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New complexes of yttrium and lanthanum bromides and erbium chloride with carbamide (Ur), [Y(Ur)4(H2O)4]Br3 (I) and [La(Ur)4(H2O)4]Br3 (II), [La(Ur)6(H2O)2]Br3 (III), and [Er(Ur)6Cl]Cl2 (IV), are synthesized and studied by X-ray diffraction analysis. In structures I–III, the coordination of the ligands (water and carbamide) by the metal occurs through the oxygen atoms. The coordination polyhedron of the rare-earth metal atoms is a distorted square antiprism (coordination number 8), and the bromide ions are not included into the internal coordination sphere of the complexes. In compound IV, the internal coordination sphere of the complex includes six carbamide molecules and one chloride ion, and the coordination polyhedron of Er is a distorted pentagonal bipyramid (coordination number 7). Specific features of the structures of the crystalline carbamide derivatives of chlorides, bromides, and iodides of the considered rare-earth metals are compared. A distortion of the planar structure of some carbamide ligands, depending on their number in the complex cation and on the nature of the complex, is observed.

Data on the synthesis and the IR spectroscopic and X-ray diffraction analyses of new complexes of yttrium chloride with carbamide (Ur), [Y(Ur)4(H2O)4]Cl3 (I) and [Y(Ur)6(H2O)2]Cl3 (II), and with acetamide (AA), [Y(AA)5(H2O)2]Cl3 (III), are presented. The coordination of the ligands occurs through the oxygen atoms. For complexes I and II, the coordination polyhedra of the Y atoms are distorted tetragonal antiprisms. For structure III, the coordination polyhedron of the Y atom is a distorted pentagonal bipyramid. The coordination of four Ur molecules in complex I does not change their planar structure, and two Ur molecules in structure II have the dihedral angle N-C(O)-N different from 180°. The chloride ions are in the external sphere. Many hydrogen bonds are observed in the structures of complexes I–III.

The synthesis and data of the study of new complexes of erbium and lutetium bromides with carbamide, [Ln(Ur)4(H2O)4]Br3 (I and III) and [Ln(Ur)6(H2O)2]Br3 (II and IV) (Ln = Er and Lu), by IR spectroscopy and X-ray diffraction analysis are presented. For all four compounds, coordination with metal occurs through the oxygen atoms of the water and carbamide molecules. The coordination polyhedra of the Ln atoms are distorted square antiprisms. Coordination of four carbamide molecules does not change their planar structures. The bromide ions are not coordinated, existing in the external sphere. Many hydrogen bonds are observed in the structures of complexes of both types.