Combined use of powder diffraction and magic-angle spinning NMR to structural chemistry
A range of 1D and 2D MAS NMR experiments have been carried out in conjunction with X-ray diffraction experiments on a number of materials from the AM(_2)O(_7) family, which exhibit the unusual phenomenon of negative thermal expansion. It has been shown that ZrP(_2)O(_7) and HfP(_2)O(_7) exist with space group Pbca rather than Pa3 as proposed in the literature, and a full structure solution has been possible for ZrP(_2)O(_7) from a combination of NMR and X-ray and neutron powder diffraction. 2D MAS NMR has been used to differentiate at least 108 unique phosphorus sites within the asymmetric unit of SnP(_2)O(_7), supporting a recent powder diffraction study presented in the literature. PbP(_2)O(_7) has been shown, by NMR, to exist as an incommensurate phase at room temperature. ZrW(_2)O(_8), a material which also shows negative thermal expansion, has been studied here primarily with variable-temperature (^17)O MAS NMR. The results presented shed important new light on oxygen migration processes occurring at the a I β-phase transition of this material. A full structure solution is presented for 2-[4-(2-hydroxy-ethylamino)-6-phenylamino-[1,3,5]triazin-2-ylamino]-ethanol from powder X-ray data, an organic material investigated as part of a study of ink-jet-dyes.