Dinuclear Cobalt(II) Complexes Containing 1,3-(or 1,5-)Bis[bis(2-pyridylmethyl)amino]-2-propanolato (or -3-pentanolato): Preparation and Reaction with Molecular Oxygen

Two dinuclear cobalt(II,II) complexes, [Co2(tpdp)(CH3COO)](ClO4)2·0.5H2O (1) and [Co2(tmdp)(CH3COO)](ClO4)2·H2O (2), were prepared, where Htpdp and Htmdp are 1,3-bis[bis(2-pyridylmethyl)amino]-2-propanol and 1,5-bis[bis(2-pyridylmethyl)amino]-3-pentanol respectively. Their electronic spectral and magnetic data revealed that 1 and 2 are five-coordinate in the high-spin state, in the same manner as [Co2(bpmp)(CH3COO)]2+ (3) (Hbpmp=2,6-bis[bis(2-pyridylmethyl)aminomethyl]-4-methylphenol). The complexes reacted with molecular oxygen to form μ-peroxo complexes in dichloromethane and acetonitrile. The oxygen affinity of the complexes decreased in the order of 3>2>1. The relationships between the oxygen affinities and (1) the donor abilities of dinucleating ligands, (2) the energies of the charge-transfer bands (O22− to Co3+) of the μ-peroxo complexes, and (3) the redox potentials of the Co3+–O2−–Co3+/Co3+–O22−–Co3+ couple indicated that a steric effect arising from the dinucleating ligands contributes significantly to the oxygen affinities of the complexes.