Pillared Layered Metal Phosphonates. Syntheses and X-ray Powder Structures of Copper and Zinc Alkylenebis(phosphonates)
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Covalently pillared layered metal phosphonate compounds were prepared by the reaction of divalent metal salts with alkylenebis(phosphonic acids). Cu(II) yields compounds Cu2[(O3PC2H4PO3)(H2O)2] (1) and Cu2[(O3- PC3H6PO3)(H2O)2]·H2O (2) when copper surfate was reacted with ethylenebis(phosphonic acid) and propylenebis(phosphonic acid), respectively. The corresponding bis(phosphonates) obtained for the reaction with zinc chloride are Zn2[(O3PC2H4PO3)(H2O)2] (3) and Zn2[(O3PC3H6PO3)] (4). The structures of these four compounds were determined ab initio from their X-ray powder diffraction data and refined by Rietveld methods. Crystal data for compound 1: space group P21/c, a = 8.0756(1) Å, b = 7.5872(1) Å, c = 7.4100(1) Å, β = 116.319(1)°, Z = 2. Crystal data for compound 2: space group Pnc2, a = 4.3276(2) Å, b = 17.3181(8) Å c = 6.7624(3) Å, Z = 2. Crystal data for compound 3: space group P21/n, a = 5.6861(8) Å, b = 15.230(2) Å, c = 4.7923(6) Å, β = 91.936(2)°. Crystal data for compound 4: space group Pna21, a = 8.4886(6) Å, b = 5.2720(4) Å, c = 18.865(1) Å, Z = 4. The metal-oxygen bridging interactions form two-dimensional layers in all four compounds. The layers are connected to each other by the alkylene groups leading to three-dimensional structures. In the copper compounds the metal atoms are five coordinate where four of the binding sites are from the phosphonate oxygens and one from the water oxygen. 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 ethylenebis-(phosphonate) have distorted octahedral geometry. The phosphonate oxygens provide five binding sites for the metal through chelation and bridging while the water oxygen occupies the sixth coordination site. The metal atoms in compound 4, on the other hand, are tetrahedrally coordinated by the phosphonate oxygens. Unlike compounds 1-3, this compound does not contain any water molecules. The interlamellar separation is 7.2 and 7.6 Å for copper ethylenebis(phosphonate) and zinc ethylenebis(phosphonate), respectively. The difference in the layer separation, however, is significant in the propylenebis(phosphonates). For copper and zinc compounds the values are 8.65 and 9.4 Å, respectively. The layer-connecting alkyl chains create open spaces whose sizes are determined by the length of the chain. Thus, a new class of pillared materials with definable cavity sizes may be prepared.
author list (cited authors)
Poojary, D. M., Zhang, B., & Clearfield, A.