Selective Guest Binding by Tailored Channels in a 3-D Porous Zinc(II)−Benzenetricarboxylate Network

Diffusion of triethylamine into an ethanol solution containing 1,3,5-benzenetricarboxylic acid (H3BTC) and zinc(II) nitrate hexahydrate yields crystalline Zn2(BTC)(NO3)·(H2O)(C2H5OH)5, which was formulated by elemental microanalysis, solid-state NMR, and single-crystal X-ray diffraction [cubic, P213, a = 14.728(2) Å, V = 3195(2) Å3, Z = 4]. This compound possesses a 3-D structure with nearly 44% of the framework represented by an extended channel system having a 14 Å cross-section, where highly mobile ethanol and water guest molecules reside. The multidentate functionality of BTC imparts rigidity to the structure, consequently allowing the guests to be removed or exchanged without destruction of the porous framework. X-ray powder diffraction, solid-state NMR (13C CP MAS and static), gas chromatography, and thermogravimetry analyses reveal that this material is highly selective to alcohols because of the coordination environment adopted by Zn(II) within its framework. Other molecular inclusions such as tetrahydrofuran, methyl ethyl ketone, acetonitrile, and acetone are not permitted into the channels, due to the specific electronic demands of the Zn(II) center and its ability to direct the inclusion process even in cases where incoming molecules have the appropriate shape and size for inclusion.