A new trinuclear mixed-valence Co(II)-Co(III) complex stabilized by a bis(salicylidene) based ligand

The present work deals with a class I mixed valence trinuclear complex [Co-II(mu-OAc)(2)(mu-L)(2)CO2III (NCS)(2)] (1) formed by partial aerial oxidation (H2L = 1,7-bis(2-hydroxyphenyl)-2,6-diazahepta-1,6-diene). The terminal Co-III N3O3 centres exhibit a uniform facial arrangement of both N-3 and O-3 donor sets and the Co-II centre is coordinated to six oxygen atoms. Variable temperature magnetic susceptibility measurement reveals that the intermediate Co(II) paramagnetic centre undergoes a very weak spin exchange (theta = -6.39 K, antiferromagnetic) interaction with the two terminal Co(III) diamagnetic centres over the range 300-2 K. A three line EPR spectra at 4 K was characterized with highly anisotropic g tensors and the one line broad spectra at 300 K indicates the strong influence of temperature on the metal spin states, consistent with a high spin Co(II) complex. Two anodic responses appeared at +0.85 (Co2+ -> Co3+, reversible) and +1.7 V (Co3+-> Co4+, irreversible) corresponding to one and two electron transfer oxidation respectively. Another reversible signal attributed to Co3+ -> Co2+ reduction occurred at -0.5 V, associated with a two electron stoichiometry. Compound 1 reacted with hydrazinc to form a square planar orange-red [Co-II(L)] species, 2. Inter conversion between 1 and 2 involves electron exchange coupled with proton transfer. (c) 2006 Elsevier Ltd. All rights reserved.