AB-INITIO STRUCTURE DETERMINATION OF AMMONIUM HYDROGEN ALKYL PHOSPHATES FROM X-RAY-POWDER DIFFRACTION DATA

The structures of three ammonium hydrogen alkyl phosphates, NH4PO2(OH) (OR) [R = Me (1), Et (2), Pr-i (3)], have been solved nb initio from X -ray powder diffraction data. The structure determinations were based on Patterson search methods combined with difference-Fourier technique s and the refinement was carried out using Rietveld methods. Powder di ffraction data were first collected for all three compounds in the ref lection mode using Cu Kalpha 1+alpha 2 radiation. A pronounced preferr ed orientation effect was found for all the samples, even by side-load ing into a flat sample holder. A random orientation of the powder part icles was obtained for (1) using a special suspension chamber for the sample preparation, while for (2) and (3) data were remeasured In capi llaries using the transmission mode. Crystals of the ammonium hydrogen methyl phosphate (1) and the ammonium hydrogen ethyl phosphate (2) bo th belong to the monoclinic space group P2(1)/c, Z = 4, with a = 9.964 5 (4), b = 7.1801 (3), c = 7.5897 (3) Angstrom and beta = 96.243 (3)de grees for (1) and 12.6453 (4), b = 7.1502 (2), c = 7.9738 (2) Angstrom and beta = 108.875 (2)degrees for (2). The ammonium hydrogen isopropy l phosphate (3) crystallizes in space group An, Z = 4, with a = 6.2475 (2). b = 29.3525 (6), c = 4.6305 (1) Angstrom and beta = 100.904 (2)d egrees. All three compounds are characterized by an extended hydrogen- bonding network involving the hydrogen phosphate units and the ammoniu m ions. forming double layers. The methyl (1), ethyl (2) and isopropyl groups (3), which point into the interlayer space, connect the layers by van der Waals interactions.