Equilibrium reactions network for the cis- or trans-bis(pyrazine)tetraammineruthenium(II/III) and ruthenium(II/III)-EDTA complexes.

The electrochemical and spectroelectrochemical behavior of the binuclear and trinuclear complexes generated from the association of cis- or trans-[Ru(NH(3))(4)(pz)(2)](3+ 2+ ) (where pz represents pyrazine) and [RuEDTA(H(2)O)](2- - ) complexes has been investigated in aqueous solution. Based on two sets of spectrophotometrically determined equilibrium constants and on the formal redox potentials, the complex network of equilibrium reactions involving mixed valence species has been elucidated.

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 (E(0) = 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.