Dicyanoaurate-based heterobimetallic uranyl coordination polymers

Abstract

The first series of uranyl ([UO₂]²⁺)-dicyanoaurate coordination polymers and molecular complexes has been synthesized. Reactions of [A][Au(CN)₂] (A = [ⁿBu₄N]⁺ or [(Ph₃P)₂N]⁺ ([PPN])) and uranyl nitrate in alcoholic solvents in ambient light led to [A]₂[(UO₂)₂(μ-η²:η²-O₂)(NO₃)₂(μ-Au(CN)₂)₂], which incorporates peroxo ligands into a one-dimensional ladder topology with alternating aurophilic and peroxo rungs. Conducting the reaction with non-alcoholic solvents formed two polymorphs of a one-dimensional chain, [PPN][UO₂(NO₃)₂Au(CN)₂], from acetone, and a molecular analogue, [PPN]₂[UO₂(NO₃)₂(Au(CN)₂)₂], from acetonitrile, none of which exhibited aurophilic interactions. The addition of 2,2′-bipyridine to the initial reaction resulted in [UO₂(bipy)(MeO)(MeOH)]₂[(μ-Au(CN)₂)(Au(CN)₂)], a one-dimensional structure which propagates via a series of linear aurophilic bonds with pendant uranyl complexes; methanol and methoxy ligands provide additional connections through hydrogen bonding. The addition of 5,5′-dimethyl-2,2′-bipyridine using solvothermal conditions resulted in the one-dimensional ladder [UO₂(Me₂bipy)Au(CN)₂]₂[(μ-OH)₂], generated through aurophilic bonds and hydroxide ligands. The incorporation of 2,2′:6′,2′′-terpyridine (terpy) using solvothermal conditions resulted in [[UO₂(terpy)]₂(μ-NO₃)(μ-O)][Au(CN)₂], a molecular salt with no aurophilic interactions. Emission spectra attributable to aurophilic interactions are observed in [ⁿBu₄N]₂[(UO₂)₂(μ-η²:η²-O₂)(NO₃)₂(μ-Au(CN)₂)₂], while all others only show emission typical of the uranyl cation.