ChemInform Abstract: Structure of Trisodium Hexafluoromanganate(III).

Abstract

Na3MnF6, Mr = 237.90, monoclinic, P21/n, a = 5.4709 (9), b = 5.6830 (6), c = 8.0734 (12) A,/3 = 88.964 (7) °, V= 250.97 (6) A 3, Z = 2, D x = 3.15 gcm -3, A(Mo Ka) = 0.7107 A., /x = 27.6 cm -1, F(000) = 224, T = 293 K, R = 0.0152, wR = 0.0144 for 550 unique reflections (Fo > 30.(Fo)). The structure is isostructural with that of the cryolite Na3A1F6 and shows the weakest static Jahn-Teller distortion known to date for (MnF6) 3- octahedra (d(Mn--F) axial 2.0176 (8), mean equatorial 1.880 (1) A). The ordering of the elongated octahedra is ferrodis- tortive. Of the Na ions, one third have octahedral and the remainder have bicapped trigonal prismatic eight coordination. Introduction. Single-crystal studies on sodiumhexa- fluorometallates(III) Na3MmF6 (M m = Cr, Fe) revealed cryolite structures closely related to that of NaaA1F6 (Naray-Szabo & Sasvari, 1938; Hawthorne & Ferguson, 1975), space group P21/n. The Cr com- pound crystallizes in the same space group (Brunton, 1969), while for the structure of the iron compound P2~ is assumed (Matvienko, Yakubovich, Simonov, Ivashchenko, Melnikov & Belov, 1981). For several other compounds Na3MF6 (M = Ga, Sc, Ti, V, Mn, Co, Ni, Cu) cryolite-type unit cells were deduced from powder diffraction data (cf. review of Babel & Tressaud, 1985). In the course of studies on the dependence of Jahn-Teller distortion on the struc- ture type, we were interested in the crystal structure of the Mn m compound. Na3MnF6 was mentioned for the first time by Siebert & Hoppe (1971). Lattice parameters have been proposed by Bucovec & Siftar (1975) (a=5.56, b=5.84, c=8.10A, /3=90.7 ° ) which were confirmed roughly by our single-crystal investigation reported here. Experimental. The title compound was prepared by heating a stoichiometric mixture of NaF and MnF3 * To whom correspondence should be addressed.