Photoinduced and dark complexation of unsaturated viologen analogues containing two ammonium tails with cucurbit[8] urilстатья

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Дата последнего поиска статьи во внешних источниках: 18 июля 2013 г.

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[1] Photoinduced and dark complexation of unsaturated viologen analogues containing two ammonium tails with cucurbit[8] uril / L. G. Kuz'mina, A. I. Vedernikov, N. A. Lobova et al. // New Journal of Chemistry. — 2006. — Vol. 30, no. 3. — P. 458–466. Complex formation between cucurbit[8] uril (CB[ 8]) and unsaturated viologen analogues 1a,b bearing two ammoniopropyl substituents was studied using H-1 NMR spectroscopy and X-ray diffraction. The complex stability constants were measured by 1 H NMR titration. CB[ 8] was found to encapsulate 1,2-di(4-pyridyl) ethylene derivative (E)- 1a in water/acetonitrile solution to form only inclusion complex of 1 : 1 composition. The high stability of CB[8] . 1a (lg K-1: 1 >= 5) is apparently due to the possibility of hydrogen bond formation between two NH3+ groups of 1a and the O=C fragments of both portals of CB[ 8]. Contrarily, the derivative of 1,2-di(4-quinolyl) ethylene (E)-1b gave three types of inclusion complexes upon mixing with CB[8]. The stability of the 1 : 1 complex ( lg K-1: 1 = 4.6) is decreased compared to ( E)-1a, suggesting a poorer fit with respect to the bulky ( E)-1b in the cavity of CB[ 8] for the simultaneous hydrogen bonding of the both ammonium groups. This is the driving force for the formation of an unusual 2 : 1 complex, {CB[ 8]}(2) . (E)-1b. The expanded pi-system of (E)-1b allows also two tetracationic molecules of the acceptor to form a 1 : 2 complex owing to stacking interactions. Crystallization of a 1b/CB[8] mixture under irradiation resulted in an inclusion complex of the Z-isomer of 1b. The supramolecular complex is formed because the shape of (Z)-1b fits well to the host cavity and the ammonium groups form a system of hydrogen bonds with oxygen atoms of both portals of CB[ 8]. The features of crystalline complexes CB[8] . (Z)-1b and CB[8] center dot HClO4 are discussed. [ DOI ]

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