Magnetic exchange interaction between paramagnetic transition metal ions and radical ligands. A 9,10dioxophenanthrenesemiquinonato adduct of a nickel(II)–tetraazamacrocycle complex and DFT description

The 9,10-dioxophenanthrenesemiquinonato adduct of a nickel(II)–CTH acceptor (CTH =dl-5,7,7,12,14,14-hexamethyl-1,4,8,11tetraazacyclotetradecane) was synthesized and structurally characterized. Temperature dependent magnetic susceptibility measurements show that this compound has a quartet electronic ground state arising from the strong ferromagnetic coupling between the S= 1 metal ion and the radical ligand. A computational DFT study carried out using the broken symmetry approach supports the observed magnetic properties as well those of the other nickel(II)–semiquinonato analogues. These results elucidate the electronic properties of the related cobalt–dioxolene complexes when undergoing valence tautomerism.