CRYSTAL-STRUCTURES OF DEHYDRATED VPI-5 AND H1 ALUMINUM PHOSPHATES FROM X-RAY-POWDER DATA
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The crystal structures of the dehydrated phases of the 18-ring aluminum phosphates VPI-5 and H1 have been determined from X-ray powder data. Both phases crystallize in the hexagonal space group P63cm with a = 18.6005 (6) , c = 8.3664 (4) for VPI-5 and a = 18.6576 (7) , c = 8.3284 (5) for H1. In the latter phase, the atoms in the six-membered ring (6MR) were found to be disordered, requiring two partially occupied structures to define the atomic positions. One structure is the regular VPI-5 framework with all six-membered rings parallel to the c-axis direction. The other requires a rotation of the 6MR phosphate groups to produce rows of 4MR, 6MR, and 10MR replacing the rows of all 6MR. The thermal instability of H1 is attributed to this disorder, which in turn is thought to arise from the low-phosphate content of H1. 1992 American Chemical Society.