Hydrothermal synthesis and crystal structure of a new three-dimensional aluminum-organic framework MIL-69 with 2,6-naphthalenedicarboxylate (ndc), Al(OH)(ndc)·H2O

A new three-dimensional aluminum-organic framework, MIL-69 or Al (OH) (O 2 C–C 10 H 6 –CO 2) ·H 2 O, has been hydrothermally synthesized at 210 °C for 16 h, by using 2, 6-naphthalenedicarboxylic acid as a rigid ligand. The model for the crystal structure of MIL-69 was determined by means of lattice energy minimizations and further refined against the powder XRD data using the Rietveld refinement method. The crystal structure consists of infinite chains of AlO 4 (OH) 2 octahedra corner-linked through the μ 2 -hydroxyl groups and connected by the 2, 6-naphthalenedicarboxylate moieties. It results in the formation of flat channels parallel to the chains of aluminum octahedra, running along the c axis. A water molecule is trapped nearby the center of the tunnels and mainly interacts via hydrogen bonds with the hydroxyl groups and the oxygen atoms of the carboxylates. Although the three-dimensional aluminum-organic framework is stable up to 450 °C, the tunnels still remain shrunk upon removal of water molecule, because of the occurrence π–π interactions between the naphthalene groups. The MIL-69 phase was characterized by solid state NMR MAS 27 Al, 1 H and 13 C 1 H-decoupled, which is consistent with the crystal structure description. Crystal data. – MIL-69, Al (OH) (O 2 C–C 10 H 6 –CO 2) ·H 2 O: Mr = 267. 11 g mol –1, monoclinic, space group C 2/ c (no. 15), a = 24. 598 (2) Å, b = 7. 5305 (6) Å, c = 6. 5472 (5) Å, β = 106. 863 (8) °, V = 1160. 6 (2) Å 3, Z = 4.