The chemistry of gold is strongly influenced by relativistic effects. Among others, formation of negatively charged anions is an extraordinary feature of this metal. These auride anions, Au-, have been proved to be a stable entities in solution and in the solid state.
Besides classical solid state synthesis routes to auride compounds at high temperatures, the solvent ammonia has been proved to be not only an ideal medium to crystallize aurides, but also to act as reaction partner, yielding auride compounds with new chemical and physical properties, as well as new structural features:
- Cesium auride ammoniate, CsAu•NH3
||The recrystallization of yellow CsAu in liquid NH3 yields blue metallic crystals of CsAu•NH3. In this compound the electron density is partly transferred from the Au– ions to the ammonia partial structure.
- Tetramethylammonium auride, (NMe4)Au
|(NMe4)Au, which only can be synthesized through ion exchange in liquid ammonia, is the first example of an auride with an organic cation. Furthermore, the NMe4+ (Me = methyl group) cations separate the Au– ions, and this compound was the first known colorless auride compound.
||In [Rb(crown-6)(NH3)3]Au•NH3 the auride anion acts as an acceptor in N-H⋅⋅⋅Au– hydrogen bonds. For the first time, experimental values for an N-H⋅⋅⋅Au– distance and the corresponding ∠NHAu angle could be determined.
A recent review:
- M. Jansen: SolidState Sc. 2005, 7, 1464.
- A.-V. Mudring, M. Jansen, J. Daniels, S. Krämer, M. Mehring, J. P. P. Ramalho, A. H. Romero, M. Parrinello:
Angew. Chem. Int. Ed. 2002, 41, 120.
- P. D. C. Dietzel, M. Jansen: Chem. Commun. 2001, 2208.
- H. Nuss, M. Jansen: Angew. Chem. Int. Ed. 2006, 118, 4476.