Heterotrimetallic Cyanide-Bridged 3d-4d-5d Frameworks Based on a Photomagnetic Secondary Building Unit

The rational design of coordination frameworks combining more than two different metal ions using a self-assembly approach is challenging because it rarely offers sufficient control over the building blocks at the actual self-assembly stage. In this work, we present a successful two-step strategy toward heterotrimetallic coordination frameworks by employing a new bimetallic [(NC)7MoIV-CN-PtIV(NH3)4-NC-MoIV(CN)7]4– secondary building unit (SBU). This anionic moiety has been isolated and characterized as a simple salt with an organic dppipH22+ cation (dppipH2)2[(NC)7MoIV-CN-PtIV(NH3)4-NC-MoIV(CN)7]·15H2O (1) (dppip = 1,4-di(4-pyridinyl)piperazine). The salt presents a second-order phase transition related to cation conformational change around 250 K and a photomagnetic effect after irradiation with 450 nm light at 10 K. When combined with aqueous solutions of MnII or CuII complexes, it forms either a one-dimensional chain [MnII(dpop)][MnII(dpop)(H2O)][(NC)7MoIV-CN-PtIV(NH3)4-NC-MoIV(CN)7]·36H2O (2) (dpop = 2,13-dimethyl-3,6,9,12,18-pentaazabicyclo-[12.3.1]octadeca-1(18),2,12,14,16-pentaene) or a photomagnetic two-dimensional honeycomb network [CuII(cyclam)]2[(NC)7MoIV-CN-PtIV(NH3)4-NC-MoIV(CN)7]·40.89H2O (3) (cyclam = 1,4,8,11-tetraazacyclotetradecane), both characterized by very large cavities in their structure filled with solvent molecules. Both 2 and 3 incorporate three different transition-metal ions and constitute a new family of 3d-4d-5d coordination frameworks. Moreover, compound 3 inherits the photomagnetic properties of the MoPtMo SBU.

Magnetic measurements. Magnetic susceptibility measurements were performed using a Quantum Design MPMS-3 Evercool magnetometer in magnetic fields up to 7 Tesla for samples packed into glass ampules (5 mm in diameter) with a small amount of mother liquor. The experimental data were corrected for the diamagnetism of the sample and the sample holder. Photomagnetic measurements were performed for samples immersed between two layers of Duraseal polyethylene foil with small amount of mother solution. S3 Irradiation was performed using high stability 300 W Xe lamp equipped with bandpass filters (473,530,585,640,690 or 740 nm; power measured at the sample position was P ≈ 0.5 mW/cm 2 ). In the case of 450 nm light a laser diode was used (L450P1600MM; power at the sample position P = 6-10 mW/cm 2 ). In order to improve the signal of the diamagnetic compound 1, its sample was mixed with a small quantity (ca. 10 μg) of a photomagnetically inactive paramagnetic salt (NH4)2Mn(SO4)2·6H2O. The paramagnetic signal measured before light irradiation is used as a background for the interpretation of the irradiation experiments. IR spectra. IR spectra were recorded using a Nicolet iN10 MX FT-IR microscope in the transmission mode. For temperature-dependent measurements FT-IR microscope was equipped with Linkam THMS350V liquid nitrogen cryostat.
Solid state UV-Vis. Spectra were measured in transmission mode for samples mixed with paraffin oil between two quartz slides using PerkinElmer Lambda 35 UV/VIS spectrophotometer equipped with an integration sphere. EPR spectroscopy. Continuous-wave EPR spectra in X-band (9.4 GHz) were conducted on a Bruker Elexsys E580 spectrometer equipped with a liquid helium cryostat (Department of Molecular Biophysics, Jagiellonian University, Kraków, Poland). Samples for irradiation experiments were attached between two layers of scotch tape and placed inside a quartz EPR tube. Irradiation was performed with 450 nm laser diode (L450P1600MM; power at the sample position P ≈ 70 mW).
Elemental Analysis. Elemental analyses were performed using ELEMENTAR Vario Micro Cube CHNS analyzer. Thermogravimetric analysis. TGA was performed using a Mettler Toledo TGA/SDTA 851e under flow of argon.
Differential scanning calorimetry. DSC measurement was performed with use of a Mettler Toledo DSC 822e.

Synthesis details
All reagents and solvents were used as supplied from commercial sources (Sigma-Aldrich, Alfa-Aesar, Acros Organics). Caesium octacyanomolybdate(V) was synthesized according to the literature S4 using potassium permanganate as an oxidizing agent. [Mn II (dpop)(H2O)2](NO3)2 was synthesized according to the literature procedure S5 starting from Mn(NO3)2·xH2O instead of MnCl2·4H2O. CAUTION: Cyanide compounds are toxic and can produce highly toxic hydrogen cyanide gas when exposed to moisture or strong acids. Contact and inhalation should be avoided. Appropriate protective goggles, gloves and lab coat should be worn all the time when working with cyanide compounds. All manipulations and reactions involving cyanide should be done behind a fume hood sash.

1,4-di(4-pyridinyl)piperazine (dppip)
1,4-di(4-pyridinyl)piperazine was synthesized by a modified literature procedure. S6 Piperazine (0.65 g, 7.5 mmol) and 4-chloropyridine hydrochloride (2.48 g, 16.5 mmol) were mixed and hand-milled in a mortar. The powder mixture was added to the solution of anhydrous potassium carbonate (2.28 g, 16.5 mmol) in 25 mL 99.8% ethanol and stirred for two hours at room temperature. The mixture was placed in a teflon cup of the stainless steel autoclave and kept at 120 °C for 72 hours. After that time the reaction mixture was cooled to room temperature and poured into 100 mL 0.5 M KOH solution in water. The obtained suspension was kept in the fridge (4 °C) for 24 hours. The resulting white solid was filtered and washed with water and diethyl ether to yield 1.3 g of product after recrystallization from acetone/CHCl3 (yield: 65 %

[(NC)7Mo IV -CN-Pt IV (NH3)4-NC-Mo IV (CN)7] 4solution (solution A)
Solution A used for further syntheses was stored in 5 mmol/L concentration. It can be prepared by a dropwise addition of [Pt(NH3)4](NO3)2 water solution (38.7 mg, 0.1 mmol in 10 mL water) into 10 mL of constantly stirred Cs3[Mo(CN)8]·2H2O solution (148 mg; 0.2 mmol in 10 mL water). Before the first use mixture was stirred for at least 15 minutes to facilitate complete formation of [(NC)7Mo IV -CN-Pt IV (NH3)4-NC-Mo IV (CN)7] 4-. (1) dppip·1.5H2O (97 mg, 0.36 mmol) was dissolved in a mixture of 10 mL water and 57 μL 65 % nitric acid. 1 mL of the solution was diluted with 8 mL water and dropwise added to 4 mL solution A diluted with 8 mL water. After 24 hours 1 crystallized as red triangular plates (yield: 15 mg, 50%). Elemental analysis, found: C: 33.61, N: 24.95, H: 4.62, calculated for (dppipH2) The difference in water content is a result of immediate solvent loss when the crystals were dried for the elemental analysis. Purity of the product was additionally confirmed by powder X-ray diffraction under mother liquor ( Figure S14). Table S1. Crystallographic data and refinement parameters for compound 1 120 and 255 K.  Figure S1. Experimental powder X-ray diffraction pattern obtained for 1 at room temperature (red line) and simulated from single crystal structure at 120 K (black line). Inset shows a close-up of the 15-21° region. Figure S2. Experimental powder X-ray diffraction pattern obtained for 1 at room temperature (red line) and simulated from single crystal structure at 255 K (black line). Inset shows a close-up the 15-21° region. Figure S3. Differential scanning calorimetry (DSC) measurement for 1 (sweep rate 10 K/min.). Figure S4. IR spectrum obtained for 1 at 275 K. Figure S5. Variable-temperature IR spectra obtained for 1 during heating. Figure S6. Variable-temperature IR spectra in 1280-1200 cm -1 region obtained for 1 during heating.   Figure S8. Experimental powder X-ray diffraction pattern obtained for 2 at room temperature (red line) and simulated from single crystal structure at 120 K (black line). Figure S9. IR spectra recorded at room temperature for 2. Figure S10. Contact surface in the water filled cavities of 2 (Mercury "Voids" function, probe radius 1.2 Å, grid spacing 0.7 Å).   Figure S14. Experimental powder X-ray diffraction pattern obtained for 3 at room temperature (red line) and simulated from single crystal structure at 120 K (black line). Figure S15. IR spectrum recorded at room temperature for 3. Figure S16. Contact surface in the water filled cavities of 3 (Mercury "Voids" function, probe radius 1.2 Å, grid spacing 0.7 Å).     . M(H) dependence obtained at T = 2.0 K for 3 before light irradiation (black points), after 450 nm light irradiation (red points) and after thermal relaxation at 250 K (blue points). Solid lines are guides for an eye. Please note that because of high reversibility experimental points obtained after relaxation overlap with those measured before irradiation. Figure S22. Experimental powder X-ray diffraction pattern obtained for 2 at room temperature after sample dehydration at 120 degrees Celsius. Figure S23. Experimental powder X-ray diffraction pattern obtained for 3 at room temperature after sample dehydration at 120 degrees Celsius.