Bonding and structure of water molecules in solid hydrates. Correlation of spectroscopic and structural data

Two new bismuth salts with succinic acid: synthesis, structural, spectroscopic and thermal characterization

Two novel bismuth succinate hydrates, namely, poly[[diaqua(μ3-butane-1,4-dicarboxylato)hemi(μ-butane-1,4-dicarboxylato)bismuth] monohydrate], {[Bi(C4H4O4)1.5(H2O)2]·H2O}n (1), and poly[[μ-aqua-aqua(μ3-butane-1,4-dicarboxylato)(μ-butane-1,4-dicarboxylato)-μ-oxido-dibismuth] monohydrate], {[Bi2(C4H4O4)2O(H2O)2]·H2O}n (2), have been synthesized. Their crystal structures were determined by single-crystal X-ray diffraction and the compounds were characterized by IR and Raman spectroscopy, powder X-ray diffraction and thermal analysis. The crystal structure analysis revealed that the compounds are coordination polymers, with 1 having a two-dimensional layered structure and 2 displaying a three-dimensional (3D) framework. Fully deprotonated succinate anions (C4H4O42-) in two different conformations (trans and gauche) are included in their composition. The Bi3+ cations are surrounded by O atoms from the carboxylate groups of succinate anions and aqua ligands. BiO9 coordination polyhedra in 1 are connected in pairs by edges. These pairs are bound together by bridging succinate ligands to form layers. Bismuth coordination polyhedra of two different types (BiO9 and BiO7) in 2 are connected by edges to form infinite ribbons. Ribbons of polyhedra with bridging succinate ligands form a 3D polymeric structure.

Terahertz Signatures of Hydrate Formation in Alkali Halide Solutions

We systematically studied the ability of 20 alkali halides to form solid hydrates in the frozen state from their aqueous solutions by terahertz time-domain spectroscopy combined with density functional theory (DFT) calculations. We experimentally observed the rise of new terahertz absorption peaks in the spectral range of 0.3-3.5 THz in frozen alkali halide solutions. The DFT calculations prove that the rise of observed new peaks in solutions containing Li⁺, Na⁺, or F^- ions indicates the formation of salt hydrates, while that in other alkali halide solutions is caused by the splitting phonon modes of the imperfectly crystallized salts in ice. As a simple empirical rule, the correlation between the terahertz signatures and the ability of 20 alkali halides to form a hydrate has been established.

Infrared and Raman spectra of strontium and barium pimelates monohydrates

The salts of dicarboxylic acids with alkaline earth metals are not very thoroughly studied and only a few such compounds are well known and characterized. In this work a detailed examination of the infrared spectra recorded at room temperature (RT) and at the liquid nitrogen boiling temperature (LNT) and Raman spectra (at room temperature) of the monohydrates of strontium and barium pimelates, [Sr(μ₆-C₇H₁₀O₄)(H₂O)]n and [Ba(μ₆-C₇H₁₀O₄)(H₂O)]n respectively, has been carried on. These isostructural salts are important nucleating agents for processing of isotactic polypropylene (iPP). The vibrational spectra of the two salts have been interpreted by using factor group analysis. For more correct and unequivocal interpretation of the vibrational spectra, samples containing partially and almost fully deuterated crystallization water have also been prepared and studied. The effect of the metal ion on the vibrations of the pimelic acid ion as well as the strength of the hydrogen bonds formed by the crystallization water molecule has been discussed.

Studies on Silver Ions Releasing Processes and Mechanical Properties of Surface-Modified Titanium Alloy Implants

Dispersed silver nanoparticles (AgNPs) on the surface of titanium alloy (Ti6Al4V) and titanium alloy modified by titania nanotube layer (Ti6Al4V/TNT) substrates were produced by the chemical vapor deposition method (CVD) using a novel precursor of the formula [Ag₅(O₂CC₂F₅)₅(H₂O)₃]. The structure and volatile properties of this compound were determined using single crystal X-ray diffractometry, variable temperature IR spectrophotometry (VT IR), and electron inducted mass spectrometry (EI MS). The morphology and the structure of the produced Ti6Al4V/AgNPs and Ti6Al4V/TNT/AgNPs composites were characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Moreover, measurements of hardness, Young's modulus, adhesion, wettability, and surface free energy have been carried out. The ability to release silver ions from the surface of produced nanocomposite materials immersed in phosphate-buffered saline (PBS) solution has been estimated using inductively coupled plasma mass spectrometry (ICP-MS). The results of our studies proved the usefulness of the CVD method to enrich of the Ti6Al4V/TNT system with silver nanoparticles. Among the studied surface-modified titanium alloy implants, the better nano-mechanical properties were noticed for the Ti6Al4V/TNT/AgNPs composite in comparison to systems non-enriched by AgNPs. The location of silver nanoparticles inside of titania nanotubes caused their lowest release rate, which may indicate suitable properties on the above-mentioned type of the composite for the construction of implants with a long term antimicrobial activity.

Role of Anomalous Water Constraints in the Efficacy of Pharmaceuticals Probed by 1H Solid-State NMR

Water plays a complex and central role in determining the structural and reactive properties in numerous chemical systems. In crystalline materials with structural water, the primary focus is often to relate hydrogen bonding motifs to functional properties such as solubility, which is highly relevant in pharmaceutical applications. Nevertheless, understanding the full electrostatic landscape is necessary for a complete structure-function picture. Herein, a combination of tools including 1H magic angle spinning NMR and X-ray crystallography are employed to evaluate the local landscape of water in crystalline hydrates. Two hydrates of an anti-leukemia drug mercaptopurine, which exhibit dramatically different dehydration temperatures (by 90°C) and a three-fold difference in the in vivo bioavailability, are compared. The results identify an electrosteric caging mechanism for a kinetically trapped water in the hemihydrate form, which is responsible for the dramatic differences in properties.

Vibrational spectra of Mg2KH(XO4)2·15H2O (X=P, As) containing dimer units [H(XO4)2]

Infrared and Raman spectra of Mg₂KH(PO₄)₂·15H₂O and Mg₂KH(AsO₄)₂·15H₂O and a series of their partially deuterated analogues were recorded and analyzed. Compounds of the type Mg₂KH(XO₄)₂·15H₂O (X=P, As) are little-known and a rare case of phosphate and arsenate salts containing dimer units [H(XO₄)₂] in the crystal structure. The analysis of their IR spectra (recorded at room and liquid nitrogen temperature) and Raman spectra showed that the spectral characteristics of the XO₄ groups connected in a dimer through a proton are not consistent with the presence of X-O-H covalent linkage and C₁ crystallographic symmetry of the XO₄ groups. The observation of a singlet Raman band for the ν₁(XO₄) mode as well as the absence of substantial splitting of the ν₃(XO₄) modes and IR activation of the ν₁(XO₄) mode suggest that the dimer units [H(XO₄)₂] are most probably symmetric rather than non-symmetric ones. It was found that, in the vibrational spectra of Mg₂KH(AsO₄)₂·15H₂O, both ν₁(AsО₄) and ν₃(AsО₄) modes have practically the same wavenumber around 830cm^-1. It was also established that the ν₄(PО₄) modes in the deuterated hydrogendiphosphate compound are strongly coupled, most probably with HDO and/or D₂O librations. As a whole, the spectral picture of Mg₂KH(XO₄)₂·15H₂O (X=P, As) very much resembles that observed for the struvite type compounds with the formula KMgXO₄·6H₂O (X=P, As) which do not contain X-OH groups. This means that vibrations of the dimers [H(XO₄)₂] play a relatively small part in the general spectral appearance.

The crystal structure of Cs2S2O3·H2O

A reinvestigation of the alkali metal thiosulfates has led to the new phase Cs2S2O3·H2O. At first cesium thiosulfate monohydrate was obtained as a byproduct of the synthesis of Cs4In2S5. Further investigations were carried out using the traditional synthesis reported by J. Meyer and H. Eggeling. Cs2S2O3·H2O crystallizes in transparent, colorless needles. The crystal structure of the title compound was determined by single crystal X-ray diffraction at room temperature: space groupC2/m(No. 12), unit cell dimensions:a= 11.229(4),b= 5.851(2),c= 11.260(5) Å,β= 95.89(2)°, withZ= 4 and a cell volume ofV= 735.9(5) Å3. The positions of all atoms including the hydrogen atoms were located in the structure refinement. Cs2S2O3·H2O is isotypic with Rb2S2O3·H2O. Isolated tetrahedra [S2O3]2−are coordinated by the alkali metal cations, and in addition they serve as acceptors for hydrogen bonding. For both Cs atoms the shortest distances are observed to oxygen atoms of the S2O32−anions whereas the terminating sulfur atom has its shortest contacts to the water hydrogen atoms. Thus, an extended hydrogen bonding network is formed. The title compound has also been characterized by IR spectroscopy. IR spectroscopy reveals the vibrational bands of the water molecules at 3385 cm−1. They show a red shift in the OH stretching and bending modes as compared to free water. This is due both to the S···H hydrogen bonding and to the coordination of H2O molecules to the cesium atoms.

Room-Temperature Oxidation of Formaldehyde by Layered Manganese Oxide: Effect of Water

Layered manganese oxide, i.e., birnessite was prepared via the reaction of potassium permanganate with ammonium oxalate. The water content in the birnessite was adjusted by drying/calcining the samples at various temperatures (30 °C, 100 °C, 200 °C, 300 °C, and 500 °C). Thermogravimetry-mass spectroscopy showed three types of water released from birnessite, which can be ascribed to physically adsorbed H2O, interlayer H2O and hydroxyl, respectively. The activity of birnessite for formaldehyde oxidation was positively associated with its water content, i.e., the higher the water content, the better activity it has. In-situ DRIFTS and step scanning XRD analysis indicate that adsorbed formaldehyde, which is promoted by bonded water via hydrogen bonding, is transformed into formate and carbonate with the consumption of hydroxyl and bonded water. Both bonded water and water in air can compensate the consumed hydroxyl groups to sustain the mineralization of formaldehyde at room temperature. In addition, water in air stimulates the desorption of carbonate via water competitive adsorption, and accordingly the birnessite recovers its activity. This investigation elucidated the role of water in oxidizing formaldehyde by layered manganese oxides at room temperature, which may be helpful for the development of more efficient materials.

Structural, spectroscopic and theoretical studies of dimethylphenyl betaine complex with two molecules of 2,6-dichloro-4-nitro-phenol

The 1:2 complex (1) of dimethylphenyl betaine (DMPB) with two molecules of 2,6-dichloro-4-nitro-phenol (DCNP) was prepared and characterized by X-ray diffraction, B3LYP/6-311++G(d,p) and B3LYP-D3/6-311++G(d,p)calculations, FTIR and NMR spectroscopies. The crystal is monoclinic, space group P21/c with Z=4. The protons at the oxygen atoms of phenols are bonded to each oxygen atoms of the DMPB carboxylate group by two nonequivalent H-bonds with the OH⋯O distances of 2.473(5) and 2.688(4)Å. Both H-bonds in the optimized structures 2 (in vacuum), 3 (in DMSO solution) and dispersion-correlated functional (D3) 4 (in vacuum) are comparable and are slightly shorter than O(6)H(O6)⋯O(2) in the crystal. The FTIR spectrum of 1 shows a broad absorption in the 3400-2000cm(-1) region corresponding to a longer hydrogen bond and a broad absorption in the 1800-500cm(-1) region caused by the shorter H-bond. The relations between the experimental (13)C and (1)H chemical shifts (δexp) of the investigated compound 1 in DMSO solution and GIAO/B3LYP/6-311++G(d,p) magnetic isotropic shielding constants (σcalc) obtained by using the screening solvation model (COSMO) for 3 are linear and reproduce well the experimental chemical shifts described by the equation: δexp=a+b σcalc.

Infrared spectroscopic study of SO₄²⁻ ions included in M'₂M''(SeO₄)₂⋅6H₂O (Me'=K, NH₄⁺; M''=Mg, Co, Ni, Cu, Zn) and NH₄⁺ ions included in K₂M(XO₄)₂⋅6H₂O (X=S, Se; M''=Mg, Co, Ni, Cu, Zn)

Infrared spectra of Tutton compounds, M'₂M''(SeO₄)₂⋅6H₂O (M'=K, NH₄⁺; M''=Mg, Co, Ni, Cu, Zn; X=S, Se), as well as those of SO₄²⁻ guest ions included in selenate host lattices and of NH4(+) guest ions included in potassium host lattices are presented and discussed in the regions of ν₃ and ν₁ of SO₄²⁻ guest ions, ν₄ of NH₄⁺ guest ions and water librations. The SO₄²⁻ guest ions matrix-isolated in selenate matrices (approximately 2 mol%) exhibit three bands corresponding to ν₃ and one band corresponding to ν₁ in good agreement with the low site symmetry C₁ of the host selenate ions. When the larger SO₄²⁻ ions are replaced by the smaller SO₄²⁻ ions the mean values of the asymmetric stretching modes ν₃ of the included SO₄²⁻ ions are slightly shifted to lower frequencies as compared to those of the same ions in the neat sulfate compounds due to the smaller repulsion potential of the selenate matrices (larger unit-cell volumes of the selenates). It has been established that the extent of energetic distortion of the sulfate ions matrix-isolated in the ammonium selenates as deduced from the values of Δν₃ and Δν₃/νc is stronger than that of the same ions matrix-isolated in the potassium selenates due to the formation of hydrogen bonds between the SO₄²⁻ guest ions with both the water molecules in the host compounds and the NH₄⁺ host ions (for example, Δν₃ of the sulfate guest ions have values of 30 and 51 cm(-1) in the nickel potassium and ammonium compounds, and 33 and 49 cm(-1) in the zinc potassium and ammonium compounds, respectively). The infrared spectra of ammonium doped potassium sulfate matrices show three bands corresponding to Δν₄ of the included ammonium ions in agreement with the low site symmetry C₁ of the host potassium ions. However, the inclusion of ammonium ions in selenate matrices (with exception of the magnesium compound) leads to the appearance of four bands in the region of ν₄. At that stage of our knowledge we assume that some kind of disorder of the ammonium ions included in selenate lattices occurs due to the different proton acceptor capability of the SO₄²⁻ and SO₄²⁻ ions. The latter ions are known to exhibit stronger proton acceptor abilities. This fact will facilitate the formation of polyfurcate hydrogen bonds of the ammonium ions in the selenate matrices, thus leading to increasing in the coordination number of these ions, i.e. to a disorder of the ammonium guest ions. The strength of the hydrogen bonds formed in the title Tutton compounds as well as that of the hydrogen bonds in potassium compounds containing isomorphously included ammonium ions as deduced from the wavenumbers of the water librations are also discussed. The bands corresponding to water librations in the spectra of the mixed crystals K₁.₈(NH₄)₀.₂M(XO₄)₂⋅6H₂O (M=Mg, Co, Ni, Cu, Zn; X=S, Se) broaden and shift to lower frequencies as compared to those of the potassium host compounds, thus indicating that weaker hydrogen bonds are formed in the mixed crystals. These spectroscopic findings are owing to the decrease in the proton acceptor capacity of the SO₄²⁻ and SO₄²⁻ ions due to the formation of hydrogen bonds between the host anions and the guest ammonium cations additionally to water molecules (anti-cooperative or proton acceptor competitive effect). Furthermore, the band shifts in the spectra of the selenate matrices are generally larger than those observed in the spectra of the respective sulfates due to the stronger proton acceptor ability of the selenate ions.

Understanding molecular crystals with dispersion-inclusive density functional theory: pairwise corrections and beyond

CONSPECTUS: Molecular crystals are ubiquitous in many areas of science and engineering, including biology and medicine. Until recently, our ability to understand and predict their structure and properties using density functional theory was severely limited by the lack of approximate exchange-correlation functionals able to achieve sufficient accuracy. Here we show that there are many cases where the simple, minimally empirical pairwise correction scheme of Tkatchenko and Scheffler provides a useful prediction of the structure and properties of molecular crystals. After a brief introduction of the approach, we demonstrate its strength through some examples taken from our recent work. First, we show the accuracy of the approach using benchmark data sets of molecular complexes. Then we show its efficacy for structural determination using the hemozoin crystal, a challenging system possessing a wide range of strong and weak binding scenarios. Next, we show that it is equally useful for response properties by considering the elastic constants exhibited by the supramolecular diphenylalanine peptide solid and the infrared signature of water libration movements in brushite. Throughout, we emphasize lessons learned not only for the methodology but also for the chemistry and physics of the crystals in question. We further show that in many other scenarios where the simple pairwise correction scheme is not sufficiently accurate, one can go beyond it by employing a computationally inexpensive many-body dispersive approach that results in useful, quantitative accuracy, even in the presence of significant screening and/or multibody contributions to the dispersive energy. We explain the principles of the many-body approach and demonstrate its accuracy for benchmark data sets of small and large molecular complexes and molecular solids.

Vibrational spectroscopic characterization of the phosphate mineral bermanite-Mn2+Mn2(3+)(PO4)2(OH)2·4(H2O)

Bermanite Mn(2+)Mn(2)(3+)(PO(4))(2)(OH)(2)·4(H(2)O) is a mixed valent hydrated hydroxy phosphate mineral. The mineral is reddish-brown and occurs in crystal aggregates and as lamellar masses. Bermanite is a common mineral in granitic pegmatites. The chemical composition of bermanite was obtained using EDS techniques. We have studied the molecular structure of bermanite using vibrational spectroscopy. The mineral is characterized by a Raman doublet at 991 and 999 cm(-1) attributed to the phosphate stretching mode of two non-equivalent phosphate units. Raman bands at 1071, 1117 and 1142 cm(-1) are assigned to the phosphate antisymmetric stretching modes. The hydroxyl stretching spectral region is complex with overlapping bands attributed to water and hydroxyl stretching vibrations. Vibrational spectroscopy proves most useful for the study of the mineral bermanite.

Promotion of water-mediated carbon removal by nanostructured barium oxide/nickel interfaces in solid oxide fuel cells

The existing Ni-yttria-stabilized zirconia anodes in solid oxide fuel cells (SOFCs) perform poorly in carbon-containing fuels because of coking and deactivation at desired operating temperatures. Here we report a new anode with nanostructured barium oxide/nickel (BaO/Ni) interfaces for low-cost SOFCs, demonstrating high power density and stability in C3H8, CO and gasified carbon fuels at 750°C. Synchrotron-based X-ray analyses and microscopy reveal that nanosized BaO islands grow on the Ni surface, creating numerous nanostructured BaO/Ni interfaces that readily adsorb water and facilitate water-mediated carbon removal reactions. Density functional theory calculations predict that the dissociated OH from H2O on BaO reacts with C on Ni near the BaO/Ni interface to produce CO and H species, which are then electrochemically oxidized at the triple-phase boundaries of the anode. This anode offers potential for ushering in a new generation of SOFCs for efficient, low-emission conversion of readily available fuels to electricity.

Anodes composed of nickel/yttria-stabilized zirconia in solid oxide fuel cells are known to suffer from coking, which reduces their performance. Here, Yang and colleagues report a new barium oxide/nickel anode, which efficiently oxidizes fuel with minimum carbon buildup.

Thermal behavior, powder X-ray diffraction, DFT calculations and vibrational spectra of barium bis(pentacyanonitrosylchromate) octahydrate, Ba3[Cr(CN)5NO]2.8H2O(D2O)

The cell parameters of Ba3[Cr(CN)5NO]2.8H2O were determined from powder X-ray diffraction using the autoindexing program TREOR, and refined by the Le Bail methods with the FULLPROF program. An orthorhombic cell was determined with cell parameters a = 15.0324(2) A, b = 12.9542(9) A, and c = 7.5094(5) A. Two possible space groups are consistent with the systematic absences: Pmcb (#55) and P2cb (#32). Infrared spectra are reported for the polycrystalline compound, isotopically normal and partially deuterated, at temperatures ranging between ca. 80 K and 293 K together with the room temperature Raman spectrum. The assignment of the observed bands was accomplished assuming the existence of one type of pentacyanonitrosylchromate ion in the asymmetric unit, as suggested by the single band found in the NO stretching region of the deuterated anion and in the anhydrous compound. TGA-DTA data are also reported and discussed. The assignments are supported by DFT calculations of the normal modes of vibration of the [Cr(CN)5NO](3-) structure, optimized at the same level of theory.