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The crystal chemistry of complex fluorides of the general formula A2MF6 The refinement of the structure (NH4)2SiF6

F. Hanic

Slovak Academy of Sciences, Bratislava 9


Abstract: The crystal chemistry of hexafluorocomplexes of the general formula A2MF6, where A is NH4, K, Rb, Cs, and Tl and M is Si, Ti, V, Cr, Mn, Co, Ni, Ge, Zr, Rh, Pd, Sn, Hf, Os, Ir, Pt, Pb, and the exactness of the structure of (NH4)2SiF6 are described. A2MF6 crystallizes in 3 forms: the cubic (C) of the structural type K2PtCl6, the hexagonal (H) of the structural type K2MnF6, and the trigonal form (T) of the structural type K2GeF6. All 3 forms are closely related with a tight arrangement of A+ and F- ions contg. isolated groups of MF62- with an octahedral arrangement. The basic structural units of all 3 forms are parallel layer-triplets of A-MF6-A compn. A close-packed assembly of atoms of the particular form can be achieved by a parallel translation of the layer-triplets in such a way that every 2nd T or 3rd H or 4th C layer-triplet is identical with the 1st one. The sequence of the layer-triplets is aaa... in the T form, ababab... in the H form, and abcabc... in the C form. Cubic crystals of (NH4)2SiF6 are isostructural with (NH4)2PtCl6. The structure of (NH4)2SiF6 was more exactly defined from the least sqs. of the 3-dimensional x-ray data. The interat. distance Si-F in the octahedron SiF6 was detd. to be 1.676 A. All NH4+ groups are coordinated by 12F- at 3.00 A.

Full paper in Portable Document Format: 2010a738.pdf (in Slovak)


Chemical Papers 20 (10) 738–751 (1966)

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