31P MAS and 2D exchange NMR of crystalline silicon phosphates

Application of the MAS-J-HMQC experiment to a new pair of nuclei {29Si,31P}: Si5O(PO4)6 and SiP2O7 polymorphs

“…This particular phase was not clearly evidenced by XRD. The isotropic chemical shifts of the various SiP 2 O 7 polymorphs are reported in Table 1 [19,21,22]. For the SiP 2 O 7 polymorphs, it is known from XRD data that the pyrophosphate groups (involving generally two non equivalent P sites) are linked exclusively to Si VI atoms (Fig.…”

XRD and Solid-State NMR Study of Magnesium Oxide–Magnesium Orthophosphate Systems

“…Specifically, H MAS NMR spectroscopy was recently used for the structural elucidation of Al O (13), TiO -SiO (14), and V O -AlPO systems (15). Also, P MAS NMR has enabled the characterization of the local environment of phosphorus atoms in both amorphous and crystalline phosphates (16)(17)(18)(19).…”

Formation of six-coordinated silicon in calcium phosphosilicate xerogels assisted by polyols at low temperature and pressure

“…After heat treatment at higher temperature (350 8C), the 31 P resonance of the samples (a-350, b-350, c-350) shows obvious changes, besides the narrow resonance at À1.4 ppm associated with Q 0 species, additional resonance appeared at À13.4 ppm and À30.5 ppm, assigned to Q 1 and Q 3 respectively. Moreover, a resonance is also seen at around À44 ppm, which can be assigned to Q 3 phosphates linked to both four-and sixcoordinated silicon atoms through P-O-Si bridges [24]. For the samples b-350 (from phosphoric acid/IS) and c-350 (from phosphoric acid/xylitol), the intensity at this resonance ($À44 ppm) is a little stronger and more negative than the samples a-350 (from phosphoric acid), this difference infers some differences in the number and/or coordination of the silicon neighbors in the P-O-Si bridges [25][26][27].…”