Home – Home – Jornals – Journal of Structural Chemistry 2016 number 2

The review presents the main results of the studies of Prof. S. P. Gabuda, which were devoted to the NMR investigation of the mobility of atoms and molecules. The basic principles of his model for averaging local magnetic fields under the conditions of atomic and molecular mobility are outlined. This model provides a relationship between the parameters of these fields with the structural features of the mobility of atoms and molecules and intermolecular interactions. Ionic and molecular crystals, zeolites, molecular sieves, hydrated proteins, and so on are considered. Phase transitions in guest subsystems, effects of dynamic disordering and correlated electron motion on the mobility of atoms and molecules and their location are discussed.

The review presents the experimental and theoretic data on relativistic effects in solids, which were the objects of S. P. Gabuda’s studies. Coordination and cluster compounds are considered. Unique data obtained by nuclear magnetic resonance, vibrational spectroscopy, magnetochemistry and other methods are presented. The possibilities of the occurrence of polymorphic phase transitions, the Jahn-Teller effect, intermolecular interactions, and other effects due to the features of structure of relativistic wave functions are discussed.

Understanding the behaviour of solid solutions over wide ranges of temperature and pressure remains a major challenge to both theory and experiment. Here we report a detailed exchange Monte Carlo study using a classical ionic model of the model perovskite parascandolaite-neighborite (K,Na)MgF₃ solid solution and its end-members for temperatures in the range 300-1000 K and pressures from 0-8 GPa. Full account is taken of the local environment of the individual cations, clustering and thermal effects. Properties considered include the crystal structure, phase transitions, the thermodynamics of mixing and the non-ideality of the solid solution. Clustering of the potassium ions is examined via a short-range order parameter. Where experimental data are available for comparison, agreement is very good.

Structures and relative energies of binuclear iron-manganese complexes with the phosphine ligand L, which exist in vinylidene Cp(CO)(L)MnFe(m-C=CHPh)(CO)₄ (2) and benzylidene ketene h⁴-{C[Mn(CO)(L)Cp]××(CO)CHPh}Fe(CO)₃ (3) forms are calculated by the B3LYP density functional method. Four isomers with different positions of ligand L relative to the phenyl ring (conformers a and b) and the substituent Ph relative to the С=С bond (conformers E and Z) are considered for each form and their relative stability is determined. It is shown that all isomers of 2 have approximately the same energy (within 4 kcal/mol) whereas the energies of isomers of 3 differ within 21 kcal/mol. Isomer 3Ea in which the PPh₃ ligand contacts with the phenyl substituent of the vinylidene group is most energetically favorable. It is found that with an increase in the L ligand size in the order PH₃ < PH₂Ph < PHPh₂ < PPh₃ the Mn-P bond length increases to 2.37 Å in the most stable isomer of form 3 and to 2.43 Å in the isomers of 2 and three conformers of 3. A more substantial increase in the Mn-P bond length in complexes 2 and 3 correlates with their lower stability as compared to isomer Ea of 3, which is consistent with experimental data on the presence of only one conformer 3Ea in solution.

Within the density functional theory the electronic structure of triple molybdates Li₂M₃Al(MoO₄)₄, where M = Cs, Rb, is studied for the first time. It is found that all molybdates studied belong to wide band insulators with a band gap of ~4 eV. Quadrupole frequencies and asymmetry parameters of the electric field gradient near magnetic ⁷Li, ²⁷Al, ⁸⁷Rb, and ¹³³Cs nuclei are calculated and experimental NMR spectra are interpreted.

Using density functional theory the electronic structure, chemical bond parameters, phase formation energies, and intrinsic defects in metal and non-metal sublattices of chalcogenides MX₂ (M = Nb, Mo, W; X = Se, Te) are determined. For compounds with X = Te a monotonic decrease in charges on metal and non-metal atoms occurs with increasing atomic number, however, for compounds with X = Se this order is violated. With increase in the metal atomic number for both selenides and tellurides, the formation energies increases, i.e. the stability of these phases decreases. The formation energies of vacancies in both sublattices of these systems have a non-monotonic character. For MX₂ (M = Mo, W; X = Se, Te) systems the formation of vacancies in the chalcogen sublattice results in the semiconductor-metal transition, and vacancies in the metal sublattice decrease the band gap.

The B3LYР/6-31( p , d ) density functional method is applied to pheromones of the forest xylophagous insects Ips typographus L. , Monochamus urussovi Fisch ., and Monochamus galloprovincialis Oliv . to calculate the absorption spectra and find excited states. The calculated results are used to assess the possible activity of the molecules when they are affected by solar radiation.

Stacking faults along the (111) direction in low-temperature metastable aluminum oxide (η-Al₂O₃ and χ-Al₂O₃) are studied using density functional theory (DFT). The surface energy of Al₂O₃ (111) is calculated; the intermediate layer between crystalline domains is considered; the ²⁷Al nuclear quadrupole coupling constants are determined.

We review the properties of simple diatomic molecular glasses as explored by nuclear magnetic resonance techniques and measurements of the dielectric susceptibility. We focus on the behavior of classical molecular rotors formed by solid N₂-Ar mixtures and discuss the time dependent behavior in terms of replica symmetry breaking theories.

We report solid-state ³⁵Cl NMR spectra in three hexachlorides, (NH₄)₂SeCl₆, (NH₄)₂TeCl₆ and Rb₂TeCl₆. The C_Q (³⁵Cl) quadrupole coupling constants in the three compounds were found to be 41.4±0.1 MHz, 30.3±0.1 MHz and 30.3±0.1 MHz, respectively, some of the largest C_Q (³⁵Cl) quadrupole coupling constants ever measured in polycrystalline powdered solids directly via ³⁵Cl NMR spectroscopy. The ³⁵Cl EFG tensors are axial in all three cases reflecting the C _{4 v} point group symmetry of the chlorine sites. ³⁵Cl NMR experiments in these compounds were only made possible by employing the WURST-QCPMG pulse sequence in the ultrahigh magnetic field of 21.1 T. ³⁵Cl NMR results agree with the earlier reported ³⁵Cl NQR values and with the complementary plane-wave DFT calculations. The origin of the very large C_Q (³⁵Cl) quadrupole coupling constants in these and other main-group chlorides lies in the covalent-type chlorine bonding. The ionic bonding in the ionic chlorides results in significantly reduced C_Q (³⁵Cl) values as illustrated with triphenyltellurium chloride Ph₃TeCl. The high sensitivity of ³⁵Cl NMR to the chlorine coordination environment is demonstrated using tetrachlorohydroxotellurate hydrate K[TeCl₄(OH)]×0.5H₂O as an example. ¹²⁵Te MAS NMR experiments were performed for tellurium compounds to support ³⁵Cl NMR findings.

The mobility of water molecules in natural natrolite (Na₂Al₂Si₃O₁₀×2H₂O) is investigated by the ¹H NMR method. The spin-lattice relaxation times in the laboratory and rotating frames ( T ₁ and T _1r) are measured as a function of the temperature for a polycrystalline sample. From experimental T ₁ data it follows that at T > 286 K the diffusion of water molecules along channels parallel to the c axis is observed. From experimental T _1r data it follows that at T > 250 K the diffusion of water molecules in transversal channels of natrolite is also observed. At a low temperature ( T < 250 K) the dipolar interaction with paramagnetic impurities (presumably Fe³⁺ ions) becomes significant as a relaxation mechanism of ¹H nuclei.

Solid-state ¹H NMR is applied to investigate the kinetics of diffusion of H₂O molecules in the fibrous zeolite natrolite [Na₂Al₂Si₃O₁₀]×2H₂O. It is found that the stepwise heating of the zeolite in air leads to the following pattern of molecular diffusion jumps: at first they increase in number and then decrease exponentially with time. Conducting such an experiment in an aqueous medium leads to the opposite effect. The results obtained confirm our previous suggestion about the importance of interstitial defects, or over-hydrated local states, in molecular diffusion.

The ionic mobility and conductivity in the crystalline phases of PbSnF₄- x CaF₂ systems ( x = 2.5 mol.%, 5 mol.%, 7.5 mol.%, and 10 mol.%) in the temperature range of 150-500 K are studied by NMR and impedance spectroscopy. The parameters of ¹⁹F NMR spectra, types of ion motions, and ionic conductivity in the PbSnF₄ compound doped with calcium fluoride are found to be determined by the temperature and concentration of calcium fluoride. The specific conductivity of the crystalline phases in the PbSnF₄-CaF₂ systems is rather high at room temperature, and hence, one cannot exclude the possibility to use them for the creation of functional materials with a high ionic (superionic) conductivity.

Fluorophosphatometallates with the composition K₃H₃Zr₃F₃(PO₄)₅, Rb₃H₃Zr₃F₃(PO₄)₅, Rb₃H₃Hf₃F₃(PO₄)₅, CsH₂Hf₂F₂(PO₄)₃×2H₂O are studied by ³¹P, ¹⁹F, and ¹H NMR. It is found that protons enter in the composition of hydrophosphate groups and fluorine atoms occupy the terminal sites in the tetravalent metal environment. Schemes of the crystal structure of fluorophosphatometallates are proposed. It is established that in CsH₂Hf₂F₂(PO₄)₃×2H₂O water molecules are bonded to the phosphate group proton via a strong hydrogen bond and are characterized by a low energy barrier of molecular motions.

A comparative structural study of LiMPO₄ (M = Mn, Fe, Co, Ni) orthophosphates and Li₂MPO₄F (M = Co, Ni) fluorophosphates obtained by mechanochemically assisted solid-state synthesis is performed using powder XRD, IR, and NMR spectroscopy methods. It is shown that all compounds crystallize in the orthorhombic symmetry (space group Pnma ). Lattice parameters decrease on passing from Mn to Ni, which is due to the decrease in the ionic radius of the d metal. According to the IR spectroscopy data, in this series an increase in the covalency of the P-O bond is observed along with a decrease in the covalency of the M-O bond. On passing to fluorophosphates, the symmetry of PO₄ tetrahedra increases. ⁶Li and ³¹P NMR spectra of all compounds are characterized by the dependence of the contact shift on the nature of metal M and the degree of distortion of the MO₆ coordination polyhedron. ⁶Li MAS NMR line width is noticeably affected by the concentration of structural defects. Unlike orthophosphates with equivalent lithium ions, fluorophosphates contain lithium ions in three different positions.

The ²⁷Al, ¹H MAS NMR method is used to study initial nanosized metastable aluminum oxides of a pseudoboehmite series (g- and d-Al₂O₃) after being coated with graphene (С@Al₂O₃) and annealed in the air (С@Al₂O₃-Т). It is demonstrated that aluminum nanoparticles coated with graphene and annealed at high temperatures (to 750°C for g and 1180°C for d) preserve their phase composition but differ from initial oxides by a very low concentration of defects (ОН groups). After the annealing of the graphene coating the hydroxyl cover of oxides is reduced, however, the set of ОН groups differs greatly from that of the initial oxides. Only one type of terminal ОН groups with a ~0.2 ppm shift and one type of bridging m²-ОН groups with a 1.8 ppm shift for g-Al₂O₃ from OH-m²-Al_VAl _n and 2.1 ppm for d-Al₂O₃ OH-m²-Al_IVAl _n are observed. The data obtained make it possible to characterize in detail the d-Al₂O₃ pure phase.

Distributions described by the Bloembergen-Rowland (BR) formula and widely used in NMR of solids for studying polycrystalline samples, which is closely connected with the problem of constructing the convolutions of such distributions with a broadening symmetric function, are strictly area normalized. The application of the obtained methodological results is illustrated by the example of the analysis of NMR data for UF₆.

The temperature and concentration dependences of ²⁰⁷Pb NMR chemical shifts of Pb(NO₃)₂ in D₂O are reported. The results are analyzed in terms of exchange between a solvated lead ion and the Pb(NO₃)⁺ contact-ion pair. Predictions of the chemical shift difference between the aquated ion and contact-ion pair are carried out for the gas-phase entities and for the solvated species with a DFT calculation. Previously reported data on ²⁰⁷Pb NMR chemical shifts of Pb(NO₃)₂ in H₂O are reevaluated. From the analysis, the enthalpy of dissociation of the contact-ion pair is found to be -42.3±1.0 kJ/mol.

Quantum chemical calculations of the [Mo₃S₇(Et₂dtc)₃](Et₂dtc) complex in different solvents are performed. It is shown that the binding energy between the cluster [Mo₃S₇(Et₂dtc)₃]⁺ cation and the outer-sphere (Et₂dtc)^- anion exponentially decreases with increase in the solvent dielectric permittivity. By DOSY NMR it is determined that in chloroform, the cationic and anionic moieties of the complex form an associate (contact ion pair), while in strongly polar dimethyl sulfoxide these moieties move independently of one another.

Optical and magneto-optical properties of solutions of crude oil of different origin (i.e., taken from different fields) are studied in the visible and near-UV region of optical emission. Magnetic circular dichroism (MCD) spectra of oil are obtained in the vicinity of wavelengths of ~410 nm, 533 nm, and 576 nm. It is demonstrated that the intensity of the MCD signal depends on the origin of crude oil, and it is proportional to the oil concentration in the solution. The comparison of the magneto-optical spectroscopy data with the chemical composition of samples allows us to conclude that the observed magneto-optical activity is determined by the presence of VO²⁺ complexes in the oil samples studied. The revealed magneto-optical activity of conventional oil can form a basis of a new method for the analysis of the composition and properties of oil of different origin.

It is considered practically impossible to differentiate between oxygen and fluorine atoms by X-ray diffraction in disordered structures of oxyfluoride compounds due to the similarity of their ionic radii and diffusion factors. Indeed, many transition metal oxyfluoride compounds containing polar pseudo-octahedral MO _x F_{6- x} ( x = 1-3) anions form crystal structures without any fluorine-oxygen (F/O) ordering owing to a large number of local anion configurations. Because of this static disorder, it is impossible to determine the positions of O and F atoms and find the real geometry of the polyhedron. However, this becomes possible in the case of dynamic disorder of oxyfluoride anions when the central atom is displaced from the center of the octahedron toward a vertex, edge, or face (depending on the number of oxygen atoms in the polyhedron), which enables the identification of O and F atoms owing to inherent differences between M-O and M-F bonding. On cooling, such compounds undergo phase transitions of the order-disorder type with substantial changes in the entropy. The examples of static and dynamic orientational disorder in oxyfluoride compounds of d ⁰ transition metals are given.

The reasons for the preference of glide planes in natural crystals are considered by studying the results of an X-ray crystallography analysis of the minerals salzburgite, eldragonite, izoklakeite, and vikingite. The glide planes organize the combination of right- of atomic fragments, which appear during crystallization, and contribute to a uniform distribution of atoms in complex compositions and a more dense and symmetrical packing. The fact that the structures have cation and anion sublattices with similar dimensions and orientations creates a situation similar to that of beats in oscillatory systems and, hence, modulates the intensity of X-ray reflections. The progressively increasing number of structures where individual atomic positions are occupied by two or more types of atoms suggests a stable geometry of the corresponding atomic sublattices with respect to compositional variations. Analysis of these “skeletal” sublattices is a key to understanding the solid-phase transformations, contact interactions, and dynamic processes in mineral associations.

The Rietveld method is used to determine the structure of two samples of high-hydrated zeolite paranatrolite: {Na_1.15Ca_0.38Sr_0.04(H₂O)_3.1}[Al_2.19Si_2.81O₁₀] (Vishnevye Mountains, Urals) and {Na_2.01K_0.04H_0.04(H₂O)_3.8}[Al_2.10Si_2.90O₁₀] (Kirov Mine, Khibiny Massif). Paranatrolite from the Vishnevye Mountains is characterized by the presence of split water positions and a relatively low total H₂O content. Local water-cation assemblages (WCAs) of three configurations are identified in the statistical “mixture”. The extraframework subsystem in the structure of Khibiny paranatrolite is made of WCAs of one configuration. The H₂O content of this mineral is close to the maximum possible amount and is a record-breaker for natrolite-type minerals.

The inclusion compound of the composition [Zn₂(dmf)(bdc)(lac)]×[Mn(C₅H₅)(CO)₃] (C₅H₅ = cyclopentadienyl) is obtained by keeping a mixture of crystals of a porous homochiral metal-organic polymer of the composition [Zn₂(dmf)(bdc)(lac)]×DMF (DMF = N,N¢-dimethylformamide, H₂bdc = terephthalic acid, H₂lac = S -lactic acid) with the excess of cymantrene at 100°C, and the crystal structure of this compound is determined.

Based on the hypothesis advanced by S. P. Gabuda that the SiO₂ molecule could undergo a transition from the linear form to the isomeric form with a ring-shaped (bent) structure, an idea is proposed that when the mantle substance melts, a phase transition of the bent SiO₂ form into the linear SiO₂ form can occur in the lower mantle. This phase transition might be of great importance for the lower-mantle convection processes and also for the rise of mantle plumes carrying both heat energy, and broad range of platinum group and rare elements to the Earth surface.

The bibliometric and subject analysis of the scientific heritage of Professor S. P. Gabuda is carried out using the national (RSCI) and international (CAPlus, WoS, and Scopus) databases.