Synthesis, Characterization, and Water Oxidation Activity of Isomeric Ru Complexes

The
synthesis and characterization of the isomeric ruthenium complexes
with the general formula cis- and trans-[Ru­(trpy)­(qc)­X]n+ (trpy is 2,2′:6′,2″-terpyridine,
qc is 8-quinolinecarboxylate, cis-1 and trans-1, X = Cl, n = 0; cis-2 and trans-2, X=OH2, n = 1) with respect to the relative disposition of the carboxylate
and X ligands are reported. For comparison purposes, another set of
ruthenium complexes with general formula cis- and trans-[Ru­(trpy)­(pic)­(OH2)]+ (pic is
2-picolinate (cis-3, trans-3)) have been prepared. The complexes with a qc ligand
show a more distorted geometry compared to the complexes with a pic
ligand. In all of the cases, the trans isomers show lower potential
values for all of the redox couples relative to the cis isomers. Complexes cis-2 and trans-2 with six-member chelate rings show higher catalytic
activity than cis-3 and trans-3. Overall, it was shown
that the electronic perturbation to the metal center exerted by different
orientation and geometry of the ligands significantly influences both
redox properties and catalytic performance.