Fig. 2: Comparison of the structures of PST-5 and PST-6.

Structural models of PST-5 (a1) and PST-6 (b1) viewed along the c-axis. Both structures are built from the same building layer containing 4-, 6-, 8-, and 10-rings (if the OH groups, shown in red are not considered). The difference is the orientations of the (Al,P)O4 tetrahedra in the two structures. The red atoms in (a1) correspond to the OH groups bridging two Al atoms in PST-5. These Al atoms are five-coordinated. Structural models of PST-5 (a2) and PST-6 (b2) viewed along the b-axis, showing the transforms of double-crankshaft chains (dcc) and double-4-rings (d4r) in PST-5 (a1) to narsarsukite-type chains (nsc) in PST-6 (indicated by purple boxes). c Building units in PST-5 (dcc and d4r) and PST-6 (nsc).