Synthese und Kristallstruktur von Cs3(AuBr4)2Br3 / Synthesis and Crystal Structure of Cs3(AuBr4)2Br3

Abstract

Abstract Cs3(AuBr4)2Br3 is obtained in the form of red needles by adding the stoichiometric amount of CsBr to a solution of HAuBr4 and Br3- in aqueous HBr. The salt decomposes slowly at room temperature to form a mixed-valent, cubic bromo aurate(I,III), in which the linear AuBr2- ions are partially substituted by Br3- ions. At 140 °C Cs2Au2Br6 and CsBr are formed. Cs3(AuBr4)2Br3 crystallizes monoclinic with four formula units in the space group P21/c. The structure is built up by AuBr4-and Br3- anions and Cs+ cations. An average Au−Br distance of 242.2 pm was found for the square planar AuBr4- ion. The linear Br3-groups are almost symmetrical with Br−Br distances of 254.0 and 256.2 pm. Therefore only two vibrations are observed in the IR spectrum: νas = 172, δ = 56 cm-1 . The absorptions of the AuBr4- groups are: νas=250, σas=113, γ=102cm-1.