Highly localized charges control electrostriction: reaction volumes for the reduction of mononuclear and bridged ruthenium complexes.

Changes in electrostriction caused by the reduction of metal centers in monomeric Ru and bridged Ru/Fe complexes reported in this work are highly localized in a polar solvent such as water. In mononuclear complexes, such as [(edta-H)Ru(III)(H2O)], where the pendant carboxylate is protonated or not depending on pH, the charge that determines electrostricted solvent behavior is defined within distances encompassed by the first coordination sphere of the redox center (DeltaV(complex) = 1.4 +/- 0.6 cm3 mol(-1) (pH 4) or 0.9 +/- 0.6 cm3 mol(-1) (pH 1.1)). Furthermore, in dinuclear complexes, even differences in the ligand charge around the second metal center have insignificant effects on electrostrictive interaction with the solvent. Reduction of the Fe center in the systems [(NH3)5Ru(III)(mu-NC)Fe(III)(CN)5] and [(edta)Ru(III)(mu-NC)Fe(III)(CN)5]4- is virtually unaffected (-21.8 +/- 1.8 cm3 mol(-1) and -21.7 +/- 2.8 cm3 mol(-1), respectively) when the Ru center is changed from formally cationic (3+) to anionic (1-).