X-ray single crystal structures of Cd(AuF 6) 2, Mg(HF)AuF 4AuF 6 and KAuF 6 and vibrational spectra of Cd(AuF 6) 2 and KAuF 6

Abstract

Cd(AuF 6) 2 crystallizes at 200 K in the monoclinic space group C 2 / c (No. 15) with a = 1116.7 ( 7 ) pm , b = 876.66 ( 16 ) pm , c = 1008.0 ( 4 ) pm , β = 118.026 ( 5 ) ° and Z = 4 . Cadmium atoms are in an octahedral environment of fluorine, and CdF 6 octahedra are sharing their vertices with six AuF 6 units on either side of the plane formed by the Cd atoms. On that way tridimensional network is formed. Because of the reduced local symmetry in the solid state more bands are observed in vibrational spectra of the anions than expected for regular AuF 6 octahedra. Mg(HF)AuF 4AuF 6 is the first example of a mixed valence Au III/Au V ternary fluoride. It crystallizes monoclinic at 200 K with a = 531.6 ( 6 ) pm , b = 1563.2 ( 12 ) pm , c = 1026.4 ( 12 ) pm , β = 90.623 ( 4 ) ° and Z = 4 , space group P 2 1 / c (No. 14). The structure is built up from MgF 6 octahedra sharing four equatorial fluorine atoms with four planar AuF 4 units. In this way, puckered layers of rectangular rings are formed. The coordination around Mg is completed by two axial fluorine atoms provided by HF molecules and AuF 6 units, which are alternately arranged above and below puckered layers resulting in the formation of slabs. The results of X-ray diffraction analysis on single crystals of KAuF 6 are in agreement with previously known powder X-ray diffraction data. KAuF 6 crystallizes rhombohedral as a non-merohedral twin in a space group R 3 ¯ m (No. 166), a = 749.6 ( 3 ) pm , c = 731.5 ( 3 ) pm at 200 K, Z = 3 .