Ionic acetamide coordination in its complexes with rare-earth iodides

A series of [Ln(CH₃CONH₂)₄(H₂O)₄]I₃ (Ln?=?rare-earth metal) complexes was completed with seven new compounds (Ln?=?Ce, Pr, Sm, Tb, Tm, Yb, Lu); two (Ln?=?Ce, Tm) were studied by X-ray diffraction. The coordination polyhedron of eight oxygen atoms is a distorted square antiprism. No tetrad effect was found for Ln–O bond lengths. The structure is stabilized by a system of intermolecular hydrogen bonds. The most striking feature of the structures is the recently predicted ionic acetamide coordination. The acetamide molecules are non-planar (the Ln–O–C–N torsion angles are 159–170°) and Ln–O–C bond angles vary in the 146.0–156.8° range.