Synthesis of layered nickel phosphonate materials based on a topotactic approach

Layered nickel phosphonate materials Ni(O3PR). H2O [with R = C6H5, CH3, (CH2)(2)CO2H, (CH2)(2)Br and CH2C6H5] have been prepared by heating nickel(II) hydroxide with a stoichiometric quantity of the relevant phosphonic acid at the melting temperature of the phosphonic acid. Samples of Ni(O3PC6H5). H2O and Ni(O3PCH3). H2O prepared by this method are identical to those prepared previously by other synthetic routes. In addition, the novel materials Ni[O3P(CH2)(2)CO2H]. H2O, Ni[O3P(CH2)(2)Br]. H2O and Ni(O3PCH2C6H5). H2O have been synthesised by this method. The structural properties of these materials are assessed in detail, and compared with the structural properties of other materials containing the same phosphonates but different divalent metals. The synthetic method reported here appears to be a general approach for preparation of layered metal phosphonates, for cases in which the phosphonic acid undergoes melting rather than decomposition at elevated temperatures.