Charge Distribution in Bis-Dioxolene Radical Metal Complexes. Synthesis and DFT CHaracterization of Dinuclear Co(III) and Cr(III) Complexes with a Mixed-Valent, S = ~1/_2 Semiquinone-Catecholate Ligand

摘要

Bis-dioxolene bridged dinuclear metal complexes of general formula M_2(CTH)_2(diox-diox)(PF_6)_n (n = 2,3; M = Co(III), Cr(III), CTH = tetraazamacrocycle) have been synthesized suing the bis-bidentate ligand 5,5'-di-tert-butyl-3,3',4,4'-tetrahydroxybiphenyl. Thes complexes were characterized by means of ESR, UV-vis, temperature dependent magnetic susceptibility, and cyclic voltammetry. Our results unambiguously suggest that the tripositive dimetal cations can be described as containing a fully delocalized bis-dioxolene trinegative radical ligand (Cat-Sq) bridging two triopositive metal cations. In this frame the sextet electronic ground state characterizes the Cr_2(CTH)_2(Cat-SQ)~(3+) as a result of the antiferromagnetic coupling of the radical bridging ligand with the two equivalent paramagnetic metal centers. The electronic and geometrical structure and the magnetic properties of Cat-Sq and of its complexes have been studied with density functional theory.