Pore‐Size Tuning in Double‐Pillared Metal‐Organic Frameworks Containing Cadmium Clusters

This contribution describes metal‐organic frameworks based on cadmium‐clusters that are capable of generating double‐pillared architectures. A brief overview of the literature concerning such systems is presented together with the description of three new coordination polymers, [{[Cd 2 ( trans ‐1,2‐ a , a ‐chdc)( trans ‐1,2‐ e , e ‐chdcH) 2 (4,4′‐bpy) 2 ] · 8H 2 O} n ] ( 1 ), [{Cd 2 ( trans ‐1,4‐ e , e ‐chdc)( trans ‐1,4‐ a , a ‐chdc)(4,4′‐bpe) 2 } n ] ( 2 ) and[{[Cd 2 ( cis , cis ‐1,3,5‐chtc)(HCO 2 )(H 2 O)(4,4′‐bpy) 2 ] · DMF · 4H 2 O} n ] ( 3 ) [1,2‐chdc = 1,2‐cyclohexanedicarboxylate, 1,4‐chdc = 1,4‐cyclohexanedicarboxylate, 1,3,5‐chtc = 1,3,5‐cyclohexanetricarboxylate, 4,4′‐bpy = 4,4′‐bipyridine and 4,4′‐bpe = ( E )‐1,2‐bis(4‐pyridyl)ethylene]. Compound 1 has a double‐pillared two‐dimensional layer structure, while compounds 2 and 3 are double‐pillared three‐dimensional frameworks. All materials have been characterized by elemental analysis, IR spectroscopy, single‐crystal X‐ray diffraction and thermogravimetric analysis. The robustness of the open‐frameworks found for compounds 1 and 3 has been examined by X‐ray powder diffraction of dried samples, which showed that the crystal structure of the 2D coordination polymer 1 collapses whereas the 3D architecture of compound 3 remains intact. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)