Structural complexity and metal coordination flexibility in two acetophosphonates

Abstract

Two divalent metal acetophosphonates, Pb ₆ (O ₃ PCH ₂ CO ₂ ) ₄ and Mn ₃ (O ₃ PCH ₂ CO ₂ ) ₂ , have been synthesised hydrothermally. They crystallise in the triclinic system, space group P, a=11.0064(1), b=12.3604(1), c=8.9783(1) Å, α=98.632(1), β=90.474(1), γ=75.629(1)°, Z=2, for M=Pb, and a=10.0146(5), b=6.3942(4), c=8.4796(6) Å, α=101.452(4), β=106.254(2), γ=96.431(4)°, Z=2, for M=Mn. The structures were solved ab initio using direct methods from synchrotron powder diffraction data (λ0.4 Å) for M=Pb and from laboratory-ray data for M=Mn. The crystal structure of the Pb compound is very complex with 38 non-hydrogen atoms in general positions (114 refined positional parameters), it had been refined by Rietveld method using soft constraints, and converged to R _WP =6.8% and R _F =1.6%. The structure for M=Mn has a moderate complexity with 19 non-hydrogen atoms (57 refined positional parameters) which was also refined with soft constraints to R _WP =8.3%,R _F =3.9%. Both compounds show a framework built of alternate metal oxide inorganic layers, pillared by the organic groups. The metal environments in these materials are very distorted. Manganese atoms present three different distorted oxygen environments: four-, five- and six-coordinate. Thermal and IR data are also reported and discussed.