1D AND 2D SOLID-STATE NMR INVESTIGATIONS OF THE FRAMEWORK STRUCTURE OF AS-SYNTHESIZED ALPO4-14

The framework structure of As-synthesized ALPO(4)-14 has been investig ated with a combination of different one-dimensional Al-27 and P-31 so lid State NMR techniques and Al-27/P-31 double resonance methods. The results are found to be fully consistent with the assumed structural m odel. Al-27 MAS and DOR experiments at three different magnetic field strengths together with simulations show the presence of two tetrahedr al sites, one pentacoordinated and one octahedral aluminum site. The A l-27 quadrupolar coupling constants and the P-31 isotropic chemical sh ifts of the tetrahedral sites correlate well with tetrahedral shear-st rain parameters and mean P-O-Al bond angles, respectively. These corre lations allow one to assign all of the NMR resonances to specific T-si tes in the proposed framework structure. The assignments are then furt her confirmed by the application of three different two-dimensional he teronuclear correlation methods (i.e., Al-27 --> P-31 TEDOR, CP, and I NEPT) which reveal the connectivities between AlOx and PO4 polyhedra. The two-dimensional INEPT experiment is applied here for the first tim e in the solid state. (C) 1997 Published by Elsevier Science B.V.