Azidoaurates of the alkali metals

Synthesis, crystal structure as well as IR- and Raman-spectroscopic properties of the new ternary azidoaurates(III) A[Au(N-3)(4)] (A = K Rb, Cs) are reported. The translucent orangered compounds were prepared by reaction of the respective binary azides with HAuCl4 in aqueous solutions at room temperature. The crystal structures determined by single crystal X-ray diffraction methods are monoclinic (C2/c (No. 15), K/Rb/Cs[Au(N-3)(4)]: a = 1049.30(9) pm / 1033.93(10) pm / 1011.9(8) pm, b = 1047.52(8) pm / 1064.20(11) pm / 1093.8(8) pm, c = 776.97(7) pm / 809.79(8) pm / 858.4(6) pm, beta = 91.220(5)degrees / 90.322(5)degrees / 92.72(5)degrees) and provide the first examples for azidoaurates with mono-atomic cations. The unusual reduction of the lattice parameter a with increasing cation size in the isotypic series is discussed in detail. IR and Raman-spectroscopic measurements show strongly covalent gold-nitrogen contacts, a bonding situation which is further supported by quantum chemical calculations and ELF-analyses.