A. A. Starikova

Computational design of mixed-ligand adducts of Co aminovinyl ketonates with redox-active o-quinones and their derivatives

The adducts of cobalt aminovinyl ketonates with o-benzoquinones, o-benzoquinone imines, and o-benzoquinone diimines were studied by the density functional theory method (B3LYP*/6-311++G(d,p)). For all of the compounds, the ground states are low-spin structures containing a trivalent cobalt atom and a redox-active ligand in the semiquinonate form. The bulky substituents at the bis-chelate and ligand nitrogen atoms favor a decrease in the energy difference between the low-spin and high-spin isomers of the adducts containing LSCoIII and HSCoII atoms, respectively. These compounds can exhibit valence tautomerism in the crystalline state, but the relatively low stabilization energies of the high-spin isomers in solutions may induce a competing process: dissociation into the original bis-chelate and redox-active ligand.

Assessing the Viability of Extended Nonmetal Atom Chains in MnF4n+2 (M=S and Se)

Theoretical investigations to evaluate the viability of extended nonmetal atom chains on the basis of molecular models with the general formula Mn F4n+2 (M=S and Se) and corresponding solid-state systems exhibiting direct SS or SeSe bonding were performed. The proposed high-symmetry molecules were found to be minima on the potential energy surface for all Sn F4n+2 systems studied (n=2-9) and for selenium analogues up to n=6. Phonon calculations of periodic structures confirmed the dynamic stability of the -(SF4 -SF4 )∞ - chain, whereas the analogous -(SeF4 -SeF4 )∞ - chain was found to have a number of imaginary phonon frequencies. Chemical bonding analysis of the dynamically stable -(SF4 -SF4 )∞ - structure revealed a multicenter character of the SS and SF bonds. A novel definition and abbreviation (ENAC) are proposed by analogy with extended metal atom chain (EMAC) complexes.

Usefulness of the σ-Aromaticity and σ-Antiaromaticity Concepts for Clusters and Solid-State Compounds.

In this Review we present examples of clusters, molecules, and solid-state compounds, for which the use of σ-aromaticity and σ-antiaromaticity concepts is essential for understanding of chemical bonding. We show that the bonding patterns in these σ-aromatic and σ-antiaromatic compounds are similar to those of the corresponding π-aromatic and π-antiaromatic chemical systems, respectively. Undoubtedly, σ-aromaticity helps us understand why the high symmetry isomers are the most stable among myriads of other potential structures. We also show that besides systems exhibiting either σ- or π-aromatic features, there are species, which can possess multiple aromaticity/antiaromaticity, or conflicting aromaticity patterns. We believe that the σ-aromaticity and σ-antiaromaticity concepts will be helpful in rationalizing chemical bonding, structure, stability, and molecular properties of chemical species in both organic and inorganic chemistry. We hope that they will also be useful for other areas of science such as material science, catalysis, nanotechnology, and biochemistry.

Quantum-chemical study of spin crossover in cobalt complexes with an o -benzoquinone ligand

Quantum-chemical modeling of cationic cobalt complexes based on o-benzoquinone and a di-tert-butyl derivative of 2,11-diaza[3.3](2,6)pyridinophane was performed by the density functional theory method in the TPSSh/6-311++G(d,p) approximation. The ground states of the studied compounds are lowspin structures consisting of the divalent metal cation and a redox-active ligand in the semiquinone form. The calculations predict incomplete transition of these complexes to the high-spin state, which is consistent with the results of magnetochemical measurements.

Tetranuclear Cu(II) and Ni(II) complexes with 1,3,5-triketone ligands: A quantum-chemical simulation of exchange interactions

A series of tetranuclear copper and nickel coordination compounds based on 1,3,5-triketone ligands is calculated using the B3LYP/6-31G(d,p) method of the density functional theory. The antiferromagnetic exchange is predicted to be in all studied complexes, regardless of the type of the metal, the size of linker groups, and the presence of additional solvent (pyridine) molecules. The Ni(II) complexes are characterized by weak exchange interactions, which makes it possible to consider them as candidates for the development of spin qubits.

Computational modeling of chelating properties of quinoline spiropyrans

263 Unique photochromic properties underlie the use of spirocyclic compounds as media for rewritable high density optical disks and sunlight eye protection [1, 2]. The increased recent interest in studying such com pounds is caused by the possibility of designing, on their basis, high sensitivity photodynamic chemosensors for rapid determination of heavy metal ions, as well as by their ability to serve as efficient molecular switches, including those with the magnetic response function [3]. The ability of spirocyclic compounds to form com plexes with metal ions was first reported by Phillips et al. [4]. Later [5, 6], study of ionochromism of quin oline containing spiropyrans has demonstrated that the introduction of additional donor centers into spiro pyran molecules 1 facilitates the formation of chelates involving the carbonyl oxygen atom in isomeric mero cyanine structure 2 with an open pyran ring (Scheme 1).

Dual magnetic behavior of Co(II) and Fe(II) bis(chelate) adducts with Di-o-diiminobenzoquinone: Quantum chemical modeling

Computational modeling (DFT UB3LYP*/6-311++G(d,p)) of electroneutral binuclear 2: 1 adducts of cobalt and iron bis(chelates) with N-phenyl-di-o-diiminobenzoquinone bearing the dimethylene linker is performed. The geometries of all electromers of the complexes are determined, and their stabilization energies and exchange interaction parameters are calculated. The magnetic properties of the compounds under study are determined by the metal nature: the cobalt diketonate adducts undergo one- and two-step valence tautomeric rearrangements, while the mixed-ligand iron complexes are capable of demonstrating spin crossover. The calculation results make it possible to regard the studied adducts as the basis for designing molecular switches and spin qubits.

Quantum chemical modeling of valence tautomeric adducts of CoII bischelates with pyrene-4,5-diimines

Quantum chemical study of mixed-ligand (1: 1) adducts of tetracoordinated cobalt complexes (diketonates, bis-aminovinylketonates, and bis-salicylaldiminates) with pyrene-4,5-diimines using density functional theory (DFT B3LYP*/6-311++G(d,p)) revealed compounds possessing valence tautomeric properties. The mechanisms of intramolecular electron transfer accompanied by changing magnetic properties of the complexes under consideration were studied. It was shown that the variation of substituents at the nitrogen atoms of the diimine ligand and the donor groups in the cobalt bischelate, as well as the annulation of five- and six-membered rings to the azomethine fragment exerts a considerable influence on the stability of the formed adducts and the energy difference between their low- and high-spin isomers.

Computer simulation of the isomerization mechanism and spectral characteristics of spiro[1,3,4]oxadiazines

Structural and spectral characteristics of spiro[1,3,4]oxadiazines were calculated by density functional theory method (B3LYP/6-311++G(d,p)). It is shown that a fundamental difference of spirooxadiazines from known spirocyclic compounds is that the ring-opened form is more energetically favorable (by 4.9 kcal mol–1) compared to the ring-closed one. The closeness between the total energies of closed and open forms of spirooxadiazines suggests all isomers to coexist in solution. The intramolecular rearrangements of compounds under study associated with bond cleavage—formation are accompanied by overcoming of lower-energy barriers than those in the case of analogous spiropyrans and spiroxazines. The calculated electronic spectra (TD DFT) and overlapping absorption band maxima of the closed and open spirooxadiazine forms suggest a low probability of photoinitiated ring opening—closure in this compound.

Computational modeling of LD LISC and LIESST rearrangements of a Fe(II) complex with phenanthroline modified by photochromic chromene

Quantum-chemical study (B3LYP*/6-311++G(d,p)) has shown that the Fe(II) complex containing the phenanthroline ligand with annelated chromene and dihydrobis(pyrazol-1-yl)borate anions is able to exhibit thermally induced spin crossover. The calculations predict that the magnetic properties of this compound can be controlled by irradiation (LIESST and LD LISC effects).