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

Abstract

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.