SYNTHESIS AND AB-INITIO STRUCTURE DETERMINATION OF ALPO4.H2O-H4 FROM POWDER DIFFRACTION DATA

The crystal and molecular structure of aluminophosphate, AlPO4-H4, was determined solely from X-ray powder diffraction data and refined by Rietveld methods. The compound crystallizes in the monoclinic space group C2/c with a = 7.1374(2) angstrom, b = 7.0945(2) angstrom, c = 14.7377(5) angstrom, and beta = 99.102(1)-degrees. The final agreement factors are Rp = 0.095, Rwp = 0.135, and R(F) = 0.03. The Rietveld refined formula is AlPO4.H2O. There are two independent Al atoms. One is coordinated by two water molecules and four phosphate oxygens. The other is tetrahedrally coordinated by phosphate oxygens. All the phosphate oxygens are involved in bridging the Al atoms. In the synthesis procedure it was necessary to include an amine template to preclude impurities even though H4 is a condensed phase and not a molecular sieve.