Electronic structure and magnetic properties of the triangular nanographenes with radical substituents: a DFT study.

A series of neutral triangular polycyclic aromatic hydrocarbons functionalized with various radical groups (dithiadiazolyl, verdazyl, nitronylnitroxyl, tert-butyl-nitroxyl and also (2,2,6,6-tetramethylpiperidin-1-yl)oxyl) has been computationally studied by the DFT UB3LYP/6-311++G(d,p) quantum-chemical modelling of their electronic structure and magnetic properties. The dependence of the nature and strength of the exchange interactions between paramagnetic centers on the size of the triangular core, the presence of heteroatoms in the polycyclic moiety, the type of the radical substituents and their spatial arrangement has been ascertained. The molecules with the high-spin electronic ground state possessing strong ferromagnetic exchange interactions and virtually non-interacting paramagnetic centers have been revealed, which makes them promising building blocks for organic spintronics devices.

Tetrahedral nickel(ii) and cobalt(ii) bis-o-iminobenzosemiquinonates.

The new bis-o-iminobenzosemiquinonate nickel and cobalt complexes (imSQt-Bu)2M (M = Ni (1), Co (2)), where imSQ is a radical anion of 4,6-di-tert-butyl-N-(tert-butyl)-o-iminobenzoquinone, were synthesized and characterized in detail. The molecular structures of 1 and 2 have been established by single-crystal X-ray analysis. The metal atoms in 1 and 2 have a distorted tetrahedral environment, and the dihedral angles between the planes of two radical imSQ ligands are approximately 80° in both complexes.

Rational Design of Electronically Labile Dinuclear Fe and Co complexes with 1,10-Phenanthroline-5,6-Diimine: A DFT study.

A series of coordination compounds of redox-active 1,10-phenanthroline-5,6-diimine with Co bis-diketonates and Fe dihydrobis(pyrazolyl)borates has been computationally designed by means of density functional theory (DFT UB3LYP*/6-311++G(d,p)) calculations of their electronic structure, energy characteristics, and magnetic properties. Four types of complexes differing by the nature and position of the terminal metal-centered fragments have been considered. The performed systematic calculations have revealed the systems capable of undergoing thermally initiated spin-state switching rearrangements, including those governed by the synchronized mechanisms of spin crossover and valence tautomerism.

The structurally variable network of spin couplings and migrating paramagnetic centers in binuclear o-quinone Co complexes with biradical acene linkers: a computational DFT study.

A series of new magnetically-active coordination compounds comprising binuclear mixed-ligand complexes of cobalt bis-diketonates with acene linkers functionalized by two redox-active o-quinone moieties has been designed by means of density functional theory (DFT UB3LYP*/6-311++G(d,p)) calculations of their electronic structure, energy characteristics and magnetic properties. Two types of redox-active ligands include those with an acene linker bridging two o-benzoquinone fragments and the ligands containing an integrated π-conjugated system formed by annulation of o-quinone rings to the polycyclic core. The calculations reveal the dependence of spin density distribution in the compounds under study on the type of ligand.

Quantum chemical modeling of magnetically bistable metal coordination compounds. Synchronization of spin crossover, valence tautomerism and charge transfer induced spin transition mechanisms.

It has been shown that the computationally designed bimetallic complexes formed as the adducts of Co(II) diketonates and salicylaldiminates with Fe(II) chelates of 1,10-phenanthroline-5,6-dione are susceptible to the synchronized thermally induced intramolecular rearrangements between their electromeric forms LSCo(III)-SQ-LSFe(II), LSCo(III)-SQ-HSFe(II), HSCo(II)-BQ-LSFe(II), HSCo(II)-BQ-HSFe(II) and also HSCo(II)-SQ-LSFe(III), which are governed by the spin-crossover (SCO), valence tautomerism (VT) and charge-transfer-induced spin transition (CTIST) mechanisms of spin-state switching. Stability of the adducts with respect to dissociation into components, relative energies and magnetic properties of the electromers and energy barriers against VT and unprecedented one-step (SCO + VT) rearrangements (estimated as minimum energy crossing points on the seams of the intersection of the corresponding potential energy surfaces) were calculated using the DFT (B3LYP*/6-311++G(d,p)) method. The calculations showed that all these characteristics of the system as well as the energy preferred spin-state switchable mechanisms are very sensitive to the structure of the cobalt diketonate (salicylaldiminate) fragment and can be varied and interchanged by the introduction of electron withdrawing substituents into the ligands.

Theoretical modeling of valence tautomeric dinuclear cobalt complexes. Adducts of Co(II) diketonates with cyclic redox-active tetraone ligands.

The approach to the employment of the mechanism of valence tautomerism (VT) for the design of molecular 2-qubit quantum gates has been extended to adducts 5-8 of Co(II) bis-(malonates), bis-(acetylacetonates), bis-(hexafluoroacetylacetonates) and bis-(trifluoroacetylacetonates) with tetradentate tetraone (cyclic di-o-quinones) redox-active piperazine-2,3,5,6-tetraone L5 (X = NH), 3,3,6,6-tetramethylcyclohexane-1,2,4,5-tetraone L5 (X = C(CH3)2), cyclopenta[fg]acenaphthylene-1,2,5,6-tetraone L6, cyclopenta[fg]acenaphthylene-3,4,7,8-tetraone L7 and pyrene-4,5,9,10-tetraone L8 and computationally studied using the B3LYP*/6-311++G(d,p) method. The calculations reveal ferromagnetic ordering of unpaired electrons in the low-spin electromeric forms of complexes 8 (R1, R2 = H, CH3, CF3) on the basis of L8, which provides for the paramagnetic character of all three interconverting electromers of 8 and makes it possible to realize the two-step mechanism of thermally driven migration of paramagnetic centers between the pyrene-tetraone fragment and metal ions. Through the structural variation of the ancillary diketonate ligands the energy gaps between the electromeric forms of adducts 8 and energy barriers for their interconversion were adjusted to the range of values typical of thermal VT rearrangements.

Valence tautomeric dinuclear adducts of Co(II) diketonates with redox-active diquinones for the design of spin qubits: computational modeling.

The possibility of employing the mechanism of intramolecular electron transfer between metal and ligand centers in the valence tautomeric complexes formed as electrically neutral 2 : 1 adducts of Co(II) diketonates and redox-active tetradentate di-o-quinones, for quantum information processing, has been computationally studied using the DFT B3LYP*/6-311++G(d,p) method. It has been shown that by the proper choice of a linker group bridging the quinone rings and substituents in the diketonate fragments, complexes with the properties required in 2-qubit quantum gates (sufficiently narrow energy gaps between the spin states and weakly coupled paramagnetic centers) can be designed, in order to realize the mechanism of thermally driven migration of paramagnetic centers between the o-quinone fragments and metal atoms. These are exemplified by the adduct of bis-(hexafluoroacetylacetonate)Co(ii) with a diquinone containing dimethylene linker.

Computational design of valence tautomeric adducts of Co(II) diketonates with redox-active o-benzoquinone ligands.

A new concept for the structural design of valence tautomeric (VT) metal complexes involving the formation of stable adducts of a tetracoordinate transition metal complex with a suitable bidentate redox-active ligand has been computationally studied using the DFT B3LYP*/6-311++G(d,p) method. The calculations, performed on a series of adducts of Co(II) diketonates with o-benzoquinone and its mono- and diimines, showed that the mixed-ligand complexes of bis-(hexafluoroacetylacetonate) Co(II) with o-benzoquinone, o-benzoquinone imine and o-benzoquinone diimine satisfy the whole set of necessary conditions to be met by compounds exhibiting VT behaviour (stability of the adduct with respect to dissociation into the components, energy preference of the low-spin electronic state and thermally achievable energy barrier to intramolecular electron transfer determining the intrinsic mechanism of VT rearrangements). These compounds can be regarded as a feasible synthetic target of a broad series of mixed-ligand VT complexes.