Synthesis, characterization and structure determination of two novel layered aluminophosphates templated by 2-methylpiperazine

Two new two-dimensional-layered aluminophosphates with P:Al=4:3 have been synthesized hydrothermally using 2-methylpiperazine as organic templating molecule, and their structures have been solved using single-crystal X-ray diffraction data. APMep150, with the composition | (C 5N 2H 14) 3(H 2O) 10 | [Al 6P 8O 32(H 2O) 2], crystallized at 150 °C in the form of large hexagonal prisms in space group P3 (no. 143) with a=13.240(14) Å and c=9.672(5) Å. The aluminophosphate layer consists of a network of 4-, 6- and 12-membered rings. This type of layer is observed in other layered aluminophosphates, but differs here by the presence of a disordered aluminum octahedron in the unit cell. The structure contains a one-dimensional channel system along the [0 0 1] direction, generated by the alignment of the 12-rings units. These channels contain water molecules and are partially occluded by the methyl groups of 2-methylpiperazinium ions. Water molecules can be reversibly removed at moderate temperature without significant modifications of the unit cell parameters. The dehydrated compound, which contains only AlO 4 and PO 4 tetrahedra and the organic template, possesses channels with a window size of ≈4.0×6.6 Å. The other layered compound, named APMeP200, has been obtained at 200 °C and its structure is almost identical to that of AP2pip, a compound synthesized in the presence of piperazine. APMeP200 has the composition | (C 5N 2H 14) 4.5(H 2O) 2.5 | [Al 9P 12O 48], and crystallizes in space group P2 1/c (no. 14) with a=22.12(3) Å, b=19.09(2) Å, c=16.541(16) Å and β=99.96(9). The structure can accommodate the extra methyl groups without significant modifications of the unit cell, because these groups displace some of the water molecules present in AP2pip.