Structure and magnetic and electrochemical properties of (μ-aryloxo)-bis(μ-carboxylato)diruthenium(III) complexes

The dinuclear diruthenium complexes ligated by the (mu-aryloxo)bis(mu-carboxylato) system M[Ru2L(mu-O2CR)(2)] (M = Na, R = Me 1; M = Na, R = Ph 2; M = K, R = Me 3; M = K, R = Ph 4; H5L = 2-hydroxy-5-methyl-m-phenylenedimethylenedinitrilotetraacetic acid) were prepared by the reaction of [RuCl2(Me2SO)(4)] with L5- and carboxylic acid. The structure of the benzoate-bridged complex 4 0.5MeOH . 0.5EtOH . 4H(2)O was elucidated by X-ray crystallography. The Ru ... Ru distance was 3.416 Angstrom (average for two crystallographically independent molecules), comparable to those of (mu-alkoxo)bis(mu-carboxylato)diruthenium complexes The magnetic properties were analysed by a general isotropic exchange Hamiltonian H= -2JS(1). S-2 (S-1 = S-2 = 1/2) yielding meaningfully large antiferromagnetic spin coupling constants (-J= 728 and 649 cm(-1) for 1 and 2, respectively). The cyclic voltammogram of 4 in dmf demonstrated two reduction and one oxidation wave corresponding to the four redox states Ru-2(II), (RuRuIII)-Ru-II Ru-2(III), (RuRuIV)-Ru-III. The intervalence coupling constant K-c estimated from the potential gap between Ru-2II/(RuRuIII)-Ru-II and Ru(II)Run(III)/Ru-2(III), indicated that the introduction of the mu-aryloxo bridge stabilizes the (RuRuIII)-Ru-II mixed-valence species.