Syntheses, crystal structures, and thermal behavior of the rare earth amidosulfates M(NH2SO3)3•2H2O (M=Pr, Nd, Sm)

Evaporation of solutions of M3+ (M = Pr, Nd, Sm) in aqueous amidosulfonic acid leads to the amidosulfate dihydrates M(NH2SO3)(3) 2H(2)O. According to X-ray single crystal structure determinations, they contain eight-fold-coordinate M3+ ions with the [MO8] polyhedra and amidosulfate groups connected to infinite sheets which are held together via hydrogen bridges. DTA/TG investigations show that the dihydrates lose H2O in a two-step mechanism yielding amidosulfate monohydrates as intermediates. The anhydrous amidosulfates decompose in two steps to the anhydrous sulfates, M-2(SO4)(3) (M = Pr-Sm). The decomposition of these compounds has been confirmed by means of temperature-dependent X-ray powder diffraction. By very slow dehydration under flowing argon, single crystals of the monohydrate intermediate for M = Sm were obtained. This triclinic compound has a layer structure and contains eight-fold-coordinate Sm3+. However, the MI2SO3- ions are higher coordinated than is the corresponding dihydrate. Further heating yields the anhydrous amidosulfates as crystalline powders. According to the X-ray investigations, they are isotypic with La(NH2SO3)(3). The structure of the latter can be considered a derivative of the UCl3-type of structure with complex anions. (C) 2000 Elsevier Science S.A. All rights reserved.