New ABC-6 net molecular sieves ZnAPO-57 and ZnAPO-59: Framework charge density-induced transition from two- to three-dimensional porosity

• Investigation of high charge density MeAPO materials with DEDMA and ETMA SDAs.
• Gradual transition from 2- to 3-dimensional porosity with increasing framework charge density.
• Novel ABC-6 net topologies ZnAPO-57 and ZnAPO-59 reported.

In a quest to make AlPO-based compositions with higher framework charge densities, the investigation of the chemistry of the diethyldimethylammonium (DEDMA) and ethyltrimethylammonium (ETMA) structure directing agents (SDA) has yielded two new ABC-6 net framework topologies. DEDMA leads to MeAPO-57, which is the first example of an ABC-6 net structure with a 5-layer repeat sequence. The structure was solved for the ZnAPO version in the space group P-3c and refined with the lattice parameters a = 13.3538 and c = 25.5664 Å, which included a doubled c-axis to account for the alternating Al/Zn and P occupancy of the T-atom sites. The identical synthesis, except for the substitution of DEDMA with ETMA, leads to MeAPO-59, which is the first example of an ABC-6 net structure with a 7-layer repeat sequence. This structure was also solved for the ZnAPO version in the space group P-3c and refined on the lattice parameters a = 13.3756 and c = 36.2118 Å, which also included a doubled c-axis. Product framework charge densities could be altered by adding Si or changing the SDA/H3PO4 levels. At high SDA/H3PO4 levels, the addition of Si to syntheses that yield MeAPO-57 or MeAPO-59 leads to MeAPSO-64, which has the BPH topology. Lowering the SDA/H3PO4 in both ETMA and DEDMA systems leads to MeAPO-67 with the LEV topology, another ABC-6 net structure with a 9-layer repeat sequence. The ZnAPO-57, ZnAPO-59, LEV and BPH topologies all exhibit two-dimensional 8-ring pore systems perpendicular to the c-axis. Access to diffusion along the c-axis increases with SDA/H3PO4 levels and framework charge density in the order LEV < ZnAPO-57 < ZnAPO-59 < BPH, with the ABC-6 net topologies ultimately restricted to two-dimensional diffusion while BPH has a 12-ring pore along the c-axis.

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