Variable Conformation of Benzophenone in a Series of Resorcinarene-Based Supramolecular Frameworks

Ten supramolecular complexes incorporating benzophenone (BZP) as a guest have been synthesized by hydrothermal and conventional methods and characterized by X-ray diffraction. They are CMCR·3bipy·2H₂O·BZP (CMCR = C-methylcalix[4]resorcinarene; bipy = 4,4‘-bipyridine) 1, CMCR·bipy·BZP·H₂O 2, CMCR·2bpe·BZP (bpe = trans-1,4-bis(pyridyl)ethylene) 3, CMCR·2bpmh·BZP (bpmh = bis-(1-pyridin-4-yl-methylidene)-hydrazine) 4, CMCR·2bpeh·BZP·ethanol (bpeh = bis-(1-pyridin-4-yl-ethylidene)-hydrazine) 5, CMCR·2bipy·BZP 6, CECR·2bipy·BZP·0.5bipy (CECR = C-ethylcalix[4]resorcinarene) 7, CECR·2bpe·0.5BZP·0.5ethanol 8, CMCR·2bix·2BZP (bix = 1,4-bis(imidazol-1yl-methyl)benzene) 9, and CECR·2bix·2BZP 10. The resorcinarene molecule adopts a chair conformation in 1, giving rise to a 3D stepped network. Compounds 2 and 3 have a brick-wall structure with boat-shaped CMCR but different spacer connectivity. A 3D 3-fold interpenetrating network exists in compound 4, whereas a wavelike framework is found in 5. Crystals of 6, 7, and 8 contain carcerand-like capsules. The use of a more rigid spacer generates 9 and 10, which exhibit a double buckled framework with large channels. The 10 phases contain 12 independent benzophenone molecules (9 and 10 each having two independent benzophenone molecules), eight of which are fully ordered within the supramolecular framework. Benzophenone occurs as a monomer in 1, 5, 8 and as a dimer in 2, 3, 4, 6, and 7, while polymeric aggregates are found in 9 and 10. The dihedral angles between the two phenyl rings of benzophenone vary from 42.0 to 67.9°, and correlate with the central C−C−C bond angles, which decrease with increasing dihedral angle. Quantum-mechanical calculations indicate the energy of the distortion imposed by the framework to range up to 32 kJ/mol, which is significant relative to the ∼85 kJ/mol lattice energy of the known neat benzophenone phases.