Spin transition characteristics of molecular solvates of Cu^II complexes with nitroxides: sensitivity to the packing type

A method for the synthesis of solvates of dinuclear heterospin complexes of bis(hexafluoroacetylacetonato)copper(II) with 2-(4-methylpyridin-3-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl (L^Me) and 2-(4-ethylpyridin-3-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl (L^Et) of the composition [Cu(hfac)₂L^R]₂ · Solv (Solv = benzene, bromobenzene, toluene, o-xylene, p-xylene) was developed. It was found that a decrease in temperature induces structural transformations of the solid phases of the complexes followed by significant changes in the distances between the paramagnetic centers in the intramolecular exchange clusters {Cu²⁺-O^·-} from 2.321 to 1.974 Å. As a result, the temperature dependences of the effective magnetic moment μ_eff(T) exhibit magnetic features similar to spin transitions. An analysis of the shape of the μ_eff(T) curves suggested that the magnetic properties of the compounds under study depend primarily on the molecular packing. A comparison of the magneto-structural correlations typical of the [Cu(hfac)₂L^R]₂ · Solv complexes studied in this work with the data obtained earlier for analogous solvates of heterospin polymer chain complexes showed that the spin transition characteristics of the [Cu(hfac)₂L^R]₂ · Solv systems are much less sensitive to the change of the solvent than the corresponding characteristics of the heterospin polymers containing solvate molecules in the interchain space. The magnetic characteristics of the heterospin dimer molecules depend primarily on which cavity between the dimers is filled with solvate molecules. For solvates with monoclinic symmetry, changes in the solvent molecules occupying same-type cavities have almost no effect on the spin transition characteristics in the heterospin exchange cluster.