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Co‐Conformational Isomerism in a Neutral Ion‐Paired Supramolecular System
Author(s) -
Cervantes Ruy,
Sánchez Raul I.,
Tiburcio Jorge
Publication year - 2013
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201203483
Subject(s) - viologen , supramolecular chemistry , chemistry , moiety , crystallography , stacking , hydrogen bond , ion , stoichiometry , dilution , stereochemistry , molecule , crystal structure , photochemistry , organic chemistry , physics , thermodynamics
Two different counter‐ion‐free host–guest complexes have been prepared and isolated. These compounds were formed from two equally and opposite doubly‐charged species, the viologen guests 1 a 2+ and 1 b 2+ and the anti ‐disulfodibenzo[24]crown‐8 [ DSDB24C8] 2− host, which gave rise to the 1:1 neutral complexes [ 1 a⋅DSDB24C8 ] and [ 1 b⋅DSDB24C8 ]. These species are held together by hydrogen bonding and π stacking, as well as strong electrostatic interactions. The investigation of these neutral ion‐paired supramolecular systems in solution and in the solid state allowed us to establish their co‐conformational preferences. Compound [ 1 a⋅DSDB24C8 ], with small methyl groups as substituents on the viologen unit, may adopt three different geometries, 1) an exo nonthreaded, 2) a partially threaded, and 3) a threaded arrangement, depending on the relative spatial orientation between the host and guest: The partially‐threaded structure is preferred in solution and in the solid state. The presence of bulky tert ‐butylbenzyl groups in the viologen moiety in compound [ 1 b⋅DSDB24C8 ] restricts the possible geometrical arrangements to one: The exo nonthreaded arrangement. This structure was confirmed in the solid state by X‐ray crystallography. The stability of the neutral complexes in solution was determined by UV/Vis spectrophotometry. The stoichiometry of the complexes was established by continuous variation experiments, and overall equilibrium constants and Δ G ° values were determined on the basis of dilution experiments. The results observed are a consequence of only the intrinsic stability of the complexes as there are no additional contributions from counter ions.