Structures and luminescent properties of polynuclear gold(I) halides containing bridging phosphine ligands

Abstract

The complexes [AuI(PPh3)] 1, [Au2(μ-dppm)Cl2] 2 [dppm = bis(diphenylphosphine)methane], [Au2(μ-dppm)I2] 3, [Au3(μ-tppm)Cl3] 4 [tppm = tris(diphenylphosphino)methane], [Au3(μ-dpmp)I3] 5, [Au3(μ-dpmp)2Cl2]Cl 6 [dpmp = bis(diphenylphosphinomethyl)phenylphosphine] and [Au3(μ-dpmp)2I2]I 7 were prepared. The crystal structures of 5-7 have been established by X-ray crystal analysis. The measured intramolecular Au-Au distances are 3.136(1) Å in 5, 2.946(3) and 2.963(3) Å in 6 and 2.952(1) and 3.020(1) Å in 7. Extended-Hückel molecular orbital calculations revealed that the 6p orbitals of iodide and 5d orbitals of gold(I) make a significant contribution to the highest occupied molecular orbitals of 5 and of 2 and 4 respectively. The lowest unoccupied molecular orbitals of these complexes mainly comprise π* orbitals of the phosphines. The photophysical properties of 1-6 have been studied. All show dual emissions. The low-energy emissions at around 660-680 nm have a small red shift in energy from chloro to iodo complexes, and a much higher intensity at room temperature than at 77 K. These are attributed to triplet states with mixed 3m.m.l.c.t. (metal-metal to ligand charge transfer, gold→phosphine) and 3l.l.c.t. (ligand to ligand charge transfer, halide to phosphine) characters. The high-energy emissions at around 460-530 nm are more prominent at 77 K and assigned to intraligand and or 3m.l.c.t. (metal to ligand charge transfer) transitions. The temperature effects on the luminescence lifetimes of these complexes have also been studied.