Synthesis, Electronic, Magnetic and Structural Characterization of New Trinuclear Mixed-Valence CoIII-CoII-CoIII Complex

The structural, electronic, magnetic and theoretical study of the complex [ Co-3(HL)(2)(mu-AcO)(2)(AcO)(2)], 1, (HL is the dianion obtained by deprotonation of N, N'-bis(salicylidene)-2-hydroxy-1,3-propanediamine and AcO is acetate) shows that 1 crystallizes with two independent molecules in the asymmetric unit. Each molecule is a trinuclear complex. Both molecules have similar geometry, and correspond to a spin system based on trapped mixed valences on six-coordinate metal centres, Co-III(s= 0)-Co-II (s= 3/2)-Co-III(s= 0). The rigid framework formed by the tetradentate Salen-type ligands HL and the syn-syn bridging acetate anions is a characteristic feature observed in other related complexes. However, the here reported compound is the first one in this family having Z'> 1. UV-Vis spectrum shows a broad band in the visible region where d-d transition for ions CoIII and Co-II are. EPR spectra and the electronic energy estimations of the ground state show the presence of two conformers s= 3/2. The T-XM product at 300 K is 3.24 emu mol (-1) K per trinuclear unit, this product is expected for CoII where the contribution of orbital angular moment is taken into account (3.38 emu mol (-1) K for L= 3).