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 ∼50 μm) using synchrotron radiation (λ=1.46 A) and at 100 K from a larger crystal (∼250 μm) using radiation from a sealed Cu tube (λ=1.5418 A). 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) A, c=8.4526(5) A, and γ=120.00°, 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 A, Al–O=1.69–1.76 A, O–P–O=104–119°, O–Al–O=99–124° and Al–O–P=137–154°. The observed (weak) 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.