The CsBr-AlBr3 phase diagram and the crystal structure of CsAlBr4

Abstract

The phase diagram in the CsBr-AlBr3 system has been reinvestigated. An adjusted liquidus diagram is given, showing the compound CsAlBr4, which melts congruently at 360°C. The lack of consistency among previous results is presumably due to the presence of oxide impurities formed by attack of bromide on the silica ampule walls. Some molten salt density data are given. The CsAlBr4 crystal structure has been solved in the orthorhombic space group Pnma, no. 62 (D2h16), with a = 12.2137(20), b = 7.5304(14) and c = 9.9293(16) Å, by means of X-ray powder diffraction and full-profile Rietveld refinements, converging with RP = 0.0952 and AWP = 0.1236 (Rexpected = 0.0509, 'goodness of fit' = 2.42, Bragg R-factor = 0.0419, and derived RF = 0.0458). The AlBr4 tetrahedron is almost regular, with Al-Br bond distances in the range 2.20-2.35 Å, in accordance with what is to be expected from previous related structure determinations. © Acta Chemica Scandinavica 1997.