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Cocrystals of N-bromosuccinimide with 2- and 3-methylpyridine: interplay between halogen and hydrogen bonds

N-halosuccinimides represent a new group of potent halogen bond (XB) donors that form very strong and close-to-linear halogen bonds with N- and O-containing acceptors via the robust (CO)2N–Br∙∙∙N halogen bond synthon (X = Br, I) (Raatikainen and Rissanen, 2011 ; Mavračić et al, 2016). Herein we report two halogen bonded cocrystals of N-bromosuccinimide (nbs) with the following XB acceptors: 2-methylpyridine (2Mepy) and 3-methylpyridine (3Mepy). In the crystal structures of both cocrystals molecules are connected via Br∙∙∙N XBs between nbs bromine and pyridine nitrogen atoms. The Br∙∙∙N distance of 2.448 Å in (nbs)(2Mepy) is 28.0 % less than the sum of the van der Waals (VDW) radii of nitrogen (1.55 Å) and bromine (1.85 Å). Furthermore, halogen bonding in the molecular complex is assisted by a C–H∙∙∙Br hydrogen bond between the pyridine methyl group and Br atom, with a C∙∙∙Br distance of 3.527 Å. Crystal structure determination of (nbs)2(3Mepy) reveals two types of XB: the XB Br∙∙∙N between nbs and pyrdine molecule, and the Br∙∙∙O interaction between neighbouring nbs molecules, with contact distances of 2.415 and 2.685 Å which are 28.9 and 20.3 % less than the sum of the VDW radii, respectively. Both nbs-pyridine cocrystals show interesting packing motifs in the solid state. The crystal structure of (nbs)(2Mepy) can be described by the association of 1:1 halogen bonded complexes into a hydrogen bonded 3D network via C–H∙∙∙O and C–H∙∙∙C hydrogen bonds. In the crystal structure of (nbs)2(3Mepy) the molecules are connected into a 2D network via halogen bonds and C–H∙∙∙O hydrogen bonds. The overall structure results from the stacking of formed networks and it is additionally stabilized by C∙∙∙Br contacts between nbs molecules in adjacent planes.

N-bromosuccinimide ; cocrystals ; halogen bond ; hydrogen bond ; pyridine derivatives

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