Crystal Structures of Acetylurea Complexes with Rare-Earth Bromides: Surprising Structural Changes

Crystal structures of complexes of acetylurea (AcUr) with middle rare-earth bromides, [Ln(AcUr) 2 (H 2 O) 5 ]Br 3 . H 2 O (Ln = Gd, Tb), [Ln(AcUr) 2 (H 2 O) 4.5 ][Ln(AcUr) 2 (H 2 O) 4 ]Br 6 . 2H 2 O (Ln = Dy, Ho) and [Er(AcUr) 2 (H 2 O) 4 ]Br 3 , were studied by X-ray diffraction. Complex cations contain two bidentate AcUr molecules and five (Gd and Tb) or four (Er) inner-sphere water molecules; coordination numbers 9 or 8, respectively. Compounds of Dy and Ho contain two types of complex cations with coordination numbers 9 and 8.