The use of magic-angle-spinning NMR in structural studies of Si―Al―O―N phases

Crystal structures have traditionally been determined using X-ray diffraction methods. Aluminosilicate structures, however, are very difficult to solve exactly because of the very similar X-ray scattering factors for aluminium and silicon atoms. A new technique of high resolution magic angle-spinning (MAS) NMR spectroscopy, which is applicable to solids, is able to provide hitherto unavailable information on the local coordination of specific types of atom. The purpose of this letter is to demonstrate the application of MAS-NMR spectroscopy in resolving structural problems in the Si-Al-O-N system (2). The local coordination of super(29)Si or super(27)Al nuclei may be determined, and the ratio of Si/Al within sites of a particular coordination can be measured. Si-Al-O-N structures are normally based on tetrahedral (Si, Al) (O,N) sub(4) units, but in the structures discussed here both tetrahedral and octahedral coordination may occur.