EQUILIBRIA AND SPECTROELECTROCHEMICAL STUDIES ON THE FORMATION OF MULTIBRIDGED TRIS(BIPYRAZINE) RUTHENIUM(II) COMPLEXES WITH RUTHENIUM-EDTA GROUPS

The tris(bipyrazine) ruthenium(II) complex forms a series of complexes containing [Ru(II/III)EDTA]2-/- groups coordinated to the peripheral nitrogen atoms of the bipyrazine bridging ligand. These groups exhibit similar redox potentials (E0 = 0.38 V vs. SHE) and a very weak electronic coupling through the central complex. When the peripheral Ru(III) groups are reduced to the Ru(II) state, strong charge-transfer bands appear at 490 and 670 nm and the stability constants increase by 7 orders of magnitude due to d(pi)-p(pi) back-bonding interactions involving the peripheral ions and the bipyrazine ligand.