Search

A quantum chemical study was carried out for a number of iron(II) complexes [FeL2]Ai·nH2O (L = 2,6‐bis(1H‐imidazole‐2‐yl)pyridine (L1); 2,6‐(4,5‐dimethyl‐1H‐imidazole‐2‐yl)pyridine (L2); 2,6‐bis(1H‐benzimidazole‐2‐yl)pyridine (L3); A = ReO4−, B10H102−, B12H122−; n = 0–2). These complexes exist in the low spin (LS) form 1A1 (total electron spin S = 0) at room temperature and switch to the high spin (HS) form 5T2 (S = 2) upon heating. The experimental isomeric shift and quadrupole splitting values for compounds with L2 exceed those for compounds with L1 and L3 by <0.02> mm/s and <0.1> mm/s, respectively (for LS forms). Such a discrepancy between MS parameters can be explained by the assumption that chemical bonding between the iron ion and the surrounding nitrogen atoms in the compounds with L2 may be more ionic in character than that in the compounds with L1 and L3. At the same time, the results obtained with the TPSSh hybrid meta‐GGA functional gave a better agreement with the experimental data than those obtained with the B3LYP exchange‐correlation functional. [ABSTRACT FROM AUTHOR]

The potential energy surfaces (PESs) and band gap landscapes (BGLs) of MoS2 and TiS2 monolayers were studied with a set of density functional methods. For our best knowledge, the PESs for transition metal dichalcogenides as a function of sulfur atom coordinates were studied for the first time. It is found that the energy differences between chemically meaningful points of the PESs are quite stable with respect to the density functional choice. The BGLs are characterized by "wavelike" structure with maxima that refer to 2H forms and minima that refer to 1T forms and ripples between them. It is shown that thermal vibrations may reduce the band gap in 2H form of MoS2. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The magnetic properties of metal-organic framework compounds [M2(C8H4O4)2 · C6H12N2] (M = Cu, Ni, Co) were studied in the region of 300-4 K by magnetic susceptibility and 1H magic-angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy. The interaction between the magnetic ions M was found to be antiferromagnetic at the temperatures above 100-150 K. Lowering the temperature changes the interaction character to ferromagnetic. The exchange interaction was found between 1,4-diazabicyclo[2,2,2]octane (dabco) molecules and magnetic ion. Magnetic properties in metal-organic framework compound. [ABSTRACT FROM AUTHOR]

The present study provides new experimental data on the reactivity of sulfur-based ligands connected to Re atoms. It was recently discovered that oxidation of µ-S ligands within the bioctahedral [Re12CS14(µ-S)3(CN)6]6- cluster anion using H2O2 led to the formation of µ-SO2 and µ-SO3 products. This work is focused on the investigation of the opposite process - reduction of the [Re12CS14(µ-SO2)3(CN)6]6- anion to [Re12CS14(µ-S)3(CN)6]6- by sulfide ions in an aqueous medium under mild conditions. The reduction results in a slow change of the solution colour, making it possible to investigate in detail the intermediate products. Analysis of the reaction mixture by ESI mass spectrometry revealed that a series of cluster anions [Re12CS17O n(CN)6]6- ( n = 0-5) was generated during the process. This indicates stepwise chemical reduction of bridging SO2 ligands proceeding through the formation of µ-SO ligands. In this way, twelve-nuclear rhenium clusters demonstrate a unique, fully reversible redox cycle of their µ-bridging ligands, keeping the cluster core unchanged. Two mixed-ligand cluster anions, [Re12CS14(µ-SO2)2(µ-S)(CN)6]6- and [Re12CS14(µ-SO2)(µ-S)2(CN)6]6-, were found to be the major reaction intermediates. The former was crystallised with [Cu(NH3)5]2+ and [Cd(NH3) n]2+ ammine cations and investigated by single-crystal X-ray diffraction. To understand the electronic structure and charge distribution in [Re12CS17O n(CN)6]6- cluster anions, DFT calculations were also carried out. [ABSTRACT FROM AUTHOR]

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. © 2015 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

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 β-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. [ABSTRACT FROM AUTHOR]

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. © 2014 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Oxidation of the cluster anion [Re12CS17(CN)6]6- by H2O2 in water is investigated. [ABSTRACT FROM AUTHOR]