STRUCTURE REFINEMENT, ELECTRON-MICROSCOPY, AND SOLID-STATE MAGIC-ANGLE-SPINNING NUCLEAR-MAGNETIC-RESONANCE CHARACTERIZATION OF AIPO(4)-52 -AN ALUMINOPHOSPHATE WITH A LARGE CAGE

Synchrotron powder X-ray diffraction (PXRD) data for calcined AlPO4-52 were refined in space group <P(3)over bar 1c> using the Rietveld meth od. The previously proposed topology (AFT), an ABC six-ring structure type with an AABBCCAACCBB stacking sequence, was confirmed. The refine d unit cell dimensions are a = b = 13.715 (1) Angstrom and c = 29.676 (3) Angstrom. Possible causes for peak broadening in the synchrotron P XRD profile were examined. A series of PXRD patterns obtained at vario us temperatures indicated that the calcined sample used for synchrotro n PXRD was partially rehydrated. Electron diffraction patterns showed particle texture effects but no evidence for faulting or disorder. Ind ividual crystallites of AlPO4-52 are roughly equidimensional hexagonal prisms. Preferred orientation of the crystallites was not evident. So lid-state magic angle spinning nuclear magnetic resonance (MAS n.m.r.) spectra of calcined never-rehydrated AlPO4-52 showed that all aluminu m and phosphorus atoms were tetrahedrally coordinated. However, MAS n. m.r. spectra of a calcined rehydrated sample showed a 1:2 ratio of tet rahedral to octahedral aluminum atoms due to extraframework water coor dination. The P-31 MAS n.m.r. spectra are consistent with phosphorus a toms located exclusively in double six-rings.