engleski

Competition of different halogen bond acceptors in oxazole derivatives for halogen bonding with perhalogenated benzenes

In the last three decades the halogen bond has become recognized as a valuable tool in crystal engineering due to its particular directionality and tunability as compared to other noncovalent interactions. In order to study the competition of different heteroatoms as halogen bond acceptors three oxazole derivatives with multiple acceptor sites were prepared in the Van Leusen synthesis. The synthesis allows for the preparation of oxazoles from different aldehydes by a reaction with tosylmethyl isocyanide in the presence of an equimolar amount of potassium carbonate in refluxing methanol. [3] The obtained derivates were 5-(4-pyridyl)-1, 3-oxazole, 5-(2- thienyl)-1, 3-oxazole and 5-(2-furyl)-1, 3-oxazole. Cocrystals were obtained by dissolving the corresponding oxazole derivative and one from a selection of halogen bond donors, 1, 4- diiodotetrafluorobenzene, 1, 3- diiodotetrafluorobenzene, 1, 3, 5- triiodotrifluorobenzene or 1, 2- diiodotetrafluorobenzene, in an appropriate solvent. The crystallization experiments yielded eight cocrystals and were characterized by single crystal X-ray diffraction. Structural analysis revealed that the nitrogen atom in oxazole is the dominant halogen bond acceptor in eight cocrystals, featuring I···N halogen bonds with the most prominent relative shortening values that are comparable to ones between iodine atoms and pyridine nitrogen. As expected, cocrystallization with 5-(4-pyridyl)-1, 3-oxazole resulted in a larger amount of cocrystals featuring diverse supramolecular motifs with the pyridine nitrogen atom participating in halogen bonding in three of four obtained cocrystals. On the other hand, the sulfur and oxazole oxygen atoms did not participate in any halogen bonds

halogen bonding ; oxazole derivatives ; cocrystals ; heterocycles

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