Том 57, № 2 (2016)

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.

Structures and relative energies of binuclear iron-manganese complexes with the phosphine ligand L, which exist in vinylidene Cp(CO)(L)MnFe(μ-C=CHPh)(CO)₄ (2) and benzylidene ketene η⁴-{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.

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.

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 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_4v 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.

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 overhydrated local states, in molecular diffusion.

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.

The ²⁷Al, ¹H MAS NMR method is used to study initial nanosized metastable aluminum oxides of a pseudoboehmite series (γ- and δ-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 γ and 1180°C for δ) 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 μ²-ОН groups with a 1.8 ppm shift for γ-Al₂O₃ from OH-μ²-AlVAl_n and 2.1 ppm for δ-Al₂O₃ OH-μ²-AlIVAl_n are observed. The data obtained make it possible to characterize in detail the δ-Al₂O₃ pure phase.

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.

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.

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.

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.