Substrate-binding reactions of the 3[dσ*pσ] excited state of binuclear gold(I) complexes with bridging bis(dicyclohexylphosphino)methane ligands: Emission and time-resolved absorption spectroscopic studies

Abstract

The complexes [Au 2(dcpm) 2]-Y 2 (dcpm = bis(dicyclohexylphosphino)-methane; Y = ClO 4 - (1), PF 6 - (2), CF 3SO 3 - (3), Au(CN) 2 - (4), Cl - (5), SCN - (6) and I - (7)) were prepared, and the structures of 1 and 4-7 were determined by X-ray crystallography. Complexes 1-4 display intense phosphorescence with λ max at 360-368 nm in the solid state at room temperature as well as in glassy solutions at 77 K. The solid-state emission quantum yields of the powdered samples are 0.37 (1), 0.74 (2), 0.53 (3) and 0.12 (4). Crystalline solid 5 displays both high-energy UV (λ max = 366 nm) and low-energy visible emissions (λ max = 505 nm) at room temperature, whereas either 6 or 7 shows only an intense emission with λ max at 465 or 473 nm, respectively. All the complexes in degassed acetonitrile solutions exhibit an intense phosphorescence with λ max ranging from 490 to 530 nm. The high-energy UV emission is assigned to the intrinsic emission of the 3[dσ*pσ] excited state of [Au 2(dcpm) 2] 2+, whereas the visible emission is attributed to the adduct formation of the triplet excited state with the solvent/counterion. The quenching rate constants of the visible emission of [Au 2(dcpm) 2] 2+ in acetonitrile by various anions are 6.08 × 10 5 (ClO 4 -), 9.18 × 10 5 (PF 6 -), 1.55 × 10 7 (Cl -) and 4.06 × 10 9 (I -) mol -1dm 3s -1. The triplet-state difference absorption spectra of 1-4 in acetonitrile show an absorption band with λ max at 350 nm and a shoulder/absorption maxima at 395-420 nm; their relative intensities are dependent upon the halide ion present in solution. Substrate binding reactions of the 3[dσ*pσ] excited state with halide (X -) to give [Au 2(dcpm) 2X] +* would account for the lower energy absorption maxima in the triplet-state difference absorption spectra. With iodide as the counterion, complex 7 undergoes a photoinduced electron-transfer reaction with I - to give the radical anion I 2 -. © Wiley-VCH Verlag GmbH, 2001.