The synthesis and crystal structures of two anionic cadmium dicyanoaurate coordination polymers, [n Bu4 N]6 [(Cd4 Cl4 )2 (Au(CN)2 )12 ][CdCl4 ] (TCCA) and [n Bu4 N]2 [Cd(Au(CN)2 )4 ], and their reaction with ammonia vapour is reported. TCCA and the isostructural [n Bu4 N]6 [(Cd4 Br4 )2 (Au(CN)2 )12 ][CdBr4 ] form 3-D arrays with [Cd4 X4 ]4+ (X=Cl, Br) cubane clusters linked from each octahedral Cd(II) centre by three bridging [Au(CN)2 ]- units. TCCA reacts with ammonia with concentrations of 1000 ppm or higher to give a product with a quantum yield of 0.88, while [n Bu4 N]2 [Cd(Au(CN)2 )4 ], which forms a 2-D anionic Cd[Au(CN)2 ]2 sheet structure with axially pendant [Au(CN)2 ]- units, reacts with concentrated ammonia vapour to generate Cd(NH3 )2 [Au(CN)2 ]2 ; this has a similar 2-D sheet structure but with axial NH3 units. Vibrational spectroscopy illustrated that the reaction of both Cd/[Au(CN)2 ]-based materials with ammonia proceeded by breaking Cd-NC bonds. For [n Bu4 N]2 [Cd(Au(CN)2 )4 ], this results in decomposition into [n Bu4 N][Au(CN)2 ] ⋅ 0.5H2 O and Cd(NH3 )2 [Au(CN)2 ]2 , while the reaction of ammonia with TCCA is reversible by heating the ammonia-bound sample above 110 °C. Cd[Au(CN)2 ]2 can be prepared by thermal removal of NH3 units from Cd(NH3 )2 [Au(CN)2 ]2 .
Keywords: Ammonia; Aurophilicity; Coordination polymers; Cyanides; Gold.
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