chim. Acta 2014, 413, 32– 37,  DOI: 10.1016/j.ica.2013.12.032
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    Two 7,7,8,8-tetracyanoquinodimethane lead and zinc complexes featuring 3D and 0D structure: Synthesis, structure and electrochemical properties
    Li, Qiang; Wang, Yan; Yan, Pengfei; Hou, Guangfeng; Li, Guangming
    Inorganica Chimica Acta (2014), 413 (), 32-37CODEN: ICHAA3; ISSN:0020-1693. (Elsevier B.V.)
    Two 7,7,8,8-tetracyanoquinodimethane (TCNQ) Pb2+ and Zn2+ complexes, namely, {[Pb2(TCNQ)3(H2O)6](TCNQ)}n (1) and Li[Zn2(TCNQ)5(H2O)6]·[Zn(TCNQ)2(H2O)4]·6H2O (2) have been synthesized by the reactions of Li(TCNQ) with PbCl2 and Zn(TPP)2Cl2 (TPP = triphenylphosphine), resp. Single-crystal x-ray diffraction anal. reveals that complex 1 features a 3D network structure and complex 2 features a 0D structure in which a neutral mol. of [Zn(TCNQ)2(H2O)4] crystallizes in the crystal. The flexible coordination modes of TCNQ and the metal ions play essential roles on the formation of the novel 3D structure and the unique 0D ionic structure. The TCNQ mols. adapt a one-dimensional column through π-π stacking interactions. Cyclic and differential pulse voltammograms for complexes 1 and 2 show the reversible one-electron oxidn. and one-electron redn. within the electrochem. window of CH3CN. Their electrochem. HOMO-LUMO gap and reversibility were examd.
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    Lu, J.; Ojha, R.; Bond, A. M.; Martin, L. L. Systematic Approach to the Synthesis of Cobaltocenium Salts with Reduced Forms of TCNQF4: Two [Cp2Co](TCNQF4) Polymorphs and [Cp2Co]Li(TCNQF4). Cryst. Growth Des. 2019, 19, 2712– 2722,  DOI: 10.1021/acs.cgd.8b01841
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    Systematic Approach to the Synthesis of Cobaltocenium Salts with Reduced Forms of TCNQF4: Two [Cp2Co](TCNQF4) Polymorphs and [Cp2Co]Li(TCNQF4)
    Lu, Jinzhen; Ojha, Ruchika; Bond, Alan M.; Martin, Lisandra L.
    Crystal Growth & Design (2019), 19 (5), 2712-2722CODEN: CGDEFU; ISSN:1528-7483. (American Chemical Society)
    Three new crystallog. characterized compds. were prepd. in high yield from reactions between [Cp2Co]PF6 (Cp = cyclopentadiene) and lithium salts of the radical anion of 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (TCNQF41-) or the dianionic TCNQF42-. The two [Cp2Co]TCNQF4 compds. (1 and 2) with 1:1 stoichiometry were found to be polymorphic, α and β. Remarkably, the syntheses only differed by the presence of a small amt. of neutral TCNQF4 in the case of polymorph β (2). The role of the TCNQF4 has been rationalized on the basis of a transient intermediate, postulated as [Cp2Co](TCNQF4)2. Compd. 3 contains TCNQF42- and crystd. as [Cp2Co]Li(TCNQF4). This material highlights a novel coordination mode for the Li+ cation that participated in the formation of a metal-org. framework accommodating the [Cp2Co]+ cation. All complexes were comprehensively characterized by Fourier transform IR spectroscopy, UV-vis spectroscopy, and electrochem. Polymorph β (2) has a cond. of 5.8 × 10-4 S cm-1, which lies well within the semiconductor range. Previous work in this area employed redox chem. based on the reaction of cobaltocene or ferrocene with neutral TCNQ. The introduction of metathesis reactions enhances the synthetic flexibility enabling a systematic approach to new materials.
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    Černák, J.; Hegedüs, M.; Váhovská, L.; Kuchár, J.; Šoltésová, D.; Čižmár, E.; Feher, A.; Falvello, L. R. Syntheses, crystal structures and magnetic properties of complexes based on [Ni(L-L)3]2+ complex cations with dimethylderivatives of 2,2′-bipyridine and TCNQ. Solid State Sci. 2018, 77, 27– 36,  DOI: 10.1016/j.solidstatesciences.2018.01.004
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    Syntheses, crystal structures and magnetic properties of complexes based on [Ni(L-L)3]2+ complex cations with dimethylderivatives of 2,2'-bipyridine and TCNQ
    Cernak, Juraj; Hegedus, Michal; Vahovska, Lucia; Kuchar, Juraj; Soltesova, Daniela; Cizmar, Erik; Feher, Alexander; Falvello, L. R.
    Solid State Sciences (2018), 77 (), 27-36CODEN: SSSCFJ; ISSN:1293-2558. (Elsevier Masson SAS)
    From the aq.-methanolic systems Ni(NO3)2 - LiTCNQ - 5,5'-dmbpy and Ni(NO3)2 - LiTCNQ - 4,4'-dmbpy three novel complexes [Ni(5,5'-dmbpy)3](TCNQ)2 (1), [Ni(4,4'-dmbpy)3](TCNQ)2 (2) and [Ni(4,4'-dmbpy)3]2(TCNQ-TCNQ)(TCNQ)2•0.60H2O (3), were isolated in single crystal form. The new compds. were identified using chem. analyses and IR spectroscopy. Single crystal studies of all samples corroborated their compns. and have shown that their ionic structures contain the complex cations [Ni(5,5'-dmbpy)]2+ (1) or [Ni(4,4'-dmbpy)]2+ (2 and 3). The anionic parts of the resp. crystal structures 1-3 are formed by TCNQ·- anion-radicals and in 3 also by a σ-dimerized dianion (TCNQ-TCNQ)2- with a C-C distance of 1.663(5) Å. The supramol. structures are governed by weak hydrogen bonding interactions. The variable-temp. (2-300 K) magnetic studies of 1 and 3 confirmed the presence of magnetically active Ni(II) atoms with S = 1 and TCNQ·- anion-radicals with S = 1/2 while the (TCNQ-TCNQ)2- dianion is magnetically silent. The magnetic behavior was described by a complex magnetic model assuming strong antiferromagnetic interactions between some TCNQ·- anion-radicals.
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    Lu, J.; Le, T. H.; Traore, D. A. K.; Wilce, M.; Bond, A. M.; Martin, L. L. Synthetic Precursors for TCNQF42– Compounds: Synthesis, Characterization, and Electrochemical Studies of (Pr4N)2TCNQF4 and Li2TCNQF4. J. Org. Chem. 2012, 77, 10568– 10574,  DOI: 10.1021/jo301403v
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    Synthetic Precursors for TCNQF42- Compounds: Synthesis, Characterization, and Electrochemical Studies of (Pr4N)2TCNQF4 and Li2TCNQF4
    Lu, Jinzhen; Le, Thanh Hai; Traore, Daouda A. K.; Wilce, Matthew; Bond, Alan M.; Martin, Lisandra L.
    Journal of Organic Chemistry (2012), 77 (23), 10568-10574CODEN: JOCEAH; ISSN:0022-3263. (American Chemical Society)
    The lithium radical monoanion salt of tetrafluorotetracyanoquinodimethane Li(TCNQF4) and the dilithium dianion salt Li2(TCNQF4) were prepd. selectively from lithium iodide and tetrafluorotetracyanoquinodimethane (TCNQF4) by carefully controlling the reagent stoichiometry and temp. Reaction of TCNQF4 with four equiv. of LiI in boiling acetonitrile yielded Li2TCNQF4 in 90% yield; use of less than four equiv. of LiI gave mixts. of the mono- and dianionic salts. Reaction of TCNQF4 with 1.5 equiv. of LiI in acetonitrile at ambient temp. gave Li(TCNQF4) in 84% yield. The monoanion and dianion tetrapropylammonium salts of TCNQF4 were prepd. by cation exchange of Li(TCNQF4) or Li2(TCNQF4) with tetrapropylammonium bromide in hot water. The structures of (Pr4N)2(TCNQF4) and Pr4N(TCNQF4) were detd. by X-ray crystallog.
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    Tanase, S.; Ferbinteanu, M.; Andruh, M.; Mathonière, C.; Strenger, I.; Rombaut, G. Synthesis and characterization of a new molecular magnet, [Ni(ampy)2]3[Fe(CN)6]2·6H2O, and synthesis, crystal structure and magnetic properties of its mononuclear precursor, trans-[Ni(ampy)2(NO3)2] (ampy = 2-aminomethylpyridine). Polyhedron 2000, 19, 1967– 1973,  DOI: 10.1016/S0277-5387(00)00497-6
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    Synthesis and characterization of a new molecular magnet, [Ni(ampy)2]3[Fe(CN)6]2·6H2O, and synthesis, crystal structure and magnetic properties of its mononuclear precursor, trans-[Ni(ampy)2(NO3)2] (ampy = 2-aminomethylpyridine)
    Tanase, Stefania; Ferbinteanu, Marilena; Andruh, Marius; Mathoniere, Corine; Strenger, Irina; Rombaut, Guillaume
    Polyhedron (2000), 19 (16-17), 1967-1973CODEN: PLYHDE; ISSN:0277-5387. (Elsevier Science Ltd.)
    The reaction of trans-[Ni(ampy)2(NO3)2] (1, ampy = 2-aminomethylpyridine) with K3[Fe(CN)6] affords a cyano-bridged bimetallic system, [Ni(ampy)2]3[Fe(CN)6]2·6H2O (2). The crystal structure of compd. 1 was solved. It crystallizes in the monoclinic space group P121/c1 and consists of neutral mononuclear entities with the nickel atom located on an inversion center. The nickel atom exhibits a (pseudo)octahedral stereochem. with the two nitrato ligands coordinated in trans positions. The Ni-N bond distances vary from 2.0690(15) to 2.0811(15) Å, while the trans-Ni-O distances are 2.1665(13) Å. The cryomagnetic study of compd. 1 reveals an intermol. ferromagnetic coupling (θ = + 3.7 K), which is mediated by the π-π stacking interactions between the mononuclear entities. Compd. 2 is a soft ferromagnet with Tc = 7.5 K and a coercive field of 330 G at 2 K.
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    Tandon, S. S.; Chander, S.; Thompson, L. K. Ligating properties of tridentate Schiff base ligands, 2-[[(2-pyridinylmethyl)imino]methyl] phenol (HSALIMP) and 2-[[[2-(2-pyridinyl)ethyl]imino]methyl]phenol (HSALIEP) with zinc(II), cadmium(II), nickel(II) and manganese(III) ions. X-ray crystal structures of the [Zn(SALIEP)(NO3)]2 dimer, [Mn(SALIEP)2](ClO4), and [Zn(AMP)2(NO3)2]. Inorg. Chim. Acta 2000, 300-302, 683– 692,  DOI: 10.1016/S0020-1693(00)00010-4
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    Ligating properties of tridentate Schiff base ligands, 2-[[(2-pyridinylmethyl)imino]methyl]phenol (HSALIMP) and 2-[[[2-(2-pyridinyl)ethyl]imino]methyl]phenol (HSALIEP) with zinc(II), cadmium(II), nickel(II) and manganese(III) ions. X-ray crystal structures of the [Zn(SALIEP)(NO3)]2 dimer, [Mn(SALIEP)2](ClO4), and [Zn(AMP)2(NO3)2]
    Tandon, S. S.; Chander, S.; Thompson, L. K.
    Inorganica Chimica Acta (2000), 300-302 (), 683-692CODEN: ICHAA3; ISSN:0020-1693. (Elsevier Science S.A.)
    Zn(II), Cd(II), Ni(II) and Mn(III) complexes with two potentially tridentate (NNO) Schiff base ligands, 2-[[(2-pyridinylmethyl)imino]methyl]phenol (HSALIMP) and 2-[[[2-(2-pyridinyl)ethyl]imino]methyl]phenol (HSALIEP) were synthesized and structurally characterized through IR, 1H, 13C, and 2-dimensional NMR spectroscopy and in two cases by x-ray crystallog. The Schiff base ligands HSALIMP and HSALIEP are generated from 1+1 condensation of salicylaldehyde with 2-aminomethylpyridine and 2(2-aminoethyl)pyridine, resp. HSALIMP behaves as a tridentate (NNO) or a bidentate (NN) ligand, depending upon the nature of the anion. On reaction with Zn(II) salts HSALIMP gives two types of complexes, (a) [Zn(SALIMP)X]2·yH2O (X = NO3, y = 0 (I); X = I, y = 3 (II)) and (b) [Zn(HSALIMP)Cl2]·H2O (III). HSALIMP reacts with Ni(II) bromide to form mononuclear [Ni(HSALIMP)2Br2] (VIII), in which one metal ion combines with two neutral HSALIMP ligands. However HSALIEP, a similar ligand with one addnl. C atom in the chain, acts as a tridentate ligand (NNO), with the phenolate O deprotonated, irresp. of the nature of the anion, forming dimeric compds. of 1:1 metal:ligand stoichiometry with Zn(II) and Cd(II) ions, [Zn(SALIEP)X]2·yH2O (X = NO3, y = 0 (IV); X = Cl, y = 2 (V); X = I, y = 1 (VI)), [Cd(SALIEP) (NO3)]2·EtOH (VII) and a monomeric complex of 1:2 metal:ligand stoichiometry with Mn(III) ion, [Mn(SALIEP)2](ClO4) (IX). The single crystal x-ray structures of the [Zn(SALIEP)(NO3)]2 (IV) dimer, [Mn(SALIEP)2](ClO4) (IX), and [Zn(AMP)2(NO3)2] (X), a minor product obtained from the filtrate of I, were detd. IV consists of centrosym. dimer in which deprotonated phenolates bridge the two five-coordinate metal atoms and link the two halves of the dimer. The structure of IX consists of a centrosym. mol. in which the Mn(III) ion is bound to two tridentate SALIEP ligands in a nearly regular octahedral arrangement. The structure of X consists of a centrosym. monomer in which the six coordinate octahedral Zn(II) ion is bonded equatorially to two bidentate 2-aminomethylpyridine ligands and axially to two monodentate nitrate groups.
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  35. 35
    Macrae, C. F.; Sovago, I.; Cottrell, S. J.; Galek, P. T. A.; McCabe, P.; Pidcock, E.; Platings, M.; Shields, G. P.; Stevens, J. S.; Towler, M.; Wood, P. A. Mercury 4.0: from visualization to analysis, design and prediction. J. Appl. Crystallogr. 2020, 53, 226– 235,  DOI: 10.1107/S1600576719014092
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    Mercury 4.0: from visualization to analysis, design and prediction
    Macrae, Clare F.; Sovago, Ioana; Cottrell, Simon J.; Galek, Peter T. A.; McCabe, Patrick; Pidcock, Elna; Platings, Michael; Shields, Greg P.; Stevens, Joanna S.; Towler, Matthew; Wood, Peter A.
    Journal of Applied Crystallography (2020), 53 (1), 226-235CODEN: JACGAR; ISSN:1600-5767. (International Union of Crystallography)
    The program Mercury, developed at the Cambridge Crystallog. Data Center, was originally designed primarily as a crystal structure visualization tool. Over the years the fields and scientific communities of chem. crystallog. and crystal engineering have developed to require more advanced structural anal. software. Mercury has evolved alongside these scientific communities and is now a powerful anal., design and prediction platform which goes a lot further than simple structure visualization.
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    An empirical correction for absorption anisotropy
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    Acta crystallographica. Section A, Foundations of crystallography (1995), 51 ( Pt 1) (), 33-8 ISSN:0108-7673.
    A least-squares procedure is described for modeling an empirical transmission surface as sampled by multiple symmetry-equivalent and/or azimuth rotation-equivalent intensity measurements. The fitting functions are sums of real spherical harmonic functions of even order, ylm(-u0) + ylm(u1), 2 < or = l = 2n < or = 8. The arguments of the functions are the components of unit direction vectors, -u0 for the reverse incident beam and u1 for the scattered beam, referred to crystal-fixed Cartesian axes. The procedure has been checked by calculations against standard absorption test data.
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    Sheldrick, G. M. SHELXT - Integrated space-group and crystal-structure determination. Acta Crystallogr., Sect. A: Found. Adv. 2015, 71, 3– 8,  DOI: 10.1107/S2053273314026370
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    SHELXT - Integrated space-group and crystal-structure determination
    Sheldrick, George M.
    Acta Crystallographica, Section A: Foundations and Advances (2015), 71 (1), 3-8CODEN: ACSAD7; ISSN:2053-2733. (International Union of Crystallography)
    The new computer program SHELXT employs a novel dual-space algorithm to solve the phase problem for single-crystal reflection data expanded to the space group P1. Missing data are taken into account and the resoln. extended if necessary. All space groups in the specified Laue group are tested to find which are consistent with the P1 phases. After applying the resulting origin shifts and space-group symmetry, the solns. are subject to further dual-space recycling followed by a peak search and summation of the electron d. around each peak. Elements are assigned to give the best fit to the integrated peak densities and if necessary addnl. elements are considered. An isotropic refinement is followed for non-centrosym. space groups by the calcn. of a Flack parameter and, if appropriate, inversion of the structure. The structure is assembled to maximize its connectivity and centered optimally in the unit cell. SHELXT has already solved many thousand structures with a high success rate, and is optimized for multiprocessor computers. It is, however, unsuitable for severely disordered and twinned structures because it is based on the assumption that the structure consists of atoms.
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    Sheldrick, G. M. Crystal structure refinement with SHELXL. Acta Crystallogr., Sect. C: Struct. Chem. 2015, C71, 3– 8,  DOI: 10.1107/S2053229614024218
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    WinGX and ORTEP for Windows: an update
    Farrugia, Louis J.
    Journal of Applied Crystallography (2012), 45 (4), 849-854CODEN: JACGAR; ISSN:0021-8898. (International Union of Crystallography)
    The WinGX suite provides a complete set of programs for the treatment of small-mol. single-crystal diffraction data, from data redn. and processing, structure soln., model refinement and visualization, and metric anal. of mol. geometry and crystal packing, to final report prepn. in the form of a CIF. It includes several well known pieces of software and provides a repository for programs when the original authors no longer wish to, or are unable to, maintain them. It also provides menu items to execute external software, such as the SIR and SHELX suites of programs. The program ORTEP for Windows provides a graphical user interface (GUI) for the classic ORTEP program, which is the original software for the illustration of anisotropic displacement ellipsoids. The GUI code provides input capabilities for a wide variety of file formats, and extra functionality such as geometry calcns. and ray-traced outputs. The programs WinGX and ORTEP for Windows have been distributed over the internet for about 15 years, and this article describes some of the more modern features of the programs.
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    Karplus, P. A.; Diederichs, K. Assessing and maximizing data quality in macromolecular crystallography. Curr. Opin. Struct. Biol. 2015, 34, 60– 68,  DOI: 10.1016/j.sbi.2015.07.003
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    Assessing and maximizing data quality in macromolecular crystallography
    Karplus, P. Andrew; Diederichs, Kay
    Current Opinion in Structural Biology (2015), 34 (), 60-68CODEN: COSBEF; ISSN:0959-440X. (Elsevier Ltd.)
    A review. The quality of macromol. crystal structures depends, in part, on the quality and quantity of the data used to produce them. Here, the authors review recent shifts in the understanding of how to use data quality indicators to select a high resoln. cutoff that leads to the best model, and of the potential to greatly increase data quality through the merging of multiple measurements from multiple passes of single crystals or from multiple crystals. Key factors supporting this shift are the introduction of more robust correlation coeff. based indicators of the precision of merged data sets as well as the recognition of the substantial useful information present in extensive amts. of data once considered too weak to be of value.
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    Brandenburg, K. DIAMOND. Crystal Impact (Version 3.1f) GbR; Bonn: Germany, 2008.
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    Guzei, I.; Herbst-Irmer, R.; Munyaneza, A.; Darkwa, J. Detailed example of the identification and crystallographic analysis of a pseudo-merohedrally twinned crystal. Acta Crystallogr., Sect. B Struct. Sci. 2012, 68, 150– 157,  DOI: 10.1107/S0108768112002728
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    Detailed example of the identification and crystallographic analysis of a pseudo-merohedrally twinned crystal
    Guzei, Ilia; Herbst-Irmer, Regine; Munyaneza, Apollinaire; Darkwa, James
    Acta Crystallographica, Section B: Structural Science (2012), 68 (2), 150-157CODEN: ASBSDK; ISSN:0108-7681. (International Union of Crystallography)
    A detailed description of the crystal structure soln. and refinement of a pseudo-merohedrally twinned crystal of an organometallic complex is presented as a guide to the handling of similar non-routine challenging crystal structures. The interpretation of the signs of twinning and the logic behind the selection of the correct space group are explained. In this case the crystal twinning was complicated by pseudo-symmetry of the ionic species and positional disorder of several atoms. A detailed description of the procedures utilized in the non-routine X-ray single-crystal structural detn. and refinement of a pseudo-merohedrally twinned crystal of an Fe/Ni organometallic complex is presented. It illustrates to the practitioners of crystallog. how to properly handle such cases and describes the logic and concrete steps necessary to account for the twinning, pseudo-symmetry and at. positional disorder.
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    Parkin, S. R. Practical hints and tips for solution of pseudo-merohedric twins: three case studies. Acta Crystallogr., Sect. E: Crystallogr. Commun. Cryst Commun 2021, 77, 452– 465,  DOI: 10.1107/S205698902100342X
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    Practical hints and tips for solution of pseudo-merohedric twins: three case studies
    Parkin, S. R.
    Acta Crystallographica, Section E: Crystallographic Communications (2021), 77 (5), 452-465CODEN: ACSECI; ISSN:2056-9890. (International Union of Crystallography)
    Twinning by pseudo-merohedry is a common phenomenon in small-mol. crystallog. In cases where twin-component vol. fractions are markedly different, structure soln. is often no more difficult than for non-twinned structures of similar complexity. When twin-component vol. fractions are similar, however, structure soln. can be much more of a problem. This paper presents hints and tips for such cases by means of three worked examples. The first example presents the most common (and simplest) case of a two-component pseudo-orthorhombic twin. The second example describes structure soln. of a reticular threefold pseudo-hexagonal twin that benefits from use of an unconventional space-group setting. The third example covers structure soln. of a reticular fourfold pseudo-tetragonal twin. All three structures are ultimately shown to be monoclinic crystals that twin as a consequence of unit-cell metrics that mimic those of higher symmetry crystal systems.
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    Spek, A. L. checkCIF validation ALERTS: what they mean and how to respond. Acta Crystallogr., Sect. E: Crystallogr. Commun. 2020, 76, 1– 11,  DOI: 10.1107/S2056989019016244
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    checkCIF validation ALERTS: what they mean and how to respond
    Spek, Anthony L.
    Acta Crystallographica, Section E: Crystallographic Communications (2020), 76 (1), 1-11CODEN: ACSECI; ISSN:2056-9890. (International Union of Crystallography)
    A review. Authors of a paper that includes a new crystal-structure detn. are expected to not only report the structural results of interest and their interpretation, but are also expected to archive in computer-readable CIF format the exptl. data on which the crystal-structure anal. is based. Addnl., an IUCr/checkCIF validation report will be required for the review of a submitted paper. Such a validation report, automatically created from the deposited CIF file, lists as ALERTS not only potential errors or unusual findings, but also suggestions for improvement along with interesting information on the structure at hand. Major ALERTS for issues are expected to have been acted on already before the submission for publication or discussed in the assocd. paper and/or commented on in the CIF file. In addn., referees, readers and users of the data should be able to make their own judgment and interpretation of the underlying exptl. data or perform their own calcns. with the archived data. All the above is consistent with the FAIR (findable, accessible, interoperable, and reusable) initiative [Helliwell (2019). Struct. Dyn.6, 05430]. Validation can also be helpful for less experienced authors in pointing to and avoiding of crystal-structure detn. and interpretation pitfalls. The IUCr web-based checkCIF server provides such a validation report, based on data uploaded in CIF format. Alternatively, a locally installable checkCIF version is available to be used iteratively during the structure-detn. process. ALERTS come mostly as short single-line messages. There is also a short explanation of the ALERTS available through the IUCr web server or with the locally installed PLATON/checkCIF version. This paper provides addnl. background information on the checkCIF procedure and addnl. details for a no. of ALERTS along with options for how to act on them.
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    Usón, I.; Sheldrick, G. M. Advances in direct methods for protein crystallography. Curr. Opin. Struct. Biol. 1999, 9, 643– 648,  DOI: 10.1016/s0959-440x(99)00020-2
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    Advances in direct methods for protein crystallography
    Uson, Isabel; Sheldrick, George M.
    Current Opinion in Structural Biology (1999), 9 (5), 643-648CODEN: COSBEF; ISSN:0959-440X. (Current Biology Publications)
    A review with 43 refs. Recent advances in ab initio direct methods have enabled the soln. of crystal structures of small proteins from native x-ray data alone, i.e., without the use of fragments of known structure or the need to prep. heavy-atom or selenomethionine derivs., provided that the data are available to at. resoln. These methods are also proving to be useful for locating the selenium atoms or other anomalous scatterers in the multiple wavelength anomalous diffraction phasing of larger proteins at lower resoln.
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    Herbst-Irmer, R.; Sheldrick, G. M. Refinement of twinned structures with SHELX97. Acta Crystallogr., Sect. B: Struct. Sci. 1998, B 54, 443– 449,  DOI: 10.1107/S0108768197018454
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    Utilization of diffusion processes in the preparation of pure substances
    Johnston, John
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    A theoretical discussion of the conditions which favor the production of large crystals is followed by the description of an app. by means of which relatively large and hence pure crystals of rather insol. substances may be prepared.
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    Martin, S. A.; Haendler, H. M. A modified diffusion apparatus for the growth of single crystals. J. Appl. Crystallogr. 1978, 11, 62,  DOI: 10.1107/S0021889878012728
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    A modified diffusion apparatus for the growth of single crystals
    Martin, Sharon A.; Haendler, Helmut M.
    Journal of Applied Crystallography (1978), 11 (1), 62CODEN: JACGAR; ISSN:0021-8898.
    Single crystals of insol. compds. can be grown by diffusion of 2 solns. which interact to form the solid by metathesis with minimization of convection and removal of crystals without further mixing of the solns. by using a modification of the gel-diffraction app. of A. Armington and J. O'Connor (1968). The app. was used to grow single crystals of Y, Zn, Co,and Cd anthranilates with a soln. of Na anthranilate in one reservoir and a soln. of metal salt in th other. Well-shaped crystals suitable for x-ray work were grown in 2-3 wk.
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    Yan, J.-Q.; Sales, B. C.; Susner, M. A.; McGuire, M. A. Flux growth in a horizontal configuration: An analog to vapor transport growth. Phys. Rev. Mater. 2017, 1, 023402  DOI: 10.1103/PhysRevMaterials.1.023402
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    Flux growth in a horizontal configuration: an analog to vapor transport growth
    Yan, J.-Q.; Sales, B. C.; Susner, M. A.; McGuire, M. A.
    Physical Review Materials (2017), 1 (2), 023402/1-023402/11CODEN: PRMHBS; ISSN:2475-9953. (American Physical Society)
    Flux growth of single crystals is normally performed in a vertical configuration with an upright refractory container holding the flux melt. At high temps., flux dissolves the charge, forming a homogeneous soln. before nucleation and growth of crystals takes place under proper supersatn. generated by cooling or evapg. the flux. In this work, we report flux growth in a horizontal configuration with a temp. gradient along the horizontal axis: a liq. transport growth analogus to the vapor transport technique. In a typical liq. transport growth, the charge is kept at the hot end of the refractory container and the flux melt dissolves the charge and transfers it to the cold end. Once the concn. of charge is above the soly. limit at the cold end, the thermodynamically stable phase nucleates and grows. Compared to the vertical flux growth, the liq. transport growth can provide a large quantity of crystals in a single growth since the charge/flux ratio is not limited by the soly. limit at the growth temp. This technique is complementary to the vertical flux growth and can be considered when a large amt. of crystals is needed but the yield from the conventional vertical flux growth is limited. We applied this technique to the growth of IrSb3, Mo3Sb7, and MnBi from self-flux, and the growth of FeSe, CrTe3, NiPSe3, FePSe3, CuInP2S6, RuCl3, and OsCl4 from a halide flux.
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    Kim, J.; Silakov, A.; Yennawar, H. P.; Lear, B. J. Structural, Electronic, and Magnetic Characterization of a Dinuclear Zinc Complex Containing TCNQ– and a μ-[TCNQ–TCNQ]2– Ligand. Inorg. Chem. 2015, 54, 6072– 6074,  DOI: 10.1021/acs.inorgchem.5b00808
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    Structural, Electronic, and Magnetic Characterization of a Dinuclear Zinc Complex Containing TCNQ- and a μ-[TCNQ-TCNQ]2- Ligand
    Kim, Juyeong; Silakov, Alexey; Yennawar, Hemant P.; Lear, Benjamin J.
    Inorganic Chemistry (2015), 54 (13), 6072-6074CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
    A dinuclear zinc complex contg. both a σ-dimerized 7,7,8,8-tetracyanoquinodimethane (TCNQ) ligand ([TCNQ-TCNQ]2-) and TCNQ- was synthesized for the first time. This is the first instance of a single mol. complex with a bridging [TCNQ-TCNQ]2- ligand. Each zinc center is coordinated with two 2,2'-bipyrimidines and one TCNQ-, and the remaining coordination site is occupied by a [TCNQ-TCNQ]2- ligand, which bridges the two zinc centers. The complex facilitates π-stacking of TCNQ- ligands when crystd., which gives rise to a near-IR charge-transfer transition and strong antiferromagnetic coupling.
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    Abrahams, B. F.; Elliott, R. W.; Hudson, T. A.; Robson, R. A New Class of Easily Generated TCNQ2– -Based Coordination Polymers. Cryst. Growth Des. 2010, 10, 2860– 2862,  DOI: 10.1021/cg100568a
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    A new class of easily generated TCNQ2--based coordination polymers
    Abrahams, Brendan F.; Elliott, Robert W.; Hudson, Timothy A.; Robson, Richard
    Crystal Growth & Design (2010), 10 (7), 2860-2862CODEN: CGDEFU; ISSN:1528-7483. (American Chemical Society)
    New types of coordination polymers contg. [M(TCNQ)] sheets in which the TCNQ component is present as the little known dianion (TCNQ2-) were obtained in a very simple manner using readily available TCNQH2 (1,4-(NC)2CH·C6H4·CH(CN)2) as the starting material. Above and below the metal centers in the sheets, a range of pyridine derivs. can be attached, some terminal and some acting as pillars linking sheet to sheet to form a 3-dimensional coordination network. The following compds., generally in solvated form, were isolated and structurally characterized - [M(TCNQ)(pyridine)2] (M = Mn or Zn), [M(TCNQ)(quinoline)2] (M = Co or Zn), [Mn(TCNQ)(4-methylpyridine)2], [Zn(TCNQ)(4-phenylpyridine)2], [Zn(TCNQ)(isoquinoline)2], [Zn(TCNQ)(nicotinamide)2], [M(TCNQ)(bipy)] (M = Mn, Fe, Zn, Cd, and bipy =4,4'-bipyridine, which links sheet to sheet to generate 3-dimensional coordination polymers), [Zn(TCNQ)(bpe)] (bpe = 1,2-bis(4-pyridyl)ethylene), and [Zn(CH3OH)(TCNQ)(Obip)1/2] (Obip = 4,4'-bipyridine di-N-oxide). The TCNQH2/TCNQ2- approach opens the way to numerous new types of cryst. and structurally characterizable TCNQ-based networks (and not just the sheet structures that are the focus of this preliminary report) that may lead to solids with unusual and useful electronic/magnetic properties.
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    Konno, M.; Ishii, T.; Saito, Y. The crystal structures of the low- and high-temperature modifications of potassium 7,7,8,8-tetracyanoquinodimethanide. Acta Crystallogr., Sect. B: Struct. Crystallogr. Cryst. Chem. 1977, 33, 763– 770,  DOI: 10.1107/S0567740877004609
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    Richard, P. P.; Zanghi, J.-C.; Guédon, J.-F.; Hota, N. Structure cristalline du complexe de potassium avec le tétracyano-7,7,8,8 quinodiméthane. Acta Crystallogr., Sect. B: Struct. Crystallogr. Cryst. Chem. 1978, B34, 788– 792,  DOI: 10.1107/S0567740878004070
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    Crystal structure of the potassium-tetracyano-7,7,8,8-quinodimethane complex
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    Inorganic Chemistry (2000), 39 (13), 2837-2842CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
    New derivs. [M(dieneN4)](TCNQ)3, M = Ni or Cu and dieneN4 = cis- or trans-hexamethyltetraazacyclotetradecadiene, were obtained. The TCNQ units show electronic delocalization and formation of 1-dimensional stacks, with no direct interactions with the metal cations. The stack is not uniform and can be seen as formed by trimeric dianions (TCNQ)32-. The electronic delocalization favors the cond. in these materials, which behave as good semiconductors. The crystal structures of the trans derivs. were solved:[Ni(trans-dieneN4)](TCNQ)3, triclinic, P‾1, a 8.809(2), b 10.896(2), c 13.727(2) Å, α 103.04(1), β 101.23(2), γ 109.37(2)°, Z = 1; [Cu(trans-dieneN4)](TCNQ)3: triclinic, P‾1, a 7.872(1), b 9.840(1), c 14.819(1) Å, α 92.32(1), β 95.05(1), γ 95.66(1)°, Z = 1.
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    Crystal Growth & Design (2015), 15 (5), 2437-2444CODEN: CGDEFU; ISSN:1528-7483. (American Chemical Society)
    Coordination polymer strips of compn. ...Cu+2·lig2-·Cu+2·lig2-·Cu+2·lig2-... (lig2- = TCNQ2- or its 2,3,4,5-tetrafluoro analog) are obsd. with a wide range of coligands (monodentate, bidentate, and tridentate). Interdigitation of thin, planar N-heteroarom. coligands on one strip with those on a neighbor is a common structural feature. Coligands too bulky to allow interdigitation give either noninterdigitating strips or 2-dimensional sheet structures. Both strips and sheets have 2-connecting Cu centers and 4-connecting tetracynano ligands. As a consequence of the great flexibility of the Cu/tetracyano ligand assocn., the geometries of the sheet structures vary widely from almost coplanar to highly corrugated and convoluted, despite which the same topol. is present in all.
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    The new compd. Cu2I(TCNQF4II-)(MeCN)2 (TCNQF42- = dianion of 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane) was synthesized by electrochem. directed synthesis involving redn. of TCNQF4 to TCNQF42- in acetonitrile contg. [Cu(MeCN)4]+(MeCN) and 0.1 M Bu4NPF6. In one scenario, TCNQF42- is quant. formed by reductive electrolysis of TCNQF4 followed by addn. of [Cu(MeCN)4]+ to form the Cu2I(TCNQF4II-)(MeCN)2 coordination polymer. In a second scenario, TCNQF4 is reduced in situ at the electrode surface to TCNQF42-, followed by reaction with the [Cu(MeCN)4]+ present in the soln., to electrocrystallize Cu2I(TCNQF4II-)(MeCN)2. Two distinct phases of Cu2I(TCNQF4II-)(MeCN)2 are formed in this scenario; the kinetically favored form being rapidly converted to the thermodynamically favored Cu2I(TCNQF4II-)(MeCN)2. The postulated mechanism is supported by simulations. The known compd. CuITCNQF4I- also was isolated by one electron redn. of TCNQF4 and reaction with [Cu(MeCN)4]+. The soly. of both TCNQF42-- and TCNQF4•--derived solids indicates that the higher soly. of CuITCNQF4I- prevents its pptn., and thus Cu2I(TCNQF4II-)(MeCN)2 is formed. UV-visible and vibrational spectroscopies were used to characterize the materials. Cu2I(TCNQF4II-)(MeCN)2 can be photochem. transformed to CuITCNQF4I- and Cu0. SEM images reveal that CuITCNQF4I- and Cu2I(TCNQF4II-)(MeCN)2 are electrocrystd. with distinctly different morphologies. Thermogravimetric and elemental anal. data confirm the presence of CH3CN, and single-crystal x-ray diffraction data for the Cu2I(TCNQF4II-)(EtCN)2 analog shows that this compd. is structurally related to Cu2I(TCNQF4II-)(MeCN)2.
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    Paramagnetic resonance is studied on large single crystals of Cu acetate, the prepn. of which is described. The spectrum is anomalous. The anomalies in fine structure and hyperfine structure are accounted for by postulating strong interaction between isolated pairs of Cu ions, each pair forming a lower singlet and an upper triplet state, only the latter being paramagnetic. The unit cell contains 2 differently oriented pairs of ions. The structure corresponds to an effective spin of 1. The interaction forces are discussed.
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  • Abstract

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    Scheme 1

    Scheme 1. Chemical Structures of TCNQ and 2ampy
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    Figure 1

    Figure 1. Dark crystals of 1 grown on the surface of blue/purple crystals of [Ni(2ampy)2(NO3)2].

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    Figure 2

    Figure 2. Preparation of single crystals of 3. In this test, the crystals are visible under the microscope for 1 min after the addition of the reactants, and they begin to disappear about 7 min later. (a–f). Time-stamped progression of crystal growth and disappearance. (g, h) Further magnified views from panels (c, d), respectively.

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    Figure 3

    Figure 3. Molecular structure of 1 at 100 K showing the atom numbering scheme. The thermal ellipsoids are drawn at the 50% probability level. Symmetry code: (i) 1 – x, 1 – y, 1 – z.

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    Figure 4

    Figure 4. Hydrogen bonding system in 1. H-bonds are represented as yellow dashed lines. For the sake of clarity, the chelate rings and hydrogen atoms not participating in hydrogen bonds are omitted. Symmetry codes: (ii) x, y – 1, z + 1; (iii) 1 – x, 2 – y, 1 – z; (v) 1 – x, 1 – y, 2 – z.

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    Figure 5

    Figure 5. Ribbons of “Li2TCNQF4” in the crystal structure of [Li2TCNQF4(CH3CN)4]·CH3CN, (3). Symmetry codes: (ii) −x, −y, −z; (iv) 1 – x, −y, −z.

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    Figure 6

    Figure 6. Inclination of the C6F4 rings in 3.

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    Figure 7

    Figure 7. View of the chains in 3.

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    Figure 8

    Figure 8. Temperature dependence of susceptibility and χT (inset) of 2 (open symbols) measured in the applied field of 1 kOe, including the model χ = 2(1 – c)χCurie + cχdimer proposed in the text.

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    Figure 9

    Figure 9. Field dependence of the magnetization of 2 at 1.8 and 4.5 K (open symbols), including the fit of the Brillouin function representing the paramagnetic contribution of nondimerized paramagnetic TCNQ species.

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    Figure 10

    Figure 10. Temperature dependence of the susceptibility and χT (inset) of 1 (open symbols) measured in the applied field of 1 kOe, including the fit of the simplified model χ = χNi + χdimer + χ0 (solid line) and a spin-ring model (dashed line) proposed in the text.

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    Figure 11

    Figure 11. Field dependence of the magnetization of 1 at 1.8 and 4.5 K (open symbols), including the fit of the simplified (solid lines) and spin-ring model (dashed lines) proposed in the text.

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    3. 3
      Miller, J. S.; Zhang, J. H.; Reiff, W. M.; Dixon, D. A.; Preston, L. D.; Reis, A. H., Jr.; Gebert, E.; Extine, M.; Troup, J. Characterization of the charge-transfer reaction between decamethylferrocene and 7,7,8,8,-tetracyano-p-quinodimethane (1:1). The iron-57 Moessbauer spectra and structures of the paramagnetic dimeric and the metamagnetic one-dimensional salts and the molecular and electronic structures of (TCNQ)n(n = 0, −1, −2). Phys. Chem. 1987, 91, 4344– 4360,  DOI: 10.1021/j100300a028
      3
      Characterization of the charge-transfer reaction between decamethylferrocene and 7,7,8,8,-tetracyano-p-quinodimethane (1:1). The iron-57 Moessbauer spectra and structures of the paramagnetic dimeric and the metamagnetic one-dimensional salts and the molecular and electronic structures of (TCNQ)n(n = 0, -1, -2)
      Miller, Joel S.; Zhang, Jian H.; Reiff, William M.; Dixon, David A.; Preston, L. D.; Reis, Arthur H., Jr.; Gebert, Elizabeth; Extine, Michael; Troup, Jan; et al.
      Journal of Physical Chemistry (1987), 91 (16), 4344-60CODEN: JPCHAX; ISSN:0022-3654.
      The charge-transfer reaction of decamethylferrocene, Fe(C5Me5)2 (Fc1) and 7,7,8,8-tetracyano-p-quinodimethane (TCNQ) have been characterized. Three major reaction products of varying stoichiometry, cond., and magnetism are formed: a 1-D metamagnetic 1:1 salt, [Fc1]+ [TCNO]•- (I); a paramagnetic 1:1 dimeric salt, [Fc1]2+ [TCNQ]22- (II); and a conducting 1:2 salt of [Fc1]+ [TCNQ]2- compn. The crystal and mol. structures of I and II were detd. The structure of II consists of discrete stacks of DAAD dimeric (D = Fc1; A = TCNQ) units. One-dimensional stacking of ions is not obsd. The decamethylferrocenium cations have av. Fe-C distances of 2.096 (7) Å, longer than the 2.050 Å reported for neutral decamethylferrocene. The C5Me5 rings appear eclipsed; however, as a result of the disorder only one ring was partially resolvable. The C5Me5 rings are essentially parallel to the TCNQ moieties and sepd. by 3.554 Å. The TCNQ anions form a tight a1g dimer (sepd. by a short distance of 3.147 Å) and are slipped along the short TCNQ axis. Bonding arises through filling of the bonding a1% dimer orbital. The structure of I consists of discrete one-dimensional chains comprised of alternating radical cation donors, D, and anion acceptors, A, i.e., ...DADA.... The decamethylferrocenium cation has a staggered conformation with an av. Fe-C distance of 2.090 Å. The C5Me5 rings are staggered and are canted with respect to the [TCNQ]•- moieties by 3.9°. The distance between the TCNQ and the C5Me5 rings is 3.43 Å. The [TCNQ]•- anion represents the first structural characterization of an isolated [TCNQ]•- in the solid state. Ab initio MO calcns. with the STO-3G basis set were carried out for [TCNQ]n (n = 0, -1, -2). To confirm the results of the MO calcns., [TCNQ]2- [as the [Co(C5Me5)2]+ (2:1) salt] was structurally characterized for the first time. The structures of C5 and D5d decamethylcobaltocenium cations have been reported for the 1st time. The structure of [TCNQ]2- has also been detd. for the first time. The dianion is planar within the exptl. error and possesses D2h local symmetry. The C6 ring is benzene-like with an av. ring C-C distance of 1.41 Å.
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    4. 4
      O’Hare, D.; Miller, J. S. One-Dimensional Solids Containing Bis(η-Arene)Chromium Cations. Mol. Cryst. Liq. Cryst. 1989, 176, 381– 389,  DOI: 10.1080/00268948908037496
      4
      One-dimensional solids containing bis[η-arene)chromium cations
      O'Hare, Dermot; Miller, Joel S.
      Molecular Crystals and Liquid Crystals (1989), 176 (), 381-90CODEN: MCLCA5; ISSN:0026-8941.
      Charge transfer salts based on bis(η-arene)chromium cations and TCNE (TCNE = tetracyanoethylene) exhibit both para and ferromagnetic behavior depending on their structural motif. In contrast, magnetic susceptibility measurements on the thermodn. phase of [Cr(η-C6H3Me3)2]•+[TCNQ]•- (TCNQ = 7,7',8,8'-tetracyano-p-quinodimethane) indicate that the material does not obey the Curie-Weiss law. However, the magnetic susceptibility can be fitted over all temps. by considering a paramagnetic component from [Cr(η-C6H3Me3)2]•+ and [TCNQ]22- S = 0 dimers with a thermally accessible S = 1 excited state.
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    5. 5
      Clérac, R.; O’Kane, S.; Cowen, J.; Ouyang, X.; Heintz, R.; Zhao, H.; Bazile, M. J.; Dunbar, K. R. Glassy Magnets Composed of Metals Coordinated to 7,7,8,8-tetracyanoquinodimethane: M(TCNQ)2 (M = Mn, Fe, Co, Ni). Chem. Mater. 2003, 15, 1840– 1850,  DOI: 10.1021/cm021053d
      5
      Glassy Magnets Composed of Metals Coordinated to 7,7,8,8-tetracyanoquinodimethane: M(TCNQ)2 (M = Mn, Fe, Co, Ni)
      Clerac, Rodolphe; O'Kane, Shannon; Cowen, Jerry; Ouyang, Xiang; Heintz, Robert; Zhao, Hanhua; Bazile, Mervin J., Jr.; Dunbar, Kim R.
      Chemistry of Materials (2003), 15 (9), 1840-1850CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
      The homologous series M(TCNQ)2 (M = Mn(II), Fe(II), Co(II), and Ni(II); TCNQ = 7,7,8,8-tetracyanoquinodimethane) prepd. from reactions of [M(MeCN)6][BF4]2 and [Bu4N][BF4] in MeCN was carefully analyzed from the perspective of synthetic issues and phys. characterization, including complete magnetic analyses by the tools of d.c. and a.c. magnetometry. The preparative method was optimized to definitively establish the reproducibility of the chem. as judged by IR spectroscopy, TGA, powder x-ray crystallog., and elemental anal. Scanning electron microscopic (SEM) and transmission electron microscopic (TEM) studies results are also in accord with the conclusion that these materials are pure, isostructural phases. The d.c. magnetic measurements reveal a spontaneous magnetization for the four materials at low temps. with a weak field coercivity of 20, 750, 190, and 270 G at 2 K for Mn(TCNQ)2, Fe(TCNQ)2, Co(TCNQ)2, and Ni(TCNQ)2, resp. At low temps., a.c. susceptibility measurements confirm the presence of a magnetic phase at 44, 28, 7, and 24 K for Mn(TCNQ)2, Fe(TCNQ)2, Co(TCNQ)2, and Ni(TCNQ)2, resp., but do not support the description of this system as a typical magnet. In the absence of the a.c. magnetic data, the behavior is indicative of ferri- or ferromagnetic ordering (depending on the metal), but in fact a complete study of their phys. properties revealed their true nature to be a glassy magnet. The glassiness, which is a high magnetic viscosity known to originate from randomness and frustration, is revealed by a frequency dependence of the a.c. susceptibility data and is further supported by a lack of a lambda peak in the heat capacity data. These results clearly demonstrate that mol.-based materials with a presumed magnetic ordering may not always be exhibiting truly cooperative behavior.
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    6. 6
      Zhao, H.; Bazile, M. J., Jr.; Galán-Mascarós, J. R.; Dunbar, K. R. A Rare-Earth Metal TCNQ Magnet: Synthesis, Structure, and Magnetic Properties of {[Gd2(TCNQ)5(H2O)9][Gd(TCNQ)4(H2O)3]}·4 H2O. Angew. Chem., Int. Ed. 2003, 42, 1015– 1018,  DOI: 10.1002/ange.200390234
      6
      A rare-earth metal TCNQ magnet: synthesis, structure, and magnetic properties of {[Gd2(TCNQ)5(H2O)9][Gd(TCNQ)4-(H2O)3]}·4H2O
      Zhao, Hanhua; Bazile, Mervin J., Jr.; Galan-Mascaros, Jose R.; Dunbar, Kim R.
      Angewandte Chemie, International Edition (2003), 42 (9), 1015-1018CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
      The crystn. of the polymeric salt, {[Gd2(TCNQ)5(H2O)9][Gd(TCNQ)4(H2O)3]}·4H2O, is described, and was shown to consist of both cationic and anionic layers that exhibit different ratios of GdIII and TCNQ- radicals. This material is an example of a lanthanide/org. radical based magnet and is the first lanthanide-TCNQ magnet.
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    7. 7
      Alonso, C.; Ballester, L.; Gutiérrez, A.; Perpiñán, M. F.; Sánchez, A. E.; Azcondo, M. T. Tetracyanoquinodimethanido Derivatives of (Terpyridine)- and (Phenanthroline)metal Complexes – Structural and Magnetic Studies of Radical-Ion Salts. Eur. J. Inorg. Chem. 2005, 3, 486– 495,  DOI: 10.1002/ejic.200400540
      There is no corresponding record for this reference.
    8. 8
      Jain, R.; Kabir, K.; Gilroy, J. B.; Mitchell, K. A. R.; Wong, K.-Ch.; Hicks, R. G. High-temperature metal-organic magnets. Nature 2007, 445, 291– 294,  DOI: 10.1038/nature05439
      8
      High-temperature metal-organic magnets
      Jain, Rajsapan; Kabir, Khayrul; Gilroy, Joe B.; Mitchell, Keith A. R.; Wong, Kin-chung; Hicks, Robin G.
      Nature (London, United Kingdom) (2007), 445 (7125), 291-294CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)
      For over two decades there were intense efforts aimed at the development of alternatives to conventional magnets, particularly materials comprised in part or wholly of mol. components. Such alternatives offer the prospect of realizing magnets fabricated through controlled, low-temp., soln.-based chem., as opposed to high-temp. metallurgical routes, and also the possibility of tuning magnetic properties through synthesis. However, examples of magnetically ordered mol. materials at or near room temp. are extremely rare, and the properties of these materials are often capricious and difficult to reproduce. Here the authors present a versatile soln.-based route to a new class of metal-org. materials exhibiting magnetic order well above room temp. Reactions of the metal (M) precursor complex bis(1,5-cyclooctadiene)nickel with three different orgs. A-TCNE (tetracyanoethylene), TCNQ (7,7,8,8-tetracyanoquinodimethane) or DDQ (2,3-dichloro-5,6-dicyano-1,4-benzoquinone)-proceed via electron transfer from nickel to A and lead to materials contg. Ni(II) ions and reduced forms of A in a 2:1 Ni:A ratio-i.e., opposite to that of conventional (low Curie temp.) MA2-type magnets. These materials also contain oxygen-based species within their architectures. Magnetic characterization of the three compds. reveals spontaneous field-dependent magnetization and hysteresis at room temp., with ordering temps. well above ambient. The unusual stoichiometry and striking magnetic properties highlight these three compds. as members of a class of stable magnets that are at the interface between conventional inorg. magnets and genuine mol.-based magnets.
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    9. 9
      Berlie, A.; Terry, I.; Giblin, S.; Lancaster, T.; Szablewski, M. A muon spin relaxation study of the metal-organic magnet Ni(TCNQ)2. J. Appl. Phys. 2013, 113, 17E304  DOI: 10.1063/1.4798616
      There is no corresponding record for this reference.
    10. 10
      Vasylets, G. Y.; Khotkevich, A. V.; Bukrinev, A. S.; Krasnyi, A. S.; Starodub, V. A.; Kravchenko, A. A.; Medviediev, V. V. Electroconductivity of anion-radical TCNQ salts containing cations [M(bipy)3]2+ (M - Fe, Ni or Zn). Funct. Mater. 2015, 22, 338– 341,  DOI: 10.15407/fm22.03.338
      10
      Electroconductivity of anion-radical TCNQ salts containing cations [M(bipy)3]2+ (M-Fe, Ni or Zn)
      Vasylets, G. Y.; Khotkevich, A. V.; Bukrinev, A. S.; Krasnyi, A. S.; Starodub, V. A.; Kravchenko, A. A.; Medviediev, V. V.
      Functional Materials (2015), 22 (3), 338-341CODEN: FMUAB4; ISSN:2218-2993. (National Academy of Sciences of Ukraine, Institute for Single Crystals)
      Elec. resistance temp. dependence of three TCNQ anion-radical salts of complex compn. contg. cations [MII(bipy)3]2+ (M - Fe, Ni or Zn, bipy - 2,2'-dipyridil) have been studied. Measurements have been performed in the range 180-300 K on tableted samples. The compd. exhibit semiconducting properties and undergo the Peierls transition. Specific resistance at room temp. is of 7.7 Ω·cm-1 for Fe contg. salt and 2.3·10-2 Ω·cm-1 and 2.5·10-2 Ω·cm-1 for salts contg. Ni and Zn, resp.
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    11. 11
      Šoltésová, D.; Vasylets, G.; Čižmár, E.; Botko, M.; Cheranovskii, V.; Starodub, V.; Feher, A. Exchange interaction between TCNQ and transition metal ion mediated by hydrogen bonds in [Mn(phen)3](TCNQ)2·H2O and [Co(phen)3](TCNQ)2·H2O. J. Phys. Chem. Solids 2016, 99, 182– 188,  DOI: 10.1016/j.jpcs.2016.08.022
      11
      Exchange interaction between TCNQ and transition metal ion mediated by hydrogen bonds in [Mn(phen)3](TCNQ)2·H2O and [Co(phen)3](TCNQ)2·H2O
      Soltesova, D.; Vasylets, G.; Cizmar, E.; Botko, M.; Cheranovskii, V.; Starodub, V.; Feher, A.
      Journal of Physics and Chemistry of Solids (2016), 99 (), 182-188CODEN: JPCSAW; ISSN:0022-3697. (Elsevier Ltd.)
      The magnetic properties, sp. heat and EPR spectra of anion-radical salts [Mn(phen)3](TCNQ)2·H2O and [Co(phen)3](TCNQ)2·H2O, in which TCNQ mols. and transition metal ions are not connected by covalent bonds and magnetic interactions are mediated via hydrogen bonds, were investigated. Measurements of the magnetic response were performed down to 1.8 K in magnetic fields up to 7 T. The heat capacity of investigated compds. was measured in temp. range from 0.38 K to 35 K in magnetic fields up to 9 T for [Mn(phen)3](TCNQ)2·H2O and up to 3 T for [Co(phen)3](TCNQ)2·H2O. The EPR spectra of studied samples were investigated for both samples in the temp. range from 2 K to 300 K. Theor. model of weakly-coupled magnetic units composed of four TCNQ anion radicals and of two transition metal ions was proposed for interpretation of obtained data. The energy of exchange interactions between TCNQ mols. and transition metal ion is important for the description of low-temp. behavior of studied anion-radical salts and was estd. to be in the range of 1.3-1.5 K.
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    12. 12
      Šterbinská, S.; Holub, M.; Hegedüs, M.; Titiš, J.; Čižmár, E.; Falvello, L. R.; Černák, J. Temperature-dependent dimerization of TCNQ anion-radical in [Ni(bpy)3]2(TCNQ–TCNQ)(TCNQ)2·6H2O: Single-crystal structure, magnetic and quantum chemical study. Solid State Sci. 2022, 131, 106959  DOI: 10.1016/j.solidstatesciences.2022.106959
      12
      Temperature-dependent dimerization of TCNQ anion-radical in [Ni(bpy)3]2(TCNQ-TCNQ)(TCNQ)2·6H2O: Single-crystal structure, magnetic and quantum chemical study
      Sterbinska, Slavomira; Holub, Mariia; Hegedus, Michal; Titis, Jan; Cizmar, Erik; Falvello, Larry R.; Cernak, Juraj
      Solid State Sciences (2022), 131 (), 106959CODEN: SSSCFJ; ISSN:1293-2558. (Elsevier Masson SAS)
      The crystal structure of [Ni(bpy)3]2(TCNQ-TCNQ)(TCNQ)2·6H2O (1) was studied by X-ray single-crystal structure anal. at 145 K and 100 K. The crystal structures of 1 at these two temps. are essentially the same as the crystal structure studied previously at 200 K: the structure is built up of [Ni(bpy)3]2+ complex cations, two centrosym. crystallog. independent TCNQ·- anion-radicals, disordered σ- and π-dimerized (TCNQ)2 units, and water mols. of crystn. Lowering the temp. from 200 K, via 145 K-100 K has shown that at lower temps. the proportions of σ- and π-dimerization in the disordered (TCNQ)2 unit are shifted in favor of σ-dimerization; moreover, variation of the weaker C-C σ-bond formed upon dimerization was obsd. In addn., lowering the temp. led to a shortening of the distance between the two crystallog. independent anion-radicals which are stacked along the b-axis with overlapped exo groups. The σ- and π-dimerization in the disordered (TCNQ)2 unit was studied by quantum chem. calcns. which showed smallest energy difference for σ and π-dimer at 200 K with respect to 145 K and 100 K in line with a lowest proportion of the dimerization obsd. exptl. Temp.-dependent (1.8-270 K) magnetic study of 1 has shown the contribution of Ni(II) ions (S = 1) and the contribution of four S = 1/2 species carried by TCNQ radicals at higher temps., strongly coupled by antiferromagnetic (AFM) exchange interaction at 270 K while at low temp. a negligible contribution of TNCQ radical spins was obsd.
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    13. 13
      Nafady, A.; O′Mullane, A. P.; Bond, A. M. Electrochemical and photochemical routes to semiconducting transition metal-tetracyanoquinodimethane coordination polymers. Coord. Chem. Rev. 2014, 268, 101– 142,  DOI: 10.1016/j.ccr.2014.01.017
      13
      Electrochemical and photochemical routes to semiconducting transition metal-tetracyanoquinodimethane coordination polymers
      Nafady, Ayman; O'Mullane, Anthony P.; Bond, Alan M.
      Coordination Chemistry Reviews (2014), 268 (), 101-142CODEN: CCHRAM; ISSN:0010-8545. (Elsevier B.V.)
      A review. TCNQ·- radical anions (TCNQ = 7,7,8,8,-tetracyanoquinodimethane) form a wide range of semiconducting coordination polymers when coordinated to transition metals. Some materials such as CuTCNQ and AgTCNQ exhibit mol. switching and memory storage properties; others have intriguing magnetic properties and for example may behave as mol. magnets at low temp. In this review, the electro- and photo-chem. synthesis and characterization of this important class of material is reviewed. In particular, the electrochem. and the redox properties of TCNQ derivs. of coordination polymers based on Cu, Ag, Mn, Fe, Co, Ni, Zn and Cd transition metals are surveyed, with an emphasis on the mechanistic aspects of their electrochem. formation via nucleation-growth processes. Given that TCNQ is an extremely good electron acceptor, readily forming TCNQ·- and TCNQ2-, electrochem. redn. of TCNQ in the presence of a transition metal ion provides an ideal method for synthesis of metal-TCNQ materials by electrocrystn. from org. solvents and ionic liqs. or solid-solid transformation using TCNQ modified electrodes from aq. media contg. transition metal electrolytes. The significance of the reversible formal potential (E0f) in these studies is discussed. The coupling of electrocrystn. on electrode surfaces and microscopic characterization of the electrodeposited materials reveals a wide range of morphologies and phases which strongly influence their properties and applications. Since TCNQ can also be photo-reduced in the presence of suitable electron donors, analogous photochem. approaches to the synthesis of TCNQ-transition metal derivs. are available. The advantages of electrochem. and photochem. methods of synthesis relative to chem. synthesis are outlined.
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    14. 14
      Goldberg, S. Z.; Spivack, B.; Stanley, G.; Eisenberg, R.; Braitsch, D. M.; Miller, J. S.; Abkowitz, M. Synthesis, structure, and physical properties of the bis(7,7,8,8-tetracyano-p-quinodimethane) salt of the paramagnetic cluster tris[(di-μ-chloro)(hexamethylbenzene)niobium], [Nb3(μ-Cl)6(C6Me6)3]2+(TCNQ)22-. J. Am. Chem. Soc. 1977, 99, 110– 117,  DOI: 10.1021/ja00443a021
      14
      Synthesis, structure, and physical properties of the bis(7,7,8,8-tetracyano-p-quinodimethane) salt of the paramagnetic cluster tris[(di-μ-chloro)(hexamethylbenzene)niobium], [Nb3(μ-Cl)6(C6Me6)3]2+(TCNQ)22-
      Goldberg, Stephen Z.; Spivack, Bruce; Stanley, George; Eisenberg, Richard; Braitsch, David M.; Miller, Joel S.; Abkowitz, Martin
      Journal of the American Chemical Society (1977), 99 (1), 110-17CODEN: JACSAT; ISSN:0002-7863.
      The title complex was synthesized from Nb3Cl6(C6Me6)3+PF6-, Li+TCNQ-, and TCNQ in MeCN. Its crystal and mol. structures were detd. The crystal structure consists of zigzag chains of alternating di-μ-chloro-(hexamethylbenzene)niobium trimer cations and TCNQ anion dimers. The trinuclear cluster has m symmetry with two crystallog. independent Nb-Nb distances of 3.327 (2) and 3.344 (3) Å. There is one crystallog. independent TCNQ anion which forms a dimeric unit with its centrosymmetrically related form. The interplanar spacing between TCNQ moieties is 3.10 Å and the overlap between them is of an exo double bond ring type. The mea sepn. of 3.65 Å between the slightly bent hexamethylbenzene and TCNQ units suggests little interaction. The room temp. ESR spectrum consists of a nearly isotropic [g = 1.996 (2)] and relatively broad absorption [peak to peak deriv. line width of 36.95 (3) Oc]. This is consistent with the unpaired electron residing on the niobium cluster. Thus, the mol. is [Nb3Cl6(C6Me6)3]2+(TCNQ)22- and represents the solid-state stabilization of the previously postulated S = 1/2 cluster by TCNQ. The single-crystal and polycrystalline cond. data indicate a semiconductor behavior with a room temp. cond. of 0.001 ohm-1 cm-1 and an activation energy of 0.35 eV (2800 cm-1).
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    15. 15
      Bertaina, S.; Dutoit, C.-E.; van Tol, J.; Dressel, M.; Barbara, B.; Stepanov, A. Rabi oscillations of pinned solitons in spin chains: A route to quantum computation and communication. Phys. Rev. 2014, 90, 060404(R)  DOI: 10.1103/PhysRevB.90.060404
      There is no corresponding record for this reference.
    16. 16
      Leo, K.; Schneider, O. US20050179399A1, 2005.
      There is no corresponding record for this reference.
    17. 17
      Pyshkin, O.; Kamarchuk, G.; Yeremenko, A.; Kravchenko, A.; Pospelov, A.; Alexandrov, Y.; Faulques, E. Evidence for sensory effects of a 1D organic conductor under gas exposure. J. Breath Res. 2011, 5, 016005  DOI: 10.1088/1752-7155/5/1/016005
      17
      Evidence for sensory effects of a 1D organic conductor under gas exposure
      Pyshkin, O.; Kamarchuk, G.; Yeremenko, A.; Kravchenko, A.; Pospelov, A.; Alexandrov, Yu; Faulques, E.
      Journal of Breath Research (2011), 5 (1), 016005/1-016005/9CODEN: JBROBW; ISSN:1752-7155. (Institute of Physics Publishing)
      This work describes the gas-sensitive properties of a one-dimensional org. conductor before and after exposure to carbon monoxide and human breath. A sensitive material, an anion-radical salt of tetracyanoquinodimethane, has been investigated by IR spectroscopy and elec. resistivity measurements. Drastic spectral and elec. changes are found after gas exposure showing that the compd. interacts strongly with human breath, carbon monoxide, and ammonia. Under breath action the resistance changes by more than three orders of magnitude while the adsorption of CO, one of the components of breath, results in a decrease in both IR absorption and elec. cond. The intensity of the IR absorption spectrum of the material in the CO medium decreases down to 30% in the 2180-2500 cm-1 range. This absorption varies by about 10% between 750 and 2500 cm-1 after breath action. Direct elec. measurements show that actions of donor or acceptor gas result in opposite changes of elec. resistance. The elec. resistance of the sample can drop down to 0.4 MΩ due to the pulse action of ammonia at 4 ppm concn., while it increases upon exposure to carbon monoxide media at concns. of 6-25 ppm. The response signal of the investigated samples changes proportionally to the concn. of the acting gas. The results substantiate prominent gas sensitivity of the investigated material, which might find applications for breath anal., in particular, for the development of noninvasive diagnosis of gastric diseases.
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    18. 18
      Matsuda, R. Design and Synthesis of Porous Coordination Polymers Showing Unique Guest Adsorption Behaviors. Bull. Chem. Soc. Jpn. 2013, 86, 1117– 1131,  DOI: 10.1246/bcsj.20130157
      18
      Design and synthesis of porous coordination polymers showing unique guest adsorption behaviors
      Matsuda, Ryotaro
      Bulletin of the Chemical Society of Japan (2013), 86 (10), 1117-1131CODEN: BCSJA8; ISSN:0009-2673. (Chemical Society of Japan)
      A review. Methods for design and synthesis of porous coordination polymers showing unique adsorption properties are discussed. Gas storage and sepn. are becoming a high priority area of research due to economic, industrial, and environmental reasons. The last two decades have therefore witnessed dramatic growth in the search for more efficient and adaptable nanoporous materials. In particular, much attention has been focused on porous coordination polymers (PCPs) or metal org. frameworks (MOFs) as new nanoporous materials. Based on the unlimited combination of metal ions and org. ligands, PCPs can provide infinite variety of nanospace in their pores. As mol. adsorption is dependent on the size, shape, and surface nature of nanospace, many unique mol. adsorption or trapping phenomena have been reported in this class of compds. Examples include selective adsorption of acetylene over carbon dioxide in the CPL series of PCPs, using charge-transfer to induce selective adsorption of nitric oxide and oxygen in TCNQ (7,7,8,8-tetracyano-p-quinodimethane) based PCP and light-induced on-demand adsorption and structural transformations in CID-based PCPs. The guidelines underpinning such unique, highly selective guest adsorption are discussed.
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    19. 19
      Ballester, L.; Gutiérrez, A.; Perpiñán, M. F.; Azcondo, M. T. Supramolecular architectures in low dimensional TCNQ compounds containing nickel and copper polyamine fragments. Coord. Chem. Rev. 1999, 190–192, 447– 470,  DOI: 10.1016/S0010-8545(99)00098-3
      19
      Supramolecular architectures in low dimensional TCNQ compounds containing nickel and copper polyamine fragments
      Ballester, L.; Gutierrez, A.; Perpina, M. F.; Azcondo, M. T.
      Coordination Chemistry Reviews (1999), 190-192 (), 447-470CODEN: CCHRAM; ISSN:0010-8545. (Elsevier Science S.A.)
      A review, with 57 refs., discusses Ni(II) and Cu(II) polyamine derivs. which are adequate fragments to interact with the org. acceptor TCNQ, favoring the formation of σ bonds between the metal atom and the TCNQ nitrile groups. In its radical anion form, this mol. tends to form dimeric dianions (TCNQ)2 2- by overlapping of the π cloud with a neighboring radical. When the metal has a stable and coordinatively satd. environment these dianions remain uncoordinated, but if the metal has vacant positions or labile ligands formation of two M-TCNQ bonds is obsd. In these cases the dianions are bridging two metal units forming infinite chains. In the dimers, the radicals are strongly antiferromagnetically coupled behaving as diamagnetic units. These compds. with localized electrons behave as insulators, or poor semiconductors. In its neutral form the TCNQ has a low coordinative ability, but its presence favors the overlap of the dianionic dimers to form infinite stacks. When both neutral and radical-anionic TCNQ are present in the reaction mixt. the derivs. obtained usually have three TCNQ mols. per metal atom. Depending on the interactions between the TCNQ and the metal two situations are found: if all the TCNQ mols. are uncoordinated the electronic charge on the org. stack is delocalized, but if direct bonding to the metal is present, the bonded mols. show radical anion characteristics, while the uncoordinated TCNQ behave as neutral mols. The presence of this neutral TCNQ weakens the coupling in the (TCNQ)2 2- dimers and a temp. dependent contribution from the TCNQ to the magnetic susceptibility is found. These compds. having mixed valence TCNQ units show a greater electronic delocalization and behave as good semiconductors with higher cond. values and lower activation energies in the derivs. that do not show direct bonding between the metal and the TCNQ.
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    20. 20
      Černák, J.; Kočanová, I.; Orendáč, M. Copper-Nickel Heterobimetallic Compounds. Comments Inorg. Chem. 2012, 33, 2– 54,  DOI: 10.1080/02603594.2012.700970
      20
      Copper-Nickel Heterobimetallic Compounds
      Cernak, J.; Kocanova, I.; Orendac, M.
      Comments on Inorganic Chemistry (2012), 33 (1-2), 2-54CODEN: COICDZ; ISSN:0260-3594. (Taylor & Francis, Inc.)
      A review. Motivated by the theor. prediction of the existence of alternate chains in the case of one-dimensional Cu-Ni compds. the current state of these heterobimetallic compds. is described. A classification of Cu-Ni heterobimetallic compds. based on the magnetic properties of the resp. metal is considered, namely, and classes (is for diamagnetic and for paramagnetic). These four classes of Cu-Ni compds. are further classified by structure and compn. Based on these classifications representative examples for each group are described from a structural perspective as well as magnetic properties. Addnl. information is given on the typical preparative methods.
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    21. 21
      Groom, C. R.; Bruno, I. J.; Lightfoot, M. P.; Ward, S. C. The Cambridge Structural Database. Acta Crystallogr., Sect. B: Struct. Sci., Cryst. Eng. Mater. 2016, 72, 171– 179,  DOI: 10.1107/S2052520616003954
      21
      The Cambridge Structural Database
      Groom, Colin R.; Bruno, Ian J.; Lightfoot, Matthew P.; Ward, Suzanna C.
      Acta Crystallographica, Section B: Structural Science, Crystal Engineering and Materials (2016), 72 (2), 171-179CODEN: ACSBDA; ISSN:2052-5206. (International Union of Crystallography)
      The Cambridge Structural Database (CSD) contains a complete record of all published org. and metal-org. small-mol. crystal structures. The database has been in operation for over 50 years and continues to be the primary means of sharing structural chem. data and knowledge across disciplines. As well as structures that are made public to support scientific articles, it includes many structures published directly as CSD Communications. All structures are processed both computationally and by expert structural chem. editors prior to entering the database. A key component of this processing is the reliable assocn. of the chem. identity of the structure studied with the exptl. data. This important step helps ensure that data is widely discoverable and readily reusable. Content is further enriched through selective inclusion of addnl. exptl. data. Entries are available to anyone through free CSD community web services. Linking services developed and maintained by the CCDC, combined with the use of std. identifiers, facilitate discovery from other resources. Data can also be accessed through CCDC and third party software applications and through an application programming interface.
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    22. 22
      Ballester, L.; Barral, M. C.; Gutiérrez, A.; Monge, A.; Perpiñán, M. F.; Ruiz-Valero, C.; Sánchez-Pélaez, A. E. Tetracyanoquinodimethane Derivatives of Macrocyclic Nickel(II) Complexes. Synthesis and Crystal Structure of Bis(7,7,8,8-tetracyanoquinodimethanido)(1,8-bis(2-hydroxyethyl)-1,3,6,8,10,13-hexaazacyclotetradecane)nickel(II). Inorg. Chem. 1994, 33, 2142– 2146,  DOI: 10.1021/ic00088a015
      22
      Tetracyanoquinodimethane Derivatives of Macrocyclic Nickel(II) Complexes. Synthesis and Crystal Structure of Bis(7,7,8,8-tetracyanoquinodimethanido)(1,8-bis(2-hydroxyethyl)-1,3,6,8,10,13-hexaazacyclotetradecane)nickel(II)
      Ballester, Loreto; Barral, M. Carmen; Gutierrez, Angel; Monge, Angeles; Perpinan, Maria Felisa; Ruiz-Valero, Caridad; Sanchez-Pelaez, Ana E.
      Inorganic Chemistry (1994), 33 (10), 2142-6CODEN: INOCAJ; ISSN:0020-1669.
      The reactivity of the dichloro(1,8-disubstituted-1,3,6,8,10,13-hexaazacyclotetradecane)nickel(II) complex [NiCl2LR] (R = C2H4OH, Et, CH2Ph) toward LiTCNQ leads to a complete replacement of the chloride groups by the anionic TCNQ•- with formation of [NiLR(TCNQ)2]. The crystal structure of the hydroxyethyl deriv. was solved. The Ni atom is hexacoordinated surrounded by 4 nitrogens of the macrocyclic ligand and 2 axial monodentate TCNQ•- ligands, being the 1st Ni-TCNQ complex showing σ-bonds between the org. acceptor and the metal atom. Intermol. interactions between TCNQ groups from adjacent mols. forming dimeric units and H bonds involving the hydroxo groups and 1 of the N atoms of a neighboring TCNQ unit are the most significant features of the crystal structure. These compds. behave virtually as insulators at room temp.
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    23. 23
      Ballester, L.; Gutiérrez, A.; Perpiñán, M. F.; Amador, U.; Azcondo, M. T.; Sánchez, A. E.; Bellitto, C. Supramolecular Architecture in Nickel(II) Polyamine Tetracyanoquinodimethanido Systems. Inorg. Chem. 1997, 36, 6390– 6396,  DOI: 10.1021/ic970851g
      23
      Supramolecular Architecture in Nickel(II) Polyamine Tetracyanoquinodimethanido Systems
      Ballester, Loreto; Gutierrez, Angel; Perpinan, M. Felisa; Amador, Ulises; Azcondo, M. Teresa; Sanchez, Ana E.; Bellitto, Carlo
      Inorganic Chemistry (1997), 36 (27), 6390-6396CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
      Three different supramol. architectures corresponding to [Ni(dien)2](TCNQ)2 (dien = 1,4,7-triazaheptane; TCNQ = 7,7,8,8-tetracyanoquinodimethane), [Ni(trien)(TCNQ)2] (trien = 1,4,7,10-tetraazadecane), and [Ni(cyclam)(TCNQ)2] (cyclam = 1,4,8,11-tetraazacyclotetradecane) were prepd. and crystallog. characterized: [Ni(dien)2](TCNQ)2, triclinic, space group P‾1, a 8.319(2), b 9.074(2), c 11.145(3) Å, α 80.91(2), β 74.10(2), γ 82.12(2)°, Z = 1; [Ni(trien)(TCNQ)2], orthorhombic, space group Pccn, a 22.677(7), b 7.888(5), c 15.801(3) Å, Z = 4; [Ni(cyclam)(TCNQ)2], triclinic, P‾1, a 8.699(2), b 9.752(3), c 10.138(2) Å, α 87.29(2), β 77.14(2), γ 75.00(2)°, Z = 1. All of them are built by dimeric units (TCNQ)22- which are out of the coordination sphere in [Ni(dien)2](TCNQ)2 and σ-coordinated to the metal in cis and trans positions in [Ni(trien)(TCNQ)2] and [Ni(cyclam)(TCNQ)2], resp. In the two latter compds. the bonded dimeric units (TCNQ)22-, formed by intermol. interactions, give rise to infinite chains consisting of alternating [Ni(N4)]2+ and (TCNQ)22- moieties in the crystal. The existence of hydrogen bonds between the TCNQ nitriles and amine groups belonging to the metal fragments stabilizes the supramol. architecture, increasing the dimensionality of the interactions. The spectroscopic and magnetic properties are discussed according to the structural models.
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    24. 24
      Choi, H. J.; Suh, M. P. Nickel(II) Macrocyclic Complexes with Long Alkyl Pendant Chain: Synthesis, X-ray Structure, and Anion Exchange Property in the Solid State. Inorg. Chem. 2003, 42, 1151– 1157,  DOI: 10.1021/ic025971p
      24
      Nickel(II) Macrocyclic Complexes with Long Alkyl Pendant Chain: Synthesis, X-ray Structure, and Anion Exchange Property in the Solid State
      Choi, Hye Jin; Suh, Myunghyun Paik
      Inorganic Chemistry (2003), 42 (4), 1151-1157CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
      A nickel(II) pentaaza macrocyclic complex contg. a 1-hexadecyl pendant chain, [Ni(L)](ClO4)2·H2O (1; L = I), was synthesized by a 1-pot metal-template condensation reaction. Crystal data for 1: triclinic, space group P‾1, a 8.333(4), b 8.356(3), c 28.374(9) Å, α 81.865(19), β 86.242(18), γ 63.871(17), Z = 2. Solid 1 forms hydrophobic layers that are constructed by the long alkyl chains of the macrocycles. Solid 1 exchanges ClO4- with NCS-, PF6-, C2O42-, NO3-, and CF3SO3- that are dissolved in water. From the reaction of [Ni(C25H55N5)Cl2] with Et3NH(TCNQ)2 in EtOH/DMF/acetone soln., [Ni(C25H55N5)(TCNQ)2](TCNQ)·(CH3COCH3) (2) (TCNQ = 7,7,8,8-tetracyano-p-quinodimethane) was prepd. Crystal data for 2: triclinic, space group P‾1, a 8.459(0), b 13.945(1) Å, c 26.833(2) Å, α 88.744(2), β 84.536(2), γ 80.089(4), Z = 2. In 2, TCNQ anions coordinate nickel(II) at the axial sites, which form π-stacked TCNQ- dimers to give rise to 1-dimensional chains. The neutral TCNQ mols. are included between the dimerized TCNQ- species, which construct a π-stacked group of six TCNQ units as blocked by the long alkyl chains. Compd. 2 is an elec. insulator. It shows a weak signal in the EPR spectrum. The magnetic susceptibility data of 2 measured at 5-300 K exhibit a simple paramagnetism at low temps. (<100 K) but an increase in the magnetic moment at higher temps. due to the contribution of a thermally accessible triplet state for the antiferromagnetically coupled [TCNQ]22-.
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    25. 25
      Melby, L. R.; Harder, R. J.; Hetler, W. R.; Mahler, W.; Benson, R. E.; Mochel, W. E. Substituted Quinodimethans. II. Anion-radical Derivatives and Complexes of 7,7,8,8-Tetracyanoquinodimethan. J. Am. Chem. Soc. 1962, 84, 3374– 3387,  DOI: 10.1021/ja00876a029
      25
      Substituted quinodimethans. II. Anion-radical derivatives and complexes of 7,7,8,8-tetracyanoquinodimethan
      Melby, L. R.; Harder, R. J.; Hertler, W. R.; Mahler, W.; Benson, R. E.; Mochel, W. E.
      Journal of the American Chemical Society (1962), 84 (), 3374-87CODEN: JACSAT; ISSN:0002-7863.
      V is a strong Lewis acid and forms charge-transfer complexes with π-bases. Thus, 0.18 g. V in 50 ml. boiling CHCl3 was added to 0.10 g. Cu 8-quinolinate (XIV) in 50 ml. boiling CHCl3 and the soln. concd. to 50 ml. and left overnight to give 48% V-XIV π-complex, black plates, decompg. 195° resistivity (ρ) 3 × 107 ohm-cm. (unless otherwise stated ρ was detd. on mech. compacted microcryst. samples at room temp.). Similarly were prepd. (donor, solvent, appearance of complex, mole ratio of donor to V in complex, % yield, decompn. range, and ρ ohm-cm. given): p-C6H4(NH2)2, CHCl3, purple-black microcrystals, 1:1, 83, 162 to above 300°, 3 × 103 [activation energy for conductivity (Εa) 0.28 e.v.; electron paramagnetic resonance (e.p.r.) shows 4 × 1020 ± 25% unpaired electrons per mole]; 2-methyl-p-phenylenediamine, CHCl3, black microcrystals, 1:1, 44, 150-5°, 3 × 105; p-Me2NC6H4NH2, CHCl3, black leaflets, 1:1, 38, 112-17°, 2 × 109 (e.p.r. shows 4 × 1021 ± 25% unpaired electrons per mole); p-C6H4(NHMe)2, CH2Cl2, black needles, 1:1, 50, 111-14°, 2 × 104; p-C6H4(NMe2)2, CHCl3, blue-black platelets, 1:1, 71,128-9°, 106; diaminodurene, VII, purple micro-crystals, 1:1, 86,190 to above 300°, 109; 2,3-diaminonaphthalene, CHCl3, black microcrystals, 1:1, 27, 165 to above 300°, 1010; 1,5-diaminonaphthalene, CHCl3, black needles, 1:1, 59, 197°, 109 (e.p.r. shows 2 × 1019 ± 25% unpaired electrons per mole); 2-aminofluorene, MeCN, brown-black needles, 1:1, 80, 207-42°, 109; 2-aminochrysene, CH2Cl2, brown needles, 1:1, 51, 211-17° 1010; p-C6-H4(OH)2, VII, black microcrystals, 1:2, low, 180-5°, --; 1,2,3-C6H3(OH)3, CH2Cl2, --, 2:1, low, 105°, --; VIII, VII, black needles, 1:1, 42, 282-3°, 1011; pyrene, VII, purple needles, 1:1, 52, 260°, 1012; 4,6,8-trimethylazulene, VII, black crystals, 1:1, 85, 160-7°, 109; pyrrole-2-aldehydeimine (XV) Cu chelate, CHCl3, purple needles, 1:1,69,170 to above 300°, 5 × 1010; XV Ni chelate, CH2Cl2, blue-black needles, 1:1, --, 210-20°, 1011. Most of the π-complexes cannot be crystd. without some decompn., although the solids are quite thermally stable, and are best prepd. from highly purified starters. V (Q) undergoes one-electron redn. with Cu, Ag, or other metal iodides to give simple salts of the anion-radical (Q•-). Thus, 40 g. LiI (an excess is used to scavenge liberated iodine as I3-) in 100 ml. boiling MeCN added to 20.4 g. V in 2 1. boiling MeCN gave 98% Li+Q•- (XVI), purple microcrystals, decompd. above 300°, ρ 2 × 105 ohm-cm. Similarly were prepd. (cation source, salt, appearance, % yield, decompn. range, and ρ ohm-cm. given): NaI, Na+Q•-, purple microcrystals, 59, above 300° 3 × 104; KI, K+Q•-, red needles, 70, above 300°, 5 × 103; BaI2, Ba++, (Q•-)2, purple crystals, 70, --, 8 × 105; NH4I (in VII-MeOH)-NH4+•-, maroon needles, 60, 210-15°, 6 × 104; (NCCH2CH2)-Me3N+I-, (NCCH2CH2)Me3N+Q•-, blue-black crystals, --, --, 106. CsI is exceptional in that it gives a complex salt (contg. formally neutral V). A filtered soln. of 2.9 g. CsI in 50 ml. boiling MeOH added to 2.0 g. V in 200 ml. boiling MeCN gave 1.64 g. (Cs+)2(Q•-)2Q, purple prisms, ρ 9 × 104 ohm-cm. (Ea 0.36 e.v.; single crystal detns. of ρ along the 3 major axes gave 500, 6 × 104, and 6 × 104 ohm-cm.; ρ for complex salts is anisotropic). The soly. of XVI in H2O and EtOH (∼l% by wt.) allows the prepn. of simple salts by metathesis. Thus, 12 g. CuSO4.5H2O in 70 ml. H2O added to a filtered soln. of 2.2 g. XVI in 200 ml. H2O gave 2.2 g. Cu++(Q•-)2, green powder, ρ 200 ohm-cm. (Ea 0.12 e.v.). Boiling solns. of 0.84 g. XVI in 200 ml. alc. and 1.1 g. N-methylquinolinium iodide in 10 ml. alc. were mixed, the mixt. was left 2 hrs. at room temp., the product washed with cold alc. and Et2O, and recrystd. to give 76% (N-methylquinolinium)++Q•-, purple microcrystals, decompg. 240-4° (MeCN),ρ 107 ohm-cm. Similarly, the following simple salts were prepd. by metathesis in aq. soln. (cation source, product, appearance, % yield, decompn. range, and ρ ohm-cm. given): CsCl, Cs++Q•-, purple crystals, 67, --, 3 × 104 (Ea 0.15 e.v.); MnCl2, Mn++-(Q•-)2.3H2O, blue powder, 98, ∼170°, 9 × 104; FeSO4, Fe++-(Q•-)2.3H2O, blue powder, 95, ∼170°, 5 × 104; CoSO4, Co++-(Q•-)2.3H2O, blue powder, 91, ∼170°, 9 × 104; NiCl2, Ni++-(Q•-)2.3H2O, blue powder, 95, 170°, 9 × 104; CuI, Cu+Q•-, blue-black needles, 54, --, 200 (Ea 0.13 e.v.); AgNO3, Ag+Q•-(gives free V in light). blue powder, 98, --, 8 × 105; Ce(NO3)3, Ce+++(Q•-)3.6H2O (gives free V in light), blue powder, 98, --, --; Sm(NO3)3, Sm+++(Q•-)3.6H2O, blue powder, 92, --, 2 × 104; Pb(NO3)2, Pb++(Q•-)2.1.5H2O, blue powder, 99, --, 2 × 105; Cu(NH3)4SO4, Cu(NH3)2++(Q•-)2, green powder, 94, --, 700; Cu(H2NCH2CH2NH2)2SO4, Cu(H2NCH2CH2NH2)2++(Q•-)2, blue powder, 97, --, 4 × 104; CuCl2 + 2,2'-dipyridylamine, Cu-(2,2'-dipyridylamine)++(Q•-)2, --, 80, --, 40 (Ea 0.06 e.v.); FeSO4 + 1,10-phenanthroline (phen), Fe(phen)3++(Q•-)2.-6H2O, --, 95, 260°, 106; NiCl2 + phen, Ni(phen)3++(Q•-)2.-6H2O, green powder, 98, --, 108; Ni(phen)2Cl2, Ni(phen)2++-(Q•-)2.6H2O, green powder, 96, --, 2 × 108; Cr(OAc)3, (Cr+++)2-(AcO-)4(HO-)(Q•-).6H2O, blue powder, 30, --, 109; Et3N.HCl or Et3N.HBr, Et3NH+Q•- (XVIII), blue powder, 81, ∼180°, 109; Bu4NI, Bu4N+Q•-, blue powder, --, 135%, 1012; Et2Me-(NCCH2)NI, Et2Me(NCCH2)N+Q•-, blue powder, --, ∼193°,109, Ph3MePI, Ph3MeP+Q•-, purple crystals, 99, ∼170°, 4 × 1010; (Me2N)3SCl or (Me2N)3SBr, (Me2N)3S+Q•-, purple solid, 88, ∼155°, 2 × 1010; N-methylpyridinium iodide (XVIII) (in MeCN-alc.), (N-methylpyridinium)+Q•-, purple needles, trace, ∼235°, 105; 4-cyano deriv. of XVIII (in MeCN-alc.), (4-cyano-N-methylpyridinium)+Q•-, purple needles, 52, 224-6° 106; 4-cyano-N-methylquinolinium iodide (in MeCN-alc.), (4-cyano-N-methylquinolinium)+Q•-, purple needles, 51, 196-8% 105; 2-(4-dimethylaminophenylazo) deriv. of XVIII (in MeCN-alc.), [N-methyl-2-(4-dimethylaminophenylazo)pyridinium]+Q•-, metallic-green plates, 77, 237-77° 106. Some simple salts were prepd. by treatment of the free base with V (the source of the proton in the cation of the salt thus formed is unknown but is probably the amine; a possible mechanism is discussed or with a mixt. of V and VI. Thus were prepd. (reactants, solvent, product, appearance, % yield, decompn. range, and ρ ohm-cm. given): base + V, CH2Cl2, (4-hydroxy-2,3,5,6-tetramethylanilinium)+-Q•-, black microcrystals, 60, 168-74°, 160 (Εa 0.10 e.v.); base + V, CHCl3, (5,8-dihydroxyquinolinium)+Q•-, black micro-crystals, 72, 168-9°, 15 (Ea 0.07 e.v.); IV + V + VI, MeCN, (pyridinium)+Q•-, purple prisms, 59, 158-95°, 106; base + V + VI, MeCN, [2-(4-dimethylaminophenylazo)pyridinium]+Q•-, metallic-green plates, 88, 230-45°, 106. Aq. solns. of the simple salts rapidly decomp. The blue color of concd. aq. solns. is due to the presence of a dimeric species; dil. aq. solns. and solns. in org. solvents are green due to absorption by Q•-, λ (MeCN) 420 (ε 24,300), 842 (ε 43,300), 744, 760, 680, 665 mμ. Infrared spectra of the simple salts show broad bands at 4.55-4.60 and 1-1.5 μ. Tropylium iodide (XIX) reacts abnormally with XVI: a filtered soln. of 1.20 g. XVI in 120 ml. H2O was added dropwise to 1.00 g. XIX in 15 ml. H2O until the blue color persisted, the ppt. was collected, washed with H2O (1.07 g., 99%, Agl was pptd. from the filtrate and washings on addn. of 1.5 g. AgNO3in 10 ml. H2O), dissolved in CH2Cl2, and the soln. concd. to ppt. 0.39 g. V. Further concn. gave 0.09 g. solid material and finally evapn. to dryness gave 0.80 g. α,α'-ditropyl-α,α,α',α'-tetracyano-p-xylene (XX), yellow prisms, m. 200-6°. Recrystn. from C6H6 gave material, m. 201-2° (dried 1 hr. at 110°). A mechanism is proposed for the formation of XX. Complex salts can be prepd. by addn. of V to solns. of the simple salts. Thus, 0.50 g. V in 30 ml. boiling MeCN was added to a filtered soln. of 0.61 g. XVII in 25 ml. boiling MeCN and the mixt. left 20 min. at room temp. to give 0.24 g. Et3NH+(Q•-)Q (XXI), black needles, decompg. above 195°, ρ 20 ohm-cm. (Εa 0.13 e.v.; single crystal detns. of ρ gave 0.5, 40, and 1000 ohm-cm. for the 3 major axes). Similarly were prepd. (salt, % yield, decompn. range, and ρ ohm-cm. given): (2,4,6-triphenylpyrylium)+(Q•-)Q (simple salt prepd. by metathesis from 2,4,6-triphenylpyrylium fluoborate), 21, 270° 16 (Ea 0.04 e.v.); (Me2N)3S+(Q•-)Q, 89, 229°, 30 (Εa 0.11 e.v.). The iodides of org. cations give complex salts with V, although the product from morpholine hydriodide (XXII) depends on the proportions of the reactants. Thus, near boiling solns. of 0.4 g. V and 1.1 g. XXII, each in 30 ml. MeCN, were mixed and left overnight at room temp. to give 0.15 g. (morpholinium)+(Q•-), red prisms, decompg. ∼220°, ρ 109 ohm-cm. (single crystal detns. of ρ gave 6 × 108 ohm-cm. for the 3 major axes). With 0.4 g. V in 25 ml. MeCN and 0.54 g. XXII in 20 ml. MeCN the sole product was 40% (morpholinium)2+-(Q•-)2Q, black plates, decompg. 210°, ρ105 ohm-cm. (single crystal detn. of ρ gave 5 × 103 ohm-cm.). A boiling soln. of 1.0 g. V in 100 ml. VII treated with 0.57 g. Et2N.HI in 7 ml. boiling MeCN and the mixt. left 30 min. at 0° gave 0.42 g. XXI. Similarly were prepd. (cation in the salt M+Q•-Q, appearance, % yield, decompn. range, and ρ ohm-cm. given): Et3-MeN, black rods, 65, 265-74°, 6 × 103; Et4N, black crystals, 79, 255-68°, 2 × 104; (4-amino-2,3,5,6-tetramethylanilinium) (prepd. in CHCl3-alc.), blue-black needles, 75, 180-220°, 8 (Εa 0.08 e.v.); (4-cyano-N-methylpyridinium), blue-black needles, 26, 258-60°, 48; (N-methylquinolinium), blue-black needles, 22, 245-50°, 3; (4-cyano-N-methylquinolinium), blue-black needles, 39, 223-39° 58; (N-ethylquinolinium), blue-black needles, 57, 237-9°, 8; (N-propylquinolinium), black rods, 92, 226-8°, 2 (single crystal detn. of ρ gave 0.5, 6, and 450 for the 3 major axes); [N-(2-phenylethyl)quinolinium,], black needles, 78, 248-50°, 3; [N-methyl-2-(4-dimethylaminophenylazo)pyridinium], purple-black microcrystals, 74, 248-9°, 12; Ph3MeP,. --, 60, 231-3°, -- (single crystal detn. of ρ gave 60, 600, and 105 for the 3 major axes; Εa 0.25 e.v.); Ph3EtP, --, 41, 223-5°, -- (single crystal detn. of ρ gave <10, 10, and 400 for the 3 major axes); Ph4P, --, 33, 228-37°, -- (single crystal detn. of ρ gave 103, 106, and 2 × 106 for the 3 major axes); Ph3MeAs, --.56, 224-7°, -- (single crystal detn. of ρ gave 57, 900, and 105 for the 3 major axes; Εa 0.22-0.23 e.v.); Ph3EtAs, --, 44, 212-19° -- (single crystal detn. of ρ gave 2 and 6600 for 2 of the major axes); Ph4Sb, --, 42, 219-20° -- (single crystal detn. of ρ gave 13 and 1.5 × 104 for 2 of the major axes); Ph3S, --, 65, 235-40°, -- (single crystal detn. of ρ gave 1.0 for the long axis); Ph3Se, --, 71, 240-5% 400. Et3N (0.75 ml.) in VII was added to a near boiling soln. of 2.8 g. V in 250 ml. VII then left 21 hrs. at room temp. to give 1.18 g. XXI. Similarly were prepd. (solvent, cation in the salt M+Q•-Q, appearance, % yield, decompn. range, and ρ ohm-cm. given): VII, Me3NH, black crystals, 90, >215° 5 × 106; VII, (triethylenediamine-H) (in [M+]2-[Q•-]Q), black microcrystals, 26, 270°, 10; CH2Cl2, (4-hydroxy-N-benzylanilinium), black microcrystals, 36,175 to above 300° 55 (Εa 0.075 e.v.); CHCl3, (4-amino-N,N-diethylanilinium), black rods, 55, 144 to above 300°, 175 (Εa 0.09 e.v.); MeCN (10 moles ferrocene/mole V), (ferricinium), black needles, low, --, 0.24 (single crystal); MeCN, (dimethylferricinium), black needles, 60, 170° 31. (Cobalticinium)Q•-Q, ρ 6.5 ohm-cm. (Εa 0.034 e.v.), was prepd. in 20% yield by mixing aq. solns. of cobalticinium chloride and XVI. Et3N (1.5 ml.) in 15 ml. MeCN was added to a soln. prepd. by addn. of 1.0 g. VI in 50 ml. hot MeCN to 3.0 g. V in 350 ml. gently boiling MeCN and the mixt. left overnight at room temp. to give 3.16 g. (62%) XXI. Similarly were prepd. (cation in the salt M+Q•-Q, appearance, % yield, decompn. range, and ρ ohm-cm. given): tert-BuMe2NH, black crystals, 82, 214°, 9; pyridinium, blue-black needles, 42, 168-85°, 37; (2,2'-bipyridinium), --, 100, 235-68°, 0.5. The mixed complex salt Ph3MeP+Ph3MeAs+(Q•-)2Q2 was prepd. from Ph3MePI, Ph3MeAsI, and V in MeCN. (Quinolinium)+•-Q (XXIII), blue-black needles, decompg. ∼250°, has the lowest ρ of any org. compd. (0.01 ohm-cm. for the long axis of a single crystal; compaction ρ 0.5 ohm-cm.). XXIII was prepd. in 91% yield from quinoline (XXIV) hydriodide (XXV) and XVI in MeCN, in 44% yield from XXV and XVI in CH2Cl2, in 87% yield from XXIV, V, and VI in MeCN, in 71% yield from XXIV, V, and durohydroquinone in MeCN, and from XXV and V in MeCN or CH2Cl2. Spectroscopic, polarographic, and conductivity data show that in soln. the complex salts are dissocd. into cation, Q•-, and V but they can be crystd. without change in compn. In the solid state there is probably complete electron delocalization between Q•- and Q. The complex salts are characterized by low ρ which shows exponential temp. dependence typical of intrinsic semiconductors. Both simple and complex salts are decompd. by mineral acids, e.g. 2.10 g. powd. XXI was added to 30ml. 2.4N HCl, the mixt. stirred 16 hrs. at room temp., the ppt. collected, washed with 2 ml. 2.4N HCl (0.27 g. Et3N was recovered from the filtrate and washings), then with H2O, and dried to give 1.66 g. V-VI mixt. (3:1). Q•- is oxidized to V by iodine; thus, 1.0 g. iodine added to 0.2 g. XXI in 10 ml. MeCN and the mixt. warmed on a steam-bath gave 0.12 g. (79%) V. Spectroscopic, polarographic, e.p.r., and elec. data are briefly discussed. 31 references.
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    26. 26
      Sambe, K.; Hoshino, N.; Takeda, T.; Nakamura, T.; Akutagawa, T. Dynamics and Structural Diversity of Li+(Crown Ether). Supramolecular Cations in Electrically Conducting Salts. J. Phys. Chem. C 2020, 124, 13560– 13571,  DOI: 10.1021/acs.jpcc.0c02686
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      Dynamics and Structural Diversity of Li+(Crown Ether) Supramolecular Cations in Electrically Conducting Salts
      Sambe, Kohei; Hoshino, Norihisa; Takeda, Takashi; Nakamura, Takayoshi; Akutagawa, Tomoyuki
      Journal of Physical Chemistry C (2020), 124 (25), 13560-13571CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
      Li+([12]crown-4)2(TCNQ)2 (1), Li+([15]crown-5)(TCNQ)2 (2a and 2b), and Li+([18]crown-6)(TCNQ)2·(H2O)2 (3) salts (TCNQ = 7,7,8,8-tetracyano-p-quinodimethane) were prepd. and examd. in terms of crystal structures, dielec. consts., magnetic susceptibilities, and elec. conductivities. The dynamic behavior of the small Li+ was easily activated inside the cavities of [15]crown-5 and [18]crown-6. In salt 2a, a structural phase transition at 160 K is thermally activated by a change in the -CN···Li+···NC- coordination from an asym. to a sym. environment. The phase-transition temp. for salt 2a is ∼25 K lower than that for the isostructural Na+([15]crown-5)(TCNQ)2, indicating that the behavior of Li+ inside the [15]crown-5 cavity is considerably more dynamic than that of Na+ in the same situation. Crystal polymorphs 2a and 2b are obsd. for Li+([15]crown-5) supramol. cations, where the two-dimensional intermol. interactions of TCNQs in salts 2a and 2b are constructed by the spanning-overlap mode of the π-dimers and π-tetramers, resp. The packing periodicity in the latter salt is twice that in the former, and this structural difference prevents the structural phase transition for salt 2b. In salt 3, the orientational disorder of Li+ inside the cavity of the [18]crown-6 is a combination of the dynamic behavior of Li+ itself and that of Li+-coordinated polar H2O mols., which are evidenced by two types of dielec. relaxation. Li+ is considerably smaller than Na+, allowing it to form a dynamic Li+···O coordination environment.
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    27. 27
      Yan, B.; Horton, P. N.; Russell, A. E.; Wedge, Ch. J.; Weston, S. C.; Grossel, M. C. Crown ether alkali metal TCNQ complexes revisited – the impact of smaller cation complexes on their solid-state architecture and properties. CrystEngComm 2019, 21, 3273– 3279,  DOI: 10.1039/C9CE00234K
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      Crown ether alkali metal TCNQ complexes revisited - the impact of smaller cation complexes on their solid-state architecture and properties
      Yan, Bingjia; Horton, Peter N.; Russell, Andrea E.; Wedge, Christopher J.; Weston, Simon C.; Grossel, Martin C.
      CrystEngComm (2019), 21 (21), 3273-3279CODEN: CRECF4; ISSN:1466-8033. (Royal Society of Chemistry)
      The solid-state behavior of four alkali metal TCNQ complexes: (15-crown-5)LiTCNQ (1), (15-crown-5)NaTCNQ (2), (15-crown-5)Li(TCNQ)2·H2O (3·H2O) and (15-crown-5)Na(TCNQ)2·H2O (4·H2O) has been explored by single crystal X-ray diffraction, IR (IR), Raman and ESR (EPR) measurements. The presence of a small cation and ionophore leads to subtle changes in behavior compared with their larger alkali metal analogs and in the hydrated salts water bridges form links between the crown-encapsulated cations and neighboring TCNQ stacks.
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    28. 28
      Yan, B.; Horton, P. N.; Weston, S. C.; Russell, A. E.; Grossel, M. C. Novel TCNQ-stacking motifs in (12-crown-4)-complexes of alkali metal TCNQ salts. CrystEngComm 2021, 23, 6755– 6760,  DOI: 10.1039/D1CE01075A
      28
      Novel TCNQ-stacking motifs in (12-crown-4)-complexes of alkali metal TCNQ salts
      Yan, Bingjia; Horton, Peter N.; Weston, Simon C.; Russell, Andrea E.; Grossel, Martin C.
      CrystEngComm (2021), 23 (38), 6755-6760CODEN: CRECF4; ISSN:1466-8033. (Royal Society of Chemistry)
      An investigation of the solid-state behavior of five 12-crown-4 alkali metal TCNQ complexes, (12-crown-4)2LiTCNQ (1), (12-crown-4)2NaTCNQ (2), (12-crown-4)2Li(TCNQ)2 (3), (12-crown-4)2Na(TCNQ)2 (4), and (12-crown-4)2K(TCNQ)2 (5), reveals an unusual "cross-stitch" packing motif with the extended face-to-face π-stacked TCNQ̇ - columns present in complexes 1 and 2. The effect of the presence of addnl. neutral TCNQ0 has also been explored.
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    29. 29
      Li, Q.; Wang, Y.; Yan, P.; Hou, G.; Li, G. Two 7,7,8,8-tetracyanoquinodimethane lead and zinc complexes featuring 3D and 0D structure: Synthesis, structure and electrochemical properties. Inorg. Chim. Acta 2014, 413, 32– 37,  DOI: 10.1016/j.ica.2013.12.032
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      Two 7,7,8,8-tetracyanoquinodimethane lead and zinc complexes featuring 3D and 0D structure: Synthesis, structure and electrochemical properties
      Li, Qiang; Wang, Yan; Yan, Pengfei; Hou, Guangfeng; Li, Guangming
      Inorganica Chimica Acta (2014), 413 (), 32-37CODEN: ICHAA3; ISSN:0020-1693. (Elsevier B.V.)
      Two 7,7,8,8-tetracyanoquinodimethane (TCNQ) Pb2+ and Zn2+ complexes, namely, {[Pb2(TCNQ)3(H2O)6](TCNQ)}n (1) and Li[Zn2(TCNQ)5(H2O)6]·[Zn(TCNQ)2(H2O)4]·6H2O (2) have been synthesized by the reactions of Li(TCNQ) with PbCl2 and Zn(TPP)2Cl2 (TPP = triphenylphosphine), resp. Single-crystal x-ray diffraction anal. reveals that complex 1 features a 3D network structure and complex 2 features a 0D structure in which a neutral mol. of [Zn(TCNQ)2(H2O)4] crystallizes in the crystal. The flexible coordination modes of TCNQ and the metal ions play essential roles on the formation of the novel 3D structure and the unique 0D ionic structure. The TCNQ mols. adapt a one-dimensional column through π-π stacking interactions. Cyclic and differential pulse voltammograms for complexes 1 and 2 show the reversible one-electron oxidn. and one-electron redn. within the electrochem. window of CH3CN. Their electrochem. HOMO-LUMO gap and reversibility were examd.
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    30. 30
      Lu, J.; Ojha, R.; Bond, A. M.; Martin, L. L. Systematic Approach to the Synthesis of Cobaltocenium Salts with Reduced Forms of TCNQF4: Two [Cp2Co](TCNQF4) Polymorphs and [Cp2Co]Li(TCNQF4). Cryst. Growth Des. 2019, 19, 2712– 2722,  DOI: 10.1021/acs.cgd.8b01841
      30
      Systematic Approach to the Synthesis of Cobaltocenium Salts with Reduced Forms of TCNQF4: Two [Cp2Co](TCNQF4) Polymorphs and [Cp2Co]Li(TCNQF4)
      Lu, Jinzhen; Ojha, Ruchika; Bond, Alan M.; Martin, Lisandra L.
      Crystal Growth & Design (2019), 19 (5), 2712-2722CODEN: CGDEFU; ISSN:1528-7483. (American Chemical Society)
      Three new crystallog. characterized compds. were prepd. in high yield from reactions between [Cp2Co]PF6 (Cp = cyclopentadiene) and lithium salts of the radical anion of 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (TCNQF41-) or the dianionic TCNQF42-. The two [Cp2Co]TCNQF4 compds. (1 and 2) with 1:1 stoichiometry were found to be polymorphic, α and β. Remarkably, the syntheses only differed by the presence of a small amt. of neutral TCNQF4 in the case of polymorph β (2). The role of the TCNQF4 has been rationalized on the basis of a transient intermediate, postulated as [Cp2Co](TCNQF4)2. Compd. 3 contains TCNQF42- and crystd. as [Cp2Co]Li(TCNQF4). This material highlights a novel coordination mode for the Li+ cation that participated in the formation of a metal-org. framework accommodating the [Cp2Co]+ cation. All complexes were comprehensively characterized by Fourier transform IR spectroscopy, UV-vis spectroscopy, and electrochem. Polymorph β (2) has a cond. of 5.8 × 10-4 S cm-1, which lies well within the semiconductor range. Previous work in this area employed redox chem. based on the reaction of cobaltocene or ferrocene with neutral TCNQ. The introduction of metathesis reactions enhances the synthetic flexibility enabling a systematic approach to new materials.
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    31. 31
      Černák, J.; Hegedüs, M.; Váhovská, L.; Kuchár, J.; Šoltésová, D.; Čižmár, E.; Feher, A.; Falvello, L. R. Syntheses, crystal structures and magnetic properties of complexes based on [Ni(L-L)3]2+ complex cations with dimethylderivatives of 2,2′-bipyridine and TCNQ. Solid State Sci. 2018, 77, 27– 36,  DOI: 10.1016/j.solidstatesciences.2018.01.004
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      Syntheses, crystal structures and magnetic properties of complexes based on [Ni(L-L)3]2+ complex cations with dimethylderivatives of 2,2'-bipyridine and TCNQ
      Cernak, Juraj; Hegedus, Michal; Vahovska, Lucia; Kuchar, Juraj; Soltesova, Daniela; Cizmar, Erik; Feher, Alexander; Falvello, L. R.
      Solid State Sciences (2018), 77 (), 27-36CODEN: SSSCFJ; ISSN:1293-2558. (Elsevier Masson SAS)
      From the aq.-methanolic systems Ni(NO3)2 - LiTCNQ - 5,5'-dmbpy and Ni(NO3)2 - LiTCNQ - 4,4'-dmbpy three novel complexes [Ni(5,5'-dmbpy)3](TCNQ)2 (1), [Ni(4,4'-dmbpy)3](TCNQ)2 (2) and [Ni(4,4'-dmbpy)3]2(TCNQ-TCNQ)(TCNQ)2•0.60H2O (3), were isolated in single crystal form. The new compds. were identified using chem. analyses and IR spectroscopy. Single crystal studies of all samples corroborated their compns. and have shown that their ionic structures contain the complex cations [Ni(5,5'-dmbpy)]2+ (1) or [Ni(4,4'-dmbpy)]2+ (2 and 3). The anionic parts of the resp. crystal structures 1-3 are formed by TCNQ·- anion-radicals and in 3 also by a σ-dimerized dianion (TCNQ-TCNQ)2- with a C-C distance of 1.663(5) Å. The supramol. structures are governed by weak hydrogen bonding interactions. The variable-temp. (2-300 K) magnetic studies of 1 and 3 confirmed the presence of magnetically active Ni(II) atoms with S = 1 and TCNQ·- anion-radicals with S = 1/2 while the (TCNQ-TCNQ)2- dianion is magnetically silent. The magnetic behavior was described by a complex magnetic model assuming strong antiferromagnetic interactions between some TCNQ·- anion-radicals.
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    32. 32
      Lu, J.; Le, T. H.; Traore, D. A. K.; Wilce, M.; Bond, A. M.; Martin, L. L. Synthetic Precursors for TCNQF42– Compounds: Synthesis, Characterization, and Electrochemical Studies of (Pr4N)2TCNQF4 and Li2TCNQF4. J. Org. Chem. 2012, 77, 10568– 10574,  DOI: 10.1021/jo301403v
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      Synthetic Precursors for TCNQF42- Compounds: Synthesis, Characterization, and Electrochemical Studies of (Pr4N)2TCNQF4 and Li2TCNQF4
      Lu, Jinzhen; Le, Thanh Hai; Traore, Daouda A. K.; Wilce, Matthew; Bond, Alan M.; Martin, Lisandra L.
      Journal of Organic Chemistry (2012), 77 (23), 10568-10574CODEN: JOCEAH; ISSN:0022-3263. (American Chemical Society)
      The lithium radical monoanion salt of tetrafluorotetracyanoquinodimethane Li(TCNQF4) and the dilithium dianion salt Li2(TCNQF4) were prepd. selectively from lithium iodide and tetrafluorotetracyanoquinodimethane (TCNQF4) by carefully controlling the reagent stoichiometry and temp. Reaction of TCNQF4 with four equiv. of LiI in boiling acetonitrile yielded Li2TCNQF4 in 90% yield; use of less than four equiv. of LiI gave mixts. of the mono- and dianionic salts. Reaction of TCNQF4 with 1.5 equiv. of LiI in acetonitrile at ambient temp. gave Li(TCNQF4) in 84% yield. The monoanion and dianion tetrapropylammonium salts of TCNQF4 were prepd. by cation exchange of Li(TCNQF4) or Li2(TCNQF4) with tetrapropylammonium bromide in hot water. The structures of (Pr4N)2(TCNQF4) and Pr4N(TCNQF4) were detd. by X-ray crystallog.
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    33. 33
      Tanase, S.; Ferbinteanu, M.; Andruh, M.; Mathonière, C.; Strenger, I.; Rombaut, G. Synthesis and characterization of a new molecular magnet, [Ni(ampy)2]3[Fe(CN)6]2·6H2O, and synthesis, crystal structure and magnetic properties of its mononuclear precursor, trans-[Ni(ampy)2(NO3)2] (ampy = 2-aminomethylpyridine). Polyhedron 2000, 19, 1967– 1973,  DOI: 10.1016/S0277-5387(00)00497-6
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      Synthesis and characterization of a new molecular magnet, [Ni(ampy)2]3[Fe(CN)6]2·6H2O, and synthesis, crystal structure and magnetic properties of its mononuclear precursor, trans-[Ni(ampy)2(NO3)2] (ampy = 2-aminomethylpyridine)
      Tanase, Stefania; Ferbinteanu, Marilena; Andruh, Marius; Mathoniere, Corine; Strenger, Irina; Rombaut, Guillaume
      Polyhedron (2000), 19 (16-17), 1967-1973CODEN: PLYHDE; ISSN:0277-5387. (Elsevier Science Ltd.)
      The reaction of trans-[Ni(ampy)2(NO3)2] (1, ampy = 2-aminomethylpyridine) with K3[Fe(CN)6] affords a cyano-bridged bimetallic system, [Ni(ampy)2]3[Fe(CN)6]2·6H2O (2). The crystal structure of compd. 1 was solved. It crystallizes in the monoclinic space group P121/c1 and consists of neutral mononuclear entities with the nickel atom located on an inversion center. The nickel atom exhibits a (pseudo)octahedral stereochem. with the two nitrato ligands coordinated in trans positions. The Ni-N bond distances vary from 2.0690(15) to 2.0811(15) Å, while the trans-Ni-O distances are 2.1665(13) Å. The cryomagnetic study of compd. 1 reveals an intermol. ferromagnetic coupling (θ = + 3.7 K), which is mediated by the π-π stacking interactions between the mononuclear entities. Compd. 2 is a soft ferromagnet with Tc = 7.5 K and a coercive field of 330 G at 2 K.
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    34. 34
      Tandon, S. S.; Chander, S.; Thompson, L. K. Ligating properties of tridentate Schiff base ligands, 2-[[(2-pyridinylmethyl)imino]methyl] phenol (HSALIMP) and 2-[[[2-(2-pyridinyl)ethyl]imino]methyl]phenol (HSALIEP) with zinc(II), cadmium(II), nickel(II) and manganese(III) ions. X-ray crystal structures of the [Zn(SALIEP)(NO3)]2 dimer, [Mn(SALIEP)2](ClO4), and [Zn(AMP)2(NO3)2]. Inorg. Chim. Acta 2000, 300-302, 683– 692,  DOI: 10.1016/S0020-1693(00)00010-4
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      Ligating properties of tridentate Schiff base ligands, 2-[[(2-pyridinylmethyl)imino]methyl]phenol (HSALIMP) and 2-[[[2-(2-pyridinyl)ethyl]imino]methyl]phenol (HSALIEP) with zinc(II), cadmium(II), nickel(II) and manganese(III) ions. X-ray crystal structures of the [Zn(SALIEP)(NO3)]2 dimer, [Mn(SALIEP)2](ClO4), and [Zn(AMP)2(NO3)2]
      Tandon, S. S.; Chander, S.; Thompson, L. K.
      Inorganica Chimica Acta (2000), 300-302 (), 683-692CODEN: ICHAA3; ISSN:0020-1693. (Elsevier Science S.A.)
      Zn(II), Cd(II), Ni(II) and Mn(III) complexes with two potentially tridentate (NNO) Schiff base ligands, 2-[[(2-pyridinylmethyl)imino]methyl]phenol (HSALIMP) and 2-[[[2-(2-pyridinyl)ethyl]imino]methyl]phenol (HSALIEP) were synthesized and structurally characterized through IR, 1H, 13C, and 2-dimensional NMR spectroscopy and in two cases by x-ray crystallog. The Schiff base ligands HSALIMP and HSALIEP are generated from 1+1 condensation of salicylaldehyde with 2-aminomethylpyridine and 2(2-aminoethyl)pyridine, resp. HSALIMP behaves as a tridentate (NNO) or a bidentate (NN) ligand, depending upon the nature of the anion. On reaction with Zn(II) salts HSALIMP gives two types of complexes, (a) [Zn(SALIMP)X]2·yH2O (X = NO3, y = 0 (I); X = I, y = 3 (II)) and (b) [Zn(HSALIMP)Cl2]·H2O (III). HSALIMP reacts with Ni(II) bromide to form mononuclear [Ni(HSALIMP)2Br2] (VIII), in which one metal ion combines with two neutral HSALIMP ligands. However HSALIEP, a similar ligand with one addnl. C atom in the chain, acts as a tridentate ligand (NNO), with the phenolate O deprotonated, irresp. of the nature of the anion, forming dimeric compds. of 1:1 metal:ligand stoichiometry with Zn(II) and Cd(II) ions, [Zn(SALIEP)X]2·yH2O (X = NO3, y = 0 (IV); X = Cl, y = 2 (V); X = I, y = 1 (VI)), [Cd(SALIEP) (NO3)]2·EtOH (VII) and a monomeric complex of 1:2 metal:ligand stoichiometry with Mn(III) ion, [Mn(SALIEP)2](ClO4) (IX). The single crystal x-ray structures of the [Zn(SALIEP)(NO3)]2 (IV) dimer, [Mn(SALIEP)2](ClO4) (IX), and [Zn(AMP)2(NO3)2] (X), a minor product obtained from the filtrate of I, were detd. IV consists of centrosym. dimer in which deprotonated phenolates bridge the two five-coordinate metal atoms and link the two halves of the dimer. The structure of IX consists of a centrosym. mol. in which the Mn(III) ion is bound to two tridentate SALIEP ligands in a nearly regular octahedral arrangement. The structure of X consists of a centrosym. monomer in which the six coordinate octahedral Zn(II) ion is bonded equatorially to two bidentate 2-aminomethylpyridine ligands and axially to two monodentate nitrate groups.
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    35. 35
      Macrae, C. F.; Sovago, I.; Cottrell, S. J.; Galek, P. T. A.; McCabe, P.; Pidcock, E.; Platings, M.; Shields, G. P.; Stevens, J. S.; Towler, M.; Wood, P. A. Mercury 4.0: from visualization to analysis, design and prediction. J. Appl. Crystallogr. 2020, 53, 226– 235,  DOI: 10.1107/S1600576719014092
      35
      Mercury 4.0: from visualization to analysis, design and prediction
      Macrae, Clare F.; Sovago, Ioana; Cottrell, Simon J.; Galek, Peter T. A.; McCabe, Patrick; Pidcock, Elna; Platings, Michael; Shields, Greg P.; Stevens, Joanna S.; Towler, Matthew; Wood, Peter A.
      Journal of Applied Crystallography (2020), 53 (1), 226-235CODEN: JACGAR; ISSN:1600-5767. (International Union of Crystallography)
      The program Mercury, developed at the Cambridge Crystallog. Data Center, was originally designed primarily as a crystal structure visualization tool. Over the years the fields and scientific communities of chem. crystallog. and crystal engineering have developed to require more advanced structural anal. software. Mercury has evolved alongside these scientific communities and is now a powerful anal., design and prediction platform which goes a lot further than simple structure visualization.
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    36. 36
      Oxford Diffraction. CrysAlis RED and CrysAlis CCD Software (Ver. 1.171.38.41); Rigaku Oxford Diffraction Ltd: Abingdon, Oxfordshire, England, 2015.
      There is no corresponding record for this reference.
    37. 37
      Blessing, R. H. An empirical correction for absorption anisotropy. Acta Crystallogr., Sect. A: Found. Crystallogr. 1995, 51, 33– 38,  DOI: 10.1107/S0108767394005726
      37
      An empirical correction for absorption anisotropy
      Blessing R H
      Acta crystallographica. Section A, Foundations of crystallography (1995), 51 ( Pt 1) (), 33-8 ISSN:0108-7673.
      A least-squares procedure is described for modeling an empirical transmission surface as sampled by multiple symmetry-equivalent and/or azimuth rotation-equivalent intensity measurements. The fitting functions are sums of real spherical harmonic functions of even order, ylm(-u0) + ylm(u1), 2 < or = l = 2n < or = 8. The arguments of the functions are the components of unit direction vectors, -u0 for the reverse incident beam and u1 for the scattered beam, referred to crystal-fixed Cartesian axes. The procedure has been checked by calculations against standard absorption test data.
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    38. 38
      Sheldrick, G. M. SHELXT - Integrated space-group and crystal-structure determination. Acta Crystallogr., Sect. A: Found. Adv. 2015, 71, 3– 8,  DOI: 10.1107/S2053273314026370
      38
      SHELXT - Integrated space-group and crystal-structure determination
      Sheldrick, George M.
      Acta Crystallographica, Section A: Foundations and Advances (2015), 71 (1), 3-8CODEN: ACSAD7; ISSN:2053-2733. (International Union of Crystallography)
      The new computer program SHELXT employs a novel dual-space algorithm to solve the phase problem for single-crystal reflection data expanded to the space group P1. Missing data are taken into account and the resoln. extended if necessary. All space groups in the specified Laue group are tested to find which are consistent with the P1 phases. After applying the resulting origin shifts and space-group symmetry, the solns. are subject to further dual-space recycling followed by a peak search and summation of the electron d. around each peak. Elements are assigned to give the best fit to the integrated peak densities and if necessary addnl. elements are considered. An isotropic refinement is followed for non-centrosym. space groups by the calcn. of a Flack parameter and, if appropriate, inversion of the structure. The structure is assembled to maximize its connectivity and centered optimally in the unit cell. SHELXT has already solved many thousand structures with a high success rate, and is optimized for multiprocessor computers. It is, however, unsuitable for severely disordered and twinned structures because it is based on the assumption that the structure consists of atoms.
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    39. 39
      Sheldrick, G. M. Crystal structure refinement with SHELXL. Acta Crystallogr., Sect. C: Struct. Chem. 2015, C71, 3– 8,  DOI: 10.1107/S2053229614024218
      There is no corresponding record for this reference.
    40. 40
      Farrugia, L. J. WinGX and ORTEP for Windows: an update. J. Appl. Crystallogr. 2012, 45, 849– 854,  DOI: 10.1107/S0021889812029111
      40
      WinGX and ORTEP for Windows: an update
      Farrugia, Louis J.
      Journal of Applied Crystallography (2012), 45 (4), 849-854CODEN: JACGAR; ISSN:0021-8898. (International Union of Crystallography)
      The WinGX suite provides a complete set of programs for the treatment of small-mol. single-crystal diffraction data, from data redn. and processing, structure soln., model refinement and visualization, and metric anal. of mol. geometry and crystal packing, to final report prepn. in the form of a CIF. It includes several well known pieces of software and provides a repository for programs when the original authors no longer wish to, or are unable to, maintain them. It also provides menu items to execute external software, such as the SIR and SHELX suites of programs. The program ORTEP for Windows provides a graphical user interface (GUI) for the classic ORTEP program, which is the original software for the illustration of anisotropic displacement ellipsoids. The GUI code provides input capabilities for a wide variety of file formats, and extra functionality such as geometry calcns. and ray-traced outputs. The programs WinGX and ORTEP for Windows have been distributed over the internet for about 15 years, and this article describes some of the more modern features of the programs.
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    41. 41
      Karplus, P. A.; Diederichs, K. Assessing and maximizing data quality in macromolecular crystallography. Curr. Opin. Struct. Biol. 2015, 34, 60– 68,  DOI: 10.1016/j.sbi.2015.07.003
      41
      Assessing and maximizing data quality in macromolecular crystallography
      Karplus, P. Andrew; Diederichs, Kay
      Current Opinion in Structural Biology (2015), 34 (), 60-68CODEN: COSBEF; ISSN:0959-440X. (Elsevier Ltd.)
      A review. The quality of macromol. crystal structures depends, in part, on the quality and quantity of the data used to produce them. Here, the authors review recent shifts in the understanding of how to use data quality indicators to select a high resoln. cutoff that leads to the best model, and of the potential to greatly increase data quality through the merging of multiple measurements from multiple passes of single crystals or from multiple crystals. Key factors supporting this shift are the introduction of more robust correlation coeff. based indicators of the precision of merged data sets as well as the recognition of the substantial useful information present in extensive amts. of data once considered too weak to be of value.
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    42. 42
      Brandenburg, K. DIAMOND. Crystal Impact (Version 3.1f) GbR; Bonn: Germany, 2008.
      There is no corresponding record for this reference.
    43. 43
      Guzei, I.; Herbst-Irmer, R.; Munyaneza, A.; Darkwa, J. Detailed example of the identification and crystallographic analysis of a pseudo-merohedrally twinned crystal. Acta Crystallogr., Sect. B Struct. Sci. 2012, 68, 150– 157,  DOI: 10.1107/S0108768112002728
      43
      Detailed example of the identification and crystallographic analysis of a pseudo-merohedrally twinned crystal
      Guzei, Ilia; Herbst-Irmer, Regine; Munyaneza, Apollinaire; Darkwa, James
      Acta Crystallographica, Section B: Structural Science (2012), 68 (2), 150-157CODEN: ASBSDK; ISSN:0108-7681. (International Union of Crystallography)
      A detailed description of the crystal structure soln. and refinement of a pseudo-merohedrally twinned crystal of an organometallic complex is presented as a guide to the handling of similar non-routine challenging crystal structures. The interpretation of the signs of twinning and the logic behind the selection of the correct space group are explained. In this case the crystal twinning was complicated by pseudo-symmetry of the ionic species and positional disorder of several atoms. A detailed description of the procedures utilized in the non-routine X-ray single-crystal structural detn. and refinement of a pseudo-merohedrally twinned crystal of an Fe/Ni organometallic complex is presented. It illustrates to the practitioners of crystallog. how to properly handle such cases and describes the logic and concrete steps necessary to account for the twinning, pseudo-symmetry and at. positional disorder.
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    44. 44
      Parkin, S. R. Practical hints and tips for solution of pseudo-merohedric twins: three case studies. Acta Crystallogr., Sect. E: Crystallogr. Commun. Cryst Commun 2021, 77, 452– 465,  DOI: 10.1107/S205698902100342X
      44
      Practical hints and tips for solution of pseudo-merohedric twins: three case studies
      Parkin, S. R.
      Acta Crystallographica, Section E: Crystallographic Communications (2021), 77 (5), 452-465CODEN: ACSECI; ISSN:2056-9890. (International Union of Crystallography)
      Twinning by pseudo-merohedry is a common phenomenon in small-mol. crystallog. In cases where twin-component vol. fractions are markedly different, structure soln. is often no more difficult than for non-twinned structures of similar complexity. When twin-component vol. fractions are similar, however, structure soln. can be much more of a problem. This paper presents hints and tips for such cases by means of three worked examples. The first example presents the most common (and simplest) case of a two-component pseudo-orthorhombic twin. The second example describes structure soln. of a reticular threefold pseudo-hexagonal twin that benefits from use of an unconventional space-group setting. The third example covers structure soln. of a reticular fourfold pseudo-tetragonal twin. All three structures are ultimately shown to be monoclinic crystals that twin as a consequence of unit-cell metrics that mimic those of higher symmetry crystal systems.
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    45. 45
      Spek, A. L. checkCIF validation ALERTS: what they mean and how to respond. Acta Crystallogr., Sect. E: Crystallogr. Commun. 2020, 76, 1– 11,  DOI: 10.1107/S2056989019016244
      45
      checkCIF validation ALERTS: what they mean and how to respond
      Spek, Anthony L.
      Acta Crystallographica, Section E: Crystallographic Communications (2020), 76 (1), 1-11CODEN: ACSECI; ISSN:2056-9890. (International Union of Crystallography)
      A review. Authors of a paper that includes a new crystal-structure detn. are expected to not only report the structural results of interest and their interpretation, but are also expected to archive in computer-readable CIF format the exptl. data on which the crystal-structure anal. is based. Addnl., an IUCr/checkCIF validation report will be required for the review of a submitted paper. Such a validation report, automatically created from the deposited CIF file, lists as ALERTS not only potential errors or unusual findings, but also suggestions for improvement along with interesting information on the structure at hand. Major ALERTS for issues are expected to have been acted on already before the submission for publication or discussed in the assocd. paper and/or commented on in the CIF file. In addn., referees, readers and users of the data should be able to make their own judgment and interpretation of the underlying exptl. data or perform their own calcns. with the archived data. All the above is consistent with the FAIR (findable, accessible, interoperable, and reusable) initiative [Helliwell (2019). Struct. Dyn.6, 05430]. Validation can also be helpful for less experienced authors in pointing to and avoiding of crystal-structure detn. and interpretation pitfalls. The IUCr web-based checkCIF server provides such a validation report, based on data uploaded in CIF format. Alternatively, a locally installable checkCIF version is available to be used iteratively during the structure-detn. process. ALERTS come mostly as short single-line messages. There is also a short explanation of the ALERTS available through the IUCr web server or with the locally installed PLATON/checkCIF version. This paper provides addnl. background information on the checkCIF procedure and addnl. details for a no. of ALERTS along with options for how to act on them.
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    46. 46
      Usón, I.; Sheldrick, G. M. Advances in direct methods for protein crystallography. Curr. Opin. Struct. Biol. 1999, 9, 643– 648,  DOI: 10.1016/s0959-440x(99)00020-2
      46
      Advances in direct methods for protein crystallography
      Uson, Isabel; Sheldrick, George M.
      Current Opinion in Structural Biology (1999), 9 (5), 643-648CODEN: COSBEF; ISSN:0959-440X. (Current Biology Publications)
      A review with 43 refs. Recent advances in ab initio direct methods have enabled the soln. of crystal structures of small proteins from native x-ray data alone, i.e., without the use of fragments of known structure or the need to prep. heavy-atom or selenomethionine derivs., provided that the data are available to at. resoln. These methods are also proving to be useful for locating the selenium atoms or other anomalous scatterers in the multiple wavelength anomalous diffraction phasing of larger proteins at lower resoln.
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    47. 47
      Herbst-Irmer, R.; Sheldrick, G. M. Refinement of twinned structures with SHELX97. Acta Crystallogr., Sect. B: Struct. Sci. 1998, B 54, 443– 449,  DOI: 10.1107/S0108768197018454
      There is no corresponding record for this reference.
    48. 48
      Nakamoto, K. Infrared and Raman Spectra of Inorganic and Coordination Compounds; J. Wiley&Sons: New York, 2009.
      There is no corresponding record for this reference.
    49. 49
      Johnston, J. The utilization of diffusion processes in the preparation of pure substances. J. Am. Chem. Soc. 1914, 36, 16– 19,  DOI: 10.1021/ja02178a003
      49
      Utilization of diffusion processes in the preparation of pure substances
      Johnston, John
      Journal of the American Chemical Society (1914), 36 (), 16-9CODEN: JACSAT; ISSN:0002-7863.
      A theoretical discussion of the conditions which favor the production of large crystals is followed by the description of an app. by means of which relatively large and hence pure crystals of rather insol. substances may be prepared.
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    50. 50
      Martin, S. A.; Haendler, H. M. A modified diffusion apparatus for the growth of single crystals. J. Appl. Crystallogr. 1978, 11, 62,  DOI: 10.1107/S0021889878012728
      50
      A modified diffusion apparatus for the growth of single crystals
      Martin, Sharon A.; Haendler, Helmut M.
      Journal of Applied Crystallography (1978), 11 (1), 62CODEN: JACGAR; ISSN:0021-8898.
      Single crystals of insol. compds. can be grown by diffusion of 2 solns. which interact to form the solid by metathesis with minimization of convection and removal of crystals without further mixing of the solns. by using a modification of the gel-diffraction app. of A. Armington and J. O'Connor (1968). The app. was used to grow single crystals of Y, Zn, Co,and Cd anthranilates with a soln. of Na anthranilate in one reservoir and a soln. of metal salt in th other. Well-shaped crystals suitable for x-ray work were grown in 2-3 wk.
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    51. 51
      Yan, J.-Q.; Sales, B. C.; Susner, M. A.; McGuire, M. A. Flux growth in a horizontal configuration: An analog to vapor transport growth. Phys. Rev. Mater. 2017, 1, 023402  DOI: 10.1103/PhysRevMaterials.1.023402
      51
      Flux growth in a horizontal configuration: an analog to vapor transport growth
      Yan, J.-Q.; Sales, B. C.; Susner, M. A.; McGuire, M. A.
      Physical Review Materials (2017), 1 (2), 023402/1-023402/11CODEN: PRMHBS; ISSN:2475-9953. (American Physical Society)
      Flux growth of single crystals is normally performed in a vertical configuration with an upright refractory container holding the flux melt. At high temps., flux dissolves the charge, forming a homogeneous soln. before nucleation and growth of crystals takes place under proper supersatn. generated by cooling or evapg. the flux. In this work, we report flux growth in a horizontal configuration with a temp. gradient along the horizontal axis: a liq. transport growth analogus to the vapor transport technique. In a typical liq. transport growth, the charge is kept at the hot end of the refractory container and the flux melt dissolves the charge and transfers it to the cold end. Once the concn. of charge is above the soly. limit at the cold end, the thermodynamically stable phase nucleates and grows. Compared to the vertical flux growth, the liq. transport growth can provide a large quantity of crystals in a single growth since the charge/flux ratio is not limited by the soly. limit at the growth temp. This technique is complementary to the vertical flux growth and can be considered when a large amt. of crystals is needed but the yield from the conventional vertical flux growth is limited. We applied this technique to the growth of IrSb3, Mo3Sb7, and MnBi from self-flux, and the growth of FeSe, CrTe3, NiPSe3, FePSe3, CuInP2S6, RuCl3, and OsCl4 from a halide flux.
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    52. 52
      Kim, J.; Silakov, A.; Yennawar, H. P.; Lear, B. J. Structural, Electronic, and Magnetic Characterization of a Dinuclear Zinc Complex Containing TCNQ– and a μ-[TCNQ–TCNQ]2– Ligand. Inorg. Chem. 2015, 54, 6072– 6074,  DOI: 10.1021/acs.inorgchem.5b00808
      52
      Structural, Electronic, and Magnetic Characterization of a Dinuclear Zinc Complex Containing TCNQ- and a μ-[TCNQ-TCNQ]2- Ligand
      Kim, Juyeong; Silakov, Alexey; Yennawar, Hemant P.; Lear, Benjamin J.
      Inorganic Chemistry (2015), 54 (13), 6072-6074CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
      A dinuclear zinc complex contg. both a σ-dimerized 7,7,8,8-tetracyanoquinodimethane (TCNQ) ligand ([TCNQ-TCNQ]2-) and TCNQ- was synthesized for the first time. This is the first instance of a single mol. complex with a bridging [TCNQ-TCNQ]2- ligand. Each zinc center is coordinated with two 2,2'-bipyrimidines and one TCNQ-, and the remaining coordination site is occupied by a [TCNQ-TCNQ]2- ligand, which bridges the two zinc centers. The complex facilitates π-stacking of TCNQ- ligands when crystd., which gives rise to a near-IR charge-transfer transition and strong antiferromagnetic coupling.
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    53. 53
      Abrahams, B. F.; Elliott, R. W.; Hudson, T. A.; Robson, R. A New Class of Easily Generated TCNQ2– -Based Coordination Polymers. Cryst. Growth Des. 2010, 10, 2860– 2862,  DOI: 10.1021/cg100568a
      53
      A new class of easily generated TCNQ2--based coordination polymers
      Abrahams, Brendan F.; Elliott, Robert W.; Hudson, Timothy A.; Robson, Richard
      Crystal Growth & Design (2010), 10 (7), 2860-2862CODEN: CGDEFU; ISSN:1528-7483. (American Chemical Society)
      New types of coordination polymers contg. [M(TCNQ)] sheets in which the TCNQ component is present as the little known dianion (TCNQ2-) were obtained in a very simple manner using readily available TCNQH2 (1,4-(NC)2CH·C6H4·CH(CN)2) as the starting material. Above and below the metal centers in the sheets, a range of pyridine derivs. can be attached, some terminal and some acting as pillars linking sheet to sheet to form a 3-dimensional coordination network. The following compds., generally in solvated form, were isolated and structurally characterized - [M(TCNQ)(pyridine)2] (M = Mn or Zn), [M(TCNQ)(quinoline)2] (M = Co or Zn), [Mn(TCNQ)(4-methylpyridine)2], [Zn(TCNQ)(4-phenylpyridine)2], [Zn(TCNQ)(isoquinoline)2], [Zn(TCNQ)(nicotinamide)2], [M(TCNQ)(bipy)] (M = Mn, Fe, Zn, Cd, and bipy =4,4'-bipyridine, which links sheet to sheet to generate 3-dimensional coordination polymers), [Zn(TCNQ)(bpe)] (bpe = 1,2-bis(4-pyridyl)ethylene), and [Zn(CH3OH)(TCNQ)(Obip)1/2] (Obip = 4,4'-bipyridine di-N-oxide). The TCNQH2/TCNQ2- approach opens the way to numerous new types of cryst. and structurally characterizable TCNQ-based networks (and not just the sheet structures that are the focus of this preliminary report) that may lead to solids with unusual and useful electronic/magnetic properties.
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    54. 54
      Konno, M.; Ishii, T.; Saito, Y. The crystal structures of the low- and high-temperature modifications of potassium 7,7,8,8-tetracyanoquinodimethanide. Acta Crystallogr., Sect. B: Struct. Crystallogr. Cryst. Chem. 1977, 33, 763– 770,  DOI: 10.1107/S0567740877004609
      There is no corresponding record for this reference.
    55. 55
      Richard, P. P.; Zanghi, J.-C.; Guédon, J.-F.; Hota, N. Structure cristalline du complexe de potassium avec le tétracyano-7,7,8,8 quinodiméthane. Acta Crystallogr., Sect. B: Struct. Crystallogr. Cryst. Chem. 1978, B34, 788– 792,  DOI: 10.1107/S0567740878004070
      55
      Crystal structure of the potassium-tetracyano-7,7,8,8-quinodimethane complex
      Richard, Pierre; Zanghi, Jean Claude; Guedon, Jean Francois
      Acta Crystallographica, Section B: Structural Crystallography and Crystal Chemistry (1978), B34 (3), 788-92CODEN: ACBCAR; ISSN:0567-7408.
      K-TCNQ is monoclinic, space group P21/c, with a 3.543(1), b 17.784(5), c 17.868(3) Å, and β 94.96(2)° for Z = 2 (2 mols/Z). All the crystals that were studied were twinned and had the ab plane in common. The structure was solved by the symbolic addn. method and refined by least-squares to a final Rw, of 0.079 for 314 reflections. The TCNQ ions form rows along the a-axis with an interplanar spacing of 3.43 Å. The K is octahedrally surrounded by 8 TCNQ N at 2.86-2.97 Å.
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      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaE1cXhs1Wqurc%253D&md5=9604f37b7a88c2fc1925a9a6112ee704
    56. 56
      Šterbinská, S.; Batonneau-Gener, I.; Tomás, M.; Falvello, L. R.; Černák, J. Thermal properties of [Ni(5,5 ́-dmbpy)3](TCNQ)2 complex and KTCNQ. Crystal structure of KTCNQ at 473 K. In Recent Progress in Coordination, Bioinorganic, and Applied Inorganic Chemistry; Slovak Chemical Society, 2022; pp 50– 62.
      There is no corresponding record for this reference.
    57. 57
      Ballester, L.; Gutiérrez, A.; Perpiñán, M. F.; Sánchez, A. E.; Azcondo, M. T.; González, M. J. Radical-ion salts obtained from tetraazaderivatives of nickel and copper and tetracyanoquinodimethane: structural and magnetic characterization. Inorg. Chim. Acta 2004, 357, 1054– 1062,  DOI: 10.1016/j.ica.2003.09.022
      57
      Radical-ion salts obtained from tetraaza derivatives of nickel and copper and tetracyanoquinodimethane: structural and magnetic characterization
      Ballester, Loreto; Gutierrez, Angel; Perpinan, M. Felisa; Sanchez, Ana E.; Azcondo, M. Teresa; Gonzalez, M. Jesus
      Inorganica Chimica Acta (2004), 357 (4), 1054-1062CODEN: ICHAA3; ISSN:0020-1693. (Elsevier Science B.V.)
      Several derivs. [M(N4)(TCNQ)2] and [M(N4)(TCNQ)2](TCNQ) (M = Ni, Cu; N4 = 1,4,7,10-tetraazacyclododecane ([12] aneN4), 1,4,8,11-tetraazacyclotetradecane ([14] aneN4), 1,4,8,12-tetraazacyclopentadecane ([15] aneN4), 1,4,7,10-tetraazadecane (trien), N,N,N-tris(2-aminoethyl)amine (tren), 5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradeca-4,14-diene (trans-dieneN4)) were obtained by metathesis reaction of the corresponding perchlorate or nitrate derivs. and LiTCNQ or (Et3NH)(TCNQ)2. [M(aneN4)(TCNQ)2] have a six coordinated metal atom surrounded by the four macrocyclic nitrogens and two nitrogens from σ coordinated TCNQ-. The overlap with a neighboring 7,7,8,8-tetracyanoquinodimethane (TCNQ) forms the diamagnetic dianion [TCNQ]22-, and the whole structure can be seen as chains of metallomacrocyclic cations and TCNQ dianions alternating in the solid. The crystal structure of [Cu([15] aneN4)(TCNQ)2] confirms this fact. With open chain tetraamines [Cu(trien)(TCNQ)2] and [Cu(tren)(TCNQ)2] probably have the Cu in a pentacoordinated environment, with only one coordinated TCNQ. In [M(trans-dieneN4)](TCNQ)2 both TCNQ- are uncoordinated and dimerized, as the crystal structure of the Ni deriv. confirms. The derivs. with three TCNQ [M(aneN4)(TCNQ)2](TCNQ) probably have a structure derived from that of the analogous [M(aneN4)(TCNQ)2], based on the metallomacrocycle-[TCNQ]2 chains connected through the extra TCNQ which remains uncoordinated and overlaps with the coordinated anions. This fact lowers the antiferromagnetic coupling inside the dimers and a small contribution for a thermally activated triplet state is obsd. in the magnetic susceptibility of these compds.
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    58. 58
      Ballester, L.; Gil, A. M.; Gutiérrez, A.; Perpiñán, M. F.; Azcondo, M. T.; Sánchez, A. E.; Coronado, E.; Gómez-García, C. J. Delocalized TCNQ Stacks in Nickel and Copper Tetraazamacrocyclic Systems. Inorg. Chem. 2000, 39, 2837– 2842,  DOI: 10.1021/ic9912070
      58
      Delocalized TCNQ Stacks in Nickel and Copper Tetraazamacrocyclic Systems
      Ballester, Loreto; Gil, Ana M.; Gutierrez, Angel; Perpinan, M. Felisa; Azcondo, M. Teresa; Sanchez, Ana E.; Coronado, Eugenio; Gomez-Garcia, Carlos J.
      Inorganic Chemistry (2000), 39 (13), 2837-2842CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
      New derivs. [M(dieneN4)](TCNQ)3, M = Ni or Cu and dieneN4 = cis- or trans-hexamethyltetraazacyclotetradecadiene, were obtained. The TCNQ units show electronic delocalization and formation of 1-dimensional stacks, with no direct interactions with the metal cations. The stack is not uniform and can be seen as formed by trimeric dianions (TCNQ)32-. The electronic delocalization favors the cond. in these materials, which behave as good semiconductors. The crystal structures of the trans derivs. were solved:[Ni(trans-dieneN4)](TCNQ)3, triclinic, P‾1, a 8.809(2), b 10.896(2), c 13.727(2) Å, α 103.04(1), β 101.23(2), γ 109.37(2)°, Z = 1; [Cu(trans-dieneN4)](TCNQ)3: triclinic, P‾1, a 7.872(1), b 9.840(1), c 14.819(1) Å, α 92.32(1), β 95.05(1), γ 95.66(1)°, Z = 1.
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    59. 59
      Abrahams, B. F.; Elliott, R. W.; Hudson, T. A.; Robson, R.; Sutton, A. L. New Cu2I(TCNQ–II) and CuI2(F4TCNQ–II) Coordination Polymers. Cryst. Growth Des. 2015, 15, 2437– 2444,  DOI: 10.1021/acs.cgd.5b00220
      59
      New CuI2(TCNQ-II) and CuI2(F4TCNQ-II) Coordination Polymers
      Abrahams, Brendan F.; Elliott, Robert W.; Hudson, Timothy A.; Robson, Richard; Sutton, Ashley L.
      Crystal Growth & Design (2015), 15 (5), 2437-2444CODEN: CGDEFU; ISSN:1528-7483. (American Chemical Society)
      Coordination polymer strips of compn. ...Cu+2·lig2-·Cu+2·lig2-·Cu+2·lig2-... (lig2- = TCNQ2- or its 2,3,4,5-tetrafluoro analog) are obsd. with a wide range of coligands (monodentate, bidentate, and tridentate). Interdigitation of thin, planar N-heteroarom. coligands on one strip with those on a neighbor is a common structural feature. Coligands too bulky to allow interdigitation give either noninterdigitating strips or 2-dimensional sheet structures. Both strips and sheets have 2-connecting Cu centers and 4-connecting tetracynano ligands. As a consequence of the great flexibility of the Cu/tetracyano ligand assocn., the geometries of the sheet structures vary widely from almost coplanar to highly corrugated and convoluted, despite which the same topol. is present in all.
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    60. 60
      Le, T. H.; Nafady, A.; Vo, N. T.; Elliott, R. W.; Hudson, T. A.; Robson, R.; Abrahams, B. F.; Martin, L. L.; Bond, A. M. Electrochemically Directed Synthesis of Cu2I(TCNQF4II–)(MeCN)2 (TCNQF4 = 2,3,5,6-Tetrafluoro-7,7,8,8-tetracyanoquinodimethane): Voltammetry, Simulations, Bulk Electrolysis, Spectroscopy, Photoactivity, and X-ray Crystal Structure of the Cu2I(TCNQF4II–)(EtCN)2 Analogue. Inorg. Chem. 2014, 53, 3230– 3242,  DOI: 10.1021/ic500225v
      60
      Electrochemically Directed Synthesis of Cu2I(TCNQF4II-)(MeCN)2 (TCNQF4 = 2,3,5,6-Tetrafluoro-7,7,8,8-tetracyanoquinodimethane): Voltammetry, Simulations, Bulk Electrolysis, Spectroscopy, Photoactivity, and X-ray Crystal Structure of the Cu2I(TCNQF4II-)(EtCN)2 Analogue
      Le, Thanh H.; Nafady, Ayman; Vo, Nguyen T.; Elliott, Robert W.; Hudson, Timothy A.; Robson, Richard; Abrahams, Brendan F.; Martin, Lisandra L.; Bond, Alan M.
      Inorganic Chemistry (2014), 53 (6), 3230-3242CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
      The new compd. Cu2I(TCNQF4II-)(MeCN)2 (TCNQF42- = dianion of 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane) was synthesized by electrochem. directed synthesis involving redn. of TCNQF4 to TCNQF42- in acetonitrile contg. [Cu(MeCN)4]+(MeCN) and 0.1 M Bu4NPF6. In one scenario, TCNQF42- is quant. formed by reductive electrolysis of TCNQF4 followed by addn. of [Cu(MeCN)4]+ to form the Cu2I(TCNQF4II-)(MeCN)2 coordination polymer. In a second scenario, TCNQF4 is reduced in situ at the electrode surface to TCNQF42-, followed by reaction with the [Cu(MeCN)4]+ present in the soln., to electrocrystallize Cu2I(TCNQF4II-)(MeCN)2. Two distinct phases of Cu2I(TCNQF4II-)(MeCN)2 are formed in this scenario; the kinetically favored form being rapidly converted to the thermodynamically favored Cu2I(TCNQF4II-)(MeCN)2. The postulated mechanism is supported by simulations. The known compd. CuITCNQF4I- also was isolated by one electron redn. of TCNQF4 and reaction with [Cu(MeCN)4]+. The soly. of both TCNQF42-- and TCNQF4•--derived solids indicates that the higher soly. of CuITCNQF4I- prevents its pptn., and thus Cu2I(TCNQF4II-)(MeCN)2 is formed. UV-visible and vibrational spectroscopies were used to characterize the materials. Cu2I(TCNQF4II-)(MeCN)2 can be photochem. transformed to CuITCNQF4I- and Cu0. SEM images reveal that CuITCNQF4I- and Cu2I(TCNQF4II-)(MeCN)2 are electrocrystd. with distinctly different morphologies. Thermogravimetric and elemental anal. data confirm the presence of CH3CN, and single-crystal x-ray diffraction data for the Cu2I(TCNQF4II-)(EtCN)2 analog shows that this compd. is structurally related to Cu2I(TCNQF4II-)(MeCN)2.
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    61. 61
      Bleaney, B.; Bowers, K. D. Anomalous paramagnetism of copper acetate. Proc. R. Soc. London, Ser. A 1952, 214, 451– 465,  DOI: 10.1098/rspa.1952.0181
      61
      Anomalous paramagnetism of copper acetate
      Bleaney, B.; Bowers, K. D.
      Proceedings of the Royal Society of London, Series A: Mathematical, Physical and Engineering Sciences (1952), 214 (), 451-65CODEN: PRLAAZ; ISSN:1364-5021.
      Paramagnetic resonance is studied on large single crystals of Cu acetate, the prepn. of which is described. The spectrum is anomalous. The anomalies in fine structure and hyperfine structure are accounted for by postulating strong interaction between isolated pairs of Cu ions, each pair forming a lower singlet and an upper triplet state, only the latter being paramagnetic. The unit cell contains 2 differently oriented pairs of ions. The structure corresponds to an effective spin of 1. The interaction forces are discussed.
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    62. 62
      O’Connor, C. J. Magnetochemistry-Advances in Theory and Experimentation. Prog. Inorg. Chem. 2007, 203– 283,  DOI: 10.1002/9780470166307.ch4
      There is no corresponding record for this reference.
    63. 63
      Titiš, J.; Boča, R. Magnetostructural D Correlation in Nickel(II) Complexes: Reinvestigation of the Zero-Field Splitting. Inorg. Chem. 2010, 49, 3971– 3973,  DOI: 10.1021/ic902569z
      63
      Magnetostructural D Correlation in Nickel(II) Complexes: Reinvestigation of the Zero-Field Splitting
      Titis, Jan; Boca, Roman
      Inorganic Chemistry (2010), 49 (9), 3971-3973CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
      The magnetostructural D correlation interrelates the zero-field-splitting parameter D withdrawn from the magnetic data with the structural tetragonality parameter Dstr. This correlation allows the quant. prediction that D < 0 occurs for the tetragonally compressed Ni(II) complexes.
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    64. 64
      Stoll, S.; Schweiger, A. EasySpin, a comprehensive software package for spectral simulation and analysis in EPR. J. Magn. Reson. 2006, 178, 42– 55,  DOI: 10.1016/j.jmr.2005.08.013
      64
      EasySpin, a comprehensive software package for spectral simulation and analysis in EPR
      Stoll, Stefan; Schweiger, Arthur
      Journal of Magnetic Resonance (2006), 178 (1), 42-55CODEN: JMARF3; ISSN:1090-7807. (Elsevier)
      EasySpin, a computational package for spectral simulation and anal. in EPR, is described. It is based on Matlab, a com. tech. computation software. EasySpin provides extensive EPR-related functionality, ranging from elementary spin physics to data anal. It provides routines for the simulation of liq.- and solid-state EPR and ENDOR spectra. These simulation functions are built on novel algorithms that enhance scope, speed and accuracy of spectral simulations. Spin systems with an arbitrary no. of electron and nuclear spins are supported. The structure of the toolbox as well as the theor. background underlying its simulation functionality are presented, and some illustrative examples are given.
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    65. 65
      Berlie, A.; Terry, I.; Szablewski, M.; Giblin, S. R. Separating the ferromagnetic and glassy behavior within the metal-organic magnet Ni(TCNQ)2. Phys. Rev. B 2015, 92, 184431  DOI: 10.1103/PhysRevB.92.184431
      65
      Separating the ferromagnetic and glassy behavior within the metal-organic magnet Ni(TCNQ)2
      Berlie, Adam; Terry, Ian; Szablewski, Marek; Giblin, Sean R.
      Physical Review B: Condensed Matter and Materials Physics (2015), 92 (18), 184431/1-184431/15CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)
      An in-depth study of the metal-org. magnet Ni(TCNQ)2 was conducted where the deuterated form was synthesized both to attempt to alter the magnetic properties of the material and to be advantageous in techniques such as neutron scattering and muon spectroscopy. Deuteration saw a 3 K increase in TC with magnetization and heat capacity measurements demonstrating a spin wave contribution at low temps. confirming the 3D nature of the ferromagnetic state shown by Ni(TCNQ-D4)2. AC susceptibility results suggest there is a glassy component assocd. with the magnetically ordered state, though muon spectroscopy measurements did not support the presence of a spin glass state. Instead muon spectroscopy at zero magnetic field indicated the presence of two magnetic transitions, one at 20 K and another below 6 K; the latter is likely due to the system entering a quasistatic regime, similar to what one might expect of a superspin or cluster glass. Neutron diffraction measurements further supported this by revealing very weak magnetic Bragg peaks suggesting that the magnetism may have a short coherence length and be confined to small grains or clusters. The sepn. of the ferromagnetic and glassy magnetic components of the material's properties suggest that this system may show promise as a metal-org. magnet which is easily modified to change its magnetic properties, providing larger grain sizes can be synthesized.
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    66. 66
      Barclay, T. M.; Hicks, R. G.; Lemaire, M. T.; Thompson, L. K. Structure and magnetic properties of a nickel(II) complex of a tridentate verdazyl radical: strong ferromagnetic metal-radical exchange coupling. Chem. Commun. 2000, 2141– 2142,  DOI: 10.1039/b006520j
      66
      Structure and magnetic properties of a nickel(II) complex of a tridentate verdazyl radical: strong ferromagnetic metal-radical exchange coupling
      Barclay, Tosha M.; Hicks, Robin G.; Lemaire, Martin T.; Thompson, Laurence K.
      Chemical Communications (Cambridge) (2000), (21), 2141-2142CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
      Magnetic susceptibility measurements on a structurally characterized Ni(II) complex of a tridentate verdazyl radical indicate very strong ferromagnetic Ni-verdazyl intramol. exchange interactions (J > +200 cm-1). Crystal structure and magnetic data are reported for [NiL2](PF6)2·Me2CO (L = 1,5-dimethyl-3-(2,2'-bipyridin-6-yl)-6-oxoverdazyl).
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  • Supporting Information

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