Crystal structure and properties of complexes [Ln(Gly)4Im·(ClO4)4]n (Ln:Nd, Sm) constructed from eight-coordination containing square antiprism

Abstract

Two eight-coordination containing square antiprism polyhedra, [Ln(Gly)4Im·(ClO4)4]n (Ln:Nd, Sm) were synthesized through the self-assembly of Ln3+ (Ln:Nd, Sm) ions, glycine and imidazole in aqueous solution and characterized by X-ray single crystal diffraction. Both of the complexes crystallized in the C2/c space group. In the cluster, each Ln3+ ions was eight-coordination by eight oxygen atoms of the glycine. The coordination sphere of each Ln3+ ions could be described as a distorted square antiprism. Two central Ln3+ ions were connected by four bridging carboxyl groups from four glycine molecules. The Ln–O bond distances were related to the coordination geometries of the ligands. The complexes had two special solid–solid phase transitions at 224 K and 248 K, which were interpreted as a freezing-in phenomenon of the reorientational motion of perchlorate ions ClO4− and the orientational order/disorder process of ClO4− ions. The decomposition mechanism of the complexes was deduced to be three stages from 300 to 700 K. The fluorescent excitation and emission spectra showed that the complexes had strong fluorescent property.