Photophysical effect of the coordination of water by ruthenium(II) bipyridyl complexes containing hemilabile phosphine-ether ligands

A substantial concentration-dependent red shift of the absorption and emission spectra (77 K) of Ru(bpy)(2)(POMe-P,O)](2+) (1) (POMe = (2-methoxyphenyl)diphenylphosphine) is reported. NMR experiments show this shift to be due to equilibration of 1 with an aquo complex (1b) (K(eff) = (6 +/- 3) x 10(-3)) that forms upon displacement of the coordinated ether in the hemilabile POMe ligand. The excited-state lifetimes of 1 and 1b at 77 K in solid 2:1 ethanol/acetone solution are tau = 2.13 +/- 0.02 and 1.95 +/- 0.02 mus, respectively. The preparation and X-ray crystal structure of a related complex, Ru(bpy)(2)(PO(i)Pr-P)(OH(2))](PF(6))(2) (2b) (PO(i)Pr-P = (2-(2-propoxy)phenyl)diphenylphosphine), is also reported. In solution, this species exists as an equilibrium mixture of complexes that cannot be readily separated. This species also has concentration-dependent absorption spectra in 2:1 ethanol/acetone solution, with a significant red shift (20 nm) at lower concentrations.