Guang Cao

Structural studies of some new lamellar magnesium, manganese and calcium phosphonates

Abstract Layered phosphonate salts of divalent metal ions (Mg, Ca and Mn) are prepared by combining solutions of soluble metal salts and alkyl- or arylphosphonic acids. In this way the compounds Mg(O3PCnH2n+1)·H2O (n=1−12), Mg(O3PC6H5)·H2O, Mg(HO3PCH(C6H5)2)2·8 H2O, Mn(O3PCH3)·H2O, Mn(O3PC6H5)·H2O, Ca(O3PCnH2n+1)·H2O (n⩽5), Ca(HO3PC6H5)2 and Ca(HO3PCnH2n+1)2 (n⩾6) were prepared. The M(O3PC6H5)·H2O compounds show good thermal stability, losing lattice water at 250–300°C without further decomposition below 550°C. Compounds derived from alkylphosphonic acids decompose at lower temperatures. The Mg(O3PCnH2n+1)·H2O series, Mg(O3PC6H5)·H2O, and Mn(O3PC6H5)·H2O group Pmn21; for the latter compound unit cell dimensions (A) are a=5.733, b=14.298, c=4.931. The structure consists of roughly coplanar layers of metal atoms coordinated by phenylphosphonate groups above and below. Each metal atom is coordinated by five phosphonate oxygens and one lattice water molecule. Mg(O3PCnH2n+1·H2O adopts a similar structure; infrared spectra indicate all-trans alkyl chains. In Mg(HO3PCH(C6H5)2)2·8 H2O, Mg(H2O)2+6 ions and lattice water lie in hydrogen-bonded sheets; the benzhydryl groups lie above and below and make van-der-Waals contacts between layers.

Topochemical diacetylene polymerization in layered metal phosphate salts

Abstract UV- and X-ray induced polymerization of diacetylene groups in layered salts of 3,5-octadiyne bisphosphate (ODBP) with di- and trivalent metals (Zn, Mg, Mn, Ca, Cd, La, Y, and Sm) was studied. Diffuse reflectance UV-visible spectra were used to monitor the course of the polymerization reactions. From these spectra, it was found that the highest degree of polymerization was obtained with the Zn, Mg, and Mn salts; short-chain oligomers were formed with La, Y, and Sm, while the Ca and Cd salts had the lowest reactivity. These trends can be rationalized in terms of structural models for the juxtaposition of diacetylene groups in the monomeric salts and on the basis of the similarity of the spacing of phosphate coordination sites in the basal plane (4.8 A for Zn, Mg, and Mg, and 5.6 A for La, Y, and Sm) and the polydiacetylene repeat distance (4.93 A). The nucleation and growth of the polymeric phase within these layered solids followed inverse exponential kinetics and could be fitted to the Avrami equation (M. Avrami, J. Chem. Phys. 7, 1103 (1939)).

SHAPE-SELECTIVE INTERCALATION REACTIONS AND CHEMICAL SENSING IN LAYERED METAL PHOSPHATES AND PHOSPHONATES

Layered phosphonates containing open metal coordination sites intercalate ligands such as ammonia and amines shape-selectively. As thin films on piezoelectric quartz crystals, these materials form the basis of sensitive and specific gas-phase chemical sensors for these ligands. Selective intercalation of chiral analytes has also been observed in layered metal phosphates that are pillared with chiral organic cations.

Structure of [Mg{HO3PCH(C6H5)2}2].8H2O, a layered phosphonate salt

Bis(hydrogen diphenylmethylphosphonato)-magnesium octahydrate, [Mg(C13H12O3P)2].8H2O. Mr = 662.85, triclinic, P1, a = 6.1051 (15), b = 8.8308(14), c = 15.312(3) A, alpha = 78.514(13), beta = 83.993(11), gamma = 75.772(15) degrees, V = 782.8(3) A3, Z = 1, Dx = 1.41 g cm-3 (163 K), Mo K alpha, lambda = 0.71069 A, mu = 2.171 cm-1, F(000) = 350, T = 163 K, R = 0.0351 for 3749 reflections [F0 greater than or equal to 4 sigma(F0)]. The structure consists of alternating polar and nonpolar layers stacked along the crystallographic c axis. The polar layers contain Mg(H2O)26+ ions, water of hydration and the phosphonate O atoms, and the nonpolar layers contain the benzhydryl groups. Two-dimensional hydrogen-bonding networks link Mg(H2O)26+ and the water of hydration to the phosphonate O atoms. The shortest hydrogen bonds in the structure, 1.68(2) A, connect the P-OH H atom and the water of hydration. Slightly longer contacts [1.79(2), 1.85(2), 1.91(2), 1.92(2) A] connect the phosphonate O atoms (O1 and O3) to the H atoms of the Mg(H2O)26+ group. The coordination environment of the Mg atom is a very nearly regular octahedron of water O atoms.