(4;2)-connected three-dimensional nets related to the mixed-coordinated framework structures AlPO₄-15, AlPO₄-CJ2 and AlPO₄-12

Application of the same pattern for linking neighbouring 4.8² two-dimensional nets as is found in the AlPO₄-CJ2 and AlPO₄-15 structures allows the enumeration of eleven (4;2)-connected three-dimensional nets with a maximum unit-cell repeat of ~ 10 Å. Net 551 is polytypic with net 398 (the tetrahedral analogue of AlPO₄-12). The (4;2)-connected nets related to AlPO₄-15 (net 400) and AlPO₄-CJ2 (net 725) have the highest symmetry of the present nets. Synthetic zeolite Linde J may have the latter framework topology. Nets 400 and 725 relax considerably upon lowering of the space group symmetry. Geometrical refinements indicate that the mixed-coordinated AlPO₄-15 is more feasible than its (4;2)-connected relative (same space group symmetry); the feasible net 398 and the topologically simpler net 551 have not been observed so far. Geometrically optimized atomic coordinates are given for the most feasible nets obtained here.