Polymorphism, Composition, and Structural Variability in Topology in 1D, 2D, and 3D Copper Phosphonocarboxylate Materials

The syntheses and structural characterization of 1D, 2D, and 3D materials based on copper phosphonocarboxylate backbones are described. More specifically, the synthesis of materials from diethylphosphonoacetic acid (DEPAA) or the close variant hydroxyphosphonoacetic acid (HPAA) and water-soluble Cu<sup>2+</sup> salts has been studied. The initial synthesis involving copper acetate and DEPAA was carried out at 160 °C under hydrothermal conditions and a Cu:P ratio of 1:1 resulted in the formation of a mixture of products with the same composition, Cu<sub>1.5</sub>(O<sub>3</sub>PCH<sub>2</sub>CO<sub>2</sub>)·H<sub>2</sub>O. Compound <b>1</b>, which is blue in color and crystallizes in the triclinic space group <i>P</i>1̅, has a layered structure. Compound <b>2</b>, which is green in color and crystallizes in the monoclinic space group <i>P</i>2<sub>1</sub>/<i>c</i>, has a three-dimensional structure. Reduction of the reaction temperature to 140 °C results in the exclusive formation of the α-phase (<b>1</b>), while an increase in the reaction temperature to 180 °C yields a pure sample of <b>2</b>. A Cu:P ratio of 2:3 in a reaction at 180 °C yields a third, related phase, Cu(HO<sub>3</sub>PCH<sub>2</sub>CO<sub>2</sub>)·H<sub>2</sub>O, <b>3</b>, which is again triclinic but has a chain-like structure. Finally, reaction of copper chloride and HPAA in a Cu:P ratio of 1:1 at room temperature yields one-dimensional Cu(<i>R</i>,<i>S</i>-HO<sub>3</sub>PCH(OH)CO<sub>2</sub>)(H<sub>2</sub>O)<sub>2</sub>]·H<sub>2</sub>O, <b>4</b>, that incorporates both <i>R</i> and <i>S</i> HPAA stereoisomers. All materials were studied by single crystal X-ray crystallography, X-ray powder diffraction, TGA, FT-IR, and elemental analyses.