Layered aluminophosphates III.: Crystal structure and thermal properties of the novel layered aluminophosphate UiO-18

The synthesis and crystal structure of a novel layered aluminophosphate and its two high-temperature variants are described. Two of the structures were solved from powder X-ray diffraction data. The as-synthesised material (UiO-18-as) with a composition [Al(2)(OH)(2)(PO(4))(2)(H(2)O)(2)](2-)[NH(3)(CH(2))(3)NH(3)](2+)2H(2)O crystallises in the orthorhombic space group Pnma with a = 6.91809(8) Angstrom, b = 22.3000(4) Angstrom, c = 9.60666(12) Angstrom, V = 1482.053(36) Angstrom(3) and Z = 4. The aluminophosphate layers are composed of aluminium octahedra forming infinite chains along [1 0 0] that are cross-linked by phosphate tetrahedra. The layers are held together by hydrogen bonding interactions involving the interlamellar 1,3-propanediammonium ions and water molecules. A high-temperature variant exists around 100 degrees C (UiO-18-100). This compound with the composition [Al(2)(OH)(2)(PO(4))(2)](2-)[NH(3)(CH(2))(3)NH(3)](2+) crystallises in the monoclinic space group P2(1)/n with a = 21.5516(12) Angstrom, b = 6.96437(22) Angstrom, c = 8.1635(4) Angstrom, beta = 100.0112(4)degrees, V = 1206.51(11) Angstrom(3) and Z = 4. The transformation to UiO-18-100 involves removal of the interlamellar water molecules and water molecules coordinating aluminium. The inorganic sheets retain their structure with infinite chains of aluminium trigonal bipyramids cross-linked by phosphate tetrahedra. The conformation of the 1,3-propanediammonium ion changes from the straight one observed in UiO-18-as to a more staggered one. Another high-temperature variant exists around 200 degrees C (UiO-18-200). (13)C CP-MAS NMR data indicate that the 1,3-propanediammonium ion remains unaffected by the transformation to UiO-18-200, and the weight loss associated with it involves release of water molecules and probably formation of tetrahedral Al-O-Al bonding just as in UiO-15-225. Structure elucidation of this compound is, however, prevented by severe disorder. (C) 2000 Elsevier Science B.V. All rights reserved.