SPECTROSCOPY, PHOTOREDOX PROPERTIES AND X-RAY CRYSTAL-STRUCTURES OF TRIANGULAR GOLD(I) AND SILVER(I) PHOSPHINE COMPLEXES

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][ClO4]2 and [Ag3{HC(PPh2)3}2][ClO4]3 have been determined [Au3{HC(PPh2)3}2Cl][ClO4]2.2MeCN, monoclinic, space group C2/c (no. 15), a = 26.466(3), b = 12.741(2), c = 23.012(5) angstrom, beta = 98.89(1)-degrees and Z = 4; [Ag3{HC(PPh2)3}2][ClO4]3.2MeCN, monoclinic, space group, P2(1)/n, a = 14.597(4), b = 23.047(2), c = 22.485(3) angstrom, beta = 91.49(2)-degrees 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-degrees. The measured intramolecular Ag-Ag and Au-Au distances of 3.1618(5)-3.2228(9) and 2.9220(8)-3.0889(8) angstrom 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 d(sigma). --> p(sigma) 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 centered at ca. 537 nm with a lifetime of 11-mu-s [phi = (1.0 +/- 0.1) x 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).