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Structural Examination of Halogen-Bonded Co-Crystals of Tritopic Acceptors.

ABSTRACT: A series of tritopic N-heterocyclic compounds containing electrostatically and geometrically equivalent binding sites were synthesized and subjected to systematic co-crystallizations with selected perfluoroiodoarenes in order to map out their structural landscapes. More than 70% of the attempted reactions produced a co-crystal as indicated by IR spectroscopy. Four new crystal structures are reported and in all of them, at least one potential binding site on the acceptor is left vacant. The absence of halogen bonds to all sites can be ascribed primarily due to deactivation of the ?-hole on the iodo-arene donors and partially due to steric hindrance. The tritopic acceptors containing 5,6-dimethylbenzimidazole derivatives yield discrete tetrameric aggregates in the solid state, whereas the pyrazole and imidazole analogues assemble into halogen-bonded 1-D chains.

SUBMITTER: Andree SNL

PROVIDER: S-EPMC6017714 | biostudies-literature | 2018 Jan

REPOSITORIES: biostudies-literature

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Structural Examination of Halogen-Bonded Co-Crystals of Tritopic Acceptors.

Andree Stefan N L SNL Sinha Abhijeet S AS Aakeröy Christer B CB

Molecules (Basel, Switzerland) 20180113 1

A series of tritopic <i>N</i>-heterocyclic compounds containing electrostatically and geometrically equivalent binding sites were synthesized and subjected to systematic co-crystallizations with selected perfluoroiodoarenes in order to map out their structural landscapes. More than 70% of the attempted reactions produced a co-crystal as indicated by IR spectroscopy. Four new crystal structures are reported and in all of them, at least one potential binding site on the acceptor is left vacant. Th ...[more]

PMID: 29342853

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Project description:Strategies for co-crystal synthesis tend to employ either hydrogen- or halogen-bonds between different molecules. However, when both interactions are present, the structural influence that they may exert on the resulting assembly is difficult to predict a priori. To shed some light on this supramolecular challenge, we attempted to co-crystallize ten aliphatic dicarboxylic acids (co-formers) with three groups of target molecules; N-(pyridin-2-yl)picolinamides (2Pyr-X), N-(pyridin-2-yl)nicotinamides (3Pyr-X), N-(pyridin-2-yl)isonicotinamides (4Pyr-X); X=Cl/ Br/ I. The structural outcomes were compared with co-crystals prepared from the non-halogenated targets. As expected, none of the reactions with 2Pyr-X produced co-crystals due to the presence of a very stable intramolecular N-H···N hydrogen bond. In the 3Pyr series, all six structures obtained showed the same synthons, -COOH···N(py) and -COOH···N(py)-NH, that were found in the non-halogenated parent 3Pyr and were additionally accompanied by structure directing X···O(OH) interactions (X=Br/I). The co-crystals of the unhalogenated parent 4Pyr co-crystals assembled via intermolecular -COOH···N(py) and -COOH···N(py)-NH synthons. Three of the analogues 4Pyr-X co-crystals displayed only COOH···N(py) and -COOH···N(py)-NH interactions. The three co-crystals of 4Pyr-X with fumaric acid (for which no analogues structures with 4Pyr are known) formed -COOH···N(py)-NH and -NH···O=C hydrogen bonds and showed no structure-directing halogen bonds. In three co-crystals of 4Pyr-I in which -COOH···N(py)-NH hydrogen bond was present, a halogen-bond based -I···N(py) synthon replaced the -COOH···N(py) motif observed in the parent structures. The structural influence of the halogen atoms increased in the order of Cl < Br < I, as the size of ?-holes increased. Finally, it is noteworthy that isostructurality among structures of the homomeric targets was not translated to structural similarities between their respective co-crystals.

Dataset Information

Structural Examination of Halogen-Bonded Co-Crystals of Tritopic Acceptors.

Publications

Structural Examination of Halogen-Bonded Co-Crystals of Tritopic Acceptors.

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