The CsBr-AlBr3 Phase Diagram and The Crystal Structure of CsAlBr4.

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 (D_2h¹⁶), 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 R_P = 0.0952 and A_WP = 0.1236 (R_expected = 0.0509, 'goodness of fit' = 2.42, Bragg R-factor = 0.0419, and derived R_F = 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.