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2:2 Complexes from Diphenylpyridiniums and Cucurbit[8]uril: Encapsulation‐Promoted Dimerization of Electrostatically Repulsing Pyridiniums
Author(s) -
Yang Bo,
Yu ShangBo,
Wang Hui,
Zhang DanWei,
Li ZhanTing
Publication year - 2018
Publication title -
chemistry – an asian journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.18
H-Index - 106
eISSN - 1861-471X
pISSN - 1861-4728
DOI - 10.1002/asia.201701816
Subject(s) - stacking , cationic polymerization , crystallography , chemistry , antiparallel (mathematics) , stereochemistry , crystal structure , solid state , titration , inorganic chemistry , polymer chemistry , organic chemistry , physics , quantum mechanics , magnetic field
Rigid linear compounds G1 and G2 , which contained two 4‐phenylpyridinium (PhPy + ) units, have been prepared to investigate their binding with cucurbit[8]uril (CB[8]). X‐ray crystallographic structures revealed that in the solid state both compounds were included by CB[8], through antiparallel stacking, to form 2:2 quaternary complexes ( G1 ) 2 @(CB[8]) 2 and ( G2 ) 2 @(CB[8]) 2 . For the former complex, CB[8] entrapped G1 by holding two heterodimers of its Py + and benzyl units, which were at opposite ends of the backbone. In contrast, for the first time, the second complex disclosed parallel stacking of two cationic Py + units of G2 in the cavity of CB[8] in the solid state, despite the generation of important electrostatic repulsion. Isothermal titrations in water afforded high apparent association constants of 4.36×10 6 and 6.43×10 6 m −1 for 1:1 complexes G1 @CB[8] and G2 @CB[8], respectively, and 1 H NMR spectroscopy experiments in D 2 O confirmed a similar stacking pattern to that observed in the solid state. A previous study and crystal structures of the 2:1 complexes formed between three new controls, G3–5 , and CB[8] did not display such unusual stacking of the cationic Py + unit; this may be attributed to the multivalency of the two CB[8] encapsulation interactions.