Spectroscopy, photoredox properties and X-ray crystal structures of triangular gold(I) and silver(I) phosphine complexes

Abstract

The reaction of HC(PPh2)3 with K[AuCl4] in the presence of 2,2′-thiodiethanol in methanol yielded [Au3{HC(PPh2)3}2Cl]2+. The related [Ag3{HC(PPh2)3}2]3+ was prepared by the reaction of HC(PPh2)3 with Ag(CF3SO3) in dichloromethane. Both complex cations were isolated as perchlorate salts. The X-ray structures of [Au3{HC(PPh2)3}2Cl][ClO 4]2 and [Ag3{HC(PPh2)3}2][ClO 4]3 have been determined: [Au3{HC(PPh2)3}2Cl][ClO 4]2·2MeCN, monoclinic, space group C2/c (no. 15), a = 26.466(3), b = 12.741(2), c = 23.012(5) Å, β = 98.89(1)° and Z = 4; [Ag3{HC(PPh2)3}2][ClO 4]3·2MeCN, monoclinic, space group, P21/n, a = 14.597(4), b = 23.047(2), c = 22.485(3) Å, β = 91.49(2)° and Z = 4. Both [Au3{HC(PPh2)3}2Cl]2+ and [Ag3{HC(PPh2)3}2]3+ consist of three metal atoms arranged in a nearly equilateral triangle with the M-M-M angles close to 60°. The measured intramolecular Ag-Ag and Au-Au distances of 3.1618(5)-3.2228(9) and 2.9220(8)-3.0889(8) Å respectively, indicate that the Au-Au bonding interaction is much stronger than that for Ag-Ag. The UV/VIS spectrum of an acetonitrile solution of [Au3{HC(PPh2)3}2Cl]2+ exhibits intense absorption bands at 270 and 290 nm, assignable to the dσ· → pσ transitions. For [Ag3{HC(PPh2)3}2]3+ the UV/VIS spectrum is virtually identical to that of the free HC(PPh2)3. Excitation of a degassed acetonitrile solution of [Au3{HC(PPh2)3}2Cl]2+ at 300-400 nm at room temperature leads to an observed photoluminescence centred at ca. 537 nm with a lifetime of 11 μs [φ = (1.0 ± 0.1) × 10-3]. The excited-state redox potential, [Au3{HC(PPh2)3}2Cl]3+ + e- → [Au3{HC(PPh2)3}2Cl]2+ *, determined by quenching studies with a series of pyridinium acceptors, is -1.6(2) V vs. saturated sodium chloride calomel electrode (SSCE).