The Unique bis-(Disulfato)-aurate Anion [Au(S2O7)2]−: Synthesis and Characterization of Li[Au(S2O7)2] and Na[Au(S2O7)2]

The reaction of Au(OH)3 and oleum (65% SO3) in the presence of M2SO4 (M = Li, Na) afforded yellow single crystals of Li[Au(S2O7)2] (triclinic, P1̅, Z = 1, a = 532.20(3), b = 649.69(4), c = 836.72(5) pm, α = 107.982(2)°, β = 90.171(2)°, γ = 102.583(2)°, V = 267.80(3) Å3) and Na[Au(S2O7)2] (monoclinic, P21/n, Z = 2, a = 533.31(3), b = 1193.38(7), c = 907.67(5) pm, β = 98.548(3)°, V = 571.26(6) Å3). Both compounds exhibit the unprecedented [Au(S2O7)2]− anion in which a square planar coordination of the central gold atom is achieved by the chelating attachment of two disulfate groups. The disulfates were characterized by means of IR spectroscopy and DTA/TG measurements. For both compounds, the decomposition occurs via several steps and is finished at about 450 °C at the stage of elemental gold and the sulfates M2SO4 (M = Li, Na), as revealed by X-ray powder diffraction of the residues.