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

Abstract

The dinuclear diruthenium complexes ligated by the (µ-aryloxo)bis(µ-carboxylato) system M[Ru₂L(µ-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 L^5– and carboxylic acid. The structure of the benzoate-bridged complex 4·0.5MeOH·0.5EtOH·4H₂O was elucidated by X-ray crystallography. The Ru· · ·Ru distance was 3.416 Å (average for two crystallographically independent molecules), comparable to those of (µ-alkoxo)bis(µ-carboxylato)diruthenium complexes. The magnetic properties were analysed by a general isotropic exchange Hamiltonian H = –2JS₁·S₂ (S₁ = S₂ = ½), 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^II₂, Ru^IIRu^III, Ru^III₂, Ru^IIIRu^IV. The intervalence coupling constant K_C estimated from the potential gap between Ru^II₂/Ru^IIRu^III and Ru^IIRu^III/Ru^III₂ indicated that the introduction of the µ-aryloxo bridge stabilizes the Ru^IIRu^III mixed-valence species.