Synthesis and characterization of acetylurea complexes with rare-earth metal halides: Polymorphism of the praseodymium complexes

The series of rare-earth acetylurea (AcUr) complex chlorides and bromides are completed and their structures are examined. All complexes have the same composition LnX3.2AcUr.5H2O (X = Cl, Br). However, structures of the compounds differ significantly. The complexes with Ln = La–Sm contain complex cations [Ln(AcUr)2(H2O)5]3+ (coordination number 9); halide ions are outer-sphere. For Ln = Ho–Lu and Y, crystals contain complex cations [Ln(AcUr)2(H2O)4]3+ (coordination number 8), uncoordinated halide ions and water molecules. High barrier of internal rotation of plane acetylurea ligands makes possible formation of various conformers. Polymorphs for praseodymium complexes were studied by X-ray diffraction at 296 and 100 K.