AlMethylPO₄.H₂O:THE AB INITIO STRUCTURE SOLUTION OF A NEW LAYERED COMPOUND. Sawers, L-J. M., Carter, V., Armstrong, A. R., Bruce, P. G., Wright, P. A., Dept. Of Chemistry, University of St. Andrews, St. Andrews, Fife, Scotland

Micro-porous and layered alumino-methyl phosphonates offer wide-ranging possibilities in separation and catalysis. The title compound is a novel structure made up of alumino phosphonate layers containing bound water, the layers being separated by methyl groups. The synthesis and structure solution of AlmethylPO₄.H₂O is described. The structure was solved ab initio from laboratory X-ray data using a combination of Direct Methods, molecular modeling and Rietveld refinement. Indexing gave a monoclinic unit cell of:-a = 9.45Å, b = 7.06 Å, c = 7.85 Å and [[beta]] = 106.6deg. in the space group P2₁/a. A default run of the Direct Methods package SIRPOW gave a starting structure consisting of 1P, 1Al and 3O's. The remaining atoms were found through the use of difference fourier maps and the Biosym modeling package, Insight. Which, combined with a prior knowledge of bond angles and distances for both octahedral and tetrahedral aluminium sites was used in the latter stages of the Rietveld refinement to determine starting positions for 2O's and 5H's. The result was a final structure solution with an R_Wp of 7.85%, an R_p of 5.87% and a chi² of 5.39%.