X-ray single crystal structures of Cd(AuF6)2, Mg(HF)AuF4AuF6 and KAuF6 and vibrational spectra of Cd(AuF6)2 and KAuF6

Cd(AuF6)2 crystallizes at 200 K in the monoclinic space group C2/cC2/c (No. 15) with a=1116.7(7)pm, b=876.66(16)pm, c=1008.0(4)pm, β=118.026(5)°β=118.026(5)° and Z=4Z=4. Cadmium atoms are in an octahedral environment of fluorine, and CdF6 octahedra are sharing their vertices with six AuF6 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 AuF6 octahedra. Mg(HF)AuF4AuF6 is the first example of a mixed valence AuIII/AuV 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)°β=90.623(4)° and Z=4Z=4, space group P21/cP21/c (No. 14). The structure is built up from MgF6 octahedra sharing four equatorial fluorine atoms with four planar AuF4 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 AuF6 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 KAuF6 are in agreement with previously known powder X-ray diffraction data. KAuF6 crystallizes rhombohedral as a non-merohedral twin in a space group R3¯m (No. 166), a=749.6(3)pm, c=731.5(3)pm at 200 K, Z=3Z=3.

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