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Breathing and Twisting: An Investigation of Framework Deformation and Guest Packing in Single Crystals of a Microporous Vanadium Benzenedicarboxylate

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posted on 07.03.2011, 00:00 by Xiqu Wang, Juergen Eckert, Lumei Liu, Allan J. Jacobson
The structural details of the compounds vanadium benzenedicarboxylate VO(bdc)·Guest, where the Guests are the absorbed six-ring molecules: benzene, 1,4-cyclohexadiene, 1,3-cyclohexadiene, cyclohexene and cyclohexane, have been determined from single crystal X-ray data. All of the six-ring guest molecules show a high degree of ordering inside the channels of VO(bdc). The interactions between the guests and the host framework are dominated by van der Waals bonding. The six-ring molecules are all packed in two columns in the channels, either in herringbone or close to parallel patterns. The packing changes the space group symmetry of VO(bdc) from Pnma to the noncentrosymmetric space group P212121. The VO(bdc) framework deforms to closely adapt to the shape and thickness changes of the double columns of the guest molecules. In addition to the well studied breathing deformation, a twisting deformation mechanism that involves a cooperative rotation of the octahedral chains accompanied by bending of the bdc ligand is apparent in the detailed structural data. More quantitative information on the remarkable flexibility of the VO(bdc) framework was obtained from ab initio calculations.