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

The complexes [AuI(PPh(3))] 1, [Au-2(mu-dppm)Cl-2] 2 [dppm = bis(diphenylphosphine)methane], [Au-2(mu-dppm)I-2] 3, [Au-3(mu-tppm)Cl-3] 4 [tppm = tris(diphenylphosphino)methane], [Au-3(mu-tppm)I-3] 5, [Au-3(mu-dpmp)(2)Cl-2]Cl 6 [dpmp = bis(diphenylphosphinomethyl)phenylphosphine] and [Au-3(mu-dpmp)(2)I-2]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) Angstrom in 5, 2.946(3) and 2.963(3) Angstrom in 6 and 2.952(1) and 3.020(1) Angstrom in 7. Extended-Huckel 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 pi* 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 (3)m.m.l.c.t. (metal-metal to ligand charge transfer, gold-->phosphine) and (3)l.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 (3)m.l.c.t. (metal to ligand charge transfer) transitions. The temperature effects on the luminescence lifetimes of these complexes have also been studied.