The structures of as-synthesized AlPO 4-53(A), calcined dehydrated AlPO 4-53(B), and AlPO 4-53(C), a new phase determined by the FOCUS method

Abstract

AlPO 4-53 was synthesized hydrothermally with methylamine as a structure-directing agent. The structure of as-synthesized AlPO-53(A) was solved using AlPO-EN3 as a starting model. The Rietveld refinement converged ( R P = 0.140) in space group P2 12 12 1 ( a=10.3212(1) Å, b=13.6308(1) Å and c=17.4539(1) Å) for unit cell composition: Al 24P 24O 96·8.5CH 3NH 2·14H 2O. AlPO-53(A) is isotypic with as-synthesized AlPO-EN3, JDF-2, UiO-12-as, and presumably CFSAPO-1(A). The structure of calcined dehydrated AlPO-53(B) was solved by direct methods, and refined to R P=0.084 in Pbca ( a=18.0241(1) Å, b=13.9174(1) Å and c=9.6554(1) Å). The topology of AlPO-53(B), the tetrahedral equivalent of AlPO-EN3, is iso-structural with MCS-1 and UiO-12-500. This topology (structure type code AEN) has two 8-ring channels that intersect to form a 2D system. Heating AlPO 4-53 to 700°C yields a new condensed phase, AlPO-53(C). The structure of AlPO-53(C) was solved with the FOCUS program and refined to R P=0.124 in C121 with a=16.4440(4) Å, b=5.1075(1) Å, c=13.4846(4) Å, and β=88.259(1)°. AlPO-53(C) has a new topology described as brw nets in the ac plane, linked by single and double zigzag chains, parallel to b. The elliptical 8-ring pores, parallel to b, produce a 1D channel system. The highly distorted 4-, 6-, and 8-rings in AlPO-53(B) become more regular in AlPO-53(C). The thermal transformation of AlPO-53(B) to AlPO-53(C) is illustrated.