Hydrothermal synthesis, structural, Raman, and luminescence studies of Am[M(CN)2]3·3H2O and Nd[M(CN)2]3·3H2O (M=Ag, Au): Bimetallic coordination polymers containing both trans-plutonium and transition metal elements

The polymeric compounds consisting of the man-made element, americium, and gold and silver dicyanides were prepared under mild hydrothermal conditions at 120 °C. It was found that the americium ion and the transition metal ions are interconnected through cyanide bridging in the compounds. Given the similarities in the radii of americium and neodymium, crystals of the latter were also characterized for comparison purposes. The four compounds are isostructural and crystallize in the hexagonal space group, P63/mcm, with only slight differences in their unit cell parameters. Crystallographic data (MoKα, λ=0.71073 Å): Am[Ag(CN)2]3·3H2O (1), a=6.7205(10) Å, c=18.577(3) Å, V=726.64(19), Z=2; Am[Au(CN)2]3·3H2O (2), a=6.666(2) Å, c=18.342(3) Å, V=705.9(4), Z=2; Nd[Ag(CN)2]3·3H2O (3), a=6.7042(4) Å, c=18.6199(14) Å, V=724.77(8), Z=2; and Nd[Au(CN)2]3·3H2O (4), a=6.6573(13) Å, c=18.431(4) Å, V=707.2(2), Z=2. The coordination around the Am and/or Nd consists of six N-bound CN− groups resulting in a trigonal prismatic arrangement. Three capping oxygen atoms of coordinated water molecules complete the tricapped trigonal prismatic coordination environment, providing a total coordination number of nine for the f-elements. Raman spectroscopy, which compliments the structural analyses, reveals that the four compounds display strong signals in the νCN stretching region. When compared with KAg(CN)2 or KAu(CN)2, the νCN stretching frequencies for these compounds blue-shift due to bridging of the dicyanometallate ions with the f-element ions. There is subsequent reduction in electron density at the cyanide center. Compared with the silver systems, the νCN frequency appears at higher energy in the gold dicyanide complexes. This shift is consistent with the structural data where the carbon–nitrogen bond distance is found to be shorter in the gold dicyanides.