ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

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 MF₆^2- 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)