Novel tris-o-semiquinonato cobalt complexes, where quinonato fragments are modified by cyclic substituents

Octacarbonyldicobalt reacts with tricyclic 5,8-di(tert-butyl)-2,3-dihydro-1,4-ethanoquinoxaline-6,7-dione and 5,8-di-tert-butyl-2,3-dihydrobenzo[b][1,4]dioxine-6,7-dione to give tris-o-semiquinonato complexes (1 and 2, respectively). X-ray structural study indicate exact trigonal prismatic environment of cobalt in 1 and slightly twisted one in 2. Rigid and flexible steric configurations of N,N′-piperazino- and O,O′-ethane-1,2-diolato-cyclic fragments of ligands are responsible for trigonal prismatic molecular geometry of 1 and twisted one for 2. Magnetic moment temperature dependences have very close shapes for 1 and 2 and correspond to S = 1/2 ground state. High temperature limits exceed spin-only value calculated for three noninteracting spins on three semiquinones. Precision calorimetric study of temperature dependence of heat capacity of 1 does not detect significant anomalies.

Graphical abstractNovel tris-o-semiquinonato cobalt complexes with N,N′-piperazino- and O,O′-ethane-1,2-diolato-cycles in quinonato back positions have molecular geometry close to trigonal prism. High temperature limits of magnetic moment exceed spin-only values for three unpaired electrons.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► We have obtained two novel tris-o-semiquinonato cobalt complexes. ► Heterocyclic fragments in semiquinones define trigonal prismatic molecular geometry. ► High temperature limit of magnetic moment exceeds value for quartet state.