The structurally variable network of spin couplings and migrating paramagnetic centers in binuclear o-quinone CoII 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. The considered binuclear CoII diketonate adducts manifest the capability of undergoing one- and two-step spin transitions induced by intramolecular electron transfers between the metal ions and the ligand system. An increase in the number of condensed rings of the acene linker promotes the stabilization of the biradicaloid state of the linker and enhances exchange interactions between all paramagnetic centers of the complexes giving rise to the formation of a flexible spin coupling network. The predicted unusual magnetic properties make the binuclear cobalt complexes with di-o-quinone ligand containing acene linker groups the promising building blocks for molecular electronic and spintronic devices.

Dinuclear adducts of di-o-iminoquinone ligands with CoII diketonates: computational insights into two-step valence tautomeric rearrangements

Density functional theory (DFT) computational modeling [B3LYP*/6-311++G(d,p)] of a series of potentially valence tautomeric (VT) dinuclear 2:1 adducts of Co^II bis-acetylacetonate, bis-trifluoroacetylacetonate and bis-hexafluoroacetylacetonate with redox-active tetradentate di-o-iminoquinone ligands has been performed. The significant energy preference of the low-spin electromeric forms of the complexes on the basis of Co^II bis-acetylacetonate points to a low probability of VT in these compounds. Electron-withdrawing CF₃-groups in the diketonate moiety of the mixed-ligand complexes promote narrowing of the energy gaps between the electronic states, which allows one-step VT rearrangements to be expected in the adducts of Co^II bis-trifluoromethylacetylacetonate. The most suitable energy parameters for the occurrence of two-step VT conversion (stability of the adduct with respect to dissociation into the components, small relative energies of electromeric forms and thermally achievable energy barriers to intramolecular electron transfers estimated as minimum energy crossing points) are found for the adduct of di-o-iminoquinone with Co^II bis-trifluoroacetylacetonates comprising a diphenylene linker.

Rational design of potential spin qubits manipulated by the valence tautomerism mechanism: quantum-chemical modeling of the trinuclear transition metal complexes with bischelate linkers

A new series of transition metal coordination compounds capable of manifesting the properties of logical elements of quantum computers has been computationally designed using the DFT UB3LYP*/6-311++G(d,p) calculations.

Influence of Intermolecular Interactions on Valence Tautomeric Behaviors in Two Polymorphic Dinuclear Cobalt Complexes

Two polymorphic structures have been well determined in a valence tautomeric (VT) dinuclear cobalt complex. These polymorphs showed distinct thermal- and photomagnetic behavior, and are thus ideal for studying the "pure" intermolecular factors to VT transitions. In polymorph 1A, the VT cations are arranged head-to-waist with their neighbors and exhibit weak π⋅⋅⋅π interactions, resulting in a gradual and incomplete thermal VT transition. In contrast, the cations in polymorph 1B are arranged head-to-tail and exhibit relatively strong π⋅⋅⋅π interactions, leading to an abrupt and complete thermal VT transition with adjustable hysteresis loop at around room temperature. The VT process for both polymorphs can be induced by light, but the light-excited state of 1B⋅2H₂ O has a higher thermal relaxation temperature than that of 1A⋅3H₂ O.

Magnetism and variable temperature and pressure crystal structures of a linear oligonuclear cobalt bis-semiquinonate

The crystal structure of the first oligomeric cobalt dioxolene complex, Co₃(3,5-DBSQ)₂(^tBuCOO)₄(NEt₃)₂, 1, where DBSQ is 3,5-di-tert-butyl-semiquinonate, has been studied at various temperatures between 20 and 200 K.

Theoretical modeling of valence tautomeric dinuclear cobalt complexes. Adducts of CoII diketonates with cyclic redox-active tetraone ligands

B3LYP*/6-311++G(d,p) calculated two-step VT rearrangement of a Co(ii) diketonate and a pyrene-4,5,9,10-tetraone 2 : 1 adduct occurs with the migration of paramagnetic centers.