Structure and spectroscopy of Tb[Au(CN)2]3· 3H2O

Abstract

The compound Tb[Au(CN)2]3·3H2O crystallizes in a layered structure in the hexagonal space group P6 3/mcm with the 9-coordinate environment of Tb3+ comprising six (CN) and three OH2 in a tricapped trigonal prism. The shortest Au⋯Au distance is 3.31 Å. The vibrational spectra show that the series Ln[Au(CN)2]3·3H2O (Ln = Y, Pr, Sm, Eu, Tb) are isostructural. The electronic spectra of Eu[Au(CN) 2]3·3H2O clearly show that Eu 3+ occupies one site of spectroscopic site symmetry D3h, in agreement with the crystallographic data. The electronic emission and absorption spectra of Tb[Au(CN)2]3·3H2O have been recorded at temperatures down to 1.5 K, and the f-f pure electronic transitions are interpreted in detail as arising from the lowest electronic states (in D3h symmetry) (7F6)E′ in absorption and (5D4)E″ in emission. At low energy, further bands are assigned to the vibronic structure of the C≡N stretching and water stretching modes, with the latter more predominant. Although the C≡N stretching vibrations show exclusive infrared or Raman activity in Tb[Au(CN)2]3·3H2O, both of these infrared and Raman active modes are observed in the two-center vibronic transitions. The reasons for this are discussed. © 2005 American Chemical Society.