Structural variability of rare-earth bromide complexes with acetylurea

New coordination compounds of light rare-earth (RE) bromides with acetylurea (AsUr) were synthesized, [Y(AcUr)2(H2O)4]1.39[Y(AcUr)2(H2O)5]0.61Br6·2H2O (I), [La(AcUr)2(H2O)5]Br3 (II), [Ce(AcUr)2(H2O)5]Br3 (III), [Nd(AcUr)2(H2O)5]Br3 (IV), [Sm(AcUr)2(H2O)5]Br3 (V); elemental analysis, IR spectroscopy and X-ray diffraction were used to determine their compositions and structural features. Compound I is built of the [Y(AcUr)2(H2O)4]3+ and [Y(AcUr)2(H2O)5]3+ cations in the 2.28 : 1; they differ by the number of the inner-sphere water molecules (4 and 5 for coordination numbers 8 and 9, respectively), non-coordinated Br— ions and H2O molecules. Compounds II and III are built of the [Ln(AcUr)2(H2O)5]3+ (Ln = La, Ce) cations and outer-sphere Br— ions. The structures changes on cooling from 296 K to 100 K being isostructural at both temperatures. Compounds IV and V have the same composition, but different structures. They also have different polymorphous modifications at 100 and 296 K. Samarium, terbium and dysprosium bromide complexes of acetyl urea show photoluminescence.