Supramolecular Chemistry And Self-assembly Special Feature: Cluster self-assembly of digold(I)halonium cations

摘要

Treatment of gold(I) halide complexes of the type L-Au-X [where L = PPh3, PEt3 with X = Cl, Br, I, or L = 2,6-(MeO)2C6H3PPh2 with X = Cl] with AgSbF6 in the molar ratio 2:1 in dichloromethane/tetrahydrofuran at −78°C affords high yields of di[gold(I)]halonium salts of the formula {X[Au(PR3)]2}⁺ SbF (2-8). A determination of the crystal structures of the four triarylphosphine complexes (2-4, 8) revealed the presence of novel tetranuclear dications with a highly symmetrical structure (point group S4) that arises from self-assembly of the dinuclear monocations through a set of four equivalent aurophilic Au–Au interactions. A comparison with two reference structures of corresponding chloronium perchlorate and bromonium tetrafluoroborate salts with monomeric, dinuclear cations shows that the geometry of the latter is greatlyaltered on dimerization to optimize the interactions between theclosed-shell metal centers (Au: 5d¹⁰). Weakmetallophilic bonding clearly becomes significant only incrystal lattices where anions with a larger ionic radius(SbF vs. BF,ClO) reduce the otherwise dominant role of stronginterionic Coulomb forces. The results indicate that aurophilic bondingis indeed an ubiquitous, quite dependable mode of intermetallicinteractions provided that the right environment is chosen to allow theweak forces to become operative.