Synthesis and X-ray powder structures of covalently pillared lamellar zinc bis(phosphonates)

Two new lamellar metal phosphonates, zinc phenylenebis(phosphonate), Zn-2[(O3PC6H4PO3)(H2O)(2)] (1), and zinc biphenylylenebis(phosphonate), Zn[HO3P(C6H4)(2)PO3H] (2), have been synthesized. The structures of these compounds were solved ab initio from X-ray powder diffraction data and refined by Rietveld methods. Compound 1 is orthorhombic: space group Pnnm, a=19.2991(6) Angstrom, b=4.8232(2) Angstrom, c=5.6545(2) Angstrom, and Z=2. The structure is layered, and its layer arrangement is similar to that in zinc phenylphosphonate. The zinc atoms are octahedrally coordinated. Two of the oxygens of the phosphonate group are involved in chelation and bridging the metal atoms. The third oxygen binds to only one metal atom. The sixth coordination site is occupied by a water molecule. The adjacent layers are bridged by the phenylene group of the bis(phosphonate). Compound 2 is triclinic: space group <P(1)over bar>, a=9.5097(3) Angstrom, b=5.0074(2) Angstrom, c=14.2109(4) Angstrom, alpha=92.797(3)degrees, beta=99.725(3)degrees, gamma=92.003(3)degrees, and Z=2. In this case the metal atoms are tetrahedrally coordinated by four oxygens. two from each of the phosphonate groups of the bis(phosphonate). The third oxygen of the phosphonate group is protonated and is not involved in metal binding. The structure consists of double chains with alternating Zn and P atoms connected to each other by phosphonate bridges. These double chains run along the b axis and are linked to similar chains along the a direction through hydrogen bonds involving P-OH groups. This arrangement leads to loosely bound metal-CPO3 networks in the ab plane which are bridged by the biphenylylene groups along the c axis. Thus in a broad sense this compound may also be considered as layered.