Lipophilicity Assessment of Ruthenium(II)-Arene Complexes by the Means of Reversed-Phase Thin-Layer Chromatography and DFT Calculations

The lipophilicity of ten ruthenium(II)-arene complexes was assessed by reversed-phase thin-layer chromatography (RP-TLC) on octadecyl silica stationary phase. The binary solvent systems composed of water and acetonitrile were used as mobile phase in order to determine chromatographic descriptors for lipophilicity estimation. Octanol-water partition coefficient, logK(OW), of tested complexes was experimentally determined using twenty-eight standard solutes which were analyzed under the same chromatographic conditions as target substances. In addition, ab initio density functional theory (DFT) computational approach was employed to calculate logK(OW) values from the differences in Gibbs' free solvation energies of the solute transfer from n-octanol to water. A good overall agreement between DFT calculated and experimentally determined logK(OW) values was established (R-2 = 0.8024-0.9658)

Density functional theory study of the multimode Jahn-Teller effect – ground state distortion of benzene cation

The multideterminental-DFT approach performed to analyze Jahn-Teller (JT) active molecules is described. Extension of this method for the analysis of the adiabatic potential energy surfaces and the multimode JT effect is presented. Conceptually a simple model, based on the analogy between the JT distortion and reaction coordinates gives further information about microscopic origin of the JT effect. Within the harmonic approximation the JT distortion can be expressed as a linear combination of all totally symmetric normal modes in the low symmetry minimum energy conformation, which allows calculating the Intrinsic Distortion Path, IDP, exactly from the high symmetry nuclear configuration to the low symmetry energy minimum. It is possible to quantify the contribution of different normal modes to the distortion, their energy contribution to the total stabilization energy and how their contribution changes along the IDP. It is noteworthy that the results obtained by both multideterminental-DFT and IDP methods for different classes of JT active molecules are consistent and in agreement with available theoretical and experimental values. As an example, detailed description of the ground state distortion of benzene cation is given

Exploring the applicability of density functional tight binding to transition metal ions. Parameterization for nickel with the spin-polarized DFTB3 model

In this work, we explore the applicability and limitations of the current third order density functional tight binding (DFTB3) formalism for treating transition metal ions using nickel as an example. To be consistent with recent parameterization of DFTB3 for copper, the parametrization for nickel is conducted in a spin-polarized formulation and with orbital-resolved Hubbard parameters and their charge derivatives. The performance of the current parameter set is evaluated based on structural and energetic properties of a set of nickel-containing compounds that involve biologically relevant ligands. Qualitatively similar to findings in previous studies of copper complexes, the DFTB3 results are more reliable for nickel complexes with neutral ligands than for charged ligands; nevertheless, encouraging agreement is noted in comparison to the reference method, B3LYP/aug-cc-pVTZ, especially for structural properties, including cases that exhibit Jahn–Teller distortions; the structures also compare favorably to available X-ray data in the Cambridge Crystallographic Database for a number of nickel-containing compounds. As to limitations, we find it is necessary to use different d shell Hubbard charge derivatives for Ni(I) and Ni(II), due to the distinct electronic configurations for the nickel ion in the respective complexes, and substantial errors are observed for ligand binding energies, especially for charged ligands, d orbital splitting energies and splitting between singlet and triplet spin states for Ni(II) compounds. These observations highlight that future improvement in intra-d correlation and ligand polarization is required to enable the application of the DFTB3 model to complex transition metal ions. © 2018 Wiley Periodicals, Inc. © 2018 Wiley Periodicals, Inc

Kinetics, mechanism, and DFT calculations of thermal degradation of a Zn(II) complex with N-benzyloxycarbonylglycinato ligands

A Zn(II) complex with N-benzyloxycarbonylglycinato ligands was studied by non-isothermal methods, in particular Kissinger-Akahira-Sunose's method, and further analysis of these results was performed by Vyazovkin's algorithm and an artificial compensation effect. Density functional theory calculations of thermodynamic quantities were performed, and results obtained by both methods are consistent, thus clarifying the mechanism of this very interesting multi-step degradation

Composition related properties of (Yb,Y)(2)O-3 nanoparticles synthesized by controlled thermal degradation of AA complexes

After controlled thermal degradation of acetylacetonato (AA) complexes, mixtures of monodisperse similar to 5 nm large isometric particles of Y2-xYbxO3 (x = 0.06, 0.10, 0.20, 0.40) were synthesized. Detailed information on nanoparticles' microstructure and core crystal structure is reported. The Yb3+ ions occupy preferently C-3i sites for low Yb3+ concentrations, while for 20 at.% Yb3+, a random distribution was found. It was shown that the particle/crystallite size and strain as well as Raman modes positions and widths are influenced by Yb3+ concentration. Crystallographic and Raman spectroscopy results indicate that the particles are core/shell structured with cubic crystalline core and monoclinic-like disordered shell. Most probable particle's shell/core volume ratio decreased with annealing at 500 degrees C and the shell disappeared when annealed at 1000 degrees C. (C) 2010 Elsevier B.V. All rights reserved

A Practical Computational Approach to Study Molecular Instability Using the Pseudo-Jahn-Teller Effect

Vibronic coupling theory shows that the cause for spontaneous instability in systems presenting a nondegenerate ground state is the so-called pseudo-Jahn-Teller effect, and thus its study can be extremely helpful to understand the structure of many molecules. While this theory, based on the mixing of the ground and excited states with a distortion, has been long studied, there are two obscure points that we try to clarify in the present work. First, the operators involved in both the vibronic and nonvibronic parts of the force constant take only into account electron nuclear and nuclear nuclear interactions, apparently leaving electron electron repulsions and the electron's kinetic energy out of the chemical picture. Second, a fully quantitative computational appraisal of this effect has been up to now problematic. Here, we present a reformulation of the pseudo-Jahn-Teller theory that explicitly shows the contributions of all operators in the molecular Hamiltonian and allows connecting the results obtained with this model to other chemical theories relating electron distribution and geometry. Moreover, we develop a practical approach based on Hartree-Fock and density functional theory that allows quantification of the pseudo-Jahn-Teller effect. We demonstrate the usefulness of our method studying the pyramidal distortion in ammonia and its absence in borane, revealing the strong importance of the kinetic energy of the electrons in the lowest a(2)'' orbital to trigger this instability. The present tool opens a window for exploring in detail the actual microscopic origin of structural instabilities in molecules and solids