Ruthenium mononitro and mononitroso terpyridine complexes incorporating azoimine based ancillary ligands. Synthesis, crystal structure, spectroelectrochemical properties and kinetic aspects

Ruthenium mononitro and mononitroso terpyridine complexes incorporating str ong pi -acidic azopyridine ligands of the types [Ru-II(trpy)(L)(NO2)]ClO4 6 -10 and [Ru-II(trpy)(L)(NO)][ClO4](3) 11-15 [trpy=2,2':6',2"-terpyridine; L =NC5H4N=NC6H4(R), R=H, m-Me/Cl or p-Me/Cl] respectively have been synthesiz ed starting from [Ru-II(trpy)L(H2O)](2+) 1-5. The single crystal X-ray stru cture of the nitro complex 7 has been determined. In acetonitrile solvent t he nitro complexes exhibit strong MLCT transitions near 500 nm and the same MLCT bands are observed to be blue shifted near 370 nm in the case of the nitroso derivatives. The nitrosyl complexes exhibit nu (NO) in the range 19 60-1950 cm(-1). The nitro (6-10) and nitroso (11-15) complexes exhibit ruth enium(II)-ruthenium(III) oxidation in the ranges 1.33-1.47 V and 1.62-1.72 V versus SCE respectively. The nitroso complexes exhibit two successive one -electron reductions near 0.7 and 0.0 V due to reductions of coordinated NO +--> NO and NO --> NO- respectively. All the complexes (6-15) systematicall y display three ligand based (trpy and L) reductions to negative potentials of the SCE. The nitro complexes (6-10) display weak emissions near 700 nm (Phi =0.83x10(-2)-2.98x10(-2)). The electrochemically generated 6(+)-10(+) show LMCT transitions near 490 nm and rhombic EPR spectra in acetonitrile a t 77 K. The pseudo first order rate constants (k) and the thermodynamic par ameters (DeltaH double dagger, DeltaS double dagger and K) for formation of the nitro complexes, [Ru-II(trpy)(L)(H2O)](2+)--> [Ru-II(trpy)(L)(NO2)](+) , and the conversion [Ru-II(trpy)(L)(NO)](3+)--> [Ru-II(trpy)(L)(NO2)](+) h ave been determined.