Evaporation of solutions of M3+ (M = Pr, Nd, Sm) in aqueous amidosulfonic a
cid leads to the amidosulfate dihydrates M(NH2SO3)(3) 2H(2)O. According to
X-ray single crystal structure determinations, they contain eight-fold-coor
dinate M3+ ions with the [MO8] polyhedra and amidosulfate groups connected
to infinite sheets which are held together via hydrogen bridges. DTA/TG inv
estigations show that the dihydrates lose H2O in a two-step mechanism yield
ing 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 temper
ature-dependent X-ray powder diffraction. By very slow dehydration under fl
owing argon, single crystals of the monohydrate intermediate for M = Sm wer
e obtained. This triclinic compound has a layer structure and contains eigh
t-fold-coordinate Sm3+. However, the MI2SO3- ions are higher coordinated th
an is the corresponding dihydrate. Further heating yields the anhydrous ami
dosulfates as crystalline powders. According to the X-ray investigations, t
hey are isotypic with La(NH2SO3)(3). The structure of the latter can be con
sidered a derivative of the UCl3-type of structure with complex anions. (C)
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