Vitaliy V. Koval

A Quantum Chemical Study of Bis-(iminoquinonephenolate) Zn(II) Complexes

A computational DFT B3LYP*/6-311++G(d,p) study performed on bis-(iminoquinonephenolate) Zn(II) complex [Zn(II)(C(12)H(8)NO(2))(2)] has revealed a previously unexplored mechanism for valence tautomerism inherent in transition metal complexes with redox active (noninnocent) ligands. The occurrence of energy-close isomeric forms of the complex and their low energy barrier interconversion is caused not by the intramolecular electron transfer (IET) between the metal and ligand frontier orbitals, but the intersystem conversion within a redox active ligand without involvement of a metal center. This mechanism gives a new insight into the origin of the previously experimentally studied isomeric forms of bis-(iminoquinonephenolate) Zn(II) complexes that must be assigned to [Zn(II)((1)L(-1))(2)] (8) and [Zn(II)((1)L(-1))((3)L(-1))] (9) structures. The spin-forbidden transition between the two forms of the complex proceeds via a minimal energy crossing point (MECP) corresponding to the energy barrier of 8.9 kcal mol(-1) for the 9 --> 8 transformation in the gas phase.

Quantum-chemical study of valence tautomerism of a cobalt complex with phenoxybenzoquinone imine

319 An important way to search for structures for molecular switches and memory cells of molecular computers is to study valence tautomerism of transi tion metal complexes [1–4]. This involves the exist ence of isomers with different charge and spin density distributions and, hence, different optical, electrical, and magnetic properties. Transitions between tauto meric forms accompanied by reversible intramolecu lar electron transfer have been studied in Mn and Co complexes with phenoxybenzoquinone imine [5, 6], which can form complexes with metals in the mono (Cat–N–BQ1–) and dianionic (Cat⎯N⎯SQ2–) forms.

Valence tautomerism of a manganese complex with phenoxybenzoquinone imine ligands: A quantum-chemical study

365 Valence tautomeric transition metal complexes with redox active (non innocent) ligands are good candidates for design of molecular switches since the reversible electron transfer between the complex forming metal and the ligands is accompanied by a change in the optical, electrical, and magnetic proper ties [1, 2]. This phenomenon is most commonly observed in manganese and cobalt complexes [3, 4]. In particular, according to experimental data, it takes only 10 kcal mol–1 to overcome the energy barrier for the transition from the low spin state (LSCo(III)) to the high spin state (HSCo(II)) in the cobalt complex with phenoxybenzoquinone imine [5]. This ligand can be in four different oxidative states from 0 to –3; how ever, as a rule, two of its forms are involved in complex ation, namely, the monoanionic Cat–N–BQ1– and radical dianionic (Cat–N–SQ2–) forms.

Boron, carbon, and aluminum supertetrahedral graphane analogues

The electronic and spatial structures of carbon, boron, and aluminum supertetrahedrane models of graphane have been studied by means of density functional theory methods in the supermolecular approximation (B3LYP/6-311G(df,2p)) and with imposing periodic boundary conditions (PBEPBE/6-311G (d,p), HSEH1PBE/6-311G (d,p)). Calculations predict that pure boron and aluminum structures are narrow-gap semiconductors. For supertetrahedral carbon graphane, calculations predict properties intermediate between the semiconductor and insulator properties. All bonds in the carbon system are two-center two-electron (2с–2е), while for the boron system, intratetrahedrane bonds are three-center two-electron (3с–2е), and intertetrahedrane bonds are common two-center two-electron bonds (2с–2е).

Quantum chemical study of intramolecular rearrangements of the cyclooctatetraene complexes C8H8X (X = Mg, Si, S)

Intramolecular rearrangements of the complexes of cyclooctatetraene with magnesium, silicon, and sulfur have been studied by DFT quantum chemical calculations using B3LYP functional and 6-311++G(d,p) and 6-311++G(3df,3pd) basis sets. All complexes are stabilized as nonplanar stereochemically nonrigid structures liable to fast intramolecular circular rearrangements. Valley-ridge inflection points have been detected on the potential energy surfaces of the C8H8Mg and C8H8Si systems, and the reaction path starting from a saddle point and terminating at a minimum passes through a point corresponding to a hilltop, twodimensional for the magnesium atom and four-dimensional for the silicon atom.