A new two-dimensional aluminium phosphate, [BuNH 3 ] 3 [Al 3 P 4 O 16 ], has been synthesized under solvothermal conditions at 453 K using butylamine as template. The structure, solved using single-crystal X-ray diffraction data measured at 200 K [trigonal, space group P3 ¯, a = 13.158(2), c = 9.633(2) Å, U = 1444.4 Å 3 , Z = 2], consists of AAAA-stacked [Al 3 P 4 O 16 ] 3Ϫ layers containing 12-membered rings of alternating AlO 4 and PO 4 tetrahedra. Disordered butylammonium cations lie between the layers with their hydrophobic tails pointing into the channels bounded by the 12-membered rings.

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SummaryThe model for the amphibole and pyroxene structures based on close-packed oxygen layers introduced by Thompson is investigated systematically. It is shown that different features of it can best be understood in terms of three different symbolisms: the O and S rotations of tetrahedra; the A,B, C stacking notation for close-packed layers; and the c, h notation for the relationship of close-packed layers to their neighbours. The possible stacking arrangements and their space-groups are derived systematically. Relationships between the close-packed, fully rotated, model and the extended chain model are discussed, and some important drawbacks in the former model are pointed out, especially in connection with real amphibole structures.

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