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 Au^Iin 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 P(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 Au^I–Au^I bonding interaction is anticipated in view of the intramolecular Au ⋯ Au separations. Both complexes show room-temperature photoluminescence. The red shift in the d_σ*→ p_σ 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.