Rietveld refinement of the pure aluminophosphate AlPO4-40

1D to 3D NMR study of microporous alumino‐phosphate AlPO4‐40

“…4. Because similar T 2 relaxation times (typically ∼15 ms) were measured for each Al group (Al IV−1 , Al IV−II and Al V ) and because all the sites correspond to Al-(OP) 4 environments, these curves directly translate into differences in the isotropic scalar J 2 (Al-O-P) couplings. We already know from experiments on simpler phases [10] or from selective excitation experiments [11] that these couplings may vary significantly from one Al-O-P bond to another.…”

“…[4] from a high-resolution X-ray diffraction study, the anionic [Al 32 P 32 O 128 (OH) 4 ] 4− framework of AlPO 4 -40 can be understood as constructed from two distinct types of clusters, each containing four crystallographically independent Al sites. One cluster contains four Al and four P sites plus the hydroxyl O 33 site bridging two Al V sites.…”

“…An analysis of the Al/P and P/Al bond tables (ICSD-88919 Ref. [4]) reveals that only Al 1 and Al 5 are not connected to a common P site and may thus be ascribed to the Al IV−II group. These sites are also the inner most sites of the framework structure (Fig.…”

“…Each radiofrequency channel is equipped with band-pass filters. 31 P and 27 Al chemical shifts are reported in parts per million relative to 85% H 3 PO 4 and Al(NO 3 ) 3 1M solutions.…”

“…Ribeiro (Portugal). Its structure was established from high-resolution X-ray diffraction [4] and involves eight distinct fourfold P(OAl) 4 phosphorous sites and eight distinct aluminium sites (six fourfold Al IV − Al(OP) 4 sites and two fivefold Al V − Al(OP) 4 OH sites). However, as already demonstrated by several NMR studies, its structure appears to be much more complex, involving more than eight nonequivalent sites.…”