CONTRIBUTIONS ON THE THERMAL-BEHAVIOR OF SULFATES .17. SINGLE-CRYSTALSTRUCTURE REFINEMENTS OF IN-2(SO4)(3) AND GA-2(SO4)(3)

Using chemical transport reactions well-shaped crystals of In-2(SO4)(3 ) and Ga-2(SO4)(3) can be prepared in a temperature gradient (T-2 --> T-1) using Cl-2 as transport agent. The two modifications of In-2(SO4) (3) were formed by variation of the transport temperature. The low-tem perature modification of In-2(SO4)(3) (898 K --> 848 K) is isostructur al to monoclinic Fe-2(SO4)(3) and crystallizes in P2(1)/n with a = 8.5 70(2) Angstrom, b = 8.908(2) Angstrom and c = 12.0521(1) Angstrom, bet a = 91.05(3)degrees, Z = 4. The high-temperature modification of In-2( SO4)(3) (1023 K --> 973 K) as well as Ga-2(SO4)(3) (923 K --> 873 K) i s isostructural to rhombohedral Fe-2(SO4)(3) and crystallizes in the r hombohedral space group R ($) over bar 3 with a = 8.440(2) (8.054(2)) Angstrom, c = 23.093(2) (21.840(2)) Angstrom, Z = 6 (hexagonal setting ). The crystal structures were refined to a residual R(1) = 0.028 usin g 1710 unique reflections with F-o greater than or equal to 4 sigma .( F-o) for monoclinic In-2(SO4)(3) and to R(1) = 0.031(0.037) (571(587) unique reflections with F-o greater than or equal to 4 sigma(F-o)) for rhombohedral In-2(SO4)(3)(Ga-2(SO4)(3)). The structures consist of MO (6)-octahedra and SO4-tetrahedra, which are linked via common corners to a three-dimensional network.