Magneto-structural Studies of Two M-O-M Bridged Homochiral Mixed Valence Co(II)/Co(III) Complexes

Abstract Two mixed-valence cobalt complexes, [Co II Co III 2 (mpm) 6 ](ClO 4 ) 2 ( 1 ) and [Co II 2 Co III 2 (μ 3 -OMe) 2 (μ-mpm) 4 (NO 3 ) 4 ] ( 2 ), where mpm is the deprotonated form of R or S α-methyl-2-pyridinemethanol, have been structurally and magnetically characterized. Both complexes crystallize in chiral space groups, where 1 is a trinuclear compound with a linear Co(III)–Co(II)–Co(III) topology and 2 is a tetranuclear cluster with a defect dicubane-type structure that has two missing vertices. In both cases the mpm − ligand bridges adjacent Co ions in a η 1 :η 2 :μ manner. The molecular geometries of the complexes reveal the Co ions are octahedral, where the greatest deviation from O h symmetry is apparent for the HS d 7 Co(II) ions. The chirality of 1 and 2 were studied by circular dichroism spectroscopy where opposite Cotton effects are observed for the R- and S -enantiomers of both complexes. Magnetic susceptibility studies reveal the presence of largely quenched first order orbital angular momentum together with weak ion or intermolecular dipole exchange.