SPECTROSCOPIC, LUMINESCENCE AND ELECTROCHEMICAL STUDIES ON A PAIR OF ISOMERIC COMPLEXES [(BIPY)(2)RU(AB)PTCL2] [PF6](2) AND [CL2PT(AB)RU(BIPY)(2)] [PF6](2), WHERE AB IS THE BIS-BIPYRIDYL BRIDGING LIGAND 2,2' 3',2''/6'',2'''-QUATERPYRIDINE/

The positional isomers [{bipy)(2)Ru} AB(PtCl2)][PF6](2) (Ru-AB-Pt) and [(Cl2Pt)AB{Ru(bipy)(2)}][PF6](2) (Pt-AB-Ru) (bipy = 2,2'-bipyridine) were prepared by a stepwise 'complexes-as-ligands ' method. Each conta ins d(6){Ru(bipy)(2)}(2+) and d(8) {PtCl2} fragments coordinated to th e bridging ligand 2,2':3',2 '':6 '',2 ''-quaterpyridine (AB), which co ntains two inequivalent bipyridyl chelating sites. Electrochemical stu dies show a Ru-II/Ru-III couple and four ligand-centred reductions in each case, the first two reductions being centred on the two bipyridyl fragments (A and B) of the bridging ligand, and the second two being centred on the terminal bipy ligands. The absorption and luminescence properties are consistent with the inequivalent coordination propertie s of sites A and B of AB. In particular, from 77 K luminescence spectr a, it is seen that the Ru-based energy level is 350 cm(-1) higher for Ru-AB-Pt than for Pt-AB-Ru. At room temperature, the Ru-based luminesc ence is stronger and longer-lived (phi = 2.3 x 10(-2), tau = 280 ns) f or Ru-AB-Pt than for its isomeric counterpart (phi = 7.5 x 10(-4) tau = 13 ns).