Solid-State Oxygen-17 Nuclear Magnetic Resonance Spectroscopic Studies of Zeolites and Related Systems. 2

We have obtained solid-state ¹⁷O NMR spectra of ¹⁷0-enriched gallosilicates (gallium analogues of zeolite Na-X, sodalite, and Ba²⁺-exchanged sodalite) and the porous aluminophosphates (AlPO₄-5, A1PO₄-11, and A1PO₄-17). The spectra yield nuclear quadrupole coupling constants (e²qQ/h), electric field gradient tensor asymmetry parameters (η), and isotropic chemical shifts (δ_i) for the chemically distinct oxygens in the Si-O-Ga, Si-O-Si, and Al-O-P fragments. The e²qQ/h values for these species, and for Si-O-Si and Si-O-Al in Na-A and Na-Y zeolites, are analyzed in terms of a Townes-Dailey theory, and the results are compared with the predictions of a previous wholly empirical approach (Schramm, S.; Oldfield, E. J. Am. Chem. Soc. 1984, 106, 2502). The results suggest that the empirical approach gives the best agreement between experiment and prediction when nonframework counterions are present (e.g., Si-O-Al, Si-O-Ga), but that the Townes-Dailey approximation yields the most accurate predictions in the absence of such species (e.g., Al-O-P).