Electrochemical, spectroscopic and EPR study of transition metal complexes of dipyrido[3,2-a:2′,3′-c]phenazine

The electronic structures of the complexes [Ru(dppz)(3)](2+) and (dppz)MLn, MLn=[Ru(bpy)(2)](2+), [Os(phen)(2)](2+), [Cu(PPh3)(2)](+), Re(CO)(3)Cl, Mo(CO)(4), PtPh2 or Pt(Mes)(2) (Mes=2,4,6-trimethylphenyl), have been compared, based on cyclic voltammetry and spectroscopic studies (UV/vis, EPR of paramagnetic states). According to all experimental evidence, the lowest lying pi* orbital of dppz which is singly occupied in complexes of the dppz radical anion is localised almost exclusively in the phenazine part of the ligand. Amongst the consequences of this situation are a very weak coupling of the first three reduction processes of [Ru(dppz)(3)](n), very little difference in the reduction potentials and in the EPR spectra of the radical complexes (dppz(.-))MLn, and absorption spectra with the intense MLCT transitions to higher lying alpha-diimine orbitals.