Multiple Conformations of Benzil in Resorcinarene-Based Supramolecular Host Matrixes
datasetposted on 28.11.2003, 00:00 by Bao-Qing Ma, Yuegang Zhang, Philip Coppens
Six supramolecular complexes incorporating benzil as a guest, CMCR·bipy·benzil (α) 1 (CMCR = C-methylcalixresorcinarene), CMCR·bipy·benzil (β) 2, CMCR·2bpe·benzil·ethanol 3 (bpe = trans-1,4-bis(pyridyl)ethylene), CMCR·2bpe·benzil·2H2O 4, CMCR·2bpeh·benzil·ethanol 5 (bpeh = bis-(1-pyridin-4-yl-ethylidene)-hydrazine), and CECR·2bpe·benzil 6 (CECR = C-ethylcalixresorcinarene), have been synthesized by hydrothermal and conventional methods and characterized by X-ray diffraction. Resorcinarene adopts a boat conformation in 1−4 and a bowl conformation in 5 and 6. Compounds 1−4 show a brick-wall-like framework, in which two benzil molecules are incorporated. For 5, bpeh spacers link CMCR molecules to give a one-dimensional wavelike polymer in which one benzil guest is embedded within the polymer cavity. Complex 6 forms a carcerand-like capsule in which two benzil guests are encapsulated. The OC−CO torsion angles vary from 91.8 to 139.3° and correlate with the length of the central C−C bond. The benzil concentration, which is ∼6.2 mol/L in the neat crystals, varies between 1.01 and 1.51 mol/L in the structures studied, corresponding to a 6-fold dilution. The benzil molecules are disordered in the larger cavities of 4 and 5. The two benzoyl fragments are almost perpendicular in 3, which has the next largest cavity size when solvent volume is excluded, whereas a nearly trans-coplanar conformation occurs for the cavity with the smallest volume in 6.