Evolution of the Electronic Structure of the trans-[Re6S8bipy4Cl2] Octahedral Rhenium Cluster during Reduction.

Understanding the processes that occur during the redox transformations of complexes coordinated by redox-active apical ligands is important for the design of electrochemically active compounds with functional properties. In this work, a detailed analysis of the interaction energy and electronic structure was performed for cluster complexes trans-[Re6S8bipy4Cl2]n (n = 2-, 4-, 6-, 8-), which can be obtained by stepwise electrochemical reduction of a neutral cluster trans-[Re6S8bipy4Cl2] in DMSO solution. It was shown that the formation of open-shell paramagnetic ions with S = 1, 2 and 1 is the most energetically favorable for n = 2-, 4- and 6-, respectively.

The Role of Quadruple Bonding in the Electron Transport through a Dimolybdenum Tetraacetate Molecule.

A dimolybdenum tetraacetate (Mo2(O2CCH3)4) molecule is embedded between two electrodes formed by semi-infinite 1D monatomic chains of lithium, aluminum, and titanium atoms. Electron transport through the Mo2(O2CCH3)4 molecule is calculated. The role of quadrupole bonding in the transport properties of the studied systems is analyzed.

Composite Polyvinylpyrrolidone-Sodium Alginate-Hydroxyapatite Hydrogel Films for Bone Repair and Wound Dressings Applications.

Today, the synthesis of biocompatible and bioresorbable composite materials such as "polymer matrix-mineral constituent," which stimulate the natural growth of living tissues and the restoration of damaged parts of the body, is one of the challenging problems in regenerative medicine. In this study, composite films of bioresorbable polymers of polyvinylpyrrolidone (PVP) and sodium alginate (SA) with hydroxyapatite (HA) were obtained. HA was introduced by two different methods. In one of them, it was synthesized in situ in a solution of polymer mixture, and in another one, it was added ex situ. Phase composition, microstructure, swelling properties and biocompatibility of films were investigated. The crosslinked composite PVP-SA-HA films exhibit hydrogel swelling characteristics, increasing three times in mass after immersion in a saline solution. It was found that composite PVP-SA-HA hydrogel films containing HA synthesized in situ exhibited acute cytotoxicity, associated with the presence of HA synthesis reaction byproducts-ammonia and ammonium nitrate. On the other hand, the films with HA added ex situ promoted the viability of dental pulp stem cells compared to the films containing only a polymer PVP-SA blend. The developed composite hydrogel films are recommended for such applications, such as membranes in osteoplastic surgery and wound dressing.

Chirality and Relativistic Effects in Os3(CO)12.

The energy and structural parameters were obtained for all forms of the carbonyl complex of osmium Os3(CO)12 with D3h and D3 symmetries using density functional theory (DFT) methods. The calculations took into account various levels of relativistic effects, including those associated with nonconservation of spatial parity. It was shown that the ground state of Os3(CO)12 corresponds to the D3 symmetry and thus may be characterized either as left-twisted (D3S) or right-twisted (D3R). The D3S↔D3R transitions occur through the D3h transition state with an activation barrier of ~10-14 kJ/mol. Parity violation energy difference (PVED) between D3S and D3R states equals to ~5 × 10-10 kJ/mol. An unusual three-center exchange interaction was found inside the {Os3} fragment. It was found that the cooperative effects of the mutual influence of osmium atoms suppress the chirality of the electron system in the cluster.

The {Re4} Tetrahedral Cyanometalate Cluster Anion [{Re4(µ3-CCN)4}(CN)12]8- with Inner (µ3-CCN)3- Ligands and Its Features in Coordination of Cu2+ Cations.

A reaction between ReI3 and KCN at elevated temperature led to the formation of the new cyanometalate cluster anion [{Re4(µ3-CCN)4}(CN)12]8- (1). The anion contains µ3-CCN3- ligands, which are stabilized by the coordination to the triangular faces of the tetrahedral {Re4} metallocluster in a µ3 mode. The compound crystallized as a potassium salt, and its crystal structure was determined by single-crystal X-ray diffraction analysis. It was shown that µ3-CCN3- ligands are ambidentate and can interact with transition-metal cations similarly to terminal CN groups, resulting in the polymer framework formation.

Effect of spin-phonon interactions on Urbach tails in flexible [M2(bdc)2(dabco)].

The optical properties of metal-organic frameworks [M2(bdc)2(dabco)] (M = Co, Ni, Cu, Zn) in the wavelength region of 300-1000 nm were studied, and the electronic band-to-band transitions were determined and characterized by the Kubelka-Munk approach and DFT calculations. Urbach edges for band-to-band transitions were determined. The effect of spin-phonon interactions on the width of Urbach edges in paramagnetic [M2(bdc)2(dabco)] is discussed. The obtained data may be useful to interpret polymerization, hybridization, and catalytic reactions in [M2(bdc)2(dabco)] pores and to design electronic and optical devices.

PO23- and AsO3-: Pnictogenide Ligands in the Highly Charged Re4 Cluster Anions [{Re4(PO)3(PO2)}(CN)12]8-, [{Re4As2(AsO)2}(CN)12]8-, and [{Re4(AsO)4}(CN)12]8.

New tetrahedral anionic rhenium cluster complexes [{Re4(PO)3(PO2)}(CN)12]8- (1) and [{Re4As2(AsO)2}(CN)12]8- (2) have been synthesized by the reaction of ReI3 with NaCN and Pred or KCN and Asgray, respectively. Compound 2 was further oxidized by aqueous H2O2 to produce the cluster anion [{Re4(AsO)4}(CN)12]8- (3). The anions contain new pnictogen/oxygen-based ligands, PO23- and AsO3-, which were stabilized by the coordination to the triangular faces of the tetrahedral Re4 metallocluster in µ3-mode. All three compounds were crystallized as either sodium or potassium salts, and their crystal structures were determined by single crystal X-ray diffraction analysis.

Understanding structural flexibility of the paddle-wheel Zn-SBU motif in MOFs: influence of pillar ligands.

Structural parameters and energies of secondary building units (SBUs) in Zn2(C8H4O4)2·C6H12N2 have been examined with DFT and CCSD(T) methods. The SBU structure exhibits flexibility due to close energies of formation of its D4h, D4, and D2d forms. The potential energy surfaces (PESs) calculated for these systems testify that the presence of pillar ligands with negatively charged nitrogens (NCH or DABCO) can lead to almost barrier-free transitions between structural SBU forms. The mobility regions of the SBU motif have been determined.

Parity violating energy difference for mirror conformers of DABCO linker between two M2+ cations (M = Zn, Cd, and Hg).

We have studied the potential energy surface of [ M 2 D A B C O ] 4 + cations (M = Zn, Cd, and Hg), which are considered as a model for the DABCO linker in metal-organic frameworks, a new prospective class of materials. Relativistic four-component and two-component calculations of parity violating energy difference (PVED) for twisted isomers of [ M 2 D A B C O ] 4 + cations have been performed. The right-twisted conformers of [ M 2 D A B C O ] 4 + are more stable than the left-twisted ones. The increase in PVED with the nuclear charge of the transition metal atom M (Z M ) is discussed.

From oxide to a new type of molecular tungsten compound: formation of bitetrahedral cluster complexes [{W6(µ4-O)2(µ3-CCN)4}(CN)16]10- and [{W6(µ4-O)2(µ3-As)4}(CN)16]10.

Tungsten trioxide has been found to be a convenient precursor for the synthesis of metal cluster compounds with new types of cluster cores. The reaction between WO3 and KCN led to the formation of the cluster complex [{W6(µ4-O)2(µ3-CCN)4}(CN)16]10-. Unexpectedly, it includes the fully deprotonated form of acetonitrile, the CCN3- anion, as a µ3-bridging ligand coordinated to the trigonal faces of the bitetrahedral W6 metallocluster. A similar complex [{W6(µ4-O)2(µ3-As)4}(CN)16]10- containing µ3-As3- ligands instead of µ3-CCN3- ones has been synthesized by the reaction between WO3, As and KCN.

Thermal properties of Zn2(C8H4O4)2•C6H12N2 metal-organic framework compound and mirror symmetry violation of dabco molecules.

Thermal properties of Zn2(C8H4O4)2•C6H12N2 metal-organic framework compound at 8-300 K suggest the possibility of subbarrier tunnelling transitions between left-twisted (S) and right-twisted (R) forms of C6H12N2 dabco molecules with D3 point symmetry. The data agree with those obtained for the temperature behavior of nuclear spin-lattice relaxation times. It is shown that there is a temperature range where the transitions are stopped. Therefore, Zn2(C8H4O4)2•C6H12N2 and related compounds are interesting objects to study the effect of spontaneous mirror-symmetry breaking and stabilization of chiral isomeric molecules in solids at low temperatures.

Facile Substitution of Bridging SO22- Ligands in Re12 Bioctahedral Cluster Complexes.

Selective substitution of µ-SO22- groups by either O2- or Se2- ions occurs upon heating the bioctahedral rhenium cluster complex K6[Re12CS14(µ-SO2)3(CN)6] in air atmosphere or in the presence of a Se source, respectively, manifesting the remarkable lability of SO22- ligands bound to a transition-metal cluster. A series of compounds based on the new mixed-ligand anions, [Re12CS14(µ-O)3(CN)6]6-, [Re12CS14(µ-Se)3(CN)6]6-, and [Re12CS14(µ-O)3(OH)6]6-, were isolated and their solid-state structures were elucidated by single-crystal X-ray diffraction analysis. Along with the previously reported µ-sulfide clusters, the new species constitute a series of rhenium anionic complexes with the common formula [Re12CS14(µ-Q)3L6]6- (Q = O, S, Se, L = CN-; Q = O, S, L = OH-), within which the total charge and number of cluster valence electrons (CVEs) are constant. The article presents insights into the mechanistic and synthetic aspects of the substitution process, and it comprehensively discusses the influence of inner ligand environment on the structure, spectroscopic characteristics, and electrochemical behavior of the novel compounds.

Activation Parameters of Self-Diffusion of Aromatic Chiral Molecules in External Magnetic Fields.

The mobility of aromatic chiral molecules 1-phenylethanol and 1-phenyl-1-propanol in liquids was studied by 1H NMR spectroscopy depending on the strength of the external magnetic field, temperature, and concentration ratio of enantiomers. The data obtained were analyzed using Arrhenius law. The activation parameters were found to depend on the applied field. This effect is caused by the induced magnetic moments in aromatic molecules. The use of strong magnetic fields seems to be promising for investigation of intermolecular interactions of chiral molecules.

Thermal effects in guest-host systems: [Zn2 (bdc)(S-lac)(dmf)]•PhEtOH: A DSC and NMR study.

Differential scanning calorimetry and nuclear magnetic resonance were used to investigate thermal effects in the guest-host systems where homochiral metal-organic sorbent [Zn2 (bdc)(S-lac)(dmf)] is considered as a host while 1-phenylethanol enantiomers and their racemic mixture serve as guest molecules. A maximum energy gain from the guest-host interaction was observed in the system with the racemic mixture. The effect of host-guest recognition was revealed for the case of the host and guest having a similar type of chirality in the presence of antipode guest molecules.

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.

A Localized Molecular Orbital Study of the Halogen Substitution Effect on (103)Rh NMR Shielding in [Cp*RhX2]2, Where X = Cl, Br, or I.

(103)Rh NMR parameters and the bonding structure of three complexes of [Cp*RhX2]2, where X = Cl, Br, or I, have been studied with the help of natural bond orbitals (NBOs) and natural localized molecular orbitals (NLMOs). The complexes of [Cp*RhX2]2, where X = Cl, Br, or I, have similar bonding structures, with the major difference being in the degree of covalency of the Rh-X bonds. The decomposition of (103)Rh NMR shielding into diamagnetic, paramagnetic, and spin-orbit terms shows that normal halogen dependence (NHD) of the (103)Rh NMR shift is defined mostly by the paramagnetic term, with the spin-orbit term being significantly smaller. The decomposition of (103)Rh shielding into spin-free NBO and NLMO contributions shows that (103)Rh shielding is dominated by Rh d-orbital deshielding contributions. We explain the NHD of the (103)Rh NMR shift with the increase in the energies of the virtual antibonding Rh-X orbitals along the X = Cl, Br, and I series.

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.

Volatile Heterobimetallic Complexes from PdII and CuII ß-Diketonates: Structure, Magnetic Anisotropy, and Thermal Properties Related to the Chemical Vapor Deposition of CuPd Thin Films.

A novel approach for preparing volatile heterometallic complexes for use as precursors for the chemical vapor deposition of various materials is reported. New CuPd complexes based on ß-diketonate units were prepared, and their structures and compositions were determined. [PdL2 *CuL2 ] (1) and [PdL2 *Cu(tmhd)2 ] (2) (L=2-methoxy-2,6,6-trimethylheptane-3,5-dionate; tmhd=2,2,6,6- tetramethylheptane-3,5-dionate) are 1D coordination polymers with alternating metal complexes, which are connected through weak interactions between the Cu atoms and the OCH3 groups from the ligand of the Pd complexes. The volatility and thermal stability were studied using thermogravimetric and differential thermal analyses and mass spectrometry. Compound 1 vaporizes without decomposition into monometallic complexes. It exhibits magnetic anisotropy, which was revealed from the angular variations in the EPR spectrum of a single crystal. The vapor thermolysis process for 1 was investigated using mass spectrometry, allowing the process to be framed within the temperature range of 200-350 °C. The experimental data, supported by QTAIM calculations of the allowed intermolecular interactions, suggest that 1 likely exists in the gas phase as bimetallic molecules. Compound 1 proved to be suitable as a single-source precursor for the efficient preparation of CuPd alloy films with tunable Cu/Pd ratio. A possible mechanism for the film growth is proposed based on the reported data.

Evolution of chemical bonding and electron density rearrangements during D(3h) → D(3d) reaction in monolayered TiS2: a QTAIM and ELF study.

Monolayered titanium disulfide TiS2, a prospective nanoelectronic material, was previously shown to be subject to an exothermic solid-state D3h -D3d reaction that proceeds via a newly discovered transition state. Here, we study the reaction in detail using topological methods of quantum chemistry (quantum theory of atoms in molecules and electron localization function analysis) and show how electron density and chemical bonding between the atoms change in the course of the reaction. The reaction is shown to undergo a series of topological catastrophes, associated with elementary chemical events such as break and formation of bonds (including the unexpected formation of S-S bonding between sulfur layers), and rearrangement of electron density of outer valence and core shells.

[PtBi2I12]2-: the first polyiodobismuthate containing an octahedral heterometallic unit.

The complex [Na4((CH3)2CO)15][PtBi2I12]·3(CH3)2CO (1) has been prepared by the reaction of BiI3, NaI and H2[PtCl6]·6H2O and structurally characterized using X-ray diffractometry. It represents the first example of a polyiodobismuthate with an octahedral heterometallic unit. Interatomic interactions in the [PtBi2I12](2-) anion were characterized using the topological methods QTAIM and ELF.