Spectroscopic properties and crystal structures of luminescent linear tri- and tetra-nuclear gold(I) complexes with bis(diphenylphosphinomethyl)phenylphosphine ligand

Abstract

Reaction of [AuCl4]- with 2,2′-thiodiethanol in methanol generated AuI in situ, which reacted with bis(diphenylphosphinomethyl)phenylphospine (dpmp) and NaSCN to give [Au4(dpmp)2(SCN)2]2+ and [Au3(dpmp)2]3+. The crystal structures of [Au4(dpmp)2(SCN)2][SCN]Cl and [Au3(dpmp)2][SCN]3 have been determined: [Au3(dpmp)2][SCN]3, monoclinic, space group P21/n, a = 12.474(4), b = 25.575(4), c = 20.182(6) Å, β = 92.61(3)° and Z = 4; [Au4(dpmp)2(SCN)2][SCN]Cl, space group P1 (no. 2), a = 13.799(2), b = 14.061(2), c = 19.390(4) Å, α = 88.46(2), β = 75.41(1), γ = 74.58(1)° and Z = 2. They comprise nearly linear Au3 and Au4 chains with Au-Au-Au angles of 167.21(2)° for [Au3(dpmp)2][SCN]3, 160.0(1) and 167.2(1) for [Au4(dpmp)2][SCN]Cl. A weak AuI-AuI bonding interaction is anticipated in view of the intramolecular Au ⋯ Au separations. Both complexes show room-temperature photoluminescence. The red shift in the dσ* → pσ transition energy from [Au2(dppm)2]2+ [dppm = bis(diphenylphosphino)methane] to [Au3(dpmp)2]3+ and to [Au4(dpmp)2(SCN)2]2+ has been attributed to the bonding interactions between adjacent P2Au units. The photophysical properties of [Au3(dpmp)2][SCN]3 are discussed.