Crystallographic site discrimination in aluminophosphate molecular sieves by solid-state NMR: influence of the field-dependent isotropic second-order quadrupolar shift on high-resolution aluminum-27 DOR NMR

High-Resolution Heteronuclear Correlation Spectra between 31P and 27Al in Microporous Aluminophosphates

“…2 exhibits superior resolution in the 27 Al dimension. In agreement with earlier 27 Al DOR work, two tetrahedral 27 Al resonances are observed [24,25].…”

“…However, the assignment of these pairs to Al 2 -P 2 and Al 3 -P 3 can only be made in the context of precise crystallographic data, as connectivities reported in Table 1 are the same. Both assignments have been discussed in the literature [25,26]. The quadrupolar coupling (SOQE) of the two tetrahedral sites is linearly correlated to the shear strain factor (|ψ| = i tan(θ i − θ 0 )), where the sum runs over the six O-Al-O angles, which quantifies the distortion from tetrahedral symmetry [26].…”

Interaction of Water Molecules with the VPI-5 Lattice

“…Thegeometry 9 were able to shed some light on the location of water molecules. The unsaturated valency of the oxygen atoms in the tetrahedral cluster is balanced by bonding a hydrogen atom to them, and the position of these hydrogen atoms is the adjacent T atoms in the VPI-5 structure.…”

Double rotation27Al NMR in molecular sieves

“…The influence of the field-dependent isotropic second-order quadrupolar shift on the improvement of high-resolution DOR spectra is demonstrated in the case of the aluminophosphate VPI-5 [19]. Fig.…”

“…6. The isotropical chemical shifts from these data [19] are +43.6 _ 0.2 and +41.6 + 0. With the knowledge of the isotropic chemical shift and the quadrupolar parameters it is possible now to assign further the tetrahedral lines in the 27A1 DOR spectra to the crystallographic aluminum sites of hydrated VPI-5, as determined by powder diffraction [15].…”