Hydrated aluminophosphate molecular sieves

The Al MASNMR spectrum of VPI-5 has also been reported earlier (7). The spectrum contains a major resonance near 37 ppm, a neighboring resonance at 28 ppm, and a small resonance below 0 ppm. The chemical shifts of these resonances are consistent with other hydrated aluminophosphate molecular sieves that contain tetrahedrally coordinated aluminum that are linked to four phosphorus atoms through bridging oxygen atoms (10,11). 

Conditions for A1PQ4-H3 and MCM-1 Synthesis. From previous section it cSh Be concluded that as far as the coordination of A1 is concerned, AlPC -EU is a hybrid between the aluminum phosphate hydrates like variscite and metavariscite and the aluminophosphate molecular sieves. It can be expected that the synthesis conditions under which it crystallizes will also be intermediate between those of hydrates and molecular sieves. Literature together with the present new data seem to confirm this. 

Aluminum-27 Double Rotation NMR spectroscopy (DOR) has been used to investigate framework ordering in the aluminophosphate molecular sieves VPI-5, AIPO4-5, and AIPO4-8. Well-resolved peaks in the Al DOR spectra of both hydrated and dehydrated VPI-5 allow isotropic shifts to be conelated with local framework structure. More distorted aluminum environments are reflected by broader lines in Al DOR spectra of AIPO4-5 and AIPO4-8. 

The abihty of the aluminiun to attain six coordination when associated with phosphate ligands results in the aluminophosphate molecular sieves exhibiting some unusual thermal properties. As discussed previously, D Yvoire s (n = 1 -6) materials were hydrated species with some of the aliunimun in octahedral coordination, four points attached to the phosphate in the framework, and the two remaining coordination sites occupied by molecules of water. The labihty of these water molecules is dependent on the structure. AIPO4S prepared fi-om organic-containing systems can also exhibit expanded coordination around the aluminum. 

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