A new indium trimesate In12O(OH)(12)({OH}(4),{H2O}(5))[btc](6)center dot approximate to 31H(2)O, called MIL-96, (btc = 1,3,5-benzenetricarboxylate or trimesate species) was hydrothermally synthesized under mild condition (210 degrees C, 5 h) in the presence of trimethyl 1,3,5-benzenetricarboxylate in water and characterized by single-crystal X-ray diffraction technique. The MIL-96 (In) structure exhibits a three-dimensional metal-organic framework containing isolated trinuclear (mu)over dot-oxo-bridged indium clusters and infinite chains of InO4(OH)(2) and InO2(OH)(3)(H2O) octahedra generating a hexagonal network based on 18-membered ring. The two types of indium entities are connected to each other through the trimesate species which induce corrugated chains of indium octahedra, linked via mu(2)-hydroxo bonds with the specific -cis-cis-trans- sequence. The 3D framework of MIL-96 reveals three kind of cavities (two of them have estimated approximate to 400 angstrom(3) volumes), in which are encapsulated free water molecules. The latter species are removed upon heating at 150 degrees C. (C) 2006 Elsevier Ltd. All rights reserved.