Inorganic-organic hybrid compounds: Synthesis and characterization of three new metal phosphonates with similar characteristic structural features

Article abstract of DOI:10.1016/j.jssc.2005.10.008

The phosphonocarboxylic acid H(HO₃PCH₂) ₂NH-CH₂C₆H₄-COOH (H₅L) was synthesized and characterized by NMR- and IR-spectroscopy, thermogravimetric (TG) analysis and single-crystal X-ray diffraction. Reactions of H₅L with samarium(III) chloride and calcium(II) chloride resulted in three new compounds, Sm[(O₃PCH₂)₂NH-CH₂C ₆H₄-COOH]·H₂O (1), Ca[H(O ₃PCH₂)₂NH-CH₂C₆H ₄-COOH]·H₂O (2), and Ca[(HO₃PCH ₂)₂NH-CH₂C₆H₄-COOH] ₂·4H₂O (3). The single-crystal structure determination of the title compounds reveals that in H₅L as well as in compounds 1, 2, and 3 zwitterions are present. Within the M-O building units of the metal phosphonates we observed a different degree of dimensionality, depending on the oxidation state of the metal ion and the synthesis conditions. In 1, one-dimensional chains of edge-sharing SmO₈ polyhedra are observed while in 2, isolated units of edge-sharing CaO₆ octahedra and in 3 isolated CaO₆ octahedra are observed. However, looking at the organic part, the rigid phenyl carboxylic acid moieties arrange in a zipper-like fashion and hydrogen bonding plays an important role in the stabilization of the crystal structure. The title compounds were further characterized by IR spectroscopy and TG analysis. Additionally, the thermal stability of 1 was investigated by temperature-dependent X-ray diffraction.