Synthesis, structure and magnetic properties of dinuclear cobalt-tetraoxolene complexes with bidentate terminal ligands

Abstract

The design of molecule-based systems with tuneable optical and/or magnetic properties has attracted considerable attention because of their potential applications in high-performance molecule-based electronic devices, switches, sensors and displays. In this regard, a large number of valence tautomeric tetraoxolene-bridged dinuclear cobalt complexes with tetradentate ancillary ligands have been reported, but none of these complexes contained a bidentate terminal ligand. In order to increase the scope in this field, the present report describes the synthesis, structures, electrochemical and magnetic studies of two dinuclear cobalt-tetraoxolene complexes, [Co2(dhbq)(bpy)4](PF6)3 (1(PF6)3) and [Co2(dhbq)(bpa)4](PF6)3·6H2O (2(PF6)3·6H2O), where H2dhbq is 2,5-dihydroxy-1,4-benzoquinone, with the bidentate terminal ligands 2,2′-bipyridine (bpy) and 2,2′-bipyridyl amine (bpa), respectively. An X-ray diffraction study reveals that the dianionic form of the redox active tetraoxolene ligand bridges the metal centers in these complexes, and one metal center is in the high spin cobalt(II) state while the other one is in the low spin cobalt(III) state. The present report will increase knowledge on the synthesis of such systems using bidentate terminal ligands. Variable temperature magnetic susceptibility measurements show no indication for valence tautomerism (VT) in either complex. Further attempts could be made to synthesize similar complexes from different solvents and/or using different counter ions to check whether such variations can bring VT in these systems.