CONFORMATIONAL AND CONFIGURATIONAL DIVERSITY OF SOLVENT INCLUSION COMPLEXES OF SOME CALIX[4]PYRROLES AND THEIR ANION RECOGNITION PROPERTIES
A. Sharma1, S. Obrai2, R. Kumar3, A. Kaur4, M. S. Hundal4
1Department of Chemistry, Hans Raj Mahila Maha Vidyalaya, Jalandhar, Punjab, India
apparna_2007@yahoo.com
2Department of Chemistry, Dr. B.R. Ambedkar National Institute of Technology, Jalandhar, Punjab, India
3Department of Chemistry, Lyallpur Khalsa College of Engineering, Jalandhar, Punjab, India
4Department of Chemistry, Guru Nanak Dev University, Amritsar, Punjab, India
Keywords: recrystallization, configurational diversity, crystal structure, solvent inclusion complexes, anion recognition, H NMR titration
Abstract
Sterically hindered meso -tetramethyl- meso -tetraarylcalix[4]pyrroles 1-4 where aryl is p -fluorophenyl 1, p- chlorophenyl 2, and p -methylphenyl 3, 4 (configurational isomers) are synthesized and purified by the recrystallization technique. They are characterized by IR, 1H and 13C NMR, and mass spectroscopy. Configurational isomers aabb (3) and aaaa (4) of meso -tetramethyl- meso -tetramethylphenylcalix[4]pyrroles are assigned by the 1H NMR studies and confirmed by the X-ray diffraction analysis. The single crystal X-ray diffraction analysis reveals that the ethanol adduct of 1, the acetone adduct of 2 and 3 adopt the 1,2-conformation while the acetone-water adduct of 1 and the acetone adduct of 4 adopt partial cone and cone conformations respectively. The conformational diversity is due to non-covalent interactions among the encapsulated guest, pyrrolic NH protons, and meso- substituents. Anion binding studies (F-, Cl-, CH3COO-, ) are carried out through 1H NMR titrations; the binding constants are evaluated using the EQNMR program, displaying that they are more selective towards fluoride rather than other anions with the 1:1 stoichiometry. The configuration of compounds drastically influences the ion-recognition processes.
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