Hydrothermal synthesis and crystal structures of two open-framework fluorinated aluminum phosphates templated by 1,3-diaminopropane (ULM-4 & MIL-64)

Abstract

Two fluorinated aluminophosphates called ULM-4 (Al 6(PO 4) 6F 4⋅2H 3N(CH 2) 3NH 3⋅H 2O) and MIL-64 (Al 10(PO 4) 4(HPO 4) 6F 9(H 2O) 4⋅ OH⋅4N 2C 3H 12) have been prepared in the presence of HF and 1,3-diaminopropane as a structure-directing agent under hydrothermal conditions (autogeneous pressure, 180 °C, 8–48 hours and 1 months, respectively). ULM-4 crystallises from a F/Al ratio of 1 whereas MIL-64 is obtained with F/Al = 2. The structures have been determined using room temperature single crystal X-ray diffraction data. ULM-4 is described in the noncentric monoclinic space group P2 1 (n° 4) with the unit cell parameters: a = 8.5552 ( 2 ) Å , b = 10.1133 ( 2 ) Å , c = 16.7025 ( 4 ) Å , β = 94.94 ( 1 ) ° , V = 1439.74 ( 6 ) Å 3 and MIL-64 crystallizes in the monoclinic space group C2/m (n° 12) with a = 19.2227 ( 1 ) Å , b = 12.2190 ( 2 ) Å , c = 12.7008 ( 2 ) Å , β = 129.239 ( 1 ) ° and V = 2310.52 ( 5 ) Å 3 . Both structures exhibit a three-dimensional framework. For ULM-4, it consists of hexameric units Al 3(PO 4) 3F 2 in which the aluminium atoms exhibits two types of surrounding (one octahedron, AlO 4F 2 and two trigonal bipyramids, AlO 4F). The fluorine atoms link the aluminium atoms together. This building unit is similar to that observed in the iron and gallium analogues. The connection of the hexameric units delimits rectangular-shaped 10-ring channels along [010] and 8-ring channels along [100] in which the 1,3-diaminopropane molecules are located. The subnetwork of the amines induces a non-centric symmetry. The second compound MIL-64 is composed of inorganic layers consisting of infinite zigzag chains corner-sharing (via fluorine) aluminum octahedra (AlO 4F 2, AlO 2F 3(H 2O) and AlO 3F 2(H 2O)) with the cis– trans sequence, connected to each other through fluorine and phosphate groups. The resulting sheets are linked to each other via additional AlO 4 and PO 4 tetrahedral units and this generates a three-dimensional network with cavities, encapsulating the molecular species OH 2⋯H 2N(CH 2)NH 3/OH⋯H 3N(CH 2)NH 3.