An Aluminophosphate Molecular Sieve with 36 Crystallographically Distinct Tetrahedral Sites

Abstract

The structure of the new medium-pore aluminophosphate molecular sieve PST-6 is determined by the combined use of rotation electron diffraction tomography, synchrotron X-ray powder diffraction, and computer modeling. PST-6 was prepared by calcination of another new aluminophosphate material with an unknown structure synthesized using diethylamine as a structure-directing agent, which is thought to contain bridging hydroxy groups. PST-6 has 36 crystallographically distinct tetrahedral sites in the asymmetric unit and is thus crystallographically the most complex zeolitic structure ever solved.

Two Aluminophosphate Molecular Sieves Built from Pairs of Enantiomeric Structural Building Units

“…This indicates that the occluded OSDA molecules exist mainly as the protonated form (DEA·H + )t o compensate for the negative charge of the bridging Al-OH-Al groups and thus have no lone pair of electrons on the nitrogen atom. 70 and 100 8 8C, respectively,than that observed in the TGA/DTA curves for PST-5 and AlPO 4 -21, [5] PST-13 is fairly less stable than the other two materials.V ariable-temperaturep owder XRD measurements reveal that an on-negligible portion of PST-13 is transformed to PST-14 even at 200 8 8C( Figure S8). Since this temperature is lower by ca.…”

“…Thes ynthesis conditions leading to pure PST-13 are very narrow: we are only able to synthesize this material by heating an AlPO 4 gel with the composition 1.8 DEA·1.0 Al 2 O 3 ·1.0 P 2 O 5 ·40 H 2 Oa t2 00 8 8Cf or 5days.I ti sw orth noting that the DEA/Al 2 O 3 ratio (1.8) of this AlPO 4 gel is marginally lower than the ratio (2.0) of the gel for PST-5, [5] giving asomewhat lower starting pH (ca. 9.7 vs.10.4) to the former synthesis mixture.I na ddition, while the use of aluminum isopropoxide directed the synthesis of PST-13, its replacement with the equivalent amount of pseudoboehmite under the PST-13 synthesis conditions yielded AlPO 4 -21 (AWO).…”

“…[5] Therefore,we speculate that the types of oligomeric species responsible for the formation of these three AlPO 4 materials containing penta-coordinated framework Al atoms may be different from one another. This suggests that the crystallization process of PST-13 may be kinetically,r ather than energetically,c ontrolled.…”

“…[5] This has made PST-6 most complex among the zeolite structures known to date. [5] This has made PST-6 most complex among the zeolite structures known to date.…”

“…[5] This has made PST-6 most complex among the zeolite structures known to date. [5] By utilizing the so-called continuous rotation electron diffraction (cRED) method, [6] we have very recently been able to determine the structure of PST-5, the details of which will be given elsewhere.I ndeed, this new method can allow us to collect cRED data within afew minutes and thus minimize the damage to electron beam sensitive materials like PST-5. [5] By utilizing the so-called continuous rotation electron diffraction (cRED) method, [6] we have very recently been able to determine the structure of PST-5, the details of which will be given elsewhere.I ndeed, this new method can allow us to collect cRED data within afew minutes and thus minimize the damage to electron beam sensitive materials like PST-5.…”