PILLARED LAYERED METAL PHOSPHONATES - SYNTHESES AND X-RAY-POWDER STRUCTURES OF COPPER AND ZINC ALKYLENEBIS(PHOSPHONATES)

Covalently pillared layered metal phosphonate compounds were prepared by the reaction of divalent metal salts with alkylenebis(phosphonic ac ids). Cu(II) yields compounds Cu-2[(O3PC2H4PO3)(H2O)(2)] (1) and Cu-2[ (O3PC3H6PO3)(H2O)(2)]. H2O (2) when copper sulfate was reacted with et hylenebis(phosphonic acid) and propylenebis(phosphonic acid), respecti vely. The corresponding bis(phosphonates) obtained for the reaction wi th zinc chloride are Zn-2[(O3PC2H4PO3)(H2O)(2)] (3) and Zn-2[(O3PC3H6P O3)] (4). The structures of these four compounds were determined ab in itio from their X-ray powder diffraction data and refined by Rietveld methods. Crystal data for compound 1: space group P2(1)/c, a = 8.0756( 1) Angstrom, b = 7.5872(1) Angstrom, c = 7.4100(1) Angstrom, beta = 11 6.319(1)degrees, Z = 2. Crystal data for compound 2: space group Pnc2, a = 4.3276(2) Angstrom, b = 17.3181(8) Angstrom, c = 6.7624(3) Angstr om, Z = 2. Crystal data for compound 3: space group P2(1)/n, a = 5.686 1(8) Angstrom, b = 15.230(2) Angstrom, c = 4.7923(6) Angstrom, beta = 91.936(2)degrees. Crystal data for compound 4: space group Pna2(1), a = 8.4886(6) Angstrom, b = 5.2720(4) Angstrom, c = 18.865(1) Angstrom, Z = 4. The metal-oxygen bridging interactions form two-dimensional lay ers in all four compounds. The layers are connected to each other by t he alkylene groups leading to three-dimensional structures. In the cop per compounds the metal atoms are five coordinate where four of the bi nding sites are from the phosphonate oxygens and one from the water ox ygen. The coordination geometry of the copper atoms in compounds 1 and 2 may be described as distorted square-pyramidal, but the distortion is severe in the case of compound 2. The zinc atoms in zinc ethylenebi s(phosphonate) have distorted octahedral geometry. The phosphonate oxy gens provide five binding sites for the metal through chelation and br idging while the water oxygen occupies the sixth coordination site, Th e metal atoms in compound 4, on the other hand, are tetrahedrally coor dinated by the phosphonate oxygens. Unlike compounds 1-3, this compoun d does not contain any water molecules. The interlamellar separation i s 7.2 and 7.6 Angstrom for copper ethylenebis(phosphonate) and zinc et hylenebis(phosphonate), respectively. The difference in the layer sepa ration, however, is significant in the propylenebis(phosphonates). For copper and zinc compounds the values are 8.65 and 9.3 Angstrom, respe ctively. The layer-connecting alkyl chains create open spaces whose si zes are determined by the length of the chain. Thus, a new class of pi llared materials with definable cavity sizes may be prepared.