Ruthenium terpyridine complexes incorporating azo-imine based ancillary ligands. Synthesis, crystal structure, spectroelectrochemical properties and solution reactivities

Ruthenium terpyridine complexes of the type [Ru-II(trpy)(L)(X)][ClO4](n) 1- 15 [trpy=2,2':6,2"-terpyridine; L=NC5H4N=NC6H4(R), R=H, m-Me, m-Cl, p-Me or p-Cl; X=Cl-, n=1 (1-5); H2O, n=2 (6-10) or OH-, n=1 (11-15)] have been syn thesized. The single crystal structures of 1 and 6 were determined. Complex 4 develops in two possible isomeric forms whereas all other complexes stab ilise preferentially in one isomeric form. The complexes exhibit strong MLC T bands near 500 nm and ligand based transitions in the UV region. 1-5 exhi bit moderately strong emissions at 77 K near 600 nm. The chloro (1-5) and t he hydroxo (11-15) complexes display ruthenium(III)-ruthenium(II) couples a nd three to four successive one-electron ligand based reductions. The aqua- complexes (6-10) exhibit a reversible 2e(-)/2H(+) single-step oxidation pro cess in the pH range 1-5.5 corresponding to the [Ru-II(trpy)(L)(H2O)](2+)-[ Ru-IV(trpy)(L)(O)](2+) couple and the potential decreases linearly with inc rease in pH. The chemical oxidations of 6-10 by an excess of Ce-IV in 0.5 M H2SO4 also lead to the formation of corresponding [Ru-IV(trpy)(L)(O)](2+). The oxo-complexes are stable only in the presence of an excess of Ce-IV, o therwise they catalyse the oxidation of water to dioxygen and convert back into the parent aqua-species. The pseudo first order rate constant of the p rocess [Ru-IV(trpy)(L)(O)](2+)--> [Ru-II(trpy)(L)(H2O)](2+) has been determ ined.