Synthesis, Crystallographic Characterization and Computational Study of Two Polymorphs of 5,6-Dimethyl-2-(pyridin-2-yl)-1-[(pyridin-2-yl)methyl]-1Hbenzimidazole
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Issue Date
2015-04-10
Authors
DeStefano, Matthew
Publisher
Keywords
Benzimidazole , Pharmaceutical Compound , Crystal Structure , Polymorphs , Density Functional Theory , DFT , Computational Chemistry
Abstract
The title compound was prepared by the condensation of 1,2-diamino-4,5-dimethylbenzene and 2-pyridinecarbaldehyde in 40% yield. Single crystals of polymorph I were obtained by vapor diffusion of hexane into an ethanolic solution of the benzimidazole, whereas single crystals of polymorph II were obtained by vapor diffusion of diethyl ether into a DMF solution of the benzimidazole. I crystallizes in the monoclinic space group C2/c and II crystallizes in the orthorhombic space group Pbca, each with one molecule in the asymmetric unit. Although the bond distances and angles displayed by the two molecules are virtually identical, the stereochemistry differs. In I, the 2-(pyridine-2-yl) substituent is canted by only 2.75 (11)o; however, in II, the angle is 30.68 (4)o. Both I and II are stabilized by an intramolecular C-H…N hydrogen-bonding interaction between the 1-[(pyridine-2-yl)methyl] and 2-(pyridine-2-yl) substituents. Conformational analyses employing DFT calculations for the 1-[(pyridine-2-yl)methyl] and 2-(pyridine-2-yl) substituents were performed for I and II. In addition, DFT calculations were employed to determine the basis set superposition-corrected interaction energies for pairs of molecules found in the extended structure of each polymorph. The results of the crystallographic and computation studies will be presented.