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-tppm)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.

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