STRUCTURAL COMPLEXITY AND METAL COORDINATION FLEXIBILITY IN 2 ACETOPHOSPHONATES

Two divalent metal acetophosphonates, Pb-6(O3PCH2CO2)(4) End Mn-3(O3PC H2CO2)(2), have beep synthesised hydrothermally. They crystallise in t he triclinic system, space group P (1) over bar, a = 11.0064(1), b-12. 3604(1), c=8.9783(1) Angstrom, alpha=98.632(1), beta=90.474(1), gamma= 75.629(1)degrees, Z=2, for M = Pb, and a =10.0146(5), b = 6.3942(4), c =8.4796(6) Angstrom, alpha=101.452(4), beta=106.254(2), gamma=96.431 ( 4)degrees, Z=2, for M=Mn. The structures were solved ab initio using d irect methods from synchrotron powder diffraction data (lambda approxi mate to 0.4 Angstrom) for M-Pb and from laboratory X-ray data for M = Mn. The crystal structure of the Pb compound is very complex with 38 n on-hydrogen atoms in general positions (114 refined positional paramet ers), if had been refined by Rietveld method using soft constraints, a nd converged to R-WP = 6.8% and R-F = 1.6%. The structure for M = Mn h as a moderate complexity with 19 nonhydrogen atoms (57 refined positio nal parameters) which was also refined with soft constraints to R-WP = 8.3%, R-F = 3.9%. Both compounds show a framework bu lt of alternate metal oxide inorganic layers, pillared by the organic groups. The meta l environments in these materials are very distorted. Manganese atoms present three different distorted oxygen environments: four-, five- an d six-coordinate. Thermal and IR data are also reported and discussed.