ACS Publications. Most Trusted. Most Cited. Most Read
Quick View

OR SEARCH CITATIONS

My Activity
Publications
CONTENT TYPES

Figure 1Loading Img
Download Hi-Res ImageDownload to MS-PowerPointCite This:ACS Appl. Mater. Interfaces 2022, 14, 33, 38370-38378
RETURN TO ISSUEPREVSurfaces, Interfaces...Surfaces, Interfaces, and ApplicationsNEXT

Caught while Dissolving: Revealing the Interfacial Solvation of the Mg2+ Ions on the MgO Surface

Cite this: ACS Appl. Mater. Interfaces 2022, 14, 33, 38370–38378
Publication Date (Web):August 14, 2022
https://doi.org/10.1021/acsami.2c10005

Copyright © 2022 The Authors. Published by American Chemical Society. This publication is licensed under

CC-BY 4.0.
  • Open Access

Article Views

834

Altmetric

-

Citations

2
LEARN ABOUT THESE METRICS
PDF (3 MB)
Get e-Alerts
Supporting Info (1)»
SUBJECTS:

Abstract

High Resolution Image
Download MS PowerPoint Slide

Interfaces between water and materials are ubiquitous and are crucial in materials sciences and in biology, where investigating the interaction of water with the surface under ambient conditions is key to shedding light on the main processes occurring at the interface. Magnesium oxide is a popular model system to study the metal oxide–water interface, where, for sufficient water loadings, theoretical models have suggested that reconstructed surfaces involving hydrated Mg2+ metal ions may be energetically favored. In this work, by combining experimental and theoretical surface-selective ambient pressure X-ray absorption spectroscopy with multivariate curve resolution and molecular dynamics, we evidence in real time the occurrence of Mg2+ solvation at the interphase between MgO and solvating media such as water and methanol (MeOH). Further, we show that the Mg2+ surface ions undergo a reversible solvation process, we prove the dissolution/redeposition of the Mg2+ ions belonging to the MgO surface, and we demonstrate the formation of octahedral [Mg(H2O)6]2+ and [Mg(MeOH)6]2+ intermediate solvated species. The unique surface, electronic, and structural sensitivity of the developed technique may be beneficial to access often elusive properties of low-Z metal ion intermediates involved in interfacial processes of chemical and biological interest.

This publication is licensed under

CC-BY 4.0.
  • cc licence
  • by licence
KEYWORDS:

1. Introduction

ARTICLE SECTIONS
Jump To
Achieving accurate chemical knowledge on the mechanisms of surface processes is of considerable interest both for fundamental understanding and for applications. Surfaces, in fact, provide unique platforms for the success of desirable reactive or nonreactive pathways, for instance by acting toward them as efficient energy-dissipating heat baths and by altering their symmetries significantly if compared to those in the gas or condensed phases. (1) As a consequence, interfaces display uncanny properties that may greatly differ from those of the bulk, and innovative experimental and theoretical methods are required to disentangle the intricate mechanisms involved in surface science.
The metal oxide–water interface is of paramount importance in catalysis, materials science, biology, corrosion, geochemistry, and interstellar and atmospheric chemistry. (2−4) Magnesium oxide has been frequently investigated as a model system, being one of the simplest oxides in terms of geometric and electronic structure. The interaction of a number of MgO surfaces with water (4−6) has been studied both experimentally and theoretically at various temperatures and pressures in the range between high vacuum and ambient conditions, with the MgO(001) slab being one of the most popularly evaluated by researchers. (3,7−15) While it is known that for low water coverage on the MgO(001) surface water forms a layer where 1/5 and 1/3 of the water molecules are dissociated at low (100–180 K) and higher (185–221 K) temperatures, respectively, for water coverages beyond a monolayer, the picture is less definite. (16) In the latter case the standard model (7) of a fully hydroxylated MgO(001) surface, where OH– and H+ ions form by dissociated adsorption of one water molecule per MgO surface pair and coordinate the surface Mg2+ and oxygen ions, respectively, has been put into question. The extent of MgO(001) surface hydroxylation has not in fact been settled by the numerous experiments conducted at ambient water conditions, (5,16) and recently it has been found that reconstructed surfaces, involving hydrated/hydroxylated Mg2+ ions above the MgO(001) surface, are more stable than the fully hydroxylated ones. (16) It appears therefore natural to resort to surface-specific advanced experimental techniques to address the question of which is the prevalent Mg2+ species at the MgO–water interface in ambient pressure conditions. In principle, the molecular-level rationalization of the interactions established by the metal oxide surface with water requires (i) quantitative structural details, and (ii) information on the electronic states of the arising surface species. (17) Among the cutting-edge experimental techniques that may simultaneously provide such information, X-ray absorption spectroscopy (XAS) set itself apart as an advanced tool that offers insights into the local structural and electronic environment of a selected photoabsorbing atom with an unrivaled degree of accuracy. (18−20) However, to date, the use of XAS to probe the intermediate species formed at low-Z metal oxide surfaces when these interact with water and other organic solvents has been quite limited by the requirement of soft X-rays (∼400–2000 eV), that need tailored experimental setups. (17,21) XAS in the hard X-ray regime has been widely employed for the investigation of the properties of 3d transition metals and operando XAS experiments with hard X-rays are routinely performed. (19) On the contrary, the application of XAS in the soft X-ray regime (soft-XAS) to study the interfacial properties of metal ions has been severely hampered by the need of high vacuum conditions. Very recently, specific cells have been designed that allow soft-XAS to be carried out at atmospheric pressure under operando conditions, (22−25) a technique referred to as ambient pressure near-edge X-ray fine structure spectroscopy (AP-NEXAFS). In this case soft-XAS is operated in total electron yield (TEY) detection mode which renders the technique surface sensitive due to the low electron escape depth which limits the thickness of the probed sample. Here, we use soft-XAS operando experiments in combination with state of the art chemometric and theoretical analyses to investigate the MgO surface upon interaction with water and methanol (MeOH). We found that Mg2+ ions are reversibly hydrated (solvated)/dehydrated (desolvated) at the interface, and we developed a novel experimental approach able to follow in real time the evolution of low-Z metal ion-based interfaces.

2. Experimental Methods

ARTICLE SECTIONS
Jump To
We provide a brief description of the experimental method, while the details and theoretical background concerning the data processing, multivariate curve resolution (MCR) analysis, density functional theory (DFT) cluster optimization, molecular dynamics (MD) simulations, and NEXAFS calculations are reported in the Supporting Information (SI). The experiments were carried out at the APE High Energy beamline at the Elettra Synchrotron radiation source (Basovizza, Italy). AP-NEXAFS operando measurements were enabled by the use of a specially designed reaction cell. The samples inside the reactor cell can be heated from room temperature to approximately 400 °C and can be exposed to a flux of different gases at a pressure of 1 bar. Figure S1a shows the 3D rendering of the operando NEXAFS reaction cell designed at the APE-HE beamline. On the top of the cell, a Si3N4 membrane is mounted (orange circle in Figure S1a), which separates the volume of the reactor cell at atmospheric pressure (labeled with 1 in Figure S1b) from the ultrahigh vacuum (UHV) environment of the beamline, while allowing the passage of the soft X-rays. The sample is positioned inside the reactor, normal to the incident X-rays (2). Two pipes (inlet and outlet) are connected to the reactor (3), allowing the circulation of gas inside the reactor (also during spectra acquisition). The heating of the sample is possible thanks to a ceramic heater installed below the sample, outside the reactor (4). The NEXAFS spectra are recorded in the TEY mode: two electrical contacts (one on the 100 nm thick Si3N4 membrane and one on the sample holder) allow one to polarize the membrane (positively to accelerate the electrons away from the sample) and measure the drain current of the sample through a picoammeter. The measurements were performed through the picoammeter, keeping the sample grounded and applying a positive bias voltage of 40 V to the membrane.
MgO was purchased from Sigma-Aldrich. The powder was fixed on a titanium sample holder and pressed in a pit located onto the holder. The cell was mounted in the UHV chamber coaxially with the X-ray beam. The MgO starting sample was pretreated at a temperature T = 250 °C in flowing He at 50 standard cubic centimeters per minute (SCCM), after which the working temperature was lowered to T = 50 °C. The experiments were performed collecting the Mg K-edge spectra in the energy range 1275–1355 eV at T = 50 °C and under flowing gas mixtures of 3% H2O/He or 17% MeOH/He, in both cases at 50 SCCM and 1 bar. Each operando AP-NEXAFS spectrum was recorded in approximately 5 min.

3. Results and Discussion

ARTICLE SECTIONS
Jump To
The newly developed AP-NEXAFS technique is a powerful method to unveil the structural properties and the processes occurring at the surface of a material during exposure to water or organic solvents, due to its surface sensitivity. In this work we applied this innovative experimental method, in combination with a state of the art theoretical approach to investigate the MgO–water and MgO–methanol interfaces at ambient pressure. Our experimental procedure was divided into four consecutive steps:
1.

Initially, a clean MgO sample (pretreated in He at 250 °C to eliminate superficial impurities) was exposed to water vapor for 95 min using He as a carrier gas at a working temperature of 50 °C.

2.

In the second step, the water flux was interrupted and the temperature was increased up to 250 °C with a 3.3 °C per minute rate while exposing the sample to He.

3.

To investigate the superficial interaction of MgO with an organic solvent, the same sample was then exposed to methanol vapor (with He acting as a carrier gas) at a temperature of 50 °C for 85 min.

4.

Finally, the methanol flux was interrupted and the temperature of the system was increased up to 250 °C with a 6.6 °C per minute rate while exposing the sample to an inert atmosphere.

Operando AP-NEXAFS spectra were collected at the Mg K-edge every 5 min throughout the duration of the entire experiment. Tables S1 and S2 of the SI list the temperatures at which all the spectra were recorded during the exposure of MgO to water and methanol vapors, respectively. The measured XAS data were then subjected to a mathematical decomposition procedure using a strategy belonging to the MCR family. This method allows the rationalization of operando spectroscopic data sets, (26−30) leading to the retrieval of the spectral and concentration profiles of the key Mg2+ species contributing to the experimental signal. Finally, the extracted Mg K-edge XAS spectra were quantitatively analyzed through ab initio DFT NEXAFS calculations and MD simulations.
Figures 1a and S3a present in two and three dimensions, respectively, the operando Mg K-edge AP-NEXAFS spectra recorded on the MgO sample during its exposure to water vapor at 50 °C (green background, step 1) and after flux interruption and temperature increase up to 250 °C (purple background, step 2). The first and last XAS spectra are highlighted by dark black lines (Figure 1a) and were measured, respectively, on the pristine MgO sample prior to water exposure and at the final temperature of 250 °C after water flux interruption.

Figure 1

Figure 1. Evolution of the operando Mg K-edge AP-NEXAFS spectra upon MgO exposure to water (a) and methanol (b). Constant energy cuts are drawn at 1305.7 eV (yellow dotted lines) and at 1310.2 eV (gray dotted lines). The spectral scans recorded during the flux of water and methanol at 50 °C and during the subsequent flux interruption and temperature increase up to 250 °C are highlighted using green and purple backgrounds, respectively. In both panels, the AP-NEXAFS spectra recorded before the surface exposure to the given flux and at the temperature of 250 °C after flux interruption are evidenced in bold black lines.

High Resolution Image
Download MS PowerPoint Slide
Looking at Figure 1a, one may note that during the exposure of the pristine MgO surface to water vapor, there is an appreciable spectral variation. In particular, the feature at 1310.2 eV in the initial Mg K-edge spectrum of the pristine MgO surface decreases in intensity while a feature located at 1305.7 eV appears, as evidenced by the constant energy cuts at the same energy values. The intensity time evolution of these spectral features is displayed in Figure 2a. Conversely, once the water flux is interrupted and the temperature is progressively increased to 250 °C (Figure 1a, purple background), the intensities of the features located at 1310.2 eV and at 1305.7 eV rapidly increase and decrease, respectively, to their initial values and the overall spectral appearance of the starting MgO spectrum is fully recovered. Notably, the first and last AP-NEXAFS experimental spectra are nearly superimposable, thereby strongly suggesting the complete reversibility of the temperature-assisted Mg2+–water interaction at the MgO surface. One may also observe in Figure 2a that, upon water vapor exposure, the decrease in intensity of the characteristic feature located at 1310.2 eV nearly mirrors the increase of intensity of the one at 1305.7 eV. This finding qualitatively suggests that two interconverting Mg2+ active species contribute to the measured AP-NEXAFS data. To obtain quantitative information on the number of pure chemical species contributing to the experimental XAS spectra, the percentage residual error committed in reconstructing the data set with an increasing number of components was evaluated, as shown in Figure S4a (refer to the SI for additional details). One may note that the percentual error committed in employing a number of principal components greater than two to reproduce the data set decreases very slowly, and that the percentual error committed in employing two components to reproduce the AP-NEXAFS data is ca. 3%. These evidence suggest the presence of two main components in the operando Mg K-edge NEXAFS spectra measured upon exposure of the MgO sample to water vapor.

Figure 2

Figure 2. (a) Intensity variation at 1305.7 eV (full yellow line) and at 1310.2 eV (full gray line) of the operando Mg K-edge XAS spectra measured upon MgO exposure to water vapor. The intensities of the starting XAS spectrum, of the XAS spectra recorded during the water flux at 50 °C, and of those measured during the water flux interruption and contemporary temperature increase are highlighted by black, green, and purple backgrounds, respectively. (b, c) Results of the decomposition of the Mg K-edge spectra. Extracted concentration profiles and Mg K-edge NEXAFS spectra (panels b and c, respectively). (d) Comparison between the NEXAFS spectrum of the Mg2+ intermediate species arising upon exposure of the MgO surface to water and the theoretical average Mg K-edge NEXAFS spectrum resulting from 500 MD snapshots of the fully hydrated Mg2+ ion (full indigo line).

High Resolution Image
Download MS PowerPoint Slide
To gain mechanistic and structural insights into the nature of the interaction established by the surface Mg2+ ions with the fluxed water, the experimental AP-NEXAFS data were analyzed using an MCR transition matrix (TM)-based decomposition approach employing a number of significant components equal to 2, a method fully discussed in the SI. Figures 2b,c show the extracted concentration and spectral profiles, where the first extracted spectral component (Figure 2c, gray curve) was constrained to coincide with the AP-NEXAFS spectrum of the pristine MgO surface (Figure 1a, initial dark black spectrum). The MgO material possesses good thermal stability above 600 °C (31) and has been thoroughly investigated by previous solid-state XAS studies. (32−35)
The extracted MgO XAS spectrum is in excellent agreement with previous MgO K-edge XAS measurements exhibiting a transition at 1303.0 eV and two experimentally unresolved features at 1308.0 eV and at 1310.7 eV, together with a broad shoulder at 1320.6 eV. (32,35) The second XAS component shown in Figure 2c (yellow curve) presents a single broad feature centered at ∼1305.7 eV and is assigned to the arising Mg2+ intermediate species due to the interaction of the Mg2+ surface ions with water. In fact, as shown in Figure 2b, the fractional concentration of the latter component increases rapidly during water flux, reaching values close to 75%, while the fractional concentration of MgO is largely predominant once the temperature reaches 250 °C, when water is expected to be fully desorbed from the surface. Further, we have observed an approximate 5-fold decrease in spectral intensity of the raw non-normalized XAS spectra during exposure of the MgO surface to water vapor, and consequently we may estimate the interaction between water and the interfacial Mg2+ ions to extend to the first few nanometers below the surface. Interestingly, the XAS spectrum of the Mg2+ intermediate species closely resembles the Mg K-edge XAS spectrum previously reported for [MgCl2(H2O)6] in aqueous solution and qualitatively assigned to that of a fully dissolved octahedral hexaquo Mg2+ ion. (36) The presented evidence suggests that the surface Mg2+ ions do interact with the incoming water molecules, as evidenced by the different electronic features of the two intermediate extracted AP-NEXAFS components, and that a surface Mg2+ dissolution process occurs.
To test these hypotheses and to uncover the structural and electronic properties of the Mg2+–water intermediate, an ab initio DFT-based NEXAFS theoretical analysis was carried out, (37−40) with the support of MD simulations. First, to verify the validity of the implemented framework, the theoretical NEXAFS spectrum of MgO was calculated starting from the available rock-salt crystal structure (space group Fm3̅m, and lattice parameter of 4.21 Å). (41)Figure S5 reports the theoretical spectrum calculated for the MgO crystal (full black line), along with the calculated Mg- and O-density of electronic p states (DOS), compared to the experimental MgO spectrum obtained from the multivariate analysis (full gray line). One may note that both Mg p- and O p-states contribute through hybridization to the four main calculated features A1, A2, A3, and A4, whose energy positions and relative intensities are in excellent agreement with those of the features in the experimental MgO spectrum. Having established the reliability of our theoretical approach, to explore its sensitivity to the local structural properties of the Mg2+ ion, we performed theoretical NEXAFS simulations on DFT-optimized [Mg(H2O)n]2+ molecular clusters (with n = 4, 6), (42−44) where the oxygen atoms coordinate the central metal cation in a tetrahedral and octahedral geometry, respectively. Previous investigations have reported structural features on hydrated Mg2+ both from experiments and from computer theoretical simulations, thereby providing reliable findings on which to benchmark our approach. In aqueous solution, an octahedral hexaquo Mg2+ has been evidenced through Raman spectroscopy, (45) proton NMR, (46) and an X-ray diffraction experiment conducted by difference methods, (47) and results were confirmed by Monte Carlo, (48) MD, and ab initio quantum mechanical/molecular mechanical (QM/MM) MD simulations. (49−51) The average Mg–O bond distances of our DFT octahedral [Mg(H2O)6]2+ structure was found to be equal to 2.10 Å, as listed in Table S3, and is in very good agreement with the previously reported bond length of 2.110 Å. (52) The Mg K-edge theoretical spectra calculated for the [Mg(H2O)4]2+ and [Mg(H2O)6]2+ complexes are shown in Figure S6a and S6b, respectively (full black lines), along with the associated Mg p- and O p- DOS. The overall shape of the two spectra is very different, and this shows how sensitive this technique is to the coordination of the Mg photoabsorber. In particular, the theoretical convoluted NEXAFS spectrum of the [Mg(H2O)4]2+ complex exhibits two clearly distinguishable transitions, BT1 and BT2, while that of the [Mg(H2O)6]2+ species possesses a single main transition (BO1) together with a less pronounced high-energy shoulder (BO2). The latter spectrum bears significant resemblance to the MCR-extracted XAS spectrum of the Mg2+ species interacting with water (Figure 2c, full yellow line) and with previous Mg K-edge spectra attributed to the fully hydrated Mg2+ ion in aqueous solution, both of which present a single broad main transition. (36)
For poorly ordered systems as in the case of the Mg2+ hydrated species formed on the MgO surface, the NEXAFS signal originates from the average over all the possible configurations adopted by water molecules around the ion, and a single cluster cannot be used to correctly reproduce the NEXAFS spectrum. (53−55) To overcome this problem and to properly account for thermal and structural fluctuations occurring at 50 °C, we performed a quantitative analysis of the NEXAFS spectra starting from the microscopic description of the system derived from the MD simulations. This combined method is very powerful, as disorder effects due to the dynamic distortions of the coordination shells are properly included in the calculation of the NEXAFS theoretical spectrum. In particular, classical MD simulations of the Mg2+ ion in water were performed and details are discussed in the SI. In water an octahedral geometry with coordination number (CN) of 6 and a Mg–O bond length of 2.10 Å were obtained for the first hydration shell molecules, as evidenced by the Mg–O radial distibution function and its corresponding running integration number (see Figure S7a). Next, an averaged NEXAFS theoretical spectrum has been calculated starting from the structural configurations obtained from 500 MD snapshots, and the resulting spectra are shown in Figure 3a. In all cases, the NEXAFS spectra calculated from each MD snapshot present detectable differences in all the energy range, showing the sensitivity of NEXAFS to geometrical changes and fluctuations of the Mg2+ hydration clusters and the importance of making a proper sampling of the configurational space.
Figure 3b presents the NEXAFS theoretical spectral averages for the dissolved Mg2+ ion system computed with a variable number (N) of spectra, where N belongs to a monotonely increasing sequence. One may note that the theoretical averaged NEXAFS present very small differences for N > 50 (see Figure 3b) and that they are well-converged for N = 500 (inset of Figure 3b). The NEXAFS converged average spectrum is compared in Figure 2d to the experimental NEXAFS spectrum of the intermediate Mg2+ species arising at the MgO surface upon its exposure to water vapor at 50 °C. The agreement between the theoretical and experimental curves is quite good, and the former spectrum shows a certain degree of the experimentally observed configurational broadening if compared to the NEXAFS calculation performed on the DFT-optimized [Mg(H2O)6]2+ cluster (Figure S6b, full black line). These findings strongly corroborate the picture that within our experimental conditions Mg2+ ions are partially released from the MgO surface and are coordinated at the interface in an octahedral geometry by water molecules, as described by our theoretical framework.

Figure 3

Figure 3. Theoretical NEXAFS spectra (gray full lines) calculated from 500 MD snapshots of the Mg2+ ion in water at 50 °C and converged NEXAFS average (blue full line) of the 500 spectra (a) along with a selection of average NEXAFS spectra calculated with a variable number (N) of spectra (b). The associated evolutions of the total absolute differences between averages of spectra computed with increasing N values are shown in the insets of panel b. SN and SN* are the averages of N and N* spectra, respectively, with N* immediately preceding the given value of N in the evaluated sequence (e.g., N* = 250 if N = 500).

High Resolution Image
Download MS PowerPoint Slide
This hypothesis is further supported by the subsequent operando experiment performed by exposing the same MgO sample to methanol vapor at 50 °C (step 3). Figures 1b and S3b show the operando Mg K-edge AP-NEXAFS spectra measured upon MgO exposure to methanol in 2D and 3D, respectively. Also in this experiment an appreciable NEXAFS spectral change occurs during methanol flux as evidenced by the decrease in intensity at 1310.2 eV and the corresponding increase in intensity at 1305.7 eV (see Figure 4b) and by the appearance of a low-energy transition at 1300.2 eV prior to flux interruption and temperature increase. It is important to notice that the first and last experimental spectra coincide with that of pristine MgO, suggesting that the interaction between the surface and methanol vapor is a reversible one and that the NEXAFS spectra obtained under the methanol flux are quite different from those obtained when fluxing water. Also in this case the NEXAFS signals were subjected to a MCR analysis, using a number of active components equal to two because (i) the percentual error committed by reproducing the data set using two principal components is inferior to 4% (Figure S4b), and (ii) the intensity time decay measured at 1310.2 eV closely mirrors the increase of that at 1305.7 eV, as shown in Figure 4a. Figure 4 parts b and c present, respectively, the concentration profiles and XAS spectra extracted from the matricial decomposition. Aside from the XAS spectrum of MgO, a second AP-NEXAFS spectrum contributes to the measured data (Figure 4c, full red line) and is assigned to an intermediate species arising from the interaction between Mg2+ surface ions and methanol. The XAS spectrum of this intermediate species presents a low-energy shoulder at 1300.2 eV together with an asymmetric main transition at 1305.1 eV, while its fractional concentration slowly increases upon methanol surface exposure never exceeding a value of 40% (Figure 4b, red histograms). It is interesting to outline that a smaller fraction of Mg2+ ions are fully solvated by methanol molecules as compared to the number of surface ions that are hydrated, and this is in agreement with the lower solubility of MgO in the former solvent. Similarly to the experiment involving water, also here the methanol molecules desorb from the MgO surface once the working temperature is increased to 250 °C and the fractional concentration of the MgO related component reaches 100% (Figure 4b, gray histograms). Note that also in this case the general intensity of the non-normalized XAS spectra decreases ca. 5-fold during exposure of the MgO surface to methanol vapor, thereby suggesting that the interaction between methanol and the Mg2+ ions extends to the first few nanometers below the surface. To determine the structural properties of the Mg2+–methanol interfacial intermediate, we calculated theoretical NEXAFS spectra on DFT-optimized [Mg(MeOH)4]2+ and [Mg(MeOH)6]2+ tetrahedral and octahedral clusters, which are shown in Figure S8a and S8b, respectively, and both present three main groups of peaks. In the case of the [Mg(MeOH)4]2+ species, the lowest energy peak identified as CT1 is the most intense feature, while in the spectrum of [Mg(MeOH)6]2+ the feature located at intermediate energies, CO2, is the most intense one, followed in relative intensity by the low-energy edge shoulder CO1 and the highest energy peak CO3. The origin of this difference in the relative feature intensity may be explained by analyzing the theoretical DOS evaluated for the two differently coordinated Mg2+–methanol clusters. In fact, in the case of the [Mg(MeOH)4]2+ complex, the Mg, O, and C p-DOS significantly overlap in the low-energy region of the NEXAFS spectrum, enabling a pronounced hybridization and an intense CT1 transition (see Figure S8a), while for the [Mg(MeOH)6]2+ adduct, the octahedral environment leads to a decrease in intensity and hybridization of the Mg, O, and C p-DOS in the low-energy shoulder region (see Figure S8b), depleting the intensity of the feature CO1. A visual comparison of the NEXAFS spectrum of [Mg(MeOH)6]2+ shown in Figure S8b with the AP-NEXAFS MCR-extracted spectrum associated with the Mg2+ species formed upon interaction of the MgO surface with methanol (Figure 4c, full red line) evidences that the theoretical and experimental curves show a strong degree of similarity. These results highlight the sensitivity of our theoretical method to the change in coordination number around the metal cation and strongly support the hypothesis that in our experimental conditions the Mg2+ ions at the MgO surface may indeed be coordinated in an octahedral geometry by methanol molecules. To further test this view, MD simulations were also performed for the Mg2+ ion in methanol at a temperature of 50 °C, obtaining a CN of 6 and a maximum in the Mg–O bond distribution of 2.12 Å for the first-shell molecules, as shown in Figure S7b, a distance that is in perfect agreement with the average 2.12 Å one in the DFT-optimized [Mg(MeOH)6]2+ cluster (Table S3). These results are well in line with previous investigations where X-ray diffraction, (56) NMR, (57) and ab initio MD (58) studies have indicated that the Mg2+ ion solvate shells are composed of six methanol molecules, with a likely average octahedral arrangement of OH groups around the metal cation. The theoretical NEXAFS Mg K-edge spectrum of the Mg2+ ion in methanol was then calculated as a converged average from 500 MD snapshots (see Figure S9 for the individual MD-extracted XAS spectra and convergence details) and is compared to the experimental XAS signal in Figure 4d. As one may note from Figure 4d, the three main features located at 1300.2 eV, at 1305.1 eV, and at 1310.5 eV present in the experimental curve are reproduced well by the theoretical NEXAFS spectrum (Figure 4d, full indigo line).

Figure 4

Figure 4. (a) Intensity variation at 1305.7 eV (full yellow line) and at 1310.2 eV (full gray line) of the operando Mg K-edge XAS spectra measured upon MgO exposure to methanol vapor. The intensities of the starting XAS spectrum, of the XAS spectra recorded during the methanol flux at 50 °C, and of those measured during the methanol flux interruption and contemporary temperature increase are highlighted by black, green, and purple backgrounds, respectively. (b, c) Results of the decomposition of the Mg K-edge spectroscopic data. Extracted concentration and Mg K-edge NEXAFS spectral profiles (panels b and c, respectively). (d) Comparison between the MCR-extracted AP-NEXAFS spectral component of the Mg2+ intermediate species arising upon exposure of the MgO surface to methanol and the theoretical average Mg K-edge NEXAFS spectrum resulting from 500 MD snapshots of the Mg2+ ion fully solvated by methanol molecules (full indigo line).

High Resolution Image
Download MS PowerPoint Slide
The findings reported herein may be summarized as shown in Figure 5. Within our experimental conditions, for high water and methanol coverages, Mg2+ ions are released at the MgO surface and fully solvated by water and methanol at 50 °C with temperature expected to play an important role in favoring ion mobility, release, and dissolution. The free Mg2+ ions are expected to be hydrated/solvated at the MgO surface in octahedral coordination geometries. Conversely, the generated surface O2– ions are expected to transform into OH– groups, as proposed by previous work, (16) and to possibly yield a relatively smaller fraction of structures with partially hydroxylated Mg2+ ions above the surface. (16) Given the very similar scattering properties of the water/OH– species and low sensitivity of the XAS technique in distinguishing between water and OH– ligands, one cannot exclude the presence of a small percentage of Mg2+ surface complexes where the water molecules in the first and outer coordination spheres are partially substituted by OH– groups. Further, one cannot exclude the presence of a small fraction of Mg2+ ions possessing first and second shell structures affected by the structural modifications induced by the MgO surface to the first few adsorbed water/methanol layers. However, as evidenced by the presented statistical analyses the total contribution of all the differently hydrated/solvated Mg2+ ions is not expected to exceed 4%.

Figure 5

Figure 5. Pictorial representation of the main findings presented in this work, where it is evidenced that at 50 °C, a temperature-favored reversible hydration/solvation of Mg2+ ions occurs at the MgO surface, upon its sequential exposure to water (left) and methanol (right).

High Resolution Image
Download MS PowerPoint Slide

4. Conclusions

ARTICLE SECTIONS
Jump To
In this work, the suitability of a combined advanced MCR and ab initio DFT- and MD-assisted analysis of operando AP-NEXAFS data is demonstrated for the first time in order to access through X-rays and quantitatively describe the reversible hydration (solvation)/dehydration (desolvation) of a low-Z number metal oxide surface, investigating Mg2+ as a case study. It is shown that upon controlled exposure of MgO to water and methanol vapors at 50 °C and ambient pressure, surface Mg2+ ions form [Mg(H2O)6]2+ and [Mg(MeOH)6]2+ octahedral complexes, respectively, in detectable surface concentrations. These results provide a first direct experimental confirmation of previous theoretical findings which have suggested that at the MgO–water interface, reconstructed surfaces involving hydrated Mg2+ ions are energetically favored if compared to fully hydroxylated ones (16) and extend the same picture to the MgO–methanol interface. The sensitivity of AP-NEXAFS to the structural and electronic evolution of the Mg2+ species and that of the MCR technique in uncovering the presence of labile surface intermediates are fruitfully exploited to gain quantitative information on a prototypical metal oxide–water/methanol interface. As a result, we expect this work to pave the way for the investigation of interfaces between water (and other organic solvating media) and metal ion-based solid systems through combined experimental and theoretical efforts rooted in soft-XAS.

Supporting Information

ARTICLE SECTIONS
Jump To

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsami.2c10005.

  • Experimental details, data processing, MCR decomposition of the NEXAFS spectra, details on MD simulations and DFT calculations, 3D rendering of the employed reaction cell, theoretical NEXAFS calculations of DFT-optimized structures, MD Mg–O radial distribution functions of the Mg2+ ion in water and methanol, and convergence of the NEXAFS theoretical spectra calculated from MD snapshots of the Mg2+ ion in methanol (PDF)

Terms & Conditions

Most electronic Supporting Information files are available without a subscription to ACS Web Editions. Such files may be downloaded by article for research use (if there is a public use license linked to the relevant article, that license may permit other uses). Permission may be obtained from ACS for other uses through requests via the RightsLink permission system: http://pubs.acs.org/page/copyright/permissions.html.

Author Information

ARTICLE SECTIONS
Jump To

Acknowledgments

ARTICLE SECTIONS
Jump To

The Italian Ministry of University and Research is acknowledged for financial support through the PRIN 2017 program (project 2017KKP5ZR, MOSCATo). This work was partially performed in the framework of the Nanoscience Foundry and Fine Analysis (NFFA-MIUR Italy Progetti Internazionali) facility. Part of the calculations were performed on the Marconi100 system of the CINECA supercomputing center (grant IsC81_DENADA).

References

ARTICLE SECTIONS
Jump To

This article references 58 other publications.

  1. 1
    Groß, A. Reactions at Surfaces studied by Ab Initio Dynamics Calculations. Surf. Sci. Rep. 1998, 32, 291– 340,  DOI: 10.1016/S0167-5729(98)00008-9
    [Crossref], [CAS], Google Scholar
    1
    Reactions at surfaces studied by ab initio dynamics calculations
    Gross, Axel
    Surface Science Reports (1998), 32 (8), 291-340CODEN: SSREDI; ISSN:0167-5729. (Elsevier Science B.V.)
    Owing to the development of efficient algorithms and the improvement of computer power it is now possible to map out potential energy surfaces (PESs) of reactions at surfaces in great detail. This achievement has been accompanied by an increased effort in the dynamical simulation of processes on surfaces. The paradigm for simple reactions at surfaces - the dissocn. of hydrogen on metal surfaces - can now be treated fully quantum dynamically in the mol. degrees of freedom from first principles, i.e., without invoking any adjustable parameters. This relatively new field of ab initio dynamics simulations of reactions at surfaces will be reviewed. Mainly the dissocn. of hydrogen on clean and adsorbate covered metal surfaces and on semiconductor surfaces will be discussed. In addn., the ab initio mol. dynamics treatment of reactions of hydrogen atoms with hydrogen-passivated semiconductor surfaces and recent achievements in the ab initio description of laser-induced desorption and further developments will be addressed.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1cXnslOlt7s%253D&md5=4ccff3cf607d429f040a37d427fc1772
  2. 2
    Brown, G. E.; Henrich, V. E.; Casey, W. H.; Clark, D. L.; Eggleston, C.; Felmy, A.; Goodman, D. W.; Grätzel, M.; Maciel, G.; McCarthy, M. I.; Nealson, K. H.; Sverjensky, D. A.; Toney, M. F.; Zachara, J. M. Metal Oxide Surfaces and Their Interactions with Aqueous Solutions and Microbial Organisms. Chem. Rev. 1999, 99, 77– 174,  DOI: 10.1021/cr980011z
    [ACS Full Text ACS Full Text], [CAS], Google Scholar
    2
    Metal Oxide Surfaces and Their Interactions with Aqueous Solutions and Microbial Organisms
    Brown, Gordon E., Jr.; Henrich, Victor E.; Casey, William H.; Clark, David L.; Eggleston, Carrick; Felmy, Andrew; Goodman, D. Wayne; Graetzel, Michael; Maciel, Gary; McCarthy, Maureen I.; Nealson, Kenneth H.; Sverjensky, Dimitri A.; Toney, Michael F.; Zachara, John M.
    Chemical Reviews (Washington, D. C.) (1999), 99 (1), 77-174CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
    A review with 825 refs. concerning the state of knowledge of metal oxide surfaces and their interactions with aq. solns. and microorganisms highlighting scientific and technol. contexts where this knowledge is needed and evaluating exptl. and theor. techniques needed to obtain the necessary information is given. Topics discussed include: characterization of clean metal oxide surfaces; water vapor-metal oxide interactions; aq. soln.-metal oxide interfaces; dissoln. and growth of metal (hydr)oxides; biotic processes in metal oxide surface chem.; theory; and challenges and future directions.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1cXotFaju78%253D&md5=ca7dd477811849283f4096ab04e025ab
  3. 3
    Carrasco, E.; Brown, M. A.; Sterrer, M.; Freund, H.-J.; Kwapien, K.; Sierka, M.; Sauer, J. Thickness-Dependent Hydroxylation of MgO(001) Thin Films. J. Phys. Chem. C 2010, 114, 18207– 18214,  DOI: 10.1021/jp105294e
    [ACS Full Text ACS Full Text], [CAS], Google Scholar
    3
    Thickness-Dependent Hydroxylation of MgO(001) Thin Films
    Carrasco, Esther; Brown, Matthew A.; Sterrer, Martin; Freund, Hans-Joachim; Kwapien, Karolina; Sierka, Marek; Sauer, Joachim
    Journal of Physical Chemistry C (2010), 114 (42), 18207-18214CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
    Hydroxylation of MgO surfaces has been studied from UHV to mbar pressure for MgO(001) films of different thickness grown on Ag(001) by XPS, IR reflection absorption spectroscopy, and d. functional theory calcns. In agreement with earlier studies on MgO(001) single crystals, a threshold water pressure on the order of 10-4 mbar is found for extensive hydroxylation of thick, bulklike MgO films. Decreasing the MgO film thickness shifts the threshold pressure to lower values, being 10-6 mbar in the limit of 2 monolayer MgO(001)/Ag(001). This result is explained on the basis of the precursor state of periclase MgO(001) dissoln. involving hydrolysis of Mg-O surface bonds. The enhanced structural flexibility (polaronic distortion) of the ultrathin MgO film facilitates surface hydroxylation by lowering the barrier for hydrolysis.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXht1CmtL7P&md5=0d1dc8c024d2ff8094da7e1e9df6aa70
  4. 4
    Verdaguer, A.; Sacha, G. M.; Bluhm, H.; Salmeron, M. Molecular Structure of Water at Interfaces: Wetting at the Nanometer Scale. Chem. Rev. 2006, 106, 1478– 1510,  DOI: 10.1021/cr040376l
    [ACS Full Text ACS Full Text], [CAS], Google Scholar
    4
    Molecular structure of water at interfaces: Wetting at the nanometer scale
    Verdaguer, A.; Sacha, G. M.; Bluhm, H.; Salmeron, M.
    Chemical Reviews (Washington, DC, United States) (2006), 106 (4), 1478-1510CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
    A review. A review on recent studies on the structure and growth of water films at interfaces. The structure of water films at cryogenic temps. and at ambient conditions, water/vapor interface, water confined between flat mica surfaces, anal. of the layering structure of water using at. force microscopy, water layers on metals, structure of the water monolayer, and the effect of elec. fields on the formation of water necks are discussed.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD28XivFWmur4%253D&md5=61d2a5eeab518fc927018d85abca4ef7
  5. 5
    Ewing, G. E. Ambient Thin Film Water on Insulator Surfaces. Chem. Rev. 2006, 106, 1511– 1526,  DOI: 10.1021/cr040369x
    [ACS Full Text ACS Full Text], [CAS], Google Scholar
    5
    Ambient thin film water on insulator surfaces
    Ewing, George E.
    Chemical Reviews (Washington, DC, United States) (2006), 106 (4), 1511-1526CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
    A review. A review describes the methods for studying thin film water and their properties, and presents some insulator systems of ambient thin film water.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD28XivVemu78%253D&md5=c6e44bb864522e3dfee0bd70069c0c60
  6. 6
    Woodruff, D. P. Quantitative Structural Studies of Corundum and Rocksalt Oxide Surfaces. Chem. Rev. 2013, 113, 3863– 3886,  DOI: 10.1021/cr3002998
    [ACS Full Text ACS Full Text], [CAS], Google Scholar
    6
    Quantitative Structural Studies Of Corundum and Rocksalt Oxide Surfaces
    Woodruff, D. Phillip
    Chemical Reviews (Washington, DC, United States) (2013), 113 (6), 3863-3886CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
    A review. Topics discussed include: surface of corundum-phase solids such as aluminum oxide, chromium oxide, iron oxides, vanadium oxide and adsorbate structure; and rocksalt structure oxide surface such surface of magnesia and nickel oxide.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXktV2iug%253D%253D&md5=92a058e31a61539b4baad00b0e94b416
  7. 7
    Anderson, P. J.; Horlock, R. F.; Oliver, J. F. Interaction of Water with the Magnesium Oxide Surface. Trans. Faraday Soc. 1965, 61, 2754– 2762,  DOI: 10.1039/tf9656102754
    [Crossref], [CAS], Google Scholar
    7
    Interaction of water with the magnesium oxide surface
    Anderson, P. J.; Horlock, R. F.; Oliver, J. F.
    Transactions of the Faraday Society (1965), 61 (12), 2754-62CODEN: TFSOA4; ISSN:0014-7672.
    The study illustrates the complexities of the processes involved and the marked dependence upon the previous history of the oxide. Thus, MgO, prepd. by decompn. of the hydroxide at >300° and held at 300° in vacuo for >5 hrs., retains H2O corresponding to a surface coverage σ ∼0.08 mol/A.2 An addnl. 0.1 mol/A.2 is adsorbed at room temp. and a relative pressure of 0.01. Subsequent desorption by prolonged pumping at a series of temps. yields steady-state values. A discontinuity at 250° with σ ∼0.1 suggests the existence of 2 distinct forms of adsorbed H2O, tentatively regarded as chemisorption (above 250°) and a rather strongly bound physisorption which is not completely removed on pumping below 200°. The ease with which desorption is accomplished is markedly dependent on the time during which adsorbed H2O is present on the sample, suggesting a slow conversion at room temp. to a more strongly bound state. These expts. plus ir data allow the conclusion that a surface, not previously dehydrated, is covered with surface hydroxyl groups at ∼0.11 mol/A.2 Further adsorption is in the form of mol. H2O. This value of σ, corresponding to surface satn., indicates that the relevant surface is the (100) face. The simplest model for H2O chemisorption on this face suggests OH groups in 2 different configurations. Desorption would then occur by interaction of a pair of adjacent OH groups, one of each type. The ir detns. support this model.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaF28XkslOntA%253D%253D&md5=e4d82c4467ab9b0c1645bf64f46663cc
  8. 8
    Imad-Uddin Ahmed, S.; Perry, S. S.; El-Bjeirami, O. Desorption and Reaction of Water on MgO(100) Studied as a Function of Surface Preparation. J. Phys. Chem. B 2000, 104, 3343– 3348,  DOI: 10.1021/jp9934275
    [ACS Full Text ACS Full Text], Google Scholar
    There is no corresponding record for this reference.
  9. 9
    Johnson, M. A.; Stefanovich, E. V.; Truong, T. N.; Günster, J.; Goodman, D. W. Dissociation of Water at the MgO(100)–Water Interface: Comparison of Theory with Experiment. J. Phys. Chem. B 1999, 103, 3391– 3398,  DOI: 10.1021/jp983729r
    [ACS Full Text ACS Full Text], [CAS], Google Scholar
    9
    Dissociation of Water at the MgO(100)-Water Interface: Comparison of Theory with Experiment
    Johnson, Michael A.; Stefanovich, Eugene V.; Truong, Thanh N.; Guenster, Jens; Goodman, D. W.
    Journal of Physical Chemistry B (1999), 103 (17), 3391-3398CODEN: JPCBFK; ISSN:1089-5647. (American Chemical Society)
    Dissociative chemisorption of H2O at the MgO(100)-water interface has been investigated both exptl. and theor. In particular, metastable impact electron spectroscopy (MIES) was used to image the d. of occupied states on the MgO(100)/Mo(100) surface for various degrees of water exposure. After multilayer water desorption, spectral features typical of surface hydroxyls are present. To further study the possibility of dissociative chemisorption of water, a theor. and computational method called CECILIA (combined embedded cluster at the interface with liq. approach) was used to calc. the geometry, energetics, and electronic d. of states (DOS) for interfacial species. Consistent with expt., our theor. results predict that dissociative adsorption of H2O at the MgO(100)-water interface is energetically more favorable than mol. adsorption. The stabilization of charged OH- and H+ interface adsorbates is due to polarization of the surrounding solvent.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1MXit1Wjsrk%253D&md5=12f947a6a045f8f665a16fb37a551c67
  10. 10
    Giordano, L.; Goniakowski, J.; Suzanne, J. Partial Dissociation of Water Molecules in the (3 × 2) Water Monolayer Deposited on the MgO (100) Surface. Phys. Rev. Lett. 1998, 81, 1271– 1273,  DOI: 10.1103/PhysRevLett.81.1271
    [Crossref], [CAS], Google Scholar
    10
    Partial Dissociation of Water Molecules in the (3×2) Water Monolayer Deposited on the MgO(100) Surface
    Giordano, Livia; Goniakowski, Jacek; Suzanne, Jean
    Physical Review Letters (1998), 81 (6), 1271-1273CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)
    Using the ab initio total energy method based on the gradient-cor. local d. approxn. the authors have modeled the exptl. obsd. (3×2) H2O monolayer on the MgO (100) surface. The lateral interactions between the adsorbed H2O mols., the formation of H bonds, and the resulting strong dimerization of the adsorbate promote the dissocn. of 2 out of 6 H2O mols. in the surface unit cell. Although, on the theor. grounds, H2O dissocn. on a defective MgO surface was already reported, this is the 1st theor. evidence of H2O dissocn. on the perfect MgO (100) surface.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1cXltVSrtb8%253D&md5=14dae5836bf63c4e17600cbd6f7b2ead
  11. 11
    Odelius, M. Mixed Molecular and Dissociative Water Adsorption on MgO [100]. Phys. Rev. Lett. 1999, 82, 3919– 3922,  DOI: 10.1103/PhysRevLett.82.3919
    [Crossref], [CAS], Google Scholar
    11
    Mixed Molecular and Dissociative Water Adsorption on MgO[100]
    Odelius, Michael
    Physical Review Letters (1999), 82 (19), 3919-3922CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)
    First principles mol. dynamics (MD) simulations, of H2O adsorption on the MgO[100] surface, was performed to det. the mol. structure and chem. nature of the adsorbed H2O at varying coverage. Dissociative adsorption was stabilized by hydrogen bond donation from neighboring H2O mols. The dissocn. barrier had a strong dependence on coverage. Spontaneous dissocn. was obsd. in picosecond MD simulations >1/2 monolayer (ML) coverage. Ordered structures with c[3×2] symmetry were examd. at 2/3 and 1 ML coverage. The ordered c[3×2] phase consisted of a mixt. of dissocd. and mol. adsorbed mols.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1MXjtF2gtrs%253D&md5=2890380f637997c346c22aa1301dd82a
  12. 12
    Delle Site, L.; Alavi, A.; Lynden-Bell, R. M. The Structure and Spectroscopy of Monolayers of Water on MgO: an Ab Initio Study. J. Chem. Phys. 2000, 113, 3344– 3350,  DOI: 10.1063/1.1287276
    [Crossref], [CAS], Google Scholar
    12
    The structure and spectroscopy of monolayers of water on MgO. An ab initio study
    Delle Site, L.; Alavi, A.; Lynden-Bell, R. M.
    Journal of Chemical Physics (2000), 113 (8), 3344-3350CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)
    The structure and energetics of a monolayer of water on a perfect MgO substrate is investigated by ab initio calcns. Several min. in the potential energy surface were found including both physisorbed and chemisorbed states in which one third of the water mols. were dissocd. In the more stable of the physisorbed states, the water mols. were not all parallel to the surface, but some showed hydrogen bonding with surface O ions. Even in the physisorbed state, the geometry of these surface H-bonded water mols. were distorted relative to the bulk. One of the stable chemisorbed states was the same as that found in earlier work by Giordano et al. [Phys. Rev. Lett. 81, 1271 (1998)]. Two more stable chemisorbed structures were found in which strong H-bonds to the hydroxide ions in the water layer were formed. The existence of different min. appears to be the result of a subtle interplay between H-bonding between adsorbed species and with the surface oxide ions. Harmonic vibrational frequencies were detd. for both a chemisorbed and a physisorbed states and spectroscopic features which should discriminate between chemisorbed and physisorbed states are identified.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3cXlslKktrk%253D&md5=50a177670033a1d385bda8c4e545d3d0
  13. 13
    Jug, K.; Heidberg, B.; Bredow, T. Cyclic Cluster Study of Water Adsorption Structures on the MgO(100) Surface. Surf. Sci. 2007, 601, 1529– 1535,  DOI: 10.1016/j.susc.2006.12.092
    [Crossref], [CAS], Google Scholar
    13
    Cyclic cluster study of water adsorption structures on the MgO(100) surface
    Jug, Karl; Heidberg, Bettina; Bredow, Thomas
    Surface Science (2007), 601 (6), 1529-1535CODEN: SUSCAS; ISSN:0039-6028. (Elsevier B.V.)
    Cyclic cluster calcns. were performed with the quantum chem. method MSINDO to elucidate the relative stabilities of c(4 × 2), p(3 × 2) and (1 × 1) overlayer structures of water mols. on the MgO(1 0 0) surface. For the c(4 × 2) and p(3 × 2) structures both mol. adsorption and partially dissocd. adsorption were considered. In agreement with earlier theor. studies partial dissocn. was found to be more stable than mol. adsorption. For the c(4 × 2) structure both monolayer and double layer coverage were studied. Adsorption was found to be more stabilized with increasing degree of dissocn. until 50% of the water mols. were dissocd. In the case of 50% dissocd. water mols. we found that one quarter of the Mg atoms were pulled out of the MgO surface when surface relaxation was taken into account. A new structure for the fully dissocd. (1 × 1) water monolayer was found which is considerably more stable than previously studied arrangements. In all cases surface relaxation was found to be important. The most stable structures of c(4 × 2), p(3 × 2) and (1 × 1) symmetry have adsorption energies which differ by no more than 13 kJ/mol. This offers an explanation of phase transitions of overlayer structures found by expts. between 180 and 300 K.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2sXjtVWrurs%253D&md5=091d22ecfaa300a853eea461fbb9da88
  14. 14
    Lynden-Bell, R.; Delle Site, L.; Alavi, A. Structures of Adsorbed Water Layers on MgO: an Ab Initio Study. Surf. Sci. 2002, 496, L1– L6,  DOI: 10.1016/S0039-6028(01)01669-7
    [Crossref], [CAS], Google Scholar
    14
    Structures of adsorbed water layers on MgO. An ab initio study
    Lynden-Bell, R. M.; Delle Site, L.; Alavi, A.
    Surface Science (2002), 496 (1-2), L1-L6CODEN: SUSCAS; ISSN:0039-6028. (Elsevier Science B.V.)
    A systematic search using an ab initio d.-functional method was carried out for energy min. for a monolayer of water on MgO. Min. were sought in which one third of the water mols. were dissocd., and the obsd. p(3×2) symmetry satisfied. Six such min. were found, 3 of which are within 300kB per water mol. of the lowest energy structure. We also found a structure with a similar energy with (2×2) symmetry and half the water mols. dissocd. The structures are stabilized by the donation of 3 H-bonds to each hydroxide ion.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3MXptFCmsLo%253D&md5=299a663086409c99ffda792ee2003f9d
  15. 15
    Jug, K.; Heidberg, B.; Bredow, T. Molecular Dynamics Study of Water Adsorption Structures on the MgO(100) Surface. J. Phys. Chem. C 2007, 111, 6846– 6851,  DOI: 10.1021/jp067651n
    [ACS Full Text ACS Full Text], [CAS], Google Scholar
    15
    Molecular Dynamics Study of Water Adsorption Structures on the MgO(100) Surface
    Jug, Karl; Heidberg, Bettina; Bredow, Thomas
    Journal of Physical Chemistry C (2007), 111 (18), 6846-6851CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
    Semiempirical MSINDO calcns. were performed for the study of structure and stability of c(4 × 2), p(3 × 2), and (1 × 1) overlayers of H2O on the MgO(100) surface. Born-Oppenheimer mol. dynamics (MD) techniques were used to simulate the changes in the adsorption at 300 K compared to that at 0 K. A partially dissocd. double layer of the c(4 × 2) structure with coverage θ = 3/2 attacks the MgO surface at 300 K. The hydroxylated (1 × 1) overlayer structure appears to be equally aggressive toward the MgO surface at this temp. Nucleation for the process of Mg(OH)2 formation was also obsd.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2sXktFynt70%253D&md5=f4c597d9925f6bb7666a299035d1825b
  16. 16
    Ončák, M.; Włlodarczyk, R.; Sauer, J. Water on the MgO(001) Surface: Surface Reconstruction and Ion Solvation. J. Phys. Chem. Lett. 2015, 6, 2310– 2314,  DOI: 10.1021/acs.jpclett.5b00885
    [ACS Full Text ACS Full Text], [CAS], Google Scholar
    16
    Water on the MgO(001) Surface: Surface Reconstruction and Ion Solvation
    Oncak, Milan; Wlodarczyk, Radoslaw; Sauer, Joachim
    Journal of Physical Chemistry Letters (2015), 6 (12), 2310-2314CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)
    The interaction of water with the MgO(001) surface under ambient conditions is investigated by d. functional theory combined with statistical thermodn. For water loadings of more than one monolayer, we show that the std. structure model, a fully hydroxylated surface, needs to be revised. Reconstructed surfaces, involving hydrated/hydroxylated Mg2+ ions above the surface, are more stable. These findings provide a consistent picture for surface hydroxylation between low and high water coverage that is in agreement with available XPS data.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXps1akur8%253D&md5=0baf86910c00e2eae193468bf1a84639
  17. 17
    Akabayov, B.; Doonan, C. J.; Pickering, I. J.; George, G. N.; Sagi, I. Using Softer X-ray Absorption Spectroscopy to Probe Biological Systems. J. Synchr. Rad. 2005, 12, 392– 401,  DOI: 10.1107/S0909049505010150
    [Crossref], [PubMed], [CAS], Google Scholar
    17
    Using softer X-ray absorption spectroscopy to probe biological systems
    Akabayov, Barak; Doonan, Christian J.; Pickering, Ingrid J.; George, Graham N.; Sagi, Irit
    Journal of Synchrotron Radiation (2005), 12 (4), 392-401CODEN: JSYRES; ISSN:0909-0495. (Blackwell Publishing Ltd.)
    Many inorg. species are now recognized as being essential for life, including many forms of sulfur, phosphate and numerous classes of metal ions. For example, recent progress in the fields of biochem. and biol. has pointed out the crit. importance of sulfur in the biosynthesis of vital cofactors and active sites in proteins, and in the complex reaction mechanisms often involved. Special attention has also been drawn to the diverse roles of alk. (Na+, K+) and alk. earth (Mg2+, Ca2+) metal ions in mediating the activity of RNA, proteins and many processes in living cells. While the general effect of these ions in biol. is mostly understood, information on their detailed role is deficient. Here the application of softer x-ray absorption spectroscopy (XAS) to probe the local structural and electronic environment of such ions within their biol. complexes and during physiol. reactions is discussed. In addn., the required exptl. set-up and the difficulties assocd. with conducting softer XAS expts. on biol. samples are presented.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2MXltlCns7w%253D&md5=3a58ddbc51c9a6a125d72b7ba4ff0d43
  18. 18
    Capocasa, G.; Sessa, F.; Tavani, F.; Monte, M.; Olivo, G.; Pascarelli, S.; Lanzalunga, O.; Di Stefano, S.; D’Angelo, P. Coupled X-ray Absorption/UV-vis Monitoring of Fast Oxidation Reactions Involving a Nonheme Iron-Oxo Complex. J. Am. Chem. Soc. 2019, 141, 2299– 2304,  DOI: 10.1021/jacs.8b08687
    [ACS Full Text ACS Full Text], [CAS], Google Scholar
    18
    Coupled X-ray Absorption/UV-vis Monitoring of Fast Oxidation Reactions Involving a Nonheme Iron-Oxo Complex
    Capocasa, Giorgio; Sessa, Francesco; Tavani, Francesco; Monte, Manuel; Olivo, Giorgio; Pascarelli, Sakura; Lanzalunga, Osvaldo; Di Stefano, Stefano; D'Angelo, Paola
    Journal of the American Chemical Society (2019), 141 (6), 2299-2304CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    Time-resolved X-ray absorption (XAS) and UV-vis spectroscopies with millisecond resoln. are used simultaneously to investigate oxidn. reactions of org. substrates by nonheme iron activated species. In particular, the oxidn. processes of arylsulfides and benzyl alcs. by a nonheme iron-oxo complex have been studied. We show for the first time that the pseudo-first-order rate consts. of fast bimol. processes in soln. (milliseconds and above) can be detd. by time-resolved XAS technique. By following the Fe K-edge energy shift, it is possible to detect the rate of iron oxidn. state evolution that matches that of the bimol. reaction in soln. The kinetic const. values obtained by XAS are in perfect agreement with those obtained by means of the concomitant UV-vis detection. This combined approach has the potential to provide unique insights into reaction mechanisms in the liq. phase that involve changes of the oxidn. state of a metal center, and it is particularly useful in complex chem. systems where possible interferences from species present in soln. could make it impossible to use other detection techniques.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXht1ansr4%253D&md5=f3e41d41a49eae461da02fcf69e5b404
  19. 19
    Tavani, F.; Martini, A.; Capocasa, G.; Di Stefano, S.; Lanzalunga, O.; D’Angelo, P. Direct Mechanistic Evidence for a Non-Heme Complex Reaction through a Multivariate XAS Analysis. Inorg. Chem. 2020, 59, 9979– 9989,  DOI: 10.1021/acs.inorgchem.0c01132
    [ACS Full Text ACS Full Text], [CAS], Google Scholar
    19
    Direct Mechanistic Evidence for a Nonheme Complex Reaction through a Multivariate XAS Analysis
    Tavani, Francesco; Martini, Andrea; Capocasa, Giorgio; Di Stefano, Stefano; Lanzalunga, Osvaldo; D'Angelo, Paola
    Inorganic Chemistry (2020), 59 (14), 9979-9989CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
    We propose a method to directly det. the mechanism of the reaction between the nonheme complex FeII(tris(2-pyridylmethyl)amine) ([FeII(TPA)(CH3CN)2]2+) and peracetic acid (AcOOH) in CH3CN, working at room temp. A multivariate anal. is applied to the time-resolved coupled energy-dispersive X-ray absorption spectroscopy (EDXAS) reaction data, from which a set of spectral and concn. profiles for the reaction key species is derived. These "pure" extd. EDXAS spectra are then quant. characterized by full multiple scattering (MS) calcns. As a result, structural information for the elusive reaction intermediates [FeIII(TPA)(κ2-OOAc)]2+ and [FeIV(TPA)(O)(X)]+/2+ is obtained, and it is suggested that X = AcO- in opposition to X = CH3CN. The employed strategy is promising both for the spectroscopic characterization of reaction intermediates that are labile or silent to the conventional spectroscopic techniques, as well as for the mechanistic understanding of complex redox reactions involving org. substrates. A combined multivariate and theor. XAS anal. was proven to be a powerful method to obtain direct evidence for the mechanism of the reaction between the nonheme complex FeII(tris(2-pyridymethyl)amine) ([FeII(TPA)(CH3CN)2]2+) and peroxyacetic acid. This approach allowed to det. the time evolution of the concn. profiles for all reaction intermediates and to quant. characterize their structures, suggesting the sixth coordinating ligand of the nonheme oxo complex [FeIV(TPA)(O)(X)]+/2+ is X = AcO- in opposition to X = CH3CN.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXht1Gms77L&md5=12e34f9e364b915a323d7739003d3795
  20. 20
    Busato, M.; Melchior, A.; Migliorati, V.; Colella, A.; Persson, I.; Mancini, G.; Veclani, D.; D’Angelo, P. Elusive Coordination of the Ag+ Ion in Aqueous Solution: Evidence for a Linear Structure. Inorg. Chem. 2020, 59, 17291– 17302,  DOI: 10.1021/acs.inorgchem.0c02494
    [ACS Full Text ACS Full Text], [CAS], Google Scholar
    20
    Elusive Coordination of the Ag+ Ion in Aqueous Solution: Evidence for a Linear Structure
    Busato, Matteo; Melchior, Andrea; Migliorati, Valentina; Colella, Andrea; Persson, Ingmar; Mancini, Giordano; Veclani, Daniele; D'Angelo, Paola
    Inorganic Chemistry (2020), 59 (23), 17291-17302CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
    X-ray absorption spectroscopy (XAS) has been employed to study the coordination of the Ag+ ion in aq. soln. The conjunction of extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES) data anal. provided results suggesting the preference for a first shell linear coordination with a mean Ag-O bond distance of 2.34(2) Å, different from the first generally accepted tetrahedral model with a longer mean Ag-O bond distance. Ab initio mol. dynamics simulations with the Car-Parrinello approach (CPMD) were also performed and were able to describe the coordination of the hydrated Ag+ ion in aq. soln. in very good agreement with the exptl. data. The high sensitivity for the closest environment of the photoabsorber of the EXAFS and XANES techniques, together with the long-range information provided by CPMD and large-angle X-ray scattering (LAXS), allowed us to reconstruct the three-dimensional model of the coordination geometry around the Ag+ ion in aq. soln. The obtained results from expts. and theor. simulations provided a complex picture with a certain amt. of water mols. with high configurational disorder at distances comprised between the first and second hydration spheres. This evidence may have caused the proliferation of the coordination nos. that have been proposed so far for Ag+ in water. Altogether these data show how the description of the hydration of the Ag+ ion in aq. soln. can be complex, differently from other metal species where hydration structures can be described by clusters with well-defined geometries. This diffuse hydration shell causes the Ag-O bond distance in the linear [Ag(H2O)2]+ ion to be ca. 0.2 Å longer than in isolated ions in solid state. Extended X-ray absorption fine structure (EXAFS), X-ray absorption near-edge structure (XANES), large-angle X-ray scattering (LAXS), and Car-Parrinello mol. dynamics (CPMD) provided a reliable detn. of the elusive hydration structure of the Ag+ ion. A linear first shell with a mean Ag-O distance of 2.34(2) Å is obsd., surrounded by a few water mols. at a relatively short distance, ca. 2.6 Å, and another set of waters as a swarm at ca. 4 Å.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXitl2qtLbL&md5=c833cf5ea5992612bdb7750a96c2c468
  21. 21
    Isegawa, K.; Ueda, K.; Hiwasa, S.; Amemiya, K.; Mase, K.; Kondoh, H. Formation of Carbonate on Ag(111) under Exposure to Ethylene and Oxygen Gases Evidenced by Near Ambient Pressure XPS and NEXAFS. Chem. Lett. 2019, 48, 159– 162,  DOI: 10.1246/cl.180891
    [Crossref], [CAS], Google Scholar
    21
    Formation of carbonate on Ag(111) under exposure to ethylene and oxygen gases evidenced by near ambient pressure XPS and NEXAFS
    Isegawa, Kazuhisa; Ueda, Kohei; Hiwasa, Satoru; Amemiya, Kenta; Mase, Kazuhiko; Kondoh, Hiroshi
    Chemistry Letters (2019), 48 (2), 159-162CODEN: CMLTAG; ISSN:0366-7022. (Chemical Society of Japan)
    The active oxygen species for ethylene epoxidn. on Ag surfaces has been a long-standing issue. We conducted in situ observations of Ag(111) surfaces under exposure to ethylene and oxygen gases with near ambient pressure (NAP) XPS and near-edge X-ray absorption fine structure spectroscopy. Combined results of these spectroscopies evidence that a carbonate species with a flat-lying configuration is formed on the Ag(111) surface at 370-500K under exposure to the NAP gas mixt. of ethylene and oxygen.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXotlKit7o%253D&md5=854e5bca31af9b7c9789a6abded5a8a8
  22. 22
    Castán-Guerrero, C.; Krizmancic, D.; Bonanni, V.; Edla, R.; Deluisa, A.; Salvador, F.; Rossi, G.; Panaccione, G.; Torelli, P. A Reaction Cell for Ambient Pressure Soft X-ray Absorption Spectroscopy. Rev. Sci. Instrum. 2018, 89, 054101,  DOI: 10.1063/1.5019333
    [Crossref], [PubMed], [CAS], Google Scholar
    22
    A reaction cell for ambient pressure soft x-ray absorption spectroscopy
    Castan-Guerrero, C.; Krizmancic, D.; Bonanni, V.; Edla, R.; Deluisa, A.; Salvador, F.; Rossi, G.; Panaccione, G.; Torelli, P.
    Review of Scientific Instruments (2018), 89 (5), 054101/1-054101/8CODEN: RSINAK; ISSN:0034-6748. (American Institute of Physics)
    The authors present a new exptl. setup for performing x-ray Absorption Spectroscopy (XAS) in the soft X-ray range at ambient pressure. The ambient pressure XAS setup is fully compatible with the ultra high vacuum environment of a synchrotron radiation spectroscopy beamline end station by ultrathin Si3N4 membranes acting as windows for the x-ray beam and seal of the atm. sample environment. The XAS detection is performed in total electron yield (TEY) mode by probing the drain current from the sample with a picoammeter. The high signal/noise ratio achievable in the TEY mode, combined with a continuous scanning of the x-ray energies, makes it possible recording XAS spectra in a few seconds. The 1st results show the performance of this setup to record fast XAS spectra from sample surfaces exposed at atm. pressure, even in the case of highly insulating samples. The use of a permanent magnet inside the reaction cell enables the measurement of x-ray MCD at ambient pressure. (c) 2018 American Institute of Physics.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXptVWksb4%253D&md5=5931940d1810ce8e49c1dc57a2eaea44
  23. 23
    Braglia, L.; Fracchia, M.; Ghigna, P.; Minguzzi, A.; Meroni, D.; Edla, R.; Vandichel, M.; Ahlberg, E.; Cerrato, G.; Torelli, P. Understanding Solid-Gas Reaction Mechanisms by Operando Soft X-Ray Absorption Spectroscopy at Ambient Pressure. J. Phys. Chem. C 2020, 124, 14202– 14212,  DOI: 10.1021/acs.jpcc.0c02546
    [ACS Full Text ACS Full Text], [CAS], Google Scholar
    23
    Understanding Solid-Gas Reaction Mechanisms by Operando Soft X-Ray Absorption Spectroscopy at Ambient Pressure
    Braglia, Luca; Fracchia, Martina; Ghigna, Paolo; Minguzzi, Alessandro; Meroni, Daniela; Edla, Raju; Vandichel, Matthias; Ahlberg, Elisabet; Cerrato, Giuseppina; Torelli, Piero
    Journal of Physical Chemistry C (2020), 124 (26), 14202-14212CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
    Ambient-pressure operando soft X-ray absorption spectroscopy (soft-XAS) was applied to study the reactivity of hydroxylated SnO2 nanoparticles toward reducing gases. H2 was first used as a test case, showing that the gas phase and surface states can be simultaneously probed: Soft-XAS at the O K-edge gains sensitivity toward the gas phase, while at the Sn M4,5-edges, tin surface states are explicitly probed. Results obtained by flowing hydrocarbons (CH4 and CH3CHCH2) unequivocally show that these gases react with surface hydroxyl groups to produce water without producing carbon oxides and release electrons that localize on Sn to eventually form SnO. The partially reduced SnO2-x layer at the surface of SnO2 is readily reoxidized to SnO2 by treating the sample with O2 at mild temps. (>200°C), revealing the nature of "electron sponge" of tin oxide. The expts., combined with DFT calcns., allowed devising of a mechanism for dissociative hydrocarbon adsorption on SnO2, involving direct redn. of Sn sites at the surface via cleavage of C-H bonds and the formation of methoxy- and/or methyl-tin species at the surface.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXhtV2ks7%252FK&md5=417d1e4ba6e318d56920dbe62b6da537
  24. 24
    Braglia, L.; Tavani, F.; Mauri, S.; Edla, R.; Krizmancic, D.; Tofoni, A.; Colombo, V.; D’Angelo, P.; Torelli, P. Catching the Reversible Formation and Reactivity of Surface Defective Sites in Metal–Organic Frameworks: An Operando Ambient Pressure-NEXAFS Investigation. J. Phys. Chem. Lett. 2021, 12, 9182– 9187,  DOI: 10.1021/acs.jpclett.1c02585
    [ACS Full Text ACS Full Text], [CAS], Google Scholar
    24
    Catching the Reversible Formation and Reactivity of Surface Defective Sites in Metal-Organic Frameworks: An Operando Ambient Pressure-NEXAFS Investigation
    Braglia, Luca; Tavani, Francesco; Mauri, Silvia; Edla, Raju; Krizmancic, Damjan; Tofoni, Alessandro; Colombo, Valentina; D'Angelo, Paola; Torelli, Piero
    Journal of Physical Chemistry Letters (2021), 12 (37), 9182-9187CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)
    In this work, we apply for the first time ambient pressure operando soft X-ray absorption spectroscopy (XAS) to investigate the location, structural properties, and reactivity of the defective sites present in the prototypical metal-org. framework HKUST-1. We obtained direct evidence that Cu+ defective sites form upon temp. treatment of the powd. form of HKUST-1 at 160 °C and that they are largely distributed on the material surface. Further, a thorough structural characterization of the Cu+/Cu2+ dimeric complexes arising from the temp.-induced dehydration/decarboxylation of the pristine Cu2+/Cu2+ paddlewheel units is reported. In addn. to characterizing the surface defects, we demonstrate that CO2 may be reversibly adsorbed and desorbed from the surface defective Cu+/Cu2+ sites. These findings show that ambient pressure soft-XAS, combined with state-of-the-art theor. calcns., allowed us to shed light on the mechanism involving the decarboxylation of the paddlewheel units on the surface to yield Cu+/Cu2+ complexes and their reversible restoration upon exposure to gaseous CO2..
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXitVaitL%252FO&md5=1559f49ab51f13270ae01c20fe258751
  25. 25
    Tavani, F.; Fracchia, M.; Tofoni, A.; Braglia, L.; Jouve, A.; Morandi, S.; Manzoli, M.; Torelli, P.; Ghigna, P.; D’Angelo, P. Structural and Mechanistic Insights into Low-Temperature CO Oxidation over a Prototypical High Entropy Oxide by Cu L-edge Operando Soft X-ray absorption Spectroscopy. Phys. Chem. Chem. Phys. 2021, 23, 26575– 26584,  DOI: 10.1039/D1CP03946F
    [Crossref], [PubMed], [CAS], Google Scholar
    25
    Structural and mechanistic insights into low-temperature CO oxidation over a prototypical high entropy oxide by Cu L-edge operando soft X-ray absorption spectroscopy
    Tavani, Francesco; Fracchia, Martina; Tofoni, Alessandro; Braglia, Luca; Jouve, Andrea; Morandi, Sara; Manzoli, Maela; Torelli, Piero; Ghigna, Paolo; D'Angelo, Paola
    Physical Chemistry Chemical Physics (2021), 23 (46), 26575-26584CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
    High entropy oxides (HEOs) are an emerging class of materials constituted by multicomponent systems that are receiving special interest as candidates for obtaining novel and desirable properties. In this study we present a detailed investigation of the relevant intermediates arising at the surface of the prototypical HEO Mg0.2Co0.2Ni0.2Cu0.2Zn0.2O during low-temp. CO oxidn. By combining Cu L2,3-edge operando soft X-ray absorption spectroscopy (soft-XAS) with d. functional theory simulations and in situ FT-IR spectroscopy, we propose that upon HEO exposure to CO at 235 °C reduced Cu(I) sites arise mostly coordinated to activated CO mols. and partly to bidentate carbonate species. When the HEO surface is then exposed to a stoichiometric mixt. of CO + 1/2O2 at 250 °C, CO2 is produced while bidentate carbonate moieties remain interacting with the Cu(I) sites. We structurally characterize the carbonate and CO preferential adsorption geometries on the Cu(I) surface metal centers, and find that CO adopts a bent conformation that may energetically favor its subsequent oxidn. The unique surface, structural and electronic sensitivity of soft-XAS coupled with the developed data anal. work-flow and supported by FT-IR spectroscopy may be beneficial to characterize often elusive surface properties of systems of catalytic interest.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXisVyku7bP&md5=251ff77734ad8011242619e208d468e0
  26. 26
    Martini, A.; Guda, S.; Guda, A.; Smolentsev, G.; Algasov, A.; Usoltsev, O.; Soldatov, M.; Bugaev, A.; Rusalev, Y.; Lamberti, C.; Soldatov, A. PyFitit: The Software for Quantitative Analysis of XANES Spectra Using Machine-Learning Algorithms. Comput. Phys. Commun. 2019, 107064
    Google Scholar
    There is no corresponding record for this reference.
  27. 27
    Martini, A.; Guda, A. A.; Guda, S. A.; Dulina, A.; Tavani, F.; D’Angelo, P.; Borfecchia, E.; Soldatov, A. V. In Synchrotron Radiation Science and Applications. Springer Proceedings in Physics; Di Cicco, A., Giuli, G., Trapananti, A., Eds.; Springer, 2021; Vol. 220; pp 65– 84.
    [Crossref], Google Scholar
    There is no corresponding record for this reference.
  28. 28
    Tavani, F.; Capocasa, G.; Martini, A.; Sessa, F.; Di Stefano, S.; Lanzalunga, O.; D’Angelo, P. Direct Structural and Mechanistic Insights into Fast Bimolecular Chemical Reactions in Solution through a Coupled XAS/UV-Vis Multivariate Statistical Analysis. Dalton Trans 2021, 50, 131– 142,  DOI: 10.1039/D0DT03083J
    [Crossref], [PubMed], [CAS], Google Scholar
    28
    Direct structural and mechanistic insights into fast bimolecular chemical reactions in solution through a coupled XAS/UV-Vis multivariate statistical analysis
    Tavani, Francesco; Capocasa, Giorgio; Martini, Andrea; Sessa, Francesco; Di Stefano, Stefano; Lanzalunga, Osvaldo; D'Angelo, Paola
    Dalton Transactions (2021), 50 (1), 131-142CODEN: DTARAF; ISSN:1477-9226. (Royal Society of Chemistry)
    In this work, we obtain detailed mechanistic and structural information on bimol. chem. reactions occurring in soln. on the second to millisecond time scales through the combination of a statistical, multivariate and theor. anal. of time-resolved coupled X-ray Absorption Spectroscopy (XAS) and UV-Vis data. We apply this innovative method to investigate the sulfoxidn. of p-cyanothioanisole and p-methoxythioanisole by the nonheme FeIV oxo complex [N4Py·FeIV(O)]2+ (N4Py = N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine) in acetonitrile at room temp. By employing statistical and multivariate techniques we det. the no. of key chem. species involved along the reaction paths and derive spectral and concn. profiles for the reaction intermediates. From the quant. anal. of the XAS spectra we obtain accurate structural information for all reaction intermediates and provide the first structural characterization in soln. of complex [N4Py·FeIII(OH)]2+. The employed strategy is promising for the spectroscopic characterization of transient species formed in redox reactions.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXisVejs7jE&md5=b45e428fd885b912fc580682a96acf4b
  29. 29
    Tavani, F.; Capocasa, G.; Martini, A.; Sessa, F.; Di Stefano, S.; Lanzalunga, O.; D’Angelo, P. Activation of C-H Bonds by a Nonheme Iron(IV)-Oxo Complex: Mechanistic Evidence through a Coupled EDXAS/UV-Vis Multivariate Analysis. Phys. Chem. Chem. Phys. 2021, 23, 1188– 1196,  DOI: 10.1039/D0CP04304D
    [Crossref], [PubMed], [CAS], Google Scholar
    29
    Activation of C-H bonds by a nonheme iron(IV)-oxo complex: mechanistic evidence through a coupled EDXAS/UV-Vis multivariate analysis
    Tavani, Francesco; Capocasa, Giorgio; Martini, Andrea; Sessa, Francesco; Di Stefano, Stefano; Lanzalunga, Osvaldo; D'Angelo, Paola
    Physical Chemistry Chemical Physics (2021), 23 (2), 1188-1196CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
    The understanding of reactive processes involving org. substrates is crucial to chem. knowledge and requires multidisciplinary efforts for its advancement. Herein, we apply a combined multivariate, statistical and theor. anal. of coupled time-resolved X-ray absorption (XAS)/UV-Vis data to obtain detailed mechanistic information for on the C-H bond activation of 9,10-dihydroanthracene (DHA) and diphenylmethane (Ph2CH2) by the nonheme FeIV-oxo complex [N4Py·FeIV(O)]2+ (N4Py = N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine) in CH3CN at room temp. Within this approach, we det. the no. of key chem. species present in the reaction mixts. and derive spectral and concn. profiles for the reaction intermediates. From the quant. anal. of the XAS spectra the transient intermediate species are structurally detd. As a result, it is suggested that, while DHA is oxidized by [N4Py·FeIV(O)]2+ with a hydrogen atom transfer-electron transfer (HAT-ET) mechanism, Ph2CH2 is oxidized by the nonheme iron-oxo complex through a HAT-radical dissocn. pathway. In the latter process, we prove that the intermediate FeIII complex [N4Py·FeIII(OH)]2+ is not able to oxidize the diphenylmethyl radical and we provide its structural characterization in soln. The employed combined exptl. and theor. strategy is promising for the spectroscopic characterization of transient intermediates as well as for the mechanistic investigation of redox chem. transformations on the second to millisecond time scales.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXis1SgsL%252FO&md5=3520a37ba8568225c65af4781dcdff9d
  30. 30
    Tavani, F.; Fracchia, M.; Pianta, N.; Ghigna, P.; Quartarone, E.; D’Angelo, P. Multivariate Curve Resolution Analysis of Operando XAS Data for the Investigation of the Lithiation Mechanisms in High Entropy Oxides. Chem. Phys. Lett. 2020, 760, 137968,  DOI: 10.1016/j.cplett.2020.137968
    [Crossref], [CAS], Google Scholar
    30
    Multivariate curve resolution analysis of operando XAS data for the investigation of the lithiation mechanisms in high entropy oxides
    Tavani, Francesco; Fracchia, Martina; Pianta, Nicolo; Ghigna, Paolo; Quartarone, Eliana; D'Angelo, Paola
    Chemical Physics Letters (2020), 760 (), 137968CODEN: CHPLBC; ISSN:0009-2614. (Elsevier B.V.)
    Transition metal-based high entropy oxides (TM-HEO) have recently been gaining interest for their potential use as anodes in next-generation Li-ion batteries. In such systems, however, the lithiation/delithiation mechanisms remain a matter of ongoing investigation. In this work we demonstrate the suitability of Multivariate Curve Resoln. (MCR) of operando X-ray absorption spectroscopy (XAS) data to study the lithiation mechanisms in the TM-HEO (Mg0.2Co0.2Ni0.2Cu0.2Zn0.2)O. Through the MCR anal., the no., nature and concn. evolution as a function of stored charge of all Cu-, Ni- and Co-related active species present during the first lithiation cycle is obtained.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXitVKgur3F&md5=0d3af0d5788149646bed68d0a0941318
  31. 31
    Kleiman, S.; Chaim, R. Thermal Stability of MgO Nanoparticles. Mater. Lett. 2007, 61, 4489– 4491,  DOI: 10.1016/j.matlet.2007.02.032
    [Crossref], [CAS], Google Scholar
    31
    Thermal stability of MgO nanoparticles
    Kleiman, Sagiv; Chaim, Rachman
    Materials Letters (2007), 61 (23-24), 4489-4491CODEN: MLETDJ; ISSN:0167-577X. (Elsevier B.V.)
    Thermal stability of nanocryst. MgO particles with av. diam. of 11 nm was investigated by annealing of the cold isostatically pressed compacts between 600 °C and 900 °C for various durations. Sintering time vs. grain radius at 800 °C demonstrated a linear line with the slope of ∼ 4 similar to that expected for surface diffusion. High resoln. scanning electron microscope images from different specimens showed a porous microstructure of interconnected particles typical for initial sintering. Arrhenius plot of the grain size data revealed the activation energy of 161 ±11 kJ mol-1 for the growth process in agreement with those reported for grain boundary grooving expts. It was found that MgO particles undergo coarsening already at temps. as low as 0.31 of the MgO m.p. (3125 K). Increase in the particle diam. and decrease in the surface area were assocd. with surface diffusion mechanism that leads to initial sintering between the particles.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2sXpsFOrs7g%253D&md5=b4518b8554ce09b9274e98e11e5dadc1
  32. 32
    Aritani, H.; Yamada, H.; Nishio, T.; Shiono, T.; Imamura, S.; Kudo, M.; Hasegawa, S.; Tanaka, T.; Yoshida, S. Characterization of Li-Doped MgO Catalysts for Oxidative Coupling of Methane by Means of Mg K-Edge XANES. J. Phys. Chem. B 2000, 104, 10133– 10143,  DOI: 10.1021/jp000291y
    [ACS Full Text ACS Full Text], [CAS], Google Scholar
    32
    Characterization of Li-Doped MgO Catalysts for Oxidative Coupling of Methane by Means of Mg K-Edge XANES
    Aritani, Hirofumi; Yamada, Hiroyuki; Nishio, Takashi; Shiono, Takeshi; Imamura, Seiichiro; Kudo, Masataka; Hasegawa, Sadao; Tanaka, Tsunehiro; Yoshida, Satohiro
    Journal of Physical Chemistry B (2000), 104 (44), 10133-10143CODEN: JPCBFK; ISSN:1089-5647. (American Chemical Society)
    To characterize active defect sites in the near-surface and bulk phase of MgO in Li-doped MgO, structural analyses were carried out by means of XRD, XPS, Mg K-edge XANES, and SEM techniques. For Li-MgO calcined at 873 K, Li doping at a low content (2.5 wt % as Li) brings about the formation of defect species only in the near-surface, which is due to the localization of doped Li ions in the surface. In this case, the catalytic species contg. a Li+-O- center exists in the surface region. At higher contents of more than 7.5 wt %, Li ions penetrate the MgO bulk, and its crystallinity decreases. The defect species possibly exist in the bulk phase. After oxidative coupling of methane reaction, the defect species are formed in the near-surface over MgO and Li-MgO. However, the C2 selectivity is much higher on Li-MgO than on MgO. It is concluded that the defect species contg. Li+-O- in both surface and bulk can act as the active species for producing C2 compds. with high selectivity.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3cXntlKgurw%253D&md5=240385a1df9f596b0b0b5bbc4a687d6f
  33. 33
    Klysubun, W.; Kidkhunthod, P.; Tarawarakarn, P.; Sombunchoo, P.; Kongmark, C.; Limpijumnong, S.; Rujirawat, S.; Yimnirun, R.; Tumcharern, G.; Faungnawakij, K. SUT-NANOTEC-SLRI Beamline for X-ray Absorption Spectroscopy. J. Synchr. Rad. 2017, 24, 707– 716,  DOI: 10.1107/S1600577517004830
    [Crossref], [PubMed], Google Scholar
    There is no corresponding record for this reference.
  34. 34
    Singh, J.; Kumar, M.; Lee, I.-J.; Chae, K. X-ray Reflectivity and Near Edge X-ray Absorption Fine Structure Investigations of MgO Thin Films. Appl. Sci. Lett. 2017, 3.
    Google Scholar
    There is no corresponding record for this reference.
  35. 35
    Yoshioka, S.; Tsuruta, K.; Yamamoto, T.; Yasuda, K.; Matsumura, S.; Ishikawa, N.; Kobayashi, E. X-ray Absorption Near Edge Structure and First-Principles Spectral Investigations of Cationic Disorder in MgAl2O4 Induced by Swift Heavy Ions. Phys. Chem. Chem. Phys. 2018, 20, 4962– 4969,  DOI: 10.1039/C7CP07591J
    [Crossref], [PubMed], [CAS], Google Scholar
    35
    X-ray absorption near edge structure and first-principles spectral investigations of cationic disorder in MgAl2O4 induced by swift heavy ions
    Yoshioka, S.; Tsuruta, K.; Yamamoto, T.; Yasuda, K.; Matsumura, S.; Ishikawa, N.; Kobayashi, E.
    Physical Chemistry Chemical Physics (2018), 20 (7), 4962-4969CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
    Cationic disorder in the MgAl2O4 spinel induced by swift heavy ions was investigated using the X-ray absorption near edge structure. With changes in the irradn. fluences of 200 MeV Xe ions, the Mg K-edge and Al K-edge spectra were synchronously changed. The calcd. spectra based on d. function theory indicate that the change in the exptl. spectra was due to cationic disorder between Mg in tetrahedral sites and Al in octahedral sites. These results suggest a high inversion degree to an extent that the completely random configuration is achieved in MgAl2O4 induced by the high d. electronic excitation under swift heavy ion irradn.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXitFOqsr8%253D&md5=85adb764971b46b118dafa1bfb9f04d6
  36. 36
    Witte, K.; Streeck, C.; Mantouvalou, I.; Suchkova, S. A.; Lokstein, H.; Grötzsch, D.; Martyanov, W.; Weser, J.; Kanngieer, B.; Beckhoff, B.; Stiel, H. Magnesium K-Edge NEXAFS Spectroscopy of Chlorophyll A in Solution. J. Phys. Chem. B 2016, 120, 11619– 11627,  DOI: 10.1021/acs.jpcb.6b05791
    [ACS Full Text ACS Full Text], [CAS], Google Scholar
    36
    Magnesium K-Edge NEXAFS Spectroscopy of Chlorophyll a in Solution
    Witte, Katharina; Streeck, Cornelia; Mantouvalou, Ioanna; Suchkova, Svetlana A.; Lokstein, Heiko; Groetzsch, Daniel; Martyanov, Wjatscheslav; Weser, Jan; Kanngiesser, Birgit; Beckhoff, Burkhard; Stiel, Holger
    Journal of Physical Chemistry B (2016), 120 (45), 11619-11627CODEN: JPCBFK; ISSN:1520-5207. (American Chemical Society)
    The interaction of the central magnesium atom of chlorophyll a (Chl a) with its carbon and nitrogen backbone was investigated by magnesium (Mg) K near edge x-ray absorption fine structure (NEXAFS) spectroscopy in fluorescence detection mode. Chl a was measured as 1*10-2 mol/l ethanol soln., which represents an upper limit of concn. without aggregation and as dried droplets. For the first time, the investigation of the structure of Chl a in a liq. environment by means of x-ray absorption spectroscopy is demonstrated. A preedge feature in the dissolved as well as in dried Chl a NEXFAS spectra has been identified as a characteristic transition originating from the intact Chl a mol. This result is confirmed by theor. DFT calcns. leading to MOs (MO) which are mainly situated on the magnesium atom and nitrogen and carbon atoms from the pyrrole rings. The description is the first referring to the MO distribution with respect to the central Mg ion of Chl a and the surrounding atoms. Based there upon, new approaches for the investigations of dynamic processes of mols. in soln. and the structure-function relationships of photosynthetic pigments and pigment-protein complexes in their native environment can be developed.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhslCktrbM&md5=710f7e8c001b79ec3a236b2957bef4d9
  37. 37
    Joly, Y. X-ray Absorption Near-Edge Structure Calculations Beyond the Muffin-Tin Approximation. Phys. Rev. B 2001, 63, 125120,  DOI: 10.1103/PhysRevB.63.125120
    [Crossref], [CAS], Google Scholar
    37
    x-ray absorption near-edge structure calculations beyond the muffin-tin approximation
    Joly, Y.
    Physical Review B: Condensed Matter and Materials Physics (2001), 63 (12), 125120/1-125120/10CODEN: PRBMDO; ISSN:0163-1829. (American Physical Society)
    A new scheme for calcg. the x-ray absorption near edge structure (XANES) based on the finite-difference method is proposed. It allows completely free potential shape and, in particular, is not constrained to the muffin-tin approxn. In approach, the calcn. of the final states is performed in real space. The Schrodinger equation is solved in a discrete form on the node points of a 3-dimensional grid. The unknowns are the values of the wave functions at the grid points. The validity of the method is shown on 2 different systems the metallic Cu and the CO mol.; then, the differences resulting from muffin-tin and non-muffin-tin calcns. are shown on different typical mols.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3MXhvV2qtrY%253D&md5=ff7c161f8eaa60274bd434cb6de6ea97
  38. 38
    Bunău, O.; Joly, Y. Self-Consistent Aspects of X-ray Absorption Calculations. J. Phys: Condens. Matter 2009, 21, 345501
    [Crossref], [PubMed], [CAS], Google Scholar
    38
    Self-consistent aspects of X-ray absorption calculations
    Bunau, O.; Joly, Y.
    Journal of Physics: Condensed Matter (2009), 21 (34), 345501/1-345501/11CODEN: JCOMEL; ISSN:0953-8984. (Institute of Physics Publishing)
    We implemented a self-consistent, real-space x-ray absorption calcn. within the FDMNES code. We performed the self-consistency within several schemes and identified which one is the most appropriate. We show a method that allows a rigorous setting of the Fermi level and thus an estn. of the energy cutoff for the identification and elimination of the occupied states. We investigated what are the structures where one can afford performing the self-consistent calcn. at a lesser cluster radius than the absorption one. We exemplify the effects of the self-consistency at the K-edge and for several ref. cases, including the copper Cu and the rutile TiO2. We verified the robustness of our procedure on the transitional 3d and 4d elements. Although amelioration can be noticed, the self-consistency performed at the K-edge does not bring a major improvement of the calcd. spectra. Taking into consideration a non-self-consistent, non-spherical potential gives better results than a self-consistent muffin-tin approxn. calcn.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXhtFCht77N&md5=ac5e837f05c62e7d8b5859f68768ef0f
  39. 39
    Guda, S. A.; Guda, A. A.; Soldatov, M. A.; Lomachenko, K. A.; Bugaev, A. L.; Lamberti, C.; Gawelda, W.; Bressler, C.; Smolentsev, G.; Soldatov, A. V.; Joly, Y. Optimized Finite Difference Method for the Full-Potential XANES Simulations: Application to Molecular Adsorption Geometries in MOFs and Metal-Ligand Intersystem Crossing Transients. J. Chem. Th. Comp. 2015, 11, 4512– 4521,  DOI: 10.1021/acs.jctc.5b00327
    [ACS Full Text ACS Full Text], Google Scholar
    There is no corresponding record for this reference.
  40. 40
    Pankin, I.; Borfecchia, E.; Martini, A.; Lomachenko, K.; Lamberti, C.; Soldatov, A. DFT-assisted XANES Simulations to Discriminate Different Monomeric CuII Species in CHA Catalysts. Radiat. Phys. Chem. 2020, 175, 108510,  DOI: 10.1016/j.radphyschem.2019.108510
    [Crossref], [CAS], Google Scholar
    40
    DFT-assisted XANES simulations to discriminate different monomeric CuII species in CHA catalysts
    Pankin, I. A.; Borfecchia, E.; Martini, A.; Lomachenko, K. A.; Lamberti, C.; Soldatov, A. V.
    Radiation Physics and Chemistry (2020), 175 (), 108510CODEN: RPCHDM; ISSN:0969-806X. (Elsevier B.V.)
    Herein, we present Cu K-edge XANES (X-ray Absorption Near Edge Structure) simulations for different framework interacting Z-CuII species proposed to form as an active site after high-temp. activation in Cu-exchanged chabazite zeolites, representing promising materials for selective catalytic redn. of NOx in the presence of ammonia and direct conversion of methane to methanol. We critically compare the simulated spectra to previously collected data for an O2-activated Cu-chabazite sample. D. of states (DOS) calcns. allow us to get more insights in describing the nature of XANES features obsd. in the simulated spectra. To demonstrate the potential of the method, we finally explore the impact of systematic variations of selected structural parameters on the theor. XANES features.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhvFOiur7M&md5=8e2bf422a7e8a40e85ef945375cdc85b
  41. 41
    Amodeo, J.; Merkel, S.; Tromas, C.; Carrez, P.; Korte-Kerzel, S.; Cordier, P.; Chevalier, J. Dislocations and Plastic Deformation in MgO Crystals: A Review. Crystals 2018, 8, 240 DOI: 10.3390/cryst8060240
    [Crossref], [CAS], Google Scholar
    41
    Dislocations and plastic deformation in MgO crystals: a review
    Amodeo, Jonathan; Merkel, Sebastien; Tromas, Christophe; Carrez, Philippe; Korte-Kerzel, Sandra; Cordier, Patrick; Chevalier, Jerome
    Crystals (2018), 8 (6), 240/1-240/53CODEN: CRYSBC; ISSN:2073-4352. (MDPI AG)
    This review paper focuses on dislocations and plastic deformation in magnesium oxide crystals. MgO is an archetype ionic ceramic with refractory properties which is of interest in several fields of applications such as ceramic materials fabrication, nano-scale engineering and Earth sciences. In its bulk single crystal shape, MgO can deform up to few percent plastic strain due to dislocation plasticity processes that strongly depend on external parameters such as pressure, temp., strain rate, or crystal size. This review describes how a combined approach of macro-mech. tests, multi-scale modeling, nano-mech. tests, and high pressure expts. and simulations have progressively helped to improve our understanding of MgO mech. behavior and elementary dislocation-based processes under stress.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXhvVWktLrK&md5=9e9aff857cf211adcc7067dbe0132009
  42. 42
    Becke, A. D. A New Mixing of Hartree-Fock and Local Density Functional Theories. J. Chem. Phys. 1993, 98, 1372– 1377,  DOI: 10.1063/1.464304
    [Crossref], [CAS], Google Scholar
    42
    A new mixing of Hartree-Fock and local-density-functional theories
    Becke, Axel D.
    Journal of Chemical Physics (1993), 98 (2), 1372-7CODEN: JCPSA6; ISSN:0021-9606.
    Previous attempts to combine the Hartree-Fock theory with the local d.-functional theory were unsuccessful in applications to mol. bonding. A new coupling is presented of these two theories that maintains their simplicity and computational efficiency, and yet greatly improves their predictive power. Very encouraging results of tests on atomization energies, ionization potentials, and proton affinities are reported, and the potential for future development is discussed.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK3sXhtlagt7o%253D&md5=02a9289532197e7445af684bb29f4e11
  43. 43
    Lee, C.; Yang, W.; Parr, R. G. Development of the Colle-Salvetti Correlation-Energy Formula into a Functional of the Electron Density. Phys. Rev. B 1988, 37, 785– 789,  DOI: 10.1103/PhysRevB.37.785
    [Crossref], [PubMed], [CAS], Google Scholar
    43
    Development of the Colle-Salvetti correlation-energy formula into a functional of the electron density
    Lee, Chengteh; Yang, Weitao; Parr, Robert G.
    Physical Review B: Condensed Matter and Materials Physics (1988), 37 (2), 785-9CODEN: PRBMDO; ISSN:0163-1829.
    A correlation-energy formula due to R. Colle and D. Salvetti (1975), in which the correlation energy d. is expressed in terms of the electron d. and a Laplacian of the 2nd-order Hartree-Fock d. matrix, is restated as a formula involving the d. and local kinetic-energy d. On insertion of gradient expansions for the local kinetic-energy d., d.-functional formulas for the correlation energy and correlation potential are then obtained. Through numerical calcns. on a no. of atoms, pos. ions, and mols., of both open- and closed-shell type, it is demonstrated that these formulas, like the original Colle-Salvetti formulas, give correlation energies within a few percent.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL1cXktFWrtbw%253D&md5=ee7b59267a2ff72e15171a481819ccf8
  44. 44
    Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H. P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Montgomery, J. A., Jr.; Peralta, J. E.; Ogliaro, F.; Bearpark, M.; Heyd, J. J.; Brothers, E.; Kudin, K. N.; Staroverov, V. N.; Kobayashi, R.; Normand, J.; Raghavachari, K.; Rendell, A.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Rega, N.; Millam, J. M.; Klene, M.; Knox, J. E.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Martin, R. L.; Morokuma, K.; Zakrzewski, V. G.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Dapprich, S.; Daniels, A. D.; Farkas, Ã.; Foresman, J. B.; Ortiz, J. V.; Cioslowski, J.; Fox, D. J. Gaussian 09 , Revision A.02, 2009.
    Google Scholar
    There is no corresponding record for this reference.
  45. 45
    Pye, C. C.; Rudolph, W. W. An Ab Initio and Raman Investigation of Magnesium(II) Hydration. J. Phys. Chem. A 1998, 102, 9933– 9943,  DOI: 10.1021/jp982709m
    [ACS Full Text ACS Full Text], [CAS], Google Scholar
    45
    An ab Initio and Raman Investigation of Magnesium(II) Hydration
    Pye, Cory C.; Rudolph, W. W.
    Journal of Physical Chemistry A (1998), 102 (48), 9933-9943CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)
    The weak polarized Raman band assigned to the ν1-MgO6 mode of the hexaaquo Mg(II) ion was studied over the temp. range 25 to 125°. The 356 cm-1 stretching mode frequency decreases by ∼3 cm-1 but broadens by 13 cm-1 over a 100° temp. range. A depolarized mode at 235 cm-1 could be assigned to ν2. Probably the hexaaquo Mg(II) ion is thermodynamically stable in perchlorate and chloride solns. In sulfate solns., an equil. exists between the hexaaquo ion and an inner-sphere sulfato complex. Ab initio geometry optimizations of Mg(H2O)62+ were carried out at the Hartree-Fock and Moller-Plesset levels of theory, using various basis sets up to 6-31+G*. Frequency calcns. confirm that the Th structure is a min. The unscaled frequencies of the MgO6 unit are lower than the exptl. frequencies, and scaling only marginally improves the agreement. The theor. binding enthalpy for the hexaaquo Mg(II) ion accounts for ∼70% of the exptl. hydration energy of Mg(II). A comparison of 3 models for the 2nd hydration sphere is presented, and the most suitable is one of lower symmetry T, in which alternate faces of the MgO6 octahedron are H-bonded to H2O trimers. The unscaled Hartree-Fock frequencies agree very well with exptl. observations, giving nearly exact agreement with expt.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1cXntVKntrg%253D&md5=a8f8d76e99b18342f8a0bd0ef0789569
  46. 46
    Matwiyoff, N. A.; Taube, H. Direct Determination of the Solvation Number of Magnesium(II) ion in water, Aqueous Acetone, and Methanolic Acetone solutions. J. Am. Chem. Soc. 1968, 90, 2796– 2800,  DOI: 10.1021/ja01013a012
    [ACS Full Text ACS Full Text], [CAS], Google Scholar
    46
    Direct determination of the solvation number of magnesium(II) ion in water, aqueous acetone, and methanolic acetone solutions
    Matwiyoff, N. A.; Taube, H.
    Journal of the American Chemical Society (1968), 90 (11), 2796-800CODEN: JACSAT; ISSN:0002-7863.
    At temps. below -60°, the proton magnetic resonance (pmr) signals of the solvent mols. within the primary coordination sphere of the Mg2+ ion in aq. acetone, methanolic acetone, and concd. aq. solns. can be distinguished from those of the bulk solvent. From a comparison of the areas of the pmr lines of the solvent in the free and coordinated sites, the compn. of the primary solvation sphere of the Mg2+ ion in these solvents was Mg(MeOH)62+ in methanolic acetone and Mg(OH2)62+ in aq. acetone and H2O. The relative coalescence temps. of the coordinated and free solvent pmr signals indicate that the order of increasing lability of the complex ions in Mg(MeOH)62+ < Mg(OH2)62+ in aq. acetone < Mg-(OH2)62+ in H2O.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaF1cXktFegtb8%253D&md5=a2fd838ec5de7ecba4e9ef57295cc10f
  47. 47
    Skipper, N. T.; Neilson, G. W.; Cummings, S. C. An X-ray Diffraction Study of Ni(aq)2+ and Mg(aq)2+ by Difference Methods. J. Phys.: Condensed Matter 1989, 1, 3489– 3506
    [Crossref], [CAS], Google Scholar
    47
    An x-ray diffraction study of aquated nickel(2+) and magnesium(2+) by difference methods
    Skipper, N. T.; Neilson, G. W.; Cummings, S. C.
    Journal of Physics: Condensed Matter (1989), 1 (22), 3489-506CODEN: JCOMEL; ISSN:0953-8984.
    Difference methods of x-ray diffraction were used to study the microscopic structure around Ni[aq]2+ and Mg[aq]2+ in a variety of aq. solns. Ref. to the results of neutron diffraction expts. show that Ni[aq]2+ and Mg[aq]2+ can be regarded as structurally isomorphic species, thereby enabling the local ionic structure to be measured in terms of the cation-oxygen and cation-cation radial pair distribution functions. Results are included for the dependence of these functions on concn., counter-ion species and the interchange of light and heavy water as the solvent.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL1MXkvVCqtbw%253D&md5=9868673476f5d4809cd1dc087ad4b7f4
  48. 48
    Bernal-Uruchurtu, M. I.; Ortega-Blake, I. A Refined Monte Carlo Study of Mg2+ and Ca2+ Hydration. J. Chem. Phys. 1995, 103, 1588– 1598,  DOI: 10.1063/1.469781
    [Crossref], [CAS], Google Scholar
    48
    A refined Monte Carlo study of Mg2+ and Ca2+ hydration
    Bernal-Uruchurtu, M. I.; Ortega-Blake, I.
    Journal of Chemical Physics (1995), 103 (4), 1588-98CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)
    The interaction potential used includes polarization and non-additivity factors that have been reported to be crit. for the proper description of hydration. The effect of cell size, amt. of configurations needed to attain equil., and size of the statistical sample are studied. A microscopic anal. of the hydration shows that Mg2+ and its first shell can be considered as a supermol. embedded in the solvent. For Ca2+ this character is less marked and its first shell responds to the solvent more easily. The coordination properties of both ions are discussed. The differences in the coordination properties of both ions are due to a great extent to the differences in the water depletion zone beyond the first hydration shell. The contributions of each hydration shell to the total enthalpy of hydration are analyzed as well as the local densities related to the electrostriction.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK2MXntFWltbg%253D&md5=4800a4c0a1e7999d6eda6da12dd3e7dd
  49. 49
    Obst, S.; Bradaczek, H. Molecular Dynamics Study of the Structure and Dynamics of the Hydration Shell of Alkaline and Alkaline-Earth Metal Cations. J. Phys. Chem. 1996, 100, 15677– 15687,  DOI: 10.1021/jp961384b
    [ACS Full Text ACS Full Text], [CAS], Google Scholar
    49
    Molecular Dynamics Study of the Structure and Dynamics of the Hydration Shell of Alkali and Alkaline-Earth Metal Cations
    Obst, Stefan; Bradaczek, Hans
    Journal of Physical Chemistry (1996), 100 (39), 15677-15687CODEN: JPCHAX; ISSN:0022-3654. (American Chemical Society)
    Mol.-dynamics simulations of hydrated alkali and alk. earth metal cations at room temp. (T = 300 K) were carried out by using the CHARMM22 force field. Dynamic and static properties of systems contg. one ion and 123 or 525 water mols. were investigated by anal. of trajectories of 1 ns duration and compared to exptl. and theor. results. In addn., the size and the direction of the elementary motions of both the ions and the water mols. were investigated on the scale of the integration time step of 1 fs. Comparison between systems of different size revealed that for the larger system the diffusion coeff. and the no. of hydrogen bonds were increased. Radial pair distribution functions and coordination nos. are in good agreement with x-ray and neutron scattering data. The diffusion coeff. D of bulk TIP3P water in a system with 528 water mols. was by one-fourth higher than the exptl. value. Minor differences of approx. 10% between exptl. and simulated diffusion coeffs. were found for Li+, Na+, K+, and Mg2+. On the other hand, D was underestimated by the simulation for Ca2+ and Sr2+ by as much as 30%. On the av., 2.9 hydrogen bonds per bulk water mol. were found. The obsd. order of residence times for the monovalent ions, τ(Li+) > τ(Na+) > τ(K+), is in good agreement with the literature. Although τ was expected to increase with decreasing mass of the ion, the exchange of water mols. from the solvation shell of Mg2+ occurred much faster than for Ca2+.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK28XlsVWitbY%253D&md5=417f2edcd0ab07d163e630dad0af9cb3
  50. 50
    Tongraar, A.; Michael Rode, B. The Role of Non-Additive Contributions on the Hydration Shell Structure of Mg2+ Studied by Born-Oppenheimer Ab Initio Quantum Mechanical/Molecular Mechanical Molecular Dynamics Simulation. Chem. Phys. Lett. 2001, 346, 485– 491,  DOI: 10.1016/S0009-2614(01)00923-X
    [Crossref], [CAS], Google Scholar
    50
    The role of non-additive contributions on the hydration shell structure of Mg2+ studied by Born-Oppenheimer ab initio quantum mechanical/molecular mechanical molecular dynamics simulation
    Tongraar, A.; Michael Rode, B.
    Chemical Physics Letters (2001), 346 (5,6), 485-491CODEN: CHPLBC; ISSN:0009-2614. (Elsevier Science B.V.)
    An ab initio quantum mech./mol. mech. (QM/MM) mol. dynamics simulation has been performed to investigate the effects of non-additive contributions on the hydration shell structure of Mg2+. The active-site region, the sphere including the second hydration shell of Mg2+, was treated by Born-Oppenheimer ab initio quantum mechanics, while the rest is described by classical pair potentials. A hydration complex with six inner shell waters and 12 s shell waters was obsd. It was also found that the effects of non-additive terms play an important role in the preferential orientation of water mols. inside the hydration sphere of Mg2+.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3MXnsVegsbw%253D&md5=325dccd3d7ea9019dc8a32599842c597
  51. 51
    Tongraar, A.; Rode, B. M. Structural Arrangement and Dynamics of the Hydrated Mg2+: an Ab Initio QM/MM Molecular Dynamics Simulation. Chem. Phys. Lett. 2005, 409, 304– 309,  DOI: 10.1016/j.cplett.2005.04.062
    [Crossref], [CAS], Google Scholar
    51
    Structural arrangement and dynamics of the hydrated Mg2+: An ab initio QM/MM molecular dynamics simulation
    Tongraar, Anan; Rode, Bernd Michael
    Chemical Physics Letters (2005), 409 (4-6), 304-309CODEN: CHPLBC; ISSN:0009-2614. (Elsevier B.V.)
    The structural arrangement and dynamics of solvated Mg2+ in dil. aq. soln. have been studied by ab initio QM/MM mol. dynamics simulation, in which the whole first and most of the second hydration shell of the ion were treated at Hartree-Fock level using LANL2DZ basis sets. Besides the most stable Mg2+(H2O)6 species, intermediates such as Mg2+(H2O)5(H2O), where at least one water mol. temporarily moves into the inter-shell region but remains H-bonded to inner-shell water, as well as transition complexes of the Mg2+(H2O)6(H2O) type, exist in aq. soln. The dynamics of solvate and surrounding water mols. are discussed in connection to the structure-forming' ability of Mg2+.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2MXlt1GqsLo%253D&md5=eec92e744d82f634b28e421a2cb33f72
  52. 52
    Dudev, T.; Lim, C. Incremental Binding Free Energies in Mg2+ Complexes: A DFT Study. J. Phys. Chem. A 1999, 103, 8093– 8100,  DOI: 10.1021/jp991575p
    [ACS Full Text ACS Full Text], [CAS], Google Scholar
    52
    Incremental Binding Free Energies in Mg2+ Complexes: A DFT Study
    Dudev, Todor; Lim, Carmay
    Journal of Physical Chemistry A (1999), 103 (40), 8093-8100CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)
    D. functional theory has been employed to evaluate the incremental binding energies, enthalpies, entropies, and free energies for the reactions of Mg2+ with water, methanol, formamide, and formate. The B3LYP/6-31+G* calcns. on the Mg2+ complexes show that the metal ion can accommodate no more than three neg. charged formates. For the neutral-ligand complexes, magnesium prefers to bind to methanol and formamide rather than water when the no. of ligands is less than four, but it prefers water to methanol and formamide for complexes with five or six ligands. These results have been rationalized in terms of steric crowding of the ligands around the metal ion and charge transfer from the ligand(s) to Mg2+. These two factors result in attenuation of the Mg-O bond distance and, hence, redn. in the electrostatic and polarization energies, which dominate the incremental binding energy. An empirical scheme, employing the incremental binding energies for Mg2+-single-type-ligand complexes, has been developed to accurately predict the total binding energy of Mg2+-mixed-ligand clusters.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1MXlvVGhs7w%253D&md5=4cb9ef20226ae5ca43dc2080db42737b
  53. 53
    D’Angelo, P.; Migliorati, V.; Sessa, F.; Mancini, G.; Persson, I. XANES Reveals the Flexible Nature of Hydrated Strontium in Aqueous Solution. J. Phys. Chem. B 2016, 120, 4114– 4124,  DOI: 10.1021/acs.jpcb.6b01054
    [ACS Full Text ACS Full Text], [CAS], Google Scholar
    53
    XANES Reveals the Flexible Nature of Hydrated Strontium in Aqueous Solution
    D'Angelo, Paola; Migliorati, Valentina; Sessa, Francesco; Mancini, Giordano; Persson, Ingmar
    Journal of Physical Chemistry B (2016), 120 (17), 4114-4124CODEN: JPCBFK; ISSN:1520-5207. (American Chemical Society)
    X-ray absorption near-edge structure (XANES) spectroscopy has been used to det. the structure of the hydrated strontium in aq. soln. The XANES anal. has been carried out using solid [Sr(H2O)8](OH)2 as ref. model. Classical and Car-Parrinello mol. dynamics (MD) simulations have been carried out and in the former case two different sets of Lennard-Jones parameters have been used for the Sr2+ ion. The best performing theor. approach has been chosen on the basis of the exptl. results. XANES spectra have been calcd. starting from MD trajectories, without carrying out any minimization of the structural parameters. This procedure allowed us to properly account for thermal and structural fluctuations occurring in the aq. soln. in the anal. of the exptl. spectrum. A deconvolution procedure has been applied to the raw absorption data thus increasing the sensitivity of XANES spectroscopy. One of the classical MD simulations has been found to provide a XANES theor. spectrum in better agreement with the exptl. data. An 8-fold hydration complex with a Sr-O distance of 2.60 Å has been found to be compatible with the XANES data, in agreement with previous findings. However, the hydration shells of the strontium ions have been found to have a flexible nature with a fast ligand exchange rate between the first and second hydration shell occurring in the picosecond time scale.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XlvVyqt7o%253D&md5=7bf9ff7a97f8f2e807c1d8745ed1d9dd
  54. 54
    Spezia, R.; Duvail, M.; Vitorge, P.; Cartailler, T.; Tortajada, J.; D’Angelo, P.; Gaigeot, M.-P.; Chillemi, G. A Coupled Car-Parrinello Molecular Dynamics and EXAFS Data Analysis Investigation of Aqueous Co2+. J. Phys. Chem. A 2006, 110, 13081– 13088,  DOI: 10.1021/jp064688z
    [ACS Full Text ACS Full Text], [CAS], Google Scholar
    54
    A Coupled Car-Parrinello Molecular Dynamics and EXAFS Data Analysis Investigation of Aqueous Co2+
    Spezia, Riccardo; Duvail, Magali; Vitorge, Pierre; Cartailler, Thierry; Tortajada, Jeanine; Chillemi, Giovanni; D'Angelo, Paola; Gaigeot, Marie-Pierre
    Journal of Physical Chemistry A (2006), 110 (48), 13081-13088CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)
    We have studied the microscopic solvation structure of Co2+ in liq. water by means of d. functional theory (DFT)-based Car-Parrinello mol. dynamics (CPMD) simulations and extended X-ray absorption fine structure (EXAFS) data anal. The effect of the no. of explicit water mols. in the simulation box on the first and second hydration shell structures has been considered. Classical mol. dynamics simulations, using an effective two-body potential for Co2+-water interactions, were also performed to show box size effects in a larger range. We have found that the no. of explicit solvent mols. has a marginal role on the first solvation shell structural parameters, whereas larger boxes may be necessary to provide a better description of the second solvation shell. Car-Parrinello simulations were detd. to provide a reliable description of structural and dynamical properties of Co2+ in liq. water. In particular, they seem to describe both the first and second hydration shells correctly. The EXAFS signal was reconstructed from Car-Parrinello simulations. Good agreement between the theor. and exptl. signals was obsd., thus strengthening the microscopic picture of the Co2+ solvation properties obtained using first-principle simulations.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD28XhtFyntbfF&md5=a2ecd4561da2a702035dc3d5be397682
  55. 55
    D’Angelo, P.; Roscioni, O. M.; Chillemi, G.; Della Longa, S.; Benfatto, M. Detection of Second Hydration Shells in Ionic Solutions by XANES: Computed Spectra for Ni2+ in Water Based on Molecular Dynamics. J. Am. Chem. Soc. 2006, 128, 1853– 1858,  DOI: 10.1021/ja0562503
    [ACS Full Text ACS Full Text], [CAS], Google Scholar
    55
    Detection of Second Hydration Shells in Ionic Solutions by XANES: Computed Spectra for Ni2+ in Water Based on Molecular Dynamics
    D'Angelo, Paola; Roscioni, Otello Maria; Chillemi, Giovanni; Della Longa, Stefano; Benfatto, Maurizio
    Journal of the American Chemical Society (2006), 128 (6), 1853-1858CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    A general procedure to compute X-ray absorption near-edge structure (XANES) spectra within multiple-scattering theory starting from mol. dynamics (MD) structural data has been developed and applied to the study of a Ni2+ aq. soln. This method allows one to perform a quant. anal. of the XANES spectra of disordered systems using a proper description of the thermal and structural fluctuations. The XANES spectrum of Ni2+ in aq. soln. has been calcd. using the structural information obtained from the MD simulations without carrying out any minimization in the structural parameter space. A very good reprodn. of the exptl. data was obtained including the second-shell water mols. in the calcn., thus showing that the second hydration shell provides a detectable contribution to the XANES spectra of ionic solns. The anal. including the first-shell cluster only permitted us to quant. det. the effect of disorder on the amplitude of the XANES spectra for mol. complexes. These results simultaneously confirm the reliability of the procedure and the structural results obtained from MD simulations. The combination of MD and XANES is found to be very helpful to get important new insights into the quant. estn. of structural properties of disordered systems.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD28XntFCmtA%253D%253D&md5=6823dd3bb542c0e84bb5b780c98b1757
  56. 56
    Radnai, T.; Kálmán, E.; Pollmer, K. X-Ray Diffraction Study of MgCl2 in Methanol. Zeitschrift fu̅r Naturforschung A 1984, 39, 464– 470,  DOI: 10.1515/zna-1984-0508
    [Crossref], [CAS], Google Scholar
    56
    X-ray diffraction study of magnesium chloride in methanol
    Radnai, T.; Kalman, E.; Pollmer, K.
    Zeitschrift fuer Naturforschung, Teil A: Physik, Physikalische Chemie, Kosmophysik (1984), 39A (5), 464-70CODEN: ZTAKDZ; ISSN:0340-4811.
    The structure of a concd. soln. of MgCl2 in methanol was studied by x-ray diffraction. The parameters for the ion-solvent interactions agree with those found in aq. solns. Both for Mg2+ and Cl-, the solvate shells are composed of 6 methanol mols. An av. octahedral arrangement of OH groups in the solvate shells of magnesium is probable. Octahedral sym. positions for CH3 groups proved to be unlikely.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL2cXkt12htLs%253D&md5=5f05e8b195bac6e674dee230b0212c8a
  57. 57
    Nakamura, S.; Meiboom, S. Proton Magnetic Resonance Studies of the Solvation Shell of Mg2+ in Methanol. Solvation Number and Exchange Rate. J. Am. Chem. Soc. 1967, 89, 1765– 1772,  DOI: 10.1021/ja00984a001
    [ACS Full Text ACS Full Text], [CAS], Google Scholar
    57
    Proton magnetic resonance studies of the solvation shell of magnesium(II) in methanol. Solvation number and exchange rate
    Nakamura, Shuzo; Meiboom, Saul
    Journal of the American Chemical Society (1967), 89 (8), 1765-72CODEN: JACSAT; ISSN:0002-7863.
    The exchange rate of MeOH mols. in the solvation shell of Mg++ in acidic anhyd. MeOH was detd. between -50 and 35° from the broadening of OH proton magnetic resonance signals of the free and bound MeOH. The CH3 signal of the coordinated MeOH, which was hidden behind the bulk CH3 line, can be observed by the addn. of Cu++ to the soln. From the temp. behavior of this signal, it can be concluded that ligand exchange, rather than simple OH-proton exchange, is the dominant process under the conditions of the expt. The first-order rate const. and activation parameters at 25° are: k = 4.7 × 103/sec., ΔH⧺ = 16.7 kcal mole-1, and ΔS⧺ = 14 entropy units. From relative intensity measurements of the signals at -80 and -19.2°, the solvation no. of the Mg++ was calcd. to be 6. Similar expts. with Li, Ca, Sr, and Ba perchlorates failed to show a sep. solvation-shell signal down to -110°. For these ions ligand exchange is apparently rapid down to that temp.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaF2sXht1SlsLg%253D&md5=330bf7c66f4ca1f0483fd94cd6ed560c
  58. 58
    Faralli, C.; Pagliai, M.; Cardini, G.; Schettino, V. Ab Initio Molecular Dynamics Study of Mg2+ and Ca2+ Ions in Liquid Methanol. J. Chem. Th. Comp. 2008, 4, 156– 163,  DOI: 10.1021/ct700209v
    [ACS Full Text ACS Full Text], [CAS], Google Scholar
    58
    Ab Initio Molecular Dynamics Study of Mg2+ and Ca2+ Ions in Liquid Methanol
    Faralli, Cristian; Pagliai, Marco; Cardini, Gianni; Schettino, Vincenzo
    Journal of Chemical Theory and Computation (2008), 4 (1), 156-163CODEN: JCTCCE; ISSN:1549-9618. (American Chemical Society)
    Ab initio Car-Parrinello mol. dynamics simulations have been performed in order to investigate the solvation properties of Mg2+ and Ca2+ in fully deuterated methanol soln. to better understand polarization effects induced by the ions. Charge transfer and dipole moment calcns. have been performed to give more detailed insight on the role of the electronic reorganization and its effect on the first solvation shell stability. The perturbation of the methanol H-bond network has been investigated.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2sXhsVehtbjN&md5=2ffb1d3b67734d22cf4f24cd63cd8763

Cited By

This article is cited by 2 publications.

  1. Alessandro Tofoni, Francesco Tavani, Marco Vandone, Luca Braglia, Elisa Borfecchia, Paolo Ghigna, Dragos Costantin Stoian, Toni Grell, Sara Stolfi, Valentina Colombo, Paola D’Angelo. Full Spectroscopic Characterization of the Molecular Oxygen-Based Methane to Methanol Conversion over Open Fe(II) Sites in a Metal–Organic Framework. Journal of the American Chemical Society 2023, 145 (38) , 21040-21052. https://doi.org/10.1021/jacs.3c07216
  2. Francesco Tavani, Matteo Busato, Daniele Veclani, Luca Braglia, Silvia Mauri, Piero Torelli, Paola D’Angelo. Investigating the High-Temperature Water/MgCl2 Interface through Ambient Pressure Soft X-ray Absorption Spectroscopy. ACS Applied Materials & Interfaces 2023, 15 (21) , 26166-26174. https://doi.org/10.1021/acsami.3c02985
Download PDF

  • Abstract

    High Resolution Image
    Download MS PowerPoint Slide

    Figure 1

    Figure 1. Evolution of the operando Mg K-edge AP-NEXAFS spectra upon MgO exposure to water (a) and methanol (b). Constant energy cuts are drawn at 1305.7 eV (yellow dotted lines) and at 1310.2 eV (gray dotted lines). The spectral scans recorded during the flux of water and methanol at 50 °C and during the subsequent flux interruption and temperature increase up to 250 °C are highlighted using green and purple backgrounds, respectively. In both panels, the AP-NEXAFS spectra recorded before the surface exposure to the given flux and at the temperature of 250 °C after flux interruption are evidenced in bold black lines.

    High Resolution Image
    Download MS PowerPoint Slide

    Figure 2

    Figure 2. (a) Intensity variation at 1305.7 eV (full yellow line) and at 1310.2 eV (full gray line) of the operando Mg K-edge XAS spectra measured upon MgO exposure to water vapor. The intensities of the starting XAS spectrum, of the XAS spectra recorded during the water flux at 50 °C, and of those measured during the water flux interruption and contemporary temperature increase are highlighted by black, green, and purple backgrounds, respectively. (b, c) Results of the decomposition of the Mg K-edge spectra. Extracted concentration profiles and Mg K-edge NEXAFS spectra (panels b and c, respectively). (d) Comparison between the NEXAFS spectrum of the Mg2+ intermediate species arising upon exposure of the MgO surface to water and the theoretical average Mg K-edge NEXAFS spectrum resulting from 500 MD snapshots of the fully hydrated Mg2+ ion (full indigo line).

    High Resolution Image
    Download MS PowerPoint Slide

    Figure 3

    Figure 3. Theoretical NEXAFS spectra (gray full lines) calculated from 500 MD snapshots of the Mg2+ ion in water at 50 °C and converged NEXAFS average (blue full line) of the 500 spectra (a) along with a selection of average NEXAFS spectra calculated with a variable number (N) of spectra (b). The associated evolutions of the total absolute differences between averages of spectra computed with increasing N values are shown in the insets of panel b. SN and SN* are the averages of N and N* spectra, respectively, with N* immediately preceding the given value of N in the evaluated sequence (e.g., N* = 250 if N = 500).

    High Resolution Image
    Download MS PowerPoint Slide

    Figure 4

    Figure 4. (a) Intensity variation at 1305.7 eV (full yellow line) and at 1310.2 eV (full gray line) of the operando Mg K-edge XAS spectra measured upon MgO exposure to methanol vapor. The intensities of the starting XAS spectrum, of the XAS spectra recorded during the methanol flux at 50 °C, and of those measured during the methanol flux interruption and contemporary temperature increase are highlighted by black, green, and purple backgrounds, respectively. (b, c) Results of the decomposition of the Mg K-edge spectroscopic data. Extracted concentration and Mg K-edge NEXAFS spectral profiles (panels b and c, respectively). (d) Comparison between the MCR-extracted AP-NEXAFS spectral component of the Mg2+ intermediate species arising upon exposure of the MgO surface to methanol and the theoretical average Mg K-edge NEXAFS spectrum resulting from 500 MD snapshots of the Mg2+ ion fully solvated by methanol molecules (full indigo line).

    High Resolution Image
    Download MS PowerPoint Slide

    Figure 5

    Figure 5. Pictorial representation of the main findings presented in this work, where it is evidenced that at 50 °C, a temperature-favored reversible hydration/solvation of Mg2+ ions occurs at the MgO surface, upon its sequential exposure to water (left) and methanol (right).

    High Resolution Image
    Download MS PowerPoint Slide

  • References

    ARTICLE SECTIONS
    Jump To

    This article references 58 other publications.

    1. 1
      Groß, A. Reactions at Surfaces studied by Ab Initio Dynamics Calculations. Surf. Sci. Rep. 1998, 32, 291– 340,  DOI: 10.1016/S0167-5729(98)00008-9
      [Crossref], [CAS], Google Scholar
      1
      Reactions at surfaces studied by ab initio dynamics calculations
      Gross, Axel
      Surface Science Reports (1998), 32 (8), 291-340CODEN: SSREDI; ISSN:0167-5729. (Elsevier Science B.V.)
      Owing to the development of efficient algorithms and the improvement of computer power it is now possible to map out potential energy surfaces (PESs) of reactions at surfaces in great detail. This achievement has been accompanied by an increased effort in the dynamical simulation of processes on surfaces. The paradigm for simple reactions at surfaces - the dissocn. of hydrogen on metal surfaces - can now be treated fully quantum dynamically in the mol. degrees of freedom from first principles, i.e., without invoking any adjustable parameters. This relatively new field of ab initio dynamics simulations of reactions at surfaces will be reviewed. Mainly the dissocn. of hydrogen on clean and adsorbate covered metal surfaces and on semiconductor surfaces will be discussed. In addn., the ab initio mol. dynamics treatment of reactions of hydrogen atoms with hydrogen-passivated semiconductor surfaces and recent achievements in the ab initio description of laser-induced desorption and further developments will be addressed.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1cXnslOlt7s%253D&md5=4ccff3cf607d429f040a37d427fc1772
    2. 2
      Brown, G. E.; Henrich, V. E.; Casey, W. H.; Clark, D. L.; Eggleston, C.; Felmy, A.; Goodman, D. W.; Grätzel, M.; Maciel, G.; McCarthy, M. I.; Nealson, K. H.; Sverjensky, D. A.; Toney, M. F.; Zachara, J. M. Metal Oxide Surfaces and Their Interactions with Aqueous Solutions and Microbial Organisms. Chem. Rev. 1999, 99, 77– 174,  DOI: 10.1021/cr980011z
      [ACS Full Text ACS Full Text], [CAS], Google Scholar
      2
      Metal Oxide Surfaces and Their Interactions with Aqueous Solutions and Microbial Organisms
      Brown, Gordon E., Jr.; Henrich, Victor E.; Casey, William H.; Clark, David L.; Eggleston, Carrick; Felmy, Andrew; Goodman, D. Wayne; Graetzel, Michael; Maciel, Gary; McCarthy, Maureen I.; Nealson, Kenneth H.; Sverjensky, Dimitri A.; Toney, Michael F.; Zachara, John M.
      Chemical Reviews (Washington, D. C.) (1999), 99 (1), 77-174CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
      A review with 825 refs. concerning the state of knowledge of metal oxide surfaces and their interactions with aq. solns. and microorganisms highlighting scientific and technol. contexts where this knowledge is needed and evaluating exptl. and theor. techniques needed to obtain the necessary information is given. Topics discussed include: characterization of clean metal oxide surfaces; water vapor-metal oxide interactions; aq. soln.-metal oxide interfaces; dissoln. and growth of metal (hydr)oxides; biotic processes in metal oxide surface chem.; theory; and challenges and future directions.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1cXotFaju78%253D&md5=ca7dd477811849283f4096ab04e025ab
    3. 3
      Carrasco, E.; Brown, M. A.; Sterrer, M.; Freund, H.-J.; Kwapien, K.; Sierka, M.; Sauer, J. Thickness-Dependent Hydroxylation of MgO(001) Thin Films. J. Phys. Chem. C 2010, 114, 18207– 18214,  DOI: 10.1021/jp105294e
      [ACS Full Text ACS Full Text], [CAS], Google Scholar
      3
      Thickness-Dependent Hydroxylation of MgO(001) Thin Films
      Carrasco, Esther; Brown, Matthew A.; Sterrer, Martin; Freund, Hans-Joachim; Kwapien, Karolina; Sierka, Marek; Sauer, Joachim
      Journal of Physical Chemistry C (2010), 114 (42), 18207-18214CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
      Hydroxylation of MgO surfaces has been studied from UHV to mbar pressure for MgO(001) films of different thickness grown on Ag(001) by XPS, IR reflection absorption spectroscopy, and d. functional theory calcns. In agreement with earlier studies on MgO(001) single crystals, a threshold water pressure on the order of 10-4 mbar is found for extensive hydroxylation of thick, bulklike MgO films. Decreasing the MgO film thickness shifts the threshold pressure to lower values, being 10-6 mbar in the limit of 2 monolayer MgO(001)/Ag(001). This result is explained on the basis of the precursor state of periclase MgO(001) dissoln. involving hydrolysis of Mg-O surface bonds. The enhanced structural flexibility (polaronic distortion) of the ultrathin MgO film facilitates surface hydroxylation by lowering the barrier for hydrolysis.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXht1CmtL7P&md5=0d1dc8c024d2ff8094da7e1e9df6aa70
    4. 4
      Verdaguer, A.; Sacha, G. M.; Bluhm, H.; Salmeron, M. Molecular Structure of Water at Interfaces: Wetting at the Nanometer Scale. Chem. Rev. 2006, 106, 1478– 1510,  DOI: 10.1021/cr040376l
      [ACS Full Text ACS Full Text], [CAS], Google Scholar
      4
      Molecular structure of water at interfaces: Wetting at the nanometer scale
      Verdaguer, A.; Sacha, G. M.; Bluhm, H.; Salmeron, M.
      Chemical Reviews (Washington, DC, United States) (2006), 106 (4), 1478-1510CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
      A review. A review on recent studies on the structure and growth of water films at interfaces. The structure of water films at cryogenic temps. and at ambient conditions, water/vapor interface, water confined between flat mica surfaces, anal. of the layering structure of water using at. force microscopy, water layers on metals, structure of the water monolayer, and the effect of elec. fields on the formation of water necks are discussed.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD28XivFWmur4%253D&md5=61d2a5eeab518fc927018d85abca4ef7
    5. 5
      Ewing, G. E. Ambient Thin Film Water on Insulator Surfaces. Chem. Rev. 2006, 106, 1511– 1526,  DOI: 10.1021/cr040369x
      [ACS Full Text ACS Full Text], [CAS], Google Scholar
      5
      Ambient thin film water on insulator surfaces
      Ewing, George E.
      Chemical Reviews (Washington, DC, United States) (2006), 106 (4), 1511-1526CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
      A review. A review describes the methods for studying thin film water and their properties, and presents some insulator systems of ambient thin film water.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD28XivVemu78%253D&md5=c6e44bb864522e3dfee0bd70069c0c60
    6. 6
      Woodruff, D. P. Quantitative Structural Studies of Corundum and Rocksalt Oxide Surfaces. Chem. Rev. 2013, 113, 3863– 3886,  DOI: 10.1021/cr3002998
      [ACS Full Text ACS Full Text], [CAS], Google Scholar
      6
      Quantitative Structural Studies Of Corundum and Rocksalt Oxide Surfaces
      Woodruff, D. Phillip
      Chemical Reviews (Washington, DC, United States) (2013), 113 (6), 3863-3886CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
      A review. Topics discussed include: surface of corundum-phase solids such as aluminum oxide, chromium oxide, iron oxides, vanadium oxide and adsorbate structure; and rocksalt structure oxide surface such surface of magnesia and nickel oxide.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXktV2iug%253D%253D&md5=92a058e31a61539b4baad00b0e94b416
    7. 7
      Anderson, P. J.; Horlock, R. F.; Oliver, J. F. Interaction of Water with the Magnesium Oxide Surface. Trans. Faraday Soc. 1965, 61, 2754– 2762,  DOI: 10.1039/tf9656102754
      [Crossref], [CAS], Google Scholar
      7
      Interaction of water with the magnesium oxide surface
      Anderson, P. J.; Horlock, R. F.; Oliver, J. F.
      Transactions of the Faraday Society (1965), 61 (12), 2754-62CODEN: TFSOA4; ISSN:0014-7672.
      The study illustrates the complexities of the processes involved and the marked dependence upon the previous history of the oxide. Thus, MgO, prepd. by decompn. of the hydroxide at >300° and held at 300° in vacuo for >5 hrs., retains H2O corresponding to a surface coverage σ ∼0.08 mol/A.2 An addnl. 0.1 mol/A.2 is adsorbed at room temp. and a relative pressure of 0.01. Subsequent desorption by prolonged pumping at a series of temps. yields steady-state values. A discontinuity at 250° with σ ∼0.1 suggests the existence of 2 distinct forms of adsorbed H2O, tentatively regarded as chemisorption (above 250°) and a rather strongly bound physisorption which is not completely removed on pumping below 200°. The ease with which desorption is accomplished is markedly dependent on the time during which adsorbed H2O is present on the sample, suggesting a slow conversion at room temp. to a more strongly bound state. These expts. plus ir data allow the conclusion that a surface, not previously dehydrated, is covered with surface hydroxyl groups at ∼0.11 mol/A.2 Further adsorption is in the form of mol. H2O. This value of σ, corresponding to surface satn., indicates that the relevant surface is the (100) face. The simplest model for H2O chemisorption on this face suggests OH groups in 2 different configurations. Desorption would then occur by interaction of a pair of adjacent OH groups, one of each type. The ir detns. support this model.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaF28XkslOntA%253D%253D&md5=e4d82c4467ab9b0c1645bf64f46663cc
    8. 8
      Imad-Uddin Ahmed, S.; Perry, S. S.; El-Bjeirami, O. Desorption and Reaction of Water on MgO(100) Studied as a Function of Surface Preparation. J. Phys. Chem. B 2000, 104, 3343– 3348,  DOI: 10.1021/jp9934275
      [ACS Full Text ACS Full Text], Google Scholar
      There is no corresponding record for this reference.
    9. 9
      Johnson, M. A.; Stefanovich, E. V.; Truong, T. N.; Günster, J.; Goodman, D. W. Dissociation of Water at the MgO(100)–Water Interface: Comparison of Theory with Experiment. J. Phys. Chem. B 1999, 103, 3391– 3398,  DOI: 10.1021/jp983729r
      [ACS Full Text ACS Full Text], [CAS], Google Scholar
      9
      Dissociation of Water at the MgO(100)-Water Interface: Comparison of Theory with Experiment
      Johnson, Michael A.; Stefanovich, Eugene V.; Truong, Thanh N.; Guenster, Jens; Goodman, D. W.
      Journal of Physical Chemistry B (1999), 103 (17), 3391-3398CODEN: JPCBFK; ISSN:1089-5647. (American Chemical Society)
      Dissociative chemisorption of H2O at the MgO(100)-water interface has been investigated both exptl. and theor. In particular, metastable impact electron spectroscopy (MIES) was used to image the d. of occupied states on the MgO(100)/Mo(100) surface for various degrees of water exposure. After multilayer water desorption, spectral features typical of surface hydroxyls are present. To further study the possibility of dissociative chemisorption of water, a theor. and computational method called CECILIA (combined embedded cluster at the interface with liq. approach) was used to calc. the geometry, energetics, and electronic d. of states (DOS) for interfacial species. Consistent with expt., our theor. results predict that dissociative adsorption of H2O at the MgO(100)-water interface is energetically more favorable than mol. adsorption. The stabilization of charged OH- and H+ interface adsorbates is due to polarization of the surrounding solvent.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1MXit1Wjsrk%253D&md5=12f947a6a045f8f665a16fb37a551c67
    10. 10
      Giordano, L.; Goniakowski, J.; Suzanne, J. Partial Dissociation of Water Molecules in the (3 × 2) Water Monolayer Deposited on the MgO (100) Surface. Phys. Rev. Lett. 1998, 81, 1271– 1273,  DOI: 10.1103/PhysRevLett.81.1271
      [Crossref], [CAS], Google Scholar
      10
      Partial Dissociation of Water Molecules in the (3×2) Water Monolayer Deposited on the MgO(100) Surface
      Giordano, Livia; Goniakowski, Jacek; Suzanne, Jean
      Physical Review Letters (1998), 81 (6), 1271-1273CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)
      Using the ab initio total energy method based on the gradient-cor. local d. approxn. the authors have modeled the exptl. obsd. (3×2) H2O monolayer on the MgO (100) surface. The lateral interactions between the adsorbed H2O mols., the formation of H bonds, and the resulting strong dimerization of the adsorbate promote the dissocn. of 2 out of 6 H2O mols. in the surface unit cell. Although, on the theor. grounds, H2O dissocn. on a defective MgO surface was already reported, this is the 1st theor. evidence of H2O dissocn. on the perfect MgO (100) surface.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1cXltVSrtb8%253D&md5=14dae5836bf63c4e17600cbd6f7b2ead
    11. 11
      Odelius, M. Mixed Molecular and Dissociative Water Adsorption on MgO [100]. Phys. Rev. Lett. 1999, 82, 3919– 3922,  DOI: 10.1103/PhysRevLett.82.3919
      [Crossref], [CAS], Google Scholar
      11
      Mixed Molecular and Dissociative Water Adsorption on MgO[100]
      Odelius, Michael
      Physical Review Letters (1999), 82 (19), 3919-3922CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)
      First principles mol. dynamics (MD) simulations, of H2O adsorption on the MgO[100] surface, was performed to det. the mol. structure and chem. nature of the adsorbed H2O at varying coverage. Dissociative adsorption was stabilized by hydrogen bond donation from neighboring H2O mols. The dissocn. barrier had a strong dependence on coverage. Spontaneous dissocn. was obsd. in picosecond MD simulations >1/2 monolayer (ML) coverage. Ordered structures with c[3×2] symmetry were examd. at 2/3 and 1 ML coverage. The ordered c[3×2] phase consisted of a mixt. of dissocd. and mol. adsorbed mols.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1MXjtF2gtrs%253D&md5=2890380f637997c346c22aa1301dd82a
    12. 12
      Delle Site, L.; Alavi, A.; Lynden-Bell, R. M. The Structure and Spectroscopy of Monolayers of Water on MgO: an Ab Initio Study. J. Chem. Phys. 2000, 113, 3344– 3350,  DOI: 10.1063/1.1287276
      [Crossref], [CAS], Google Scholar
      12
      The structure and spectroscopy of monolayers of water on MgO. An ab initio study
      Delle Site, L.; Alavi, A.; Lynden-Bell, R. M.
      Journal of Chemical Physics (2000), 113 (8), 3344-3350CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)
      The structure and energetics of a monolayer of water on a perfect MgO substrate is investigated by ab initio calcns. Several min. in the potential energy surface were found including both physisorbed and chemisorbed states in which one third of the water mols. were dissocd. In the more stable of the physisorbed states, the water mols. were not all parallel to the surface, but some showed hydrogen bonding with surface O ions. Even in the physisorbed state, the geometry of these surface H-bonded water mols. were distorted relative to the bulk. One of the stable chemisorbed states was the same as that found in earlier work by Giordano et al. [Phys. Rev. Lett. 81, 1271 (1998)]. Two more stable chemisorbed structures were found in which strong H-bonds to the hydroxide ions in the water layer were formed. The existence of different min. appears to be the result of a subtle interplay between H-bonding between adsorbed species and with the surface oxide ions. Harmonic vibrational frequencies were detd. for both a chemisorbed and a physisorbed states and spectroscopic features which should discriminate between chemisorbed and physisorbed states are identified.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3cXlslKktrk%253D&md5=50a177670033a1d385bda8c4e545d3d0
    13. 13
      Jug, K.; Heidberg, B.; Bredow, T. Cyclic Cluster Study of Water Adsorption Structures on the MgO(100) Surface. Surf. Sci. 2007, 601, 1529– 1535,  DOI: 10.1016/j.susc.2006.12.092
      [Crossref], [CAS], Google Scholar
      13
      Cyclic cluster study of water adsorption structures on the MgO(100) surface
      Jug, Karl; Heidberg, Bettina; Bredow, Thomas
      Surface Science (2007), 601 (6), 1529-1535CODEN: SUSCAS; ISSN:0039-6028. (Elsevier B.V.)
      Cyclic cluster calcns. were performed with the quantum chem. method MSINDO to elucidate the relative stabilities of c(4 × 2), p(3 × 2) and (1 × 1) overlayer structures of water mols. on the MgO(1 0 0) surface. For the c(4 × 2) and p(3 × 2) structures both mol. adsorption and partially dissocd. adsorption were considered. In agreement with earlier theor. studies partial dissocn. was found to be more stable than mol. adsorption. For the c(4 × 2) structure both monolayer and double layer coverage were studied. Adsorption was found to be more stabilized with increasing degree of dissocn. until 50% of the water mols. were dissocd. In the case of 50% dissocd. water mols. we found that one quarter of the Mg atoms were pulled out of the MgO surface when surface relaxation was taken into account. A new structure for the fully dissocd. (1 × 1) water monolayer was found which is considerably more stable than previously studied arrangements. In all cases surface relaxation was found to be important. The most stable structures of c(4 × 2), p(3 × 2) and (1 × 1) symmetry have adsorption energies which differ by no more than 13 kJ/mol. This offers an explanation of phase transitions of overlayer structures found by expts. between 180 and 300 K.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2sXjtVWrurs%253D&md5=091d22ecfaa300a853eea461fbb9da88
    14. 14
      Lynden-Bell, R.; Delle Site, L.; Alavi, A. Structures of Adsorbed Water Layers on MgO: an Ab Initio Study. Surf. Sci. 2002, 496, L1– L6,  DOI: 10.1016/S0039-6028(01)01669-7
      [Crossref], [CAS], Google Scholar
      14
      Structures of adsorbed water layers on MgO. An ab initio study
      Lynden-Bell, R. M.; Delle Site, L.; Alavi, A.
      Surface Science (2002), 496 (1-2), L1-L6CODEN: SUSCAS; ISSN:0039-6028. (Elsevier Science B.V.)
      A systematic search using an ab initio d.-functional method was carried out for energy min. for a monolayer of water on MgO. Min. were sought in which one third of the water mols. were dissocd., and the obsd. p(3×2) symmetry satisfied. Six such min. were found, 3 of which are within 300kB per water mol. of the lowest energy structure. We also found a structure with a similar energy with (2×2) symmetry and half the water mols. dissocd. The structures are stabilized by the donation of 3 H-bonds to each hydroxide ion.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3MXptFCmsLo%253D&md5=299a663086409c99ffda792ee2003f9d
    15. 15
      Jug, K.; Heidberg, B.; Bredow, T. Molecular Dynamics Study of Water Adsorption Structures on the MgO(100) Surface. J. Phys. Chem. C 2007, 111, 6846– 6851,  DOI: 10.1021/jp067651n
      [ACS Full Text ACS Full Text], [CAS], Google Scholar
      15
      Molecular Dynamics Study of Water Adsorption Structures on the MgO(100) Surface
      Jug, Karl; Heidberg, Bettina; Bredow, Thomas
      Journal of Physical Chemistry C (2007), 111 (18), 6846-6851CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
      Semiempirical MSINDO calcns. were performed for the study of structure and stability of c(4 × 2), p(3 × 2), and (1 × 1) overlayers of H2O on the MgO(100) surface. Born-Oppenheimer mol. dynamics (MD) techniques were used to simulate the changes in the adsorption at 300 K compared to that at 0 K. A partially dissocd. double layer of the c(4 × 2) structure with coverage θ = 3/2 attacks the MgO surface at 300 K. The hydroxylated (1 × 1) overlayer structure appears to be equally aggressive toward the MgO surface at this temp. Nucleation for the process of Mg(OH)2 formation was also obsd.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2sXktFynt70%253D&md5=f4c597d9925f6bb7666a299035d1825b
    16. 16
      Ončák, M.; Włlodarczyk, R.; Sauer, J. Water on the MgO(001) Surface: Surface Reconstruction and Ion Solvation. J. Phys. Chem. Lett. 2015, 6, 2310– 2314,  DOI: 10.1021/acs.jpclett.5b00885
      [ACS Full Text ACS Full Text], [CAS], Google Scholar
      16
      Water on the MgO(001) Surface: Surface Reconstruction and Ion Solvation
      Oncak, Milan; Wlodarczyk, Radoslaw; Sauer, Joachim
      Journal of Physical Chemistry Letters (2015), 6 (12), 2310-2314CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)
      The interaction of water with the MgO(001) surface under ambient conditions is investigated by d. functional theory combined with statistical thermodn. For water loadings of more than one monolayer, we show that the std. structure model, a fully hydroxylated surface, needs to be revised. Reconstructed surfaces, involving hydrated/hydroxylated Mg2+ ions above the surface, are more stable. These findings provide a consistent picture for surface hydroxylation between low and high water coverage that is in agreement with available XPS data.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXps1akur8%253D&md5=0baf86910c00e2eae193468bf1a84639
    17. 17
      Akabayov, B.; Doonan, C. J.; Pickering, I. J.; George, G. N.; Sagi, I. Using Softer X-ray Absorption Spectroscopy to Probe Biological Systems. J. Synchr. Rad. 2005, 12, 392– 401,  DOI: 10.1107/S0909049505010150
      [Crossref], [PubMed], [CAS], Google Scholar
      17
      Using softer X-ray absorption spectroscopy to probe biological systems
      Akabayov, Barak; Doonan, Christian J.; Pickering, Ingrid J.; George, Graham N.; Sagi, Irit
      Journal of Synchrotron Radiation (2005), 12 (4), 392-401CODEN: JSYRES; ISSN:0909-0495. (Blackwell Publishing Ltd.)
      Many inorg. species are now recognized as being essential for life, including many forms of sulfur, phosphate and numerous classes of metal ions. For example, recent progress in the fields of biochem. and biol. has pointed out the crit. importance of sulfur in the biosynthesis of vital cofactors and active sites in proteins, and in the complex reaction mechanisms often involved. Special attention has also been drawn to the diverse roles of alk. (Na+, K+) and alk. earth (Mg2+, Ca2+) metal ions in mediating the activity of RNA, proteins and many processes in living cells. While the general effect of these ions in biol. is mostly understood, information on their detailed role is deficient. Here the application of softer x-ray absorption spectroscopy (XAS) to probe the local structural and electronic environment of such ions within their biol. complexes and during physiol. reactions is discussed. In addn., the required exptl. set-up and the difficulties assocd. with conducting softer XAS expts. on biol. samples are presented.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2MXltlCns7w%253D&md5=3a58ddbc51c9a6a125d72b7ba4ff0d43
    18. 18
      Capocasa, G.; Sessa, F.; Tavani, F.; Monte, M.; Olivo, G.; Pascarelli, S.; Lanzalunga, O.; Di Stefano, S.; D’Angelo, P. Coupled X-ray Absorption/UV-vis Monitoring of Fast Oxidation Reactions Involving a Nonheme Iron-Oxo Complex. J. Am. Chem. Soc. 2019, 141, 2299– 2304,  DOI: 10.1021/jacs.8b08687
      [ACS Full Text ACS Full Text], [CAS], Google Scholar
      18
      Coupled X-ray Absorption/UV-vis Monitoring of Fast Oxidation Reactions Involving a Nonheme Iron-Oxo Complex
      Capocasa, Giorgio; Sessa, Francesco; Tavani, Francesco; Monte, Manuel; Olivo, Giorgio; Pascarelli, Sakura; Lanzalunga, Osvaldo; Di Stefano, Stefano; D'Angelo, Paola
      Journal of the American Chemical Society (2019), 141 (6), 2299-2304CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      Time-resolved X-ray absorption (XAS) and UV-vis spectroscopies with millisecond resoln. are used simultaneously to investigate oxidn. reactions of org. substrates by nonheme iron activated species. In particular, the oxidn. processes of arylsulfides and benzyl alcs. by a nonheme iron-oxo complex have been studied. We show for the first time that the pseudo-first-order rate consts. of fast bimol. processes in soln. (milliseconds and above) can be detd. by time-resolved XAS technique. By following the Fe K-edge energy shift, it is possible to detect the rate of iron oxidn. state evolution that matches that of the bimol. reaction in soln. The kinetic const. values obtained by XAS are in perfect agreement with those obtained by means of the concomitant UV-vis detection. This combined approach has the potential to provide unique insights into reaction mechanisms in the liq. phase that involve changes of the oxidn. state of a metal center, and it is particularly useful in complex chem. systems where possible interferences from species present in soln. could make it impossible to use other detection techniques.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXht1ansr4%253D&md5=f3e41d41a49eae461da02fcf69e5b404
    19. 19
      Tavani, F.; Martini, A.; Capocasa, G.; Di Stefano, S.; Lanzalunga, O.; D’Angelo, P. Direct Mechanistic Evidence for a Non-Heme Complex Reaction through a Multivariate XAS Analysis. Inorg. Chem. 2020, 59, 9979– 9989,  DOI: 10.1021/acs.inorgchem.0c01132
      [ACS Full Text ACS Full Text], [CAS], Google Scholar
      19
      Direct Mechanistic Evidence for a Nonheme Complex Reaction through a Multivariate XAS Analysis
      Tavani, Francesco; Martini, Andrea; Capocasa, Giorgio; Di Stefano, Stefano; Lanzalunga, Osvaldo; D'Angelo, Paola
      Inorganic Chemistry (2020), 59 (14), 9979-9989CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
      We propose a method to directly det. the mechanism of the reaction between the nonheme complex FeII(tris(2-pyridylmethyl)amine) ([FeII(TPA)(CH3CN)2]2+) and peracetic acid (AcOOH) in CH3CN, working at room temp. A multivariate anal. is applied to the time-resolved coupled energy-dispersive X-ray absorption spectroscopy (EDXAS) reaction data, from which a set of spectral and concn. profiles for the reaction key species is derived. These "pure" extd. EDXAS spectra are then quant. characterized by full multiple scattering (MS) calcns. As a result, structural information for the elusive reaction intermediates [FeIII(TPA)(κ2-OOAc)]2+ and [FeIV(TPA)(O)(X)]+/2+ is obtained, and it is suggested that X = AcO- in opposition to X = CH3CN. The employed strategy is promising both for the spectroscopic characterization of reaction intermediates that are labile or silent to the conventional spectroscopic techniques, as well as for the mechanistic understanding of complex redox reactions involving org. substrates. A combined multivariate and theor. XAS anal. was proven to be a powerful method to obtain direct evidence for the mechanism of the reaction between the nonheme complex FeII(tris(2-pyridymethyl)amine) ([FeII(TPA)(CH3CN)2]2+) and peroxyacetic acid. This approach allowed to det. the time evolution of the concn. profiles for all reaction intermediates and to quant. characterize their structures, suggesting the sixth coordinating ligand of the nonheme oxo complex [FeIV(TPA)(O)(X)]+/2+ is X = AcO- in opposition to X = CH3CN.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXht1Gms77L&md5=12e34f9e364b915a323d7739003d3795
    20. 20
      Busato, M.; Melchior, A.; Migliorati, V.; Colella, A.; Persson, I.; Mancini, G.; Veclani, D.; D’Angelo, P. Elusive Coordination of the Ag+ Ion in Aqueous Solution: Evidence for a Linear Structure. Inorg. Chem. 2020, 59, 17291– 17302,  DOI: 10.1021/acs.inorgchem.0c02494
      [ACS Full Text ACS Full Text], [CAS], Google Scholar
      20
      Elusive Coordination of the Ag+ Ion in Aqueous Solution: Evidence for a Linear Structure
      Busato, Matteo; Melchior, Andrea; Migliorati, Valentina; Colella, Andrea; Persson, Ingmar; Mancini, Giordano; Veclani, Daniele; D'Angelo, Paola
      Inorganic Chemistry (2020), 59 (23), 17291-17302CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
      X-ray absorption spectroscopy (XAS) has been employed to study the coordination of the Ag+ ion in aq. soln. The conjunction of extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES) data anal. provided results suggesting the preference for a first shell linear coordination with a mean Ag-O bond distance of 2.34(2) Å, different from the first generally accepted tetrahedral model with a longer mean Ag-O bond distance. Ab initio mol. dynamics simulations with the Car-Parrinello approach (CPMD) were also performed and were able to describe the coordination of the hydrated Ag+ ion in aq. soln. in very good agreement with the exptl. data. The high sensitivity for the closest environment of the photoabsorber of the EXAFS and XANES techniques, together with the long-range information provided by CPMD and large-angle X-ray scattering (LAXS), allowed us to reconstruct the three-dimensional model of the coordination geometry around the Ag+ ion in aq. soln. The obtained results from expts. and theor. simulations provided a complex picture with a certain amt. of water mols. with high configurational disorder at distances comprised between the first and second hydration spheres. This evidence may have caused the proliferation of the coordination nos. that have been proposed so far for Ag+ in water. Altogether these data show how the description of the hydration of the Ag+ ion in aq. soln. can be complex, differently from other metal species where hydration structures can be described by clusters with well-defined geometries. This diffuse hydration shell causes the Ag-O bond distance in the linear [Ag(H2O)2]+ ion to be ca. 0.2 Å longer than in isolated ions in solid state. Extended X-ray absorption fine structure (EXAFS), X-ray absorption near-edge structure (XANES), large-angle X-ray scattering (LAXS), and Car-Parrinello mol. dynamics (CPMD) provided a reliable detn. of the elusive hydration structure of the Ag+ ion. A linear first shell with a mean Ag-O distance of 2.34(2) Å is obsd., surrounded by a few water mols. at a relatively short distance, ca. 2.6 Å, and another set of waters as a swarm at ca. 4 Å.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXitl2qtLbL&md5=c833cf5ea5992612bdb7750a96c2c468
    21. 21
      Isegawa, K.; Ueda, K.; Hiwasa, S.; Amemiya, K.; Mase, K.; Kondoh, H. Formation of Carbonate on Ag(111) under Exposure to Ethylene and Oxygen Gases Evidenced by Near Ambient Pressure XPS and NEXAFS. Chem. Lett. 2019, 48, 159– 162,  DOI: 10.1246/cl.180891
      [Crossref], [CAS], Google Scholar
      21
      Formation of carbonate on Ag(111) under exposure to ethylene and oxygen gases evidenced by near ambient pressure XPS and NEXAFS
      Isegawa, Kazuhisa; Ueda, Kohei; Hiwasa, Satoru; Amemiya, Kenta; Mase, Kazuhiko; Kondoh, Hiroshi
      Chemistry Letters (2019), 48 (2), 159-162CODEN: CMLTAG; ISSN:0366-7022. (Chemical Society of Japan)
      The active oxygen species for ethylene epoxidn. on Ag surfaces has been a long-standing issue. We conducted in situ observations of Ag(111) surfaces under exposure to ethylene and oxygen gases with near ambient pressure (NAP) XPS and near-edge X-ray absorption fine structure spectroscopy. Combined results of these spectroscopies evidence that a carbonate species with a flat-lying configuration is formed on the Ag(111) surface at 370-500K under exposure to the NAP gas mixt. of ethylene and oxygen.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXotlKit7o%253D&md5=854e5bca31af9b7c9789a6abded5a8a8
    22. 22
      Castán-Guerrero, C.; Krizmancic, D.; Bonanni, V.; Edla, R.; Deluisa, A.; Salvador, F.; Rossi, G.; Panaccione, G.; Torelli, P. A Reaction Cell for Ambient Pressure Soft X-ray Absorption Spectroscopy. Rev. Sci. Instrum. 2018, 89, 054101,  DOI: 10.1063/1.5019333
      [Crossref], [PubMed], [CAS], Google Scholar
      22
      A reaction cell for ambient pressure soft x-ray absorption spectroscopy
      Castan-Guerrero, C.; Krizmancic, D.; Bonanni, V.; Edla, R.; Deluisa, A.; Salvador, F.; Rossi, G.; Panaccione, G.; Torelli, P.
      Review of Scientific Instruments (2018), 89 (5), 054101/1-054101/8CODEN: RSINAK; ISSN:0034-6748. (American Institute of Physics)
      The authors present a new exptl. setup for performing x-ray Absorption Spectroscopy (XAS) in the soft X-ray range at ambient pressure. The ambient pressure XAS setup is fully compatible with the ultra high vacuum environment of a synchrotron radiation spectroscopy beamline end station by ultrathin Si3N4 membranes acting as windows for the x-ray beam and seal of the atm. sample environment. The XAS detection is performed in total electron yield (TEY) mode by probing the drain current from the sample with a picoammeter. The high signal/noise ratio achievable in the TEY mode, combined with a continuous scanning of the x-ray energies, makes it possible recording XAS spectra in a few seconds. The 1st results show the performance of this setup to record fast XAS spectra from sample surfaces exposed at atm. pressure, even in the case of highly insulating samples. The use of a permanent magnet inside the reaction cell enables the measurement of x-ray MCD at ambient pressure. (c) 2018 American Institute of Physics.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXptVWksb4%253D&md5=5931940d1810ce8e49c1dc57a2eaea44
    23. 23
      Braglia, L.; Fracchia, M.; Ghigna, P.; Minguzzi, A.; Meroni, D.; Edla, R.; Vandichel, M.; Ahlberg, E.; Cerrato, G.; Torelli, P. Understanding Solid-Gas Reaction Mechanisms by Operando Soft X-Ray Absorption Spectroscopy at Ambient Pressure. J. Phys. Chem. C 2020, 124, 14202– 14212,  DOI: 10.1021/acs.jpcc.0c02546
      [ACS Full Text ACS Full Text], [CAS], Google Scholar
      23
      Understanding Solid-Gas Reaction Mechanisms by Operando Soft X-Ray Absorption Spectroscopy at Ambient Pressure
      Braglia, Luca; Fracchia, Martina; Ghigna, Paolo; Minguzzi, Alessandro; Meroni, Daniela; Edla, Raju; Vandichel, Matthias; Ahlberg, Elisabet; Cerrato, Giuseppina; Torelli, Piero
      Journal of Physical Chemistry C (2020), 124 (26), 14202-14212CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
      Ambient-pressure operando soft X-ray absorption spectroscopy (soft-XAS) was applied to study the reactivity of hydroxylated SnO2 nanoparticles toward reducing gases. H2 was first used as a test case, showing that the gas phase and surface states can be simultaneously probed: Soft-XAS at the O K-edge gains sensitivity toward the gas phase, while at the Sn M4,5-edges, tin surface states are explicitly probed. Results obtained by flowing hydrocarbons (CH4 and CH3CHCH2) unequivocally show that these gases react with surface hydroxyl groups to produce water without producing carbon oxides and release electrons that localize on Sn to eventually form SnO. The partially reduced SnO2-x layer at the surface of SnO2 is readily reoxidized to SnO2 by treating the sample with O2 at mild temps. (>200°C), revealing the nature of "electron sponge" of tin oxide. The expts., combined with DFT calcns., allowed devising of a mechanism for dissociative hydrocarbon adsorption on SnO2, involving direct redn. of Sn sites at the surface via cleavage of C-H bonds and the formation of methoxy- and/or methyl-tin species at the surface.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXhtV2ks7%252FK&md5=417d1e4ba6e318d56920dbe62b6da537
    24. 24
      Braglia, L.; Tavani, F.; Mauri, S.; Edla, R.; Krizmancic, D.; Tofoni, A.; Colombo, V.; D’Angelo, P.; Torelli, P. Catching the Reversible Formation and Reactivity of Surface Defective Sites in Metal–Organic Frameworks: An Operando Ambient Pressure-NEXAFS Investigation. J. Phys. Chem. Lett. 2021, 12, 9182– 9187,  DOI: 10.1021/acs.jpclett.1c02585
      [ACS Full Text ACS Full Text], [CAS], Google Scholar
      24
      Catching the Reversible Formation and Reactivity of Surface Defective Sites in Metal-Organic Frameworks: An Operando Ambient Pressure-NEXAFS Investigation
      Braglia, Luca; Tavani, Francesco; Mauri, Silvia; Edla, Raju; Krizmancic, Damjan; Tofoni, Alessandro; Colombo, Valentina; D'Angelo, Paola; Torelli, Piero
      Journal of Physical Chemistry Letters (2021), 12 (37), 9182-9187CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)
      In this work, we apply for the first time ambient pressure operando soft X-ray absorption spectroscopy (XAS) to investigate the location, structural properties, and reactivity of the defective sites present in the prototypical metal-org. framework HKUST-1. We obtained direct evidence that Cu+ defective sites form upon temp. treatment of the powd. form of HKUST-1 at 160 °C and that they are largely distributed on the material surface. Further, a thorough structural characterization of the Cu+/Cu2+ dimeric complexes arising from the temp.-induced dehydration/decarboxylation of the pristine Cu2+/Cu2+ paddlewheel units is reported. In addn. to characterizing the surface defects, we demonstrate that CO2 may be reversibly adsorbed and desorbed from the surface defective Cu+/Cu2+ sites. These findings show that ambient pressure soft-XAS, combined with state-of-the-art theor. calcns., allowed us to shed light on the mechanism involving the decarboxylation of the paddlewheel units on the surface to yield Cu+/Cu2+ complexes and their reversible restoration upon exposure to gaseous CO2..
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXitVaitL%252FO&md5=1559f49ab51f13270ae01c20fe258751
    25. 25
      Tavani, F.; Fracchia, M.; Tofoni, A.; Braglia, L.; Jouve, A.; Morandi, S.; Manzoli, M.; Torelli, P.; Ghigna, P.; D’Angelo, P. Structural and Mechanistic Insights into Low-Temperature CO Oxidation over a Prototypical High Entropy Oxide by Cu L-edge Operando Soft X-ray absorption Spectroscopy. Phys. Chem. Chem. Phys. 2021, 23, 26575– 26584,  DOI: 10.1039/D1CP03946F
      [Crossref], [PubMed], [CAS], Google Scholar
      25
      Structural and mechanistic insights into low-temperature CO oxidation over a prototypical high entropy oxide by Cu L-edge operando soft X-ray absorption spectroscopy
      Tavani, Francesco; Fracchia, Martina; Tofoni, Alessandro; Braglia, Luca; Jouve, Andrea; Morandi, Sara; Manzoli, Maela; Torelli, Piero; Ghigna, Paolo; D'Angelo, Paola
      Physical Chemistry Chemical Physics (2021), 23 (46), 26575-26584CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
      High entropy oxides (HEOs) are an emerging class of materials constituted by multicomponent systems that are receiving special interest as candidates for obtaining novel and desirable properties. In this study we present a detailed investigation of the relevant intermediates arising at the surface of the prototypical HEO Mg0.2Co0.2Ni0.2Cu0.2Zn0.2O during low-temp. CO oxidn. By combining Cu L2,3-edge operando soft X-ray absorption spectroscopy (soft-XAS) with d. functional theory simulations and in situ FT-IR spectroscopy, we propose that upon HEO exposure to CO at 235 °C reduced Cu(I) sites arise mostly coordinated to activated CO mols. and partly to bidentate carbonate species. When the HEO surface is then exposed to a stoichiometric mixt. of CO + 1/2O2 at 250 °C, CO2 is produced while bidentate carbonate moieties remain interacting with the Cu(I) sites. We structurally characterize the carbonate and CO preferential adsorption geometries on the Cu(I) surface metal centers, and find that CO adopts a bent conformation that may energetically favor its subsequent oxidn. The unique surface, structural and electronic sensitivity of soft-XAS coupled with the developed data anal. work-flow and supported by FT-IR spectroscopy may be beneficial to characterize often elusive surface properties of systems of catalytic interest.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXisVyku7bP&md5=251ff77734ad8011242619e208d468e0
    26. 26
      Martini, A.; Guda, S.; Guda, A.; Smolentsev, G.; Algasov, A.; Usoltsev, O.; Soldatov, M.; Bugaev, A.; Rusalev, Y.; Lamberti, C.; Soldatov, A. PyFitit: The Software for Quantitative Analysis of XANES Spectra Using Machine-Learning Algorithms. Comput. Phys. Commun. 2019, 107064
      Google Scholar
      There is no corresponding record for this reference.
    27. 27
      Martini, A.; Guda, A. A.; Guda, S. A.; Dulina, A.; Tavani, F.; D’Angelo, P.; Borfecchia, E.; Soldatov, A. V. In Synchrotron Radiation Science and Applications. Springer Proceedings in Physics; Di Cicco, A., Giuli, G., Trapananti, A., Eds.; Springer, 2021; Vol. 220; pp 65– 84.
      [Crossref], Google Scholar
      There is no corresponding record for this reference.
    28. 28
      Tavani, F.; Capocasa, G.; Martini, A.; Sessa, F.; Di Stefano, S.; Lanzalunga, O.; D’Angelo, P. Direct Structural and Mechanistic Insights into Fast Bimolecular Chemical Reactions in Solution through a Coupled XAS/UV-Vis Multivariate Statistical Analysis. Dalton Trans 2021, 50, 131– 142,  DOI: 10.1039/D0DT03083J
      [Crossref], [PubMed], [CAS], Google Scholar
      28
      Direct structural and mechanistic insights into fast bimolecular chemical reactions in solution through a coupled XAS/UV-Vis multivariate statistical analysis
      Tavani, Francesco; Capocasa, Giorgio; Martini, Andrea; Sessa, Francesco; Di Stefano, Stefano; Lanzalunga, Osvaldo; D'Angelo, Paola
      Dalton Transactions (2021), 50 (1), 131-142CODEN: DTARAF; ISSN:1477-9226. (Royal Society of Chemistry)
      In this work, we obtain detailed mechanistic and structural information on bimol. chem. reactions occurring in soln. on the second to millisecond time scales through the combination of a statistical, multivariate and theor. anal. of time-resolved coupled X-ray Absorption Spectroscopy (XAS) and UV-Vis data. We apply this innovative method to investigate the sulfoxidn. of p-cyanothioanisole and p-methoxythioanisole by the nonheme FeIV oxo complex [N4Py·FeIV(O)]2+ (N4Py = N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine) in acetonitrile at room temp. By employing statistical and multivariate techniques we det. the no. of key chem. species involved along the reaction paths and derive spectral and concn. profiles for the reaction intermediates. From the quant. anal. of the XAS spectra we obtain accurate structural information for all reaction intermediates and provide the first structural characterization in soln. of complex [N4Py·FeIII(OH)]2+. The employed strategy is promising for the spectroscopic characterization of transient species formed in redox reactions.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXisVejs7jE&md5=b45e428fd885b912fc580682a96acf4b
    29. 29
      Tavani, F.; Capocasa, G.; Martini, A.; Sessa, F.; Di Stefano, S.; Lanzalunga, O.; D’Angelo, P. Activation of C-H Bonds by a Nonheme Iron(IV)-Oxo Complex: Mechanistic Evidence through a Coupled EDXAS/UV-Vis Multivariate Analysis. Phys. Chem. Chem. Phys. 2021, 23, 1188– 1196,  DOI: 10.1039/D0CP04304D
      [Crossref], [PubMed], [CAS], Google Scholar
      29
      Activation of C-H bonds by a nonheme iron(IV)-oxo complex: mechanistic evidence through a coupled EDXAS/UV-Vis multivariate analysis
      Tavani, Francesco; Capocasa, Giorgio; Martini, Andrea; Sessa, Francesco; Di Stefano, Stefano; Lanzalunga, Osvaldo; D'Angelo, Paola
      Physical Chemistry Chemical Physics (2021), 23 (2), 1188-1196CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
      The understanding of reactive processes involving org. substrates is crucial to chem. knowledge and requires multidisciplinary efforts for its advancement. Herein, we apply a combined multivariate, statistical and theor. anal. of coupled time-resolved X-ray absorption (XAS)/UV-Vis data to obtain detailed mechanistic information for on the C-H bond activation of 9,10-dihydroanthracene (DHA) and diphenylmethane (Ph2CH2) by the nonheme FeIV-oxo complex [N4Py·FeIV(O)]2+ (N4Py = N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine) in CH3CN at room temp. Within this approach, we det. the no. of key chem. species present in the reaction mixts. and derive spectral and concn. profiles for the reaction intermediates. From the quant. anal. of the XAS spectra the transient intermediate species are structurally detd. As a result, it is suggested that, while DHA is oxidized by [N4Py·FeIV(O)]2+ with a hydrogen atom transfer-electron transfer (HAT-ET) mechanism, Ph2CH2 is oxidized by the nonheme iron-oxo complex through a HAT-radical dissocn. pathway. In the latter process, we prove that the intermediate FeIII complex [N4Py·FeIII(OH)]2+ is not able to oxidize the diphenylmethyl radical and we provide its structural characterization in soln. The employed combined exptl. and theor. strategy is promising for the spectroscopic characterization of transient intermediates as well as for the mechanistic investigation of redox chem. transformations on the second to millisecond time scales.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXis1SgsL%252FO&md5=3520a37ba8568225c65af4781dcdff9d
    30. 30
      Tavani, F.; Fracchia, M.; Pianta, N.; Ghigna, P.; Quartarone, E.; D’Angelo, P. Multivariate Curve Resolution Analysis of Operando XAS Data for the Investigation of the Lithiation Mechanisms in High Entropy Oxides. Chem. Phys. Lett. 2020, 760, 137968,  DOI: 10.1016/j.cplett.2020.137968
      [Crossref], [CAS], Google Scholar
      30
      Multivariate curve resolution analysis of operando XAS data for the investigation of the lithiation mechanisms in high entropy oxides
      Tavani, Francesco; Fracchia, Martina; Pianta, Nicolo; Ghigna, Paolo; Quartarone, Eliana; D'Angelo, Paola
      Chemical Physics Letters (2020), 760 (), 137968CODEN: CHPLBC; ISSN:0009-2614. (Elsevier B.V.)
      Transition metal-based high entropy oxides (TM-HEO) have recently been gaining interest for their potential use as anodes in next-generation Li-ion batteries. In such systems, however, the lithiation/delithiation mechanisms remain a matter of ongoing investigation. In this work we demonstrate the suitability of Multivariate Curve Resoln. (MCR) of operando X-ray absorption spectroscopy (XAS) data to study the lithiation mechanisms in the TM-HEO (Mg0.2Co0.2Ni0.2Cu0.2Zn0.2)O. Through the MCR anal., the no., nature and concn. evolution as a function of stored charge of all Cu-, Ni- and Co-related active species present during the first lithiation cycle is obtained.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXitVKgur3F&md5=0d3af0d5788149646bed68d0a0941318
    31. 31
      Kleiman, S.; Chaim, R. Thermal Stability of MgO Nanoparticles. Mater. Lett. 2007, 61, 4489– 4491,  DOI: 10.1016/j.matlet.2007.02.032
      [Crossref], [CAS], Google Scholar
      31
      Thermal stability of MgO nanoparticles
      Kleiman, Sagiv; Chaim, Rachman
      Materials Letters (2007), 61 (23-24), 4489-4491CODEN: MLETDJ; ISSN:0167-577X. (Elsevier B.V.)
      Thermal stability of nanocryst. MgO particles with av. diam. of 11 nm was investigated by annealing of the cold isostatically pressed compacts between 600 °C and 900 °C for various durations. Sintering time vs. grain radius at 800 °C demonstrated a linear line with the slope of ∼ 4 similar to that expected for surface diffusion. High resoln. scanning electron microscope images from different specimens showed a porous microstructure of interconnected particles typical for initial sintering. Arrhenius plot of the grain size data revealed the activation energy of 161 ±11 kJ mol-1 for the growth process in agreement with those reported for grain boundary grooving expts. It was found that MgO particles undergo coarsening already at temps. as low as 0.31 of the MgO m.p. (3125 K). Increase in the particle diam. and decrease in the surface area were assocd. with surface diffusion mechanism that leads to initial sintering between the particles.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2sXpsFOrs7g%253D&md5=b4518b8554ce09b9274e98e11e5dadc1
    32. 32
      Aritani, H.; Yamada, H.; Nishio, T.; Shiono, T.; Imamura, S.; Kudo, M.; Hasegawa, S.; Tanaka, T.; Yoshida, S. Characterization of Li-Doped MgO Catalysts for Oxidative Coupling of Methane by Means of Mg K-Edge XANES. J. Phys. Chem. B 2000, 104, 10133– 10143,  DOI: 10.1021/jp000291y
      [ACS Full Text ACS Full Text], [CAS], Google Scholar
      32
      Characterization of Li-Doped MgO Catalysts for Oxidative Coupling of Methane by Means of Mg K-Edge XANES
      Aritani, Hirofumi; Yamada, Hiroyuki; Nishio, Takashi; Shiono, Takeshi; Imamura, Seiichiro; Kudo, Masataka; Hasegawa, Sadao; Tanaka, Tsunehiro; Yoshida, Satohiro
      Journal of Physical Chemistry B (2000), 104 (44), 10133-10143CODEN: JPCBFK; ISSN:1089-5647. (American Chemical Society)
      To characterize active defect sites in the near-surface and bulk phase of MgO in Li-doped MgO, structural analyses were carried out by means of XRD, XPS, Mg K-edge XANES, and SEM techniques. For Li-MgO calcined at 873 K, Li doping at a low content (2.5 wt % as Li) brings about the formation of defect species only in the near-surface, which is due to the localization of doped Li ions in the surface. In this case, the catalytic species contg. a Li+-O- center exists in the surface region. At higher contents of more than 7.5 wt %, Li ions penetrate the MgO bulk, and its crystallinity decreases. The defect species possibly exist in the bulk phase. After oxidative coupling of methane reaction, the defect species are formed in the near-surface over MgO and Li-MgO. However, the C2 selectivity is much higher on Li-MgO than on MgO. It is concluded that the defect species contg. Li+-O- in both surface and bulk can act as the active species for producing C2 compds. with high selectivity.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3cXntlKgurw%253D&md5=240385a1df9f596b0b0b5bbc4a687d6f
    33. 33
      Klysubun, W.; Kidkhunthod, P.; Tarawarakarn, P.; Sombunchoo, P.; Kongmark, C.; Limpijumnong, S.; Rujirawat, S.; Yimnirun, R.; Tumcharern, G.; Faungnawakij, K. SUT-NANOTEC-SLRI Beamline for X-ray Absorption Spectroscopy. J. Synchr. Rad. 2017, 24, 707– 716,  DOI: 10.1107/S1600577517004830
      [Crossref], [PubMed], Google Scholar
      There is no corresponding record for this reference.
    34. 34
      Singh, J.; Kumar, M.; Lee, I.-J.; Chae, K. X-ray Reflectivity and Near Edge X-ray Absorption Fine Structure Investigations of MgO Thin Films. Appl. Sci. Lett. 2017, 3.
      Google Scholar
      There is no corresponding record for this reference.
    35. 35
      Yoshioka, S.; Tsuruta, K.; Yamamoto, T.; Yasuda, K.; Matsumura, S.; Ishikawa, N.; Kobayashi, E. X-ray Absorption Near Edge Structure and First-Principles Spectral Investigations of Cationic Disorder in MgAl2O4 Induced by Swift Heavy Ions. Phys. Chem. Chem. Phys. 2018, 20, 4962– 4969,  DOI: 10.1039/C7CP07591J
      [Crossref], [PubMed], [CAS], Google Scholar
      35
      X-ray absorption near edge structure and first-principles spectral investigations of cationic disorder in MgAl2O4 induced by swift heavy ions
      Yoshioka, S.; Tsuruta, K.; Yamamoto, T.; Yasuda, K.; Matsumura, S.; Ishikawa, N.; Kobayashi, E.
      Physical Chemistry Chemical Physics (2018), 20 (7), 4962-4969CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
      Cationic disorder in the MgAl2O4 spinel induced by swift heavy ions was investigated using the X-ray absorption near edge structure. With changes in the irradn. fluences of 200 MeV Xe ions, the Mg K-edge and Al K-edge spectra were synchronously changed. The calcd. spectra based on d. function theory indicate that the change in the exptl. spectra was due to cationic disorder between Mg in tetrahedral sites and Al in octahedral sites. These results suggest a high inversion degree to an extent that the completely random configuration is achieved in MgAl2O4 induced by the high d. electronic excitation under swift heavy ion irradn.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXitFOqsr8%253D&md5=85adb764971b46b118dafa1bfb9f04d6
    36. 36
      Witte, K.; Streeck, C.; Mantouvalou, I.; Suchkova, S. A.; Lokstein, H.; Grötzsch, D.; Martyanov, W.; Weser, J.; Kanngieer, B.; Beckhoff, B.; Stiel, H. Magnesium K-Edge NEXAFS Spectroscopy of Chlorophyll A in Solution. J. Phys. Chem. B 2016, 120, 11619– 11627,  DOI: 10.1021/acs.jpcb.6b05791
      [ACS Full Text ACS Full Text], [CAS], Google Scholar
      36
      Magnesium K-Edge NEXAFS Spectroscopy of Chlorophyll a in Solution
      Witte, Katharina; Streeck, Cornelia; Mantouvalou, Ioanna; Suchkova, Svetlana A.; Lokstein, Heiko; Groetzsch, Daniel; Martyanov, Wjatscheslav; Weser, Jan; Kanngiesser, Birgit; Beckhoff, Burkhard; Stiel, Holger
      Journal of Physical Chemistry B (2016), 120 (45), 11619-11627CODEN: JPCBFK; ISSN:1520-5207. (American Chemical Society)
      The interaction of the central magnesium atom of chlorophyll a (Chl a) with its carbon and nitrogen backbone was investigated by magnesium (Mg) K near edge x-ray absorption fine structure (NEXAFS) spectroscopy in fluorescence detection mode. Chl a was measured as 1*10-2 mol/l ethanol soln., which represents an upper limit of concn. without aggregation and as dried droplets. For the first time, the investigation of the structure of Chl a in a liq. environment by means of x-ray absorption spectroscopy is demonstrated. A preedge feature in the dissolved as well as in dried Chl a NEXFAS spectra has been identified as a characteristic transition originating from the intact Chl a mol. This result is confirmed by theor. DFT calcns. leading to MOs (MO) which are mainly situated on the magnesium atom and nitrogen and carbon atoms from the pyrrole rings. The description is the first referring to the MO distribution with respect to the central Mg ion of Chl a and the surrounding atoms. Based there upon, new approaches for the investigations of dynamic processes of mols. in soln. and the structure-function relationships of photosynthetic pigments and pigment-protein complexes in their native environment can be developed.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhslCktrbM&md5=710f7e8c001b79ec3a236b2957bef4d9
    37. 37
      Joly, Y. X-ray Absorption Near-Edge Structure Calculations Beyond the Muffin-Tin Approximation. Phys. Rev. B 2001, 63, 125120,  DOI: 10.1103/PhysRevB.63.125120
      [Crossref], [CAS], Google Scholar
      37
      x-ray absorption near-edge structure calculations beyond the muffin-tin approximation
      Joly, Y.
      Physical Review B: Condensed Matter and Materials Physics (2001), 63 (12), 125120/1-125120/10CODEN: PRBMDO; ISSN:0163-1829. (American Physical Society)
      A new scheme for calcg. the x-ray absorption near edge structure (XANES) based on the finite-difference method is proposed. It allows completely free potential shape and, in particular, is not constrained to the muffin-tin approxn. In approach, the calcn. of the final states is performed in real space. The Schrodinger equation is solved in a discrete form on the node points of a 3-dimensional grid. The unknowns are the values of the wave functions at the grid points. The validity of the method is shown on 2 different systems the metallic Cu and the CO mol.; then, the differences resulting from muffin-tin and non-muffin-tin calcns. are shown on different typical mols.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3MXhvV2qtrY%253D&md5=ff7c161f8eaa60274bd434cb6de6ea97
    38. 38
      Bunău, O.; Joly, Y. Self-Consistent Aspects of X-ray Absorption Calculations. J. Phys: Condens. Matter 2009, 21, 345501
      [Crossref], [PubMed], [CAS], Google Scholar
      38
      Self-consistent aspects of X-ray absorption calculations
      Bunau, O.; Joly, Y.
      Journal of Physics: Condensed Matter (2009), 21 (34), 345501/1-345501/11CODEN: JCOMEL; ISSN:0953-8984. (Institute of Physics Publishing)
      We implemented a self-consistent, real-space x-ray absorption calcn. within the FDMNES code. We performed the self-consistency within several schemes and identified which one is the most appropriate. We show a method that allows a rigorous setting of the Fermi level and thus an estn. of the energy cutoff for the identification and elimination of the occupied states. We investigated what are the structures where one can afford performing the self-consistent calcn. at a lesser cluster radius than the absorption one. We exemplify the effects of the self-consistency at the K-edge and for several ref. cases, including the copper Cu and the rutile TiO2. We verified the robustness of our procedure on the transitional 3d and 4d elements. Although amelioration can be noticed, the self-consistency performed at the K-edge does not bring a major improvement of the calcd. spectra. Taking into consideration a non-self-consistent, non-spherical potential gives better results than a self-consistent muffin-tin approxn. calcn.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXhtFCht77N&md5=ac5e837f05c62e7d8b5859f68768ef0f
    39. 39
      Guda, S. A.; Guda, A. A.; Soldatov, M. A.; Lomachenko, K. A.; Bugaev, A. L.; Lamberti, C.; Gawelda, W.; Bressler, C.; Smolentsev, G.; Soldatov, A. V.; Joly, Y. Optimized Finite Difference Method for the Full-Potential XANES Simulations: Application to Molecular Adsorption Geometries in MOFs and Metal-Ligand Intersystem Crossing Transients. J. Chem. Th. Comp. 2015, 11, 4512– 4521,  DOI: 10.1021/acs.jctc.5b00327
      [ACS Full Text ACS Full Text], Google Scholar
      There is no corresponding record for this reference.
    40. 40
      Pankin, I.; Borfecchia, E.; Martini, A.; Lomachenko, K.; Lamberti, C.; Soldatov, A. DFT-assisted XANES Simulations to Discriminate Different Monomeric CuII Species in CHA Catalysts. Radiat. Phys. Chem. 2020, 175, 108510,  DOI: 10.1016/j.radphyschem.2019.108510
      [Crossref], [CAS], Google Scholar
      40
      DFT-assisted XANES simulations to discriminate different monomeric CuII species in CHA catalysts
      Pankin, I. A.; Borfecchia, E.; Martini, A.; Lomachenko, K. A.; Lamberti, C.; Soldatov, A. V.
      Radiation Physics and Chemistry (2020), 175 (), 108510CODEN: RPCHDM; ISSN:0969-806X. (Elsevier B.V.)
      Herein, we present Cu K-edge XANES (X-ray Absorption Near Edge Structure) simulations for different framework interacting Z-CuII species proposed to form as an active site after high-temp. activation in Cu-exchanged chabazite zeolites, representing promising materials for selective catalytic redn. of NOx in the presence of ammonia and direct conversion of methane to methanol. We critically compare the simulated spectra to previously collected data for an O2-activated Cu-chabazite sample. D. of states (DOS) calcns. allow us to get more insights in describing the nature of XANES features obsd. in the simulated spectra. To demonstrate the potential of the method, we finally explore the impact of systematic variations of selected structural parameters on the theor. XANES features.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhvFOiur7M&md5=8e2bf422a7e8a40e85ef945375cdc85b
    41. 41
      Amodeo, J.; Merkel, S.; Tromas, C.; Carrez, P.; Korte-Kerzel, S.; Cordier, P.; Chevalier, J. Dislocations and Plastic Deformation in MgO Crystals: A Review. Crystals 2018, 8, 240 DOI: 10.3390/cryst8060240
      [Crossref], [CAS], Google Scholar
      41
      Dislocations and plastic deformation in MgO crystals: a review
      Amodeo, Jonathan; Merkel, Sebastien; Tromas, Christophe; Carrez, Philippe; Korte-Kerzel, Sandra; Cordier, Patrick; Chevalier, Jerome
      Crystals (2018), 8 (6), 240/1-240/53CODEN: CRYSBC; ISSN:2073-4352. (MDPI AG)
      This review paper focuses on dislocations and plastic deformation in magnesium oxide crystals. MgO is an archetype ionic ceramic with refractory properties which is of interest in several fields of applications such as ceramic materials fabrication, nano-scale engineering and Earth sciences. In its bulk single crystal shape, MgO can deform up to few percent plastic strain due to dislocation plasticity processes that strongly depend on external parameters such as pressure, temp., strain rate, or crystal size. This review describes how a combined approach of macro-mech. tests, multi-scale modeling, nano-mech. tests, and high pressure expts. and simulations have progressively helped to improve our understanding of MgO mech. behavior and elementary dislocation-based processes under stress.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXhvVWktLrK&md5=9e9aff857cf211adcc7067dbe0132009
    42. 42
      Becke, A. D. A New Mixing of Hartree-Fock and Local Density Functional Theories. J. Chem. Phys. 1993, 98, 1372– 1377,  DOI: 10.1063/1.464304
      [Crossref], [CAS], Google Scholar
      42
      A new mixing of Hartree-Fock and local-density-functional theories
      Becke, Axel D.
      Journal of Chemical Physics (1993), 98 (2), 1372-7CODEN: JCPSA6; ISSN:0021-9606.
      Previous attempts to combine the Hartree-Fock theory with the local d.-functional theory were unsuccessful in applications to mol. bonding. A new coupling is presented of these two theories that maintains their simplicity and computational efficiency, and yet greatly improves their predictive power. Very encouraging results of tests on atomization energies, ionization potentials, and proton affinities are reported, and the potential for future development is discussed.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK3sXhtlagt7o%253D&md5=02a9289532197e7445af684bb29f4e11
    43. 43
      Lee, C.; Yang, W.; Parr, R. G. Development of the Colle-Salvetti Correlation-Energy Formula into a Functional of the Electron Density. Phys. Rev. B 1988, 37, 785– 789,  DOI: 10.1103/PhysRevB.37.785
      [Crossref], [PubMed], [CAS], Google Scholar
      43
      Development of the Colle-Salvetti correlation-energy formula into a functional of the electron density
      Lee, Chengteh; Yang, Weitao; Parr, Robert G.
      Physical Review B: Condensed Matter and Materials Physics (1988), 37 (2), 785-9CODEN: PRBMDO; ISSN:0163-1829.
      A correlation-energy formula due to R. Colle and D. Salvetti (1975), in which the correlation energy d. is expressed in terms of the electron d. and a Laplacian of the 2nd-order Hartree-Fock d. matrix, is restated as a formula involving the d. and local kinetic-energy d. On insertion of gradient expansions for the local kinetic-energy d., d.-functional formulas for the correlation energy and correlation potential are then obtained. Through numerical calcns. on a no. of atoms, pos. ions, and mols., of both open- and closed-shell type, it is demonstrated that these formulas, like the original Colle-Salvetti formulas, give correlation energies within a few percent.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL1cXktFWrtbw%253D&md5=ee7b59267a2ff72e15171a481819ccf8
    44. 44
      Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H. P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Montgomery, J. A., Jr.; Peralta, J. E.; Ogliaro, F.; Bearpark, M.; Heyd, J. J.; Brothers, E.; Kudin, K. N.; Staroverov, V. N.; Kobayashi, R.; Normand, J.; Raghavachari, K.; Rendell, A.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Rega, N.; Millam, J. M.; Klene, M.; Knox, J. E.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Martin, R. L.; Morokuma, K.; Zakrzewski, V. G.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Dapprich, S.; Daniels, A. D.; Farkas, Ã.; Foresman, J. B.; Ortiz, J. V.; Cioslowski, J.; Fox, D. J. Gaussian 09 , Revision A.02, 2009.
      Google Scholar
      There is no corresponding record for this reference.
    45. 45
      Pye, C. C.; Rudolph, W. W. An Ab Initio and Raman Investigation of Magnesium(II) Hydration. J. Phys. Chem. A 1998, 102, 9933– 9943,  DOI: 10.1021/jp982709m
      [ACS Full Text ACS Full Text], [CAS], Google Scholar
      45
      An ab Initio and Raman Investigation of Magnesium(II) Hydration
      Pye, Cory C.; Rudolph, W. W.
      Journal of Physical Chemistry A (1998), 102 (48), 9933-9943CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)
      The weak polarized Raman band assigned to the ν1-MgO6 mode of the hexaaquo Mg(II) ion was studied over the temp. range 25 to 125°. The 356 cm-1 stretching mode frequency decreases by ∼3 cm-1 but broadens by 13 cm-1 over a 100° temp. range. A depolarized mode at 235 cm-1 could be assigned to ν2. Probably the hexaaquo Mg(II) ion is thermodynamically stable in perchlorate and chloride solns. In sulfate solns., an equil. exists between the hexaaquo ion and an inner-sphere sulfato complex. Ab initio geometry optimizations of Mg(H2O)62+ were carried out at the Hartree-Fock and Moller-Plesset levels of theory, using various basis sets up to 6-31+G*. Frequency calcns. confirm that the Th structure is a min. The unscaled frequencies of the MgO6 unit are lower than the exptl. frequencies, and scaling only marginally improves the agreement. The theor. binding enthalpy for the hexaaquo Mg(II) ion accounts for ∼70% of the exptl. hydration energy of Mg(II). A comparison of 3 models for the 2nd hydration sphere is presented, and the most suitable is one of lower symmetry T, in which alternate faces of the MgO6 octahedron are H-bonded to H2O trimers. The unscaled Hartree-Fock frequencies agree very well with exptl. observations, giving nearly exact agreement with expt.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1cXntVKntrg%253D&md5=a8f8d76e99b18342f8a0bd0ef0789569
    46. 46
      Matwiyoff, N. A.; Taube, H. Direct Determination of the Solvation Number of Magnesium(II) ion in water, Aqueous Acetone, and Methanolic Acetone solutions. J. Am. Chem. Soc. 1968, 90, 2796– 2800,  DOI: 10.1021/ja01013a012
      [ACS Full Text ACS Full Text], [CAS], Google Scholar
      46
      Direct determination of the solvation number of magnesium(II) ion in water, aqueous acetone, and methanolic acetone solutions
      Matwiyoff, N. A.; Taube, H.
      Journal of the American Chemical Society (1968), 90 (11), 2796-800CODEN: JACSAT; ISSN:0002-7863.
      At temps. below -60°, the proton magnetic resonance (pmr) signals of the solvent mols. within the primary coordination sphere of the Mg2+ ion in aq. acetone, methanolic acetone, and concd. aq. solns. can be distinguished from those of the bulk solvent. From a comparison of the areas of the pmr lines of the solvent in the free and coordinated sites, the compn. of the primary solvation sphere of the Mg2+ ion in these solvents was Mg(MeOH)62+ in methanolic acetone and Mg(OH2)62+ in aq. acetone and H2O. The relative coalescence temps. of the coordinated and free solvent pmr signals indicate that the order of increasing lability of the complex ions in Mg(MeOH)62+ < Mg(OH2)62+ in aq. acetone < Mg-(OH2)62+ in H2O.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaF1cXktFegtb8%253D&md5=a2fd838ec5de7ecba4e9ef57295cc10f
    47. 47
      Skipper, N. T.; Neilson, G. W.; Cummings, S. C. An X-ray Diffraction Study of Ni(aq)2+ and Mg(aq)2+ by Difference Methods. J. Phys.: Condensed Matter 1989, 1, 3489– 3506
      [Crossref], [CAS], Google Scholar
      47
      An x-ray diffraction study of aquated nickel(2+) and magnesium(2+) by difference methods
      Skipper, N. T.; Neilson, G. W.; Cummings, S. C.
      Journal of Physics: Condensed Matter (1989), 1 (22), 3489-506CODEN: JCOMEL; ISSN:0953-8984.
      Difference methods of x-ray diffraction were used to study the microscopic structure around Ni[aq]2+ and Mg[aq]2+ in a variety of aq. solns. Ref. to the results of neutron diffraction expts. show that Ni[aq]2+ and Mg[aq]2+ can be regarded as structurally isomorphic species, thereby enabling the local ionic structure to be measured in terms of the cation-oxygen and cation-cation radial pair distribution functions. Results are included for the dependence of these functions on concn., counter-ion species and the interchange of light and heavy water as the solvent.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL1MXkvVCqtbw%253D&md5=9868673476f5d4809cd1dc087ad4b7f4
    48. 48
      Bernal-Uruchurtu, M. I.; Ortega-Blake, I. A Refined Monte Carlo Study of Mg2+ and Ca2+ Hydration. J. Chem. Phys. 1995, 103, 1588– 1598,  DOI: 10.1063/1.469781
      [Crossref], [CAS], Google Scholar
      48
      A refined Monte Carlo study of Mg2+ and Ca2+ hydration
      Bernal-Uruchurtu, M. I.; Ortega-Blake, I.
      Journal of Chemical Physics (1995), 103 (4), 1588-98CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)
      The interaction potential used includes polarization and non-additivity factors that have been reported to be crit. for the proper description of hydration. The effect of cell size, amt. of configurations needed to attain equil., and size of the statistical sample are studied. A microscopic anal. of the hydration shows that Mg2+ and its first shell can be considered as a supermol. embedded in the solvent. For Ca2+ this character is less marked and its first shell responds to the solvent more easily. The coordination properties of both ions are discussed. The differences in the coordination properties of both ions are due to a great extent to the differences in the water depletion zone beyond the first hydration shell. The contributions of each hydration shell to the total enthalpy of hydration are analyzed as well as the local densities related to the electrostriction.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK2MXntFWltbg%253D&md5=4800a4c0a1e7999d6eda6da12dd3e7dd
    49. 49
      Obst, S.; Bradaczek, H. Molecular Dynamics Study of the Structure and Dynamics of the Hydration Shell of Alkaline and Alkaline-Earth Metal Cations. J. Phys. Chem. 1996, 100, 15677– 15687,  DOI: 10.1021/jp961384b
      [ACS Full Text ACS Full Text], [CAS], Google Scholar
      49
      Molecular Dynamics Study of the Structure and Dynamics of the Hydration Shell of Alkali and Alkaline-Earth Metal Cations
      Obst, Stefan; Bradaczek, Hans
      Journal of Physical Chemistry (1996), 100 (39), 15677-15687CODEN: JPCHAX; ISSN:0022-3654. (American Chemical Society)
      Mol.-dynamics simulations of hydrated alkali and alk. earth metal cations at room temp. (T = 300 K) were carried out by using the CHARMM22 force field. Dynamic and static properties of systems contg. one ion and 123 or 525 water mols. were investigated by anal. of trajectories of 1 ns duration and compared to exptl. and theor. results. In addn., the size and the direction of the elementary motions of both the ions and the water mols. were investigated on the scale of the integration time step of 1 fs. Comparison between systems of different size revealed that for the larger system the diffusion coeff. and the no. of hydrogen bonds were increased. Radial pair distribution functions and coordination nos. are in good agreement with x-ray and neutron scattering data. The diffusion coeff. D of bulk TIP3P water in a system with 528 water mols. was by one-fourth higher than the exptl. value. Minor differences of approx. 10% between exptl. and simulated diffusion coeffs. were found for Li+, Na+, K+, and Mg2+. On the other hand, D was underestimated by the simulation for Ca2+ and Sr2+ by as much as 30%. On the av., 2.9 hydrogen bonds per bulk water mol. were found. The obsd. order of residence times for the monovalent ions, τ(Li+) > τ(Na+) > τ(K+), is in good agreement with the literature. Although τ was expected to increase with decreasing mass of the ion, the exchange of water mols. from the solvation shell of Mg2+ occurred much faster than for Ca2+.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK28XlsVWitbY%253D&md5=417f2edcd0ab07d163e630dad0af9cb3
    50. 50
      Tongraar, A.; Michael Rode, B. The Role of Non-Additive Contributions on the Hydration Shell Structure of Mg2+ Studied by Born-Oppenheimer Ab Initio Quantum Mechanical/Molecular Mechanical Molecular Dynamics Simulation. Chem. Phys. Lett. 2001, 346, 485– 491,  DOI: 10.1016/S0009-2614(01)00923-X
      [Crossref], [CAS], Google Scholar
      50
      The role of non-additive contributions on the hydration shell structure of Mg2+ studied by Born-Oppenheimer ab initio quantum mechanical/molecular mechanical molecular dynamics simulation
      Tongraar, A.; Michael Rode, B.
      Chemical Physics Letters (2001), 346 (5,6), 485-491CODEN: CHPLBC; ISSN:0009-2614. (Elsevier Science B.V.)
      An ab initio quantum mech./mol. mech. (QM/MM) mol. dynamics simulation has been performed to investigate the effects of non-additive contributions on the hydration shell structure of Mg2+. The active-site region, the sphere including the second hydration shell of Mg2+, was treated by Born-Oppenheimer ab initio quantum mechanics, while the rest is described by classical pair potentials. A hydration complex with six inner shell waters and 12 s shell waters was obsd. It was also found that the effects of non-additive terms play an important role in the preferential orientation of water mols. inside the hydration sphere of Mg2+.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3MXnsVegsbw%253D&md5=325dccd3d7ea9019dc8a32599842c597
    51. 51
      Tongraar, A.; Rode, B. M. Structural Arrangement and Dynamics of the Hydrated Mg2+: an Ab Initio QM/MM Molecular Dynamics Simulation. Chem. Phys. Lett. 2005, 409, 304– 309,  DOI: 10.1016/j.cplett.2005.04.062
      [Crossref], [CAS], Google Scholar
      51
      Structural arrangement and dynamics of the hydrated Mg2+: An ab initio QM/MM molecular dynamics simulation
      Tongraar, Anan; Rode, Bernd Michael
      Chemical Physics Letters (2005), 409 (4-6), 304-309CODEN: CHPLBC; ISSN:0009-2614. (Elsevier B.V.)
      The structural arrangement and dynamics of solvated Mg2+ in dil. aq. soln. have been studied by ab initio QM/MM mol. dynamics simulation, in which the whole first and most of the second hydration shell of the ion were treated at Hartree-Fock level using LANL2DZ basis sets. Besides the most stable Mg2+(H2O)6 species, intermediates such as Mg2+(H2O)5(H2O), where at least one water mol. temporarily moves into the inter-shell region but remains H-bonded to inner-shell water, as well as transition complexes of the Mg2+(H2O)6(H2O) type, exist in aq. soln. The dynamics of solvate and surrounding water mols. are discussed in connection to the structure-forming' ability of Mg2+.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2MXlt1GqsLo%253D&md5=eec92e744d82f634b28e421a2cb33f72
    52. 52
      Dudev, T.; Lim, C. Incremental Binding Free Energies in Mg2+ Complexes: A DFT Study. J. Phys. Chem. A 1999, 103, 8093– 8100,  DOI: 10.1021/jp991575p
      [ACS Full Text ACS Full Text], [CAS], Google Scholar
      52
      Incremental Binding Free Energies in Mg2+ Complexes: A DFT Study
      Dudev, Todor; Lim, Carmay
      Journal of Physical Chemistry A (1999), 103 (40), 8093-8100CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)
      D. functional theory has been employed to evaluate the incremental binding energies, enthalpies, entropies, and free energies for the reactions of Mg2+ with water, methanol, formamide, and formate. The B3LYP/6-31+G* calcns. on the Mg2+ complexes show that the metal ion can accommodate no more than three neg. charged formates. For the neutral-ligand complexes, magnesium prefers to bind to methanol and formamide rather than water when the no. of ligands is less than four, but it prefers water to methanol and formamide for complexes with five or six ligands. These results have been rationalized in terms of steric crowding of the ligands around the metal ion and charge transfer from the ligand(s) to Mg2+. These two factors result in attenuation of the Mg-O bond distance and, hence, redn. in the electrostatic and polarization energies, which dominate the incremental binding energy. An empirical scheme, employing the incremental binding energies for Mg2+-single-type-ligand complexes, has been developed to accurately predict the total binding energy of Mg2+-mixed-ligand clusters.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1MXlvVGhs7w%253D&md5=4cb9ef20226ae5ca43dc2080db42737b
    53. 53
      D’Angelo, P.; Migliorati, V.; Sessa, F.; Mancini, G.; Persson, I. XANES Reveals the Flexible Nature of Hydrated Strontium in Aqueous Solution. J. Phys. Chem. B 2016, 120, 4114– 4124,  DOI: 10.1021/acs.jpcb.6b01054
      [ACS Full Text ACS Full Text], [CAS], Google Scholar
      53
      XANES Reveals the Flexible Nature of Hydrated Strontium in Aqueous Solution
      D'Angelo, Paola; Migliorati, Valentina; Sessa, Francesco; Mancini, Giordano; Persson, Ingmar
      Journal of Physical Chemistry B (2016), 120 (17), 4114-4124CODEN: JPCBFK; ISSN:1520-5207. (American Chemical Society)
      X-ray absorption near-edge structure (XANES) spectroscopy has been used to det. the structure of the hydrated strontium in aq. soln. The XANES anal. has been carried out using solid [Sr(H2O)8](OH)2 as ref. model. Classical and Car-Parrinello mol. dynamics (MD) simulations have been carried out and in the former case two different sets of Lennard-Jones parameters have been used for the Sr2+ ion. The best performing theor. approach has been chosen on the basis of the exptl. results. XANES spectra have been calcd. starting from MD trajectories, without carrying out any minimization of the structural parameters. This procedure allowed us to properly account for thermal and structural fluctuations occurring in the aq. soln. in the anal. of the exptl. spectrum. A deconvolution procedure has been applied to the raw absorption data thus increasing the sensitivity of XANES spectroscopy. One of the classical MD simulations has been found to provide a XANES theor. spectrum in better agreement with the exptl. data. An 8-fold hydration complex with a Sr-O distance of 2.60 Å has been found to be compatible with the XANES data, in agreement with previous findings. However, the hydration shells of the strontium ions have been found to have a flexible nature with a fast ligand exchange rate between the first and second hydration shell occurring in the picosecond time scale.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XlvVyqt7o%253D&md5=7bf9ff7a97f8f2e807c1d8745ed1d9dd
    54. 54
      Spezia, R.; Duvail, M.; Vitorge, P.; Cartailler, T.; Tortajada, J.; D’Angelo, P.; Gaigeot, M.-P.; Chillemi, G. A Coupled Car-Parrinello Molecular Dynamics and EXAFS Data Analysis Investigation of Aqueous Co2+. J. Phys. Chem. A 2006, 110, 13081– 13088,  DOI: 10.1021/jp064688z
      [ACS Full Text ACS Full Text], [CAS], Google Scholar
      54
      A Coupled Car-Parrinello Molecular Dynamics and EXAFS Data Analysis Investigation of Aqueous Co2+
      Spezia, Riccardo; Duvail, Magali; Vitorge, Pierre; Cartailler, Thierry; Tortajada, Jeanine; Chillemi, Giovanni; D'Angelo, Paola; Gaigeot, Marie-Pierre
      Journal of Physical Chemistry A (2006), 110 (48), 13081-13088CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)
      We have studied the microscopic solvation structure of Co2+ in liq. water by means of d. functional theory (DFT)-based Car-Parrinello mol. dynamics (CPMD) simulations and extended X-ray absorption fine structure (EXAFS) data anal. The effect of the no. of explicit water mols. in the simulation box on the first and second hydration shell structures has been considered. Classical mol. dynamics simulations, using an effective two-body potential for Co2+-water interactions, were also performed to show box size effects in a larger range. We have found that the no. of explicit solvent mols. has a marginal role on the first solvation shell structural parameters, whereas larger boxes may be necessary to provide a better description of the second solvation shell. Car-Parrinello simulations were detd. to provide a reliable description of structural and dynamical properties of Co2+ in liq. water. In particular, they seem to describe both the first and second hydration shells correctly. The EXAFS signal was reconstructed from Car-Parrinello simulations. Good agreement between the theor. and exptl. signals was obsd., thus strengthening the microscopic picture of the Co2+ solvation properties obtained using first-principle simulations.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD28XhtFyntbfF&md5=a2ecd4561da2a702035dc3d5be397682
    55. 55
      D’Angelo, P.; Roscioni, O. M.; Chillemi, G.; Della Longa, S.; Benfatto, M. Detection of Second Hydration Shells in Ionic Solutions by XANES: Computed Spectra for Ni2+ in Water Based on Molecular Dynamics. J. Am. Chem. Soc. 2006, 128, 1853– 1858,  DOI: 10.1021/ja0562503
      [ACS Full Text ACS Full Text], [CAS], Google Scholar
      55
      Detection of Second Hydration Shells in Ionic Solutions by XANES: Computed Spectra for Ni2+ in Water Based on Molecular Dynamics
      D'Angelo, Paola; Roscioni, Otello Maria; Chillemi, Giovanni; Della Longa, Stefano; Benfatto, Maurizio
      Journal of the American Chemical Society (2006), 128 (6), 1853-1858CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      A general procedure to compute X-ray absorption near-edge structure (XANES) spectra within multiple-scattering theory starting from mol. dynamics (MD) structural data has been developed and applied to the study of a Ni2+ aq. soln. This method allows one to perform a quant. anal. of the XANES spectra of disordered systems using a proper description of the thermal and structural fluctuations. The XANES spectrum of Ni2+ in aq. soln. has been calcd. using the structural information obtained from the MD simulations without carrying out any minimization in the structural parameter space. A very good reprodn. of the exptl. data was obtained including the second-shell water mols. in the calcn., thus showing that the second hydration shell provides a detectable contribution to the XANES spectra of ionic solns. The anal. including the first-shell cluster only permitted us to quant. det. the effect of disorder on the amplitude of the XANES spectra for mol. complexes. These results simultaneously confirm the reliability of the procedure and the structural results obtained from MD simulations. The combination of MD and XANES is found to be very helpful to get important new insights into the quant. estn. of structural properties of disordered systems.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD28XntFCmtA%253D%253D&md5=6823dd3bb542c0e84bb5b780c98b1757
    56. 56
      Radnai, T.; Kálmán, E.; Pollmer, K. X-Ray Diffraction Study of MgCl2 in Methanol. Zeitschrift fu̅r Naturforschung A 1984, 39, 464– 470,  DOI: 10.1515/zna-1984-0508
      [Crossref], [CAS], Google Scholar
      56
      X-ray diffraction study of magnesium chloride in methanol
      Radnai, T.; Kalman, E.; Pollmer, K.
      Zeitschrift fuer Naturforschung, Teil A: Physik, Physikalische Chemie, Kosmophysik (1984), 39A (5), 464-70CODEN: ZTAKDZ; ISSN:0340-4811.
      The structure of a concd. soln. of MgCl2 in methanol was studied by x-ray diffraction. The parameters for the ion-solvent interactions agree with those found in aq. solns. Both for Mg2+ and Cl-, the solvate shells are composed of 6 methanol mols. An av. octahedral arrangement of OH groups in the solvate shells of magnesium is probable. Octahedral sym. positions for CH3 groups proved to be unlikely.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL2cXkt12htLs%253D&md5=5f05e8b195bac6e674dee230b0212c8a
    57. 57
      Nakamura, S.; Meiboom, S. Proton Magnetic Resonance Studies of the Solvation Shell of Mg2+ in Methanol. Solvation Number and Exchange Rate. J. Am. Chem. Soc. 1967, 89, 1765– 1772,  DOI: 10.1021/ja00984a001
      [ACS Full Text ACS Full Text], [CAS], Google Scholar
      57
      Proton magnetic resonance studies of the solvation shell of magnesium(II) in methanol. Solvation number and exchange rate
      Nakamura, Shuzo; Meiboom, Saul
      Journal of the American Chemical Society (1967), 89 (8), 1765-72CODEN: JACSAT; ISSN:0002-7863.
      The exchange rate of MeOH mols. in the solvation shell of Mg++ in acidic anhyd. MeOH was detd. between -50 and 35° from the broadening of OH proton magnetic resonance signals of the free and bound MeOH. The CH3 signal of the coordinated MeOH, which was hidden behind the bulk CH3 line, can be observed by the addn. of Cu++ to the soln. From the temp. behavior of this signal, it can be concluded that ligand exchange, rather than simple OH-proton exchange, is the dominant process under the conditions of the expt. The first-order rate const. and activation parameters at 25° are: k = 4.7 × 103/sec., ΔH⧺ = 16.7 kcal mole-1, and ΔS⧺ = 14 entropy units. From relative intensity measurements of the signals at -80 and -19.2°, the solvation no. of the Mg++ was calcd. to be 6. Similar expts. with Li, Ca, Sr, and Ba perchlorates failed to show a sep. solvation-shell signal down to -110°. For these ions ligand exchange is apparently rapid down to that temp.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaF2sXht1SlsLg%253D&md5=330bf7c66f4ca1f0483fd94cd6ed560c
    58. 58
      Faralli, C.; Pagliai, M.; Cardini, G.; Schettino, V. Ab Initio Molecular Dynamics Study of Mg2+ and Ca2+ Ions in Liquid Methanol. J. Chem. Th. Comp. 2008, 4, 156– 163,  DOI: 10.1021/ct700209v
      [ACS Full Text ACS Full Text], [CAS], Google Scholar
      58
      Ab Initio Molecular Dynamics Study of Mg2+ and Ca2+ Ions in Liquid Methanol
      Faralli, Cristian; Pagliai, Marco; Cardini, Gianni; Schettino, Vincenzo
      Journal of Chemical Theory and Computation (2008), 4 (1), 156-163CODEN: JCTCCE; ISSN:1549-9618. (American Chemical Society)
      Ab initio Car-Parrinello mol. dynamics simulations have been performed in order to investigate the solvation properties of Mg2+ and Ca2+ in fully deuterated methanol soln. to better understand polarization effects induced by the ions. Charge transfer and dipole moment calcns. have been performed to give more detailed insight on the role of the electronic reorganization and its effect on the first solvation shell stability. The perturbation of the methanol H-bond network has been investigated.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2sXhsVehtbjN&md5=2ffb1d3b67734d22cf4f24cd63cd8763

  • Supporting Information

    Supporting Information

    ARTICLE SECTIONS
    Jump To

    The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsami.2c10005.

    • Experimental details, data processing, MCR decomposition of the NEXAFS spectra, details on MD simulations and DFT calculations, 3D rendering of the employed reaction cell, theoretical NEXAFS calculations of DFT-optimized structures, MD Mg–O radial distribution functions of the Mg2+ ion in water and methanol, and convergence of the NEXAFS theoretical spectra calculated from MD snapshots of the Mg2+ ion in methanol (PDF)


    Terms & Conditions

    Most electronic Supporting Information files are available without a subscription to ACS Web Editions. Such files may be downloaded by article for research use (if there is a public use license linked to the relevant article, that license may permit other uses). Permission may be obtained from ACS for other uses through requests via the RightsLink permission system: http://pubs.acs.org/page/copyright/permissions.html.

PDF [ 3MB]

Pair your accounts.

Export articles to Mendeley

Get article recommendations from ACS based on references in your Mendeley library.

Pair your accounts.

Export articles to Mendeley

Get article recommendations from ACS based on references in your Mendeley library.

You’ve supercharged your research process with ACS and Mendeley!

STEP 1:
Click to create an ACS ID

Please note: If you switch to a different device, you may be asked to login again with only your ACS ID.

Please note: If you switch to a different device, you may be asked to login again with only your ACS ID.

Please note: If you switch to a different device, you may be asked to login again with only your ACS ID.

MENDELEY PAIRING EXPIRED
Your Mendeley pairing has expired. Please reconnect