Synthesis and X-ray Powder Structures of Two Lamellar Copper Arylenebis(phosphonates)

Abstract

Reaction of copper salts with 1,4-phenylenebis(phosphonic acid) yielded a conventional layered compound, Cu₂[(O₃PC₆H₄PO₃)(H₂O)₂], while a similar reaction with 4,4‘-biphenylenebis(phosphonic acid) resulted in a new lamellar structure with composition Cu[HO₃P(C₆H₄)₂PO₃H]. The structures of these compounds were solved ab initio by using X-ray powder diffraction data. The crystals of the phenylenebis(phosphonate) compound are monoclinic, space group C2/c, with a = 18.8892(4) Å, b = 7.6222(2) Å, c = 7.4641(2) Å, β = 90.402(2)°, and Z = 4. The layer structure in this case is similar to that in copper phenylphosphonate, Cu[O₃PC₆H₅]. The metal atoms display a distorted square pyramidal geometry where four of the coordination sites are occupied by the phosphonate oxygens. The remaining site is filled by an oxygen atom of the water molecule. Adjacent metal−O₃PC layers are covalently pillared by the phenyl group of the phosphonates to create a 3-dimensional structure. Cu[HO₃P(C₆H₄)₂PO₃H] is triclinic, space group P1̄, with a = 4.856(2) Å, b = 14.225(5) Å, c = 4.788(2) Å, α = 97.85(1)°, β = 110.14(1)°, γ = 89.38(1)°, and Z = 1. The structure in this case, ideally consists of linear chains of copper atoms. The copper atoms are bridged by centrosymmetrically related phosphonate groups utilizing two of their oxygen atoms. This binding mode leads to square planar geometry for the copper atoms. The third oxygen atom of the phosphonate is protonated and is involved in linking adjacent linear chains through hydrogen bonds. At the same time, these hydroxyl oxygens interact weakly (Cu−O = 3.14 Å) with the copper atoms of the adjacent chain. Considering these long Cu−O interactions, the geometry of the copper atom may be described as distorted square bipyramidal. As in the phenylphosphonate structure, the biphenyl groups covalently link the Cu−O₃PC networks in the perpendicular direction.