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Abstract
Design, synthesis and complexation with inorganic anions of first (1L) and second (2L) generation tripodal polyamine receptors are reported here. The C3v symmetric second-generation tripodal receptor (2L) possesses large enough cavity to encapsulate larger hydrogen sulfate dimer in a unimolecular capsular fashion [(HSO4)2⊂2]. The dimer is stabilised by (NH)+⋯O type H-bonding and electrostatic interactions between and ammonium group. Water of crystallisation form hybrid anion–water cluster [(HSO4)–(H2O)
with
ions located outside the cavity. The [(HSO4)–(H2O)
cluster and Cl⋯Cl halogen bond play templating role in the supramolecular aggregation of unimolecular capsule [(HSO4)2⊂2]. On the other hand, first-generation receptor (1L) encapsulates only fluoride ion due to its smaller cavity size and thus form unimolecular fluoride complex [F⊂1]. Overall study shows cavity size-induced anion encapsulation. All complexes are well characterised by FT-IR, NMR, TGA, DSC and XRD experiments.
Two polyammonium based tripodal receptors (1L and 2L) with varied size and length shows significant anion inclusion (of particular size and shape) through unimolecular capsular complex formation. We also recognized [(HSO4)-(H2O)]44‾ cluster which plays a crucial role in supramolecular aggregation of the unimolecular capsule of 2L.
Acknowledgements
CIF, IITG and DST-FIST have been acknowledged for providing instrument facilities. N.H. thanks IITG for fellowship.
Funding
This work was supported by Council for Scientific and Industrial Research (CSIR) [grant number 01-2235/08/EMR-II]; Science and Engineering Research Board (SERB) [grant number SR/S1/OC-62/2011], New Delhi, India.
Disclosure statement
The authors declare no competing financial interests.
