Maxim R. Ryzhikov

Solid‐state reaction as a mechanism of 1T ↔ 2H transformation in MoS2 monolayers

Monolayers of molybdenum disulfide MoS2 are considered to be prospective materials for nanoelectronics and various catalytic processes. Since in certain conditions they undergo 1T ↔ 2H phase transitions, studying these phase changes is an urgent task. We present a DFT research of these transitions to show that they can proceed as a solid‐state reaction. Two transition states were discovered with energy barriers 1.03 and 1.40 eV. Sulfur atoms in the transition states are shown to be displaced relative to molybdenum atoms so that a tendency of one structural modification to transform into the other modification is seen. This kind of displacements agrees with electron microscopy data reported earlier. The energy parameters indicate that 1T → 2H reactions are exothermic for both transition states and can possibly proceed in a self‐sustained manner when initially activated by some external energy impact.

Dithiolene dimetallic molybdenum(V) complexes displaying intraligand charge transfer (ILCT) emission.

Bifunctional dithiolene ligands have been coordinated to the Mo(V)(O)(μ-S2)Mo(V)(O) unit to afford [Mo2O2(μ-S)2(BPyDTS2)2](2-) (1(2-)) (BPyDTS2 (2-bis-(2-pyridyl)methylene-1,3-dithiolene) dianions. Reaction of the 1(2-) molybdenum dimer with pentacarbonylchlorothenium(i) affords a tetrametallic complex of formula [Mo2O2(μ-S)2(BPyDTS2)2{Re(CO)3Cl}2](2-) (2(2-)). The monomeric (CH3)2Sn(BPyDTS2) (3) tin complex has also been prepared for comparative purposes. In the structure of (Et4N)2[1], the two metal atoms are in a square pyramidal coordination environment defined by two bridging sulfur atoms, one terminal oxygen atom and the two sulfur atoms of the bifunctional dithiolene ligand. This arrangement leaves two nitrogen atoms on each side which coordinate to two Re atoms in the 2(2-) tetrametallic complex. Compound 3 has a distorted tetrahedral structure defined by two carbon atoms of the methyl groups and two sulfur atoms of the dithiolene ligand. The luminescence properties of all three complexes in acetonitrile have been investigated. Detailed studies supported on quantum mechanical calculations revealed that complex 1(2-) shows photoluminescence in the 600-800 nm region with a maximum wavelength of 628 nm and an emission quantum yield of 0.092, associated with an intraligand charge transfer (ILCT) transition. Coordination of two Re(CO)3Cl fragments to 1(2-) to afford 2(2-) does not affect the emission spectrum and shape although it decreases the quantum yield, approximately by a factor of 4.6. Compound 3 exhibits a similar emission spectrum to those of the complexes 1(2-) and 2(2-) in good agreement with the ILCT assignment. The quantum yield of 3 lies between that of the 1(2-) and 2(2-) complexes.

Synthesis and structures of new octahedral heterometal rhenium-osmium cluster complexes

New octahedral anionic heterometal rhenium-osmium cluster complexes [Re5OsSe8(OH)6]3− and [Re4Os2Se8(OH)6]2− were synthesized starting from [Re5OsSe8Cl6]3− and [Re4Os2Se8Cl6]2−, respectively. They were isolated as salts of the compositions Cs3[Re5OsSe8(OH)6] · 11H2O (I), K3[Re5OsSe8(OH)6] · 7H2O (II), and K2[Re4Os2Se8(OH)6] · 3H2O (III). The protonation of the terminal OH ligands of [Re5OsSe8(OH)6]3− in an aqueous solution resulted in crystallization of a neutral complex [Re5OsSe8(H2O)3(OH)3] · 12H2O (IV). The compounds have been characterized by single-crystal X-ray diffraction analysis. The luminescence properties of [Re5OsSe8(OH)6]3− and [Re4Os2Se8(OH)6]2− were studied. In addition, the electronic structures of the complexes were elucidated by DFT calculations.

Metal-metal bond excitation in colloidal solution of NbS3.

For the first time the comparison of the theoretical and experimental data have shown that UV-vis absorption in the region of 600nm in colloidal solution of NbS3 can be described by the d-d electronic transitions to the antibonding molecular orbital. It is proved that the process leads to excitation of metal-metal bond.

Telluride clusters of molybdenum: Synthesis, structures, and NMR spectra

High-temperature reactions of Mo, chalcogen (S or Se), Te, and Br2 in molar ratio Mo: S/Se: Te: Br = 3: 1: 6: 4 were carried out. The reaction products were subjected to mechanochemical activation with K(Dtp) (Dtp = (EtO)2PS2) in a vibrational mill, resulting in the formation of new compounds [Mo3(μ3-Q)0.5(μ3-O)0.5(μ2-Te2)3(Dtp)3](Dtp) (Q = Se (I) and S (II)). The structure of compound I has been established by X-ray diffraction analysis. Solutions of compounds I and II contain mixtures of [Mo3(μ3-Q)(μ2-Te2)3(Dtp)3]+ and [Mo3(μ3-O)(μ2-Te2)3(Dtp)3]+, which is confirmed by mass spectrometry and 31P, 77Se, and 125Te NMR spectroscopy. Quantum-chemical calculations of the 125Te NMR chemical shifts were performed. The compounds are also characterized by IR spectroscopy, Raman spectroscopy, and elemental analysis. Structure I contains short nonvalent contacts between the sulfur atom of the out-of-sphere Dtp anion and the axial tellurium atoms of the cluster.

Induced currents and an 1 H NMR chemical shifts in transition metal clusters (μ-H) 2 Fe 3 (μ 3 -Q)(CO) 9 (Q = S, Se, Te)

The quantum chemical calculations of induced electric currents in (μ-H)2Fe3(μ3-Q)(CO)9 complexes, where Q = S, Se, Te, are carried out. It is demonstrated that the appearance of anomalous 1Н NMR chemical shifts on bridging hydrogen atoms is, first of all, due to the effect of induced currents on iron atoms.

Cluster [Re3S5(Dppe)3]+ and its oxidation to [Re3S4(SO2)(Dppe)3]+

The reaction of cluster [Re3S4(Dppe)3Br3]Br with sodium tert-butyl thiolate affords trinuclear cationic cluster [Re3S5(Dppe)3]Br (I). The oxidation of cluster I with air gives [Re3S4(SO2)(Dppe)3]Cl (II), which is characterized by X-ray diffraction analysis in the form of solvate II · 3.5CH2Cl2 (CIF file CCDC 1401732). The DFT calculations indicate the triplet ground state of the [Re3S5(Dppe)3]+ cation and a significant spin density on the equatorial sulfide ligands, favoring the oxidation of the cluster.

Relativistic effects in oxides and halides of transition and post-transition metals

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.

Cation-anion interactions in [Mo3S7(Et2dtc)3](Et2dtc) solutions

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 outersphere (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.