The Elusive Structures of Pentakis [(triphenilphosphine)gold]ammonium(2+)Bis[tetraflouroborate(1-)]

Abstract

{Pentakis[(triphenylphosphine)gold(I)]ammonium(2+)} bis[(tetrafluoroborate)(1-)] was prepared from {tetrakis-[(triphenylphosphine)gold(I)]-ammonium(1+)} [tetrafluoroborate(1-)] and [(triphenylphosphine)gold(I)] tetrafluoroborate in hexamethyl phosphoric triamide and tetrahydrofuran at 20 °C in 53% yield and crystallized from dichloromethane as the new solvate {[(Ph 3P)Au] 5N} 3 [BF 4] 6 [CH 2Cl 2] 4. The crystal structure of this product has been determined by single-crystal X-ray methods [monoclinic, P2 1/n, a = 34.200(3), b = 15.285(1), c = 53.127(3) Å, β = 107.262(2)°, V = 26521(3) Å 3, Z = 12, at 153 K]. The lattice contains three independent trinuclear dications that have no crystallographically imposed symmetry and are mutually similar in their molecular structure. The geometry of the [Au 5N] core with pentacoordinate nitrogen atoms is intermediate between trigonal-bipyramidal and square pyramidal with severe distortions to minimize the Au-Au distances along some of the edges of the polyhedra. The three structures are thus different from that found previously in the tetrahydrofuran solvate {[(Ph 3P)-Au] 5N}(BF 4) 2(C 4H 8O) 2, where the geometry of the same trinuclear dication is closer to the trigonal-bipyramidal reference model. The new results are discussed in the light of the structures of tetra(gold)ammonium cations in salts of the type {[(Ph 3P)Au] 4N} +X - and of related tetra-, penta-, and hexacoordinate poly(gold)phosphonium, -arsonium, -sulfonium, and -selenonium cations.