Absolute configuration and domain structure of AlPO4-5 studied by single crystal X-ray diffraction

The absolute configuration of AlPO4-5 has been determined from single crystal X-ray diffraction data. The intensities of Friedel related reflections were measured at room temperature from a microcrystal (maximum size similar to 50 mu m) using synchrotron radiation (lambda = 1.46 Angstrom) and at 100 K from a larger crystal (similar to 250 mu m) using radiation from a sealed Cu tube (lambda = 1.5418 Angstrom). Both data sets indicate the same absolute configuration. The Al(O)P vector, parallel to the polar channel axis, points along the main growth direction. Perpendicular to the main growth direction, the crystal is terminated by an Al(O)P plane with the Al atoms at the surface. The crystal structure of AlPO4-5, a = b = 13.718(1) Angstrom, c = 8.4526(5) Angstrom, and gamma = 120.00 degrees, is described as consisting of three types of microdomains, each exhibiting P6 symmetry. The domains are related by two sets of glide planes. The average structure has P6cc symmetry. All observed angles and distances are within acceptable limits: P-O = 1.50-1.57 Angstrom, Al-O = 1.69-1.76 Angstrom, O-P-O = 104-119 degrees, O-Al-O = 99-124 degrees and Al-O-P = 137-154 degrees. The observed tweak) diffuse scattering might be caused, besides, the disorder of the template molecules, by incoherent scattering of domain walls, which exhibit geometries slightly different from each of the three domains. (C) 2000 Elsevier Science B.V. All rights reserved.