Synthesis, PtS-type structure, and anomalous mechanics of the Cd(CN)(2) precursor Cd(NH3)(2)[Cd(CN)(4)]

摘要

We report the nonaqueous synthesis of Cd(CN)(2) by oxidation of cadmium metal with Hg(CN)(2) in liquid ammonia. The reaction proceeds via an intermediate of composition Cd(NH3)(2)[Cd(CN)(4)], which converts to Cd(CN)(2) on prolonged heating. Powder X-ray diffraction measurements allow us to determine the crystal structure of the previously-unreported Cd(NH3)(2)[Cd(CN)(4)], which we find to adopt a twofold interpenetrating PtS topology. We discuss the effect of partial oxidation on the Cd/Hg composition of this intermediate, as well as its implications for the reconstructive nature of the deammination process. Variable-temperature X-ray diffraction measurements allow us to characterise the anisotropic negative thermal expansion (NTE) behaviour of Cd(NH3)(2)[Cd(CN)(4)] together with the effect of Cd/Hg substitution; ab initio density functional theory (DFT) calculations reveal a similarly anomalous mechanical response in the form of both negative linear compressibility (NLC) and negative Poisson's ratios.