Field-induced single-molecule magnet behaviour in a series of dinuclear cobalt(III,II) complexes

Abstract

We present the synthesis, structure and magnetic characterization of four dinuclear cobalt(III,II) complexes: [(NCS)CoIII(Ln)(µ–OAc)CoII(NCS)]·G, with n/G = 1/CH3OH (1), 2/CH3CN (2), 3/- (3) and 4/CH3OH (4), being H2Ln, four closely related reduced Schiff base ligands: H2L1 = (1,3-propanediyl)bis(iminomethylene)bis(6-methoxyphenol), H2L2 = (1,3-propanediyl)bis(iminomethylene)bis(6-ethoxyphenol), H2L3= (2,2-dimethyl-1,3-propanediyl)-bis(iminomethylene)bis(6-methoxyphenol) and H2L4= (2,2-dimethyl-1,3-propanediyl)-bis(iminomethylene)bis(6-ethoxyphenol). The single crystal X-ray structures of complexes 1–4 show that both cobalt centres in the four complexes adopt a distorted octahedral geometry with Co(III) and Co(II) centres residing at inner N2O2 and outer O4 pockets of the reduced Schiff base, respectively. Magnetic measurements show that all complexes behave as Co(II) monomers, confirming the presence of diamagnetic low spin Co(III) ions, which have also been supported by the spin-density calculation using Density Functional Theory. Additionally, complexes 1–4 show a field-induced slow relaxation of the magnetization at low temperatures that follow direct and Raman mechanisms.