MU-(PYRIMIDINE) (TRIETHYLENETETRAAMINEHEXAACETATO)DIRUTHENATE(II, III) - NEARLY CLASS-I BEHAVIOR FOR A MIXED-VALENCE COMPLEX WITH POLYAMINOPOLYCARBOXYLATE LIGAND DONORS

The pyrimidine-bridged [Ru2II(ttha)]2- complex [2, pym, 2] has been prepared and characterized in solution by several spectral methods. The mixed-oxidation state species [2, pym, 3] undergoes dissociation of the Ru(III)-pym bond. However, electrochemical methods have been used to determine a corrected comproportionation constant K(c)' = 5.7, for [2, pym, 3] prior to dissociation. Similar evaluations have been carried out with [Ru(hedta)]2(pz)- (K(c)' = 190) and [Ru(hedta)]2(pym)- (K(c)' = 22.7). Comparison with literature data reveals a decrease in stability for the mixed-valence species in a polyaminopolycarboxylate ligand environment compared to a pentaammine ligand environment. This effect is attributed to the role of the carboxylate anionic donors in stabilizing Ru(III), giving virtually isolated valence properties for these mixed-oxidation state binuclear ruthenium polyaminopolycarboxylate complexes (virtual class I behaviour).