Cadmium Dicyanoaurates and Their Reaction with Ammonia

Abstract

The synthesis and crystal structures of two anionic cadmium dicyanoaurate coordination polymers, [nBu4N]6[(Cd4Cl4)2(Au(CN)2)12][CdCl4] (TCCA) and [nBu4N]2[Cd(Au(CN)2)4], and their reaction with ammonia vapour is reported. TCCA and the isostructural [nBu4N]6[(Cd4Br4)2(Au(CN)2)12][CdBr4] form 3‐D arrays with [Cd4X4]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 [nBu4N]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 [nBu4N]2[Cd(Au(CN)2)4], this results in decomposition into [nBu4N][Au(CN)2] ⋅ 0.5H2O 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.