Synthesis, crystal structure and 71Ga solid state NMR of a MOF-type gallium trimesate (MIL-96) with μ3-oxo bridged trinuclear units and a hexagonal 18-ring network

A new gallium trimesate Ga12O(OH)(12)({OH}(4), {H2O}(5))[btc](6)center dot approximate to;24H(2)O, called MIL-96 (btc = 1,3,5- benzenetricarboxylate or trimesate species) was hydrothermally synthesized under mild conditions (210 degrees C, 5 h) in the presence of trimethyl 1,3,5-benzene tricarboxylate in water and characterized by single-crystal X-ray diffraction technique. The MIL-96 (Ga) structure exhibits a three-dimensional metalorganic framework containing isolated trinuclear mu(3)-oxo-bridged gallium clusters and infinite chains of GaO4(OH)(2) and GaO2(OH)(4) octahedra generating a hexagonal network based on 18-membered ring. The two types of gallium groups are connected to each other through the trimesate species which induce corrugated chains of gallium octahedra, linked via 1-12-hydroxo bonds with, the specific-cis-cis-trans-sequence. The 3D framework of MIL-96 reveals three kinds of cavities (two of them have estimated pore volumes of approximate to 480 and 860 angstrom(3)), in which are encapsulated free water molecules. The latter species are removed upon beating at 150 degrees C. The MIL-96 (Ga) compound was characterized by Ga-71 solid state NMR at different magnetic fields (14.1 and 17.6 T). Ga-71 spectra of MIL-96 (Ga) show the gallium exhibits relatively weak quadrupolar interactions compared to those observed in other MOF-type gallium carboxylates that have very strong quadrupolar interactions (MIL-61 and MIL-53). (C) 2007 Elsevier Inc. All rights reserved.