The Synthesis and Characterization of a Novel Gallium Diphosphonate
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The Synthesis and Characterization of a Novel Gallium Diphosphonate Martin P. Attfield and Howard G. Harvey1 School of Crystallography, Birkbeck College, Malet Street, Bloomsbury, London, WC1E 7HX, UK. 1 Davy-Faraday Research Laboratory, The Royal Institution of Great Britain, 21 Albemarle Street, London, W1S 4BS, UK. ABSTRACT
The gallium diphosphonate, Ga2[O3PC2H4PO3](H2O)2F2·H2O, has been prepared under solvothermal conditions from a HF/ pyridine solvent system. The structure of the material was determined by Rietveld refinement using the isostructural aluminium compound as the starting model for refinement. The structure consists of chains of corner sharing GaO4F2 octahedra with bridging F atoms linking the octahedra. The chains of octahedra are linked together in two directions perpendicular to the chain direction by the ethylenediphosphonate groups. The resulting structure contains a one-dimensional channel system in which extra-framework water molecules reside. Thermal gravimetric analysis of the material shows that 40 % of the extraframework water can be reversibly absorbed. Thermodiffraction studies show that the material retains its structural integrity until all the extra-framework water is lost and then undergoes a considerable loss in crystallinity as the framework water molecules are lost. The crystallinity of the material then progressively decreases as the temperature is increased. INTRODUCTION
The chemistry of metal phosphonates has received much interest in recent years because of the wide variety of possible structures accessible and their potential for use as sorbents, catalysts and optic materials [1]. The main attraction of such materials stems from the inclusion of an organic moiety into the compound that may be modified to impart particular chemical functionality and structure on the material and introduce a high degree of hydrophobicity. The latter property can lead to improvements in catalytic performances in particular systems [2, 3]. Initially, synthetic work focussed primarily on using phosphonic acids for the synthesis of new materials, this has been extended to include the utilization of diphosphonic acids ((HO)2OPRPO(OH)2, where R is an organic group). The attraction of the incorporation of the diphosphonic acid is that through careful selection of the R group the interlamellar distance, or pore size, and potentially the shape selective properties within the resulting structure can be controlled. Metal diphosphonates containing various metal cations have been reported [1]. As far as the authors are aware, no reports of gallium diphosphonates have hitherto been reported, which is surprising considering the possible chemical similarities between this type of material and the important gallophosphate and gallofluorophosphate family of compounds. Three gallium methylphosphonates have been reported [4, 5], one, Ga(OH)0.28F0.72(CH3PO3)·H2O [4], of which has an analogous structure to AlMepO-ζ [6] and another, Ga3(OH)3F3(CH3PO3)2(H2NC3H6NH3) [4], that contains an organic structural directing
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