Type II Halogen-Halogen Contacts in the Single-Crystal X-ray Diffraction Structure of a 1:1 Halogen-Bonded Cocrystal of 2,3,5,6-Tetramethylpyrazine and 1,3,4,5-Tetrabromo-2,6-difluorobenzene

Abstract

A cocrystal of 2,3,5,6-tetramethylpyrazine and 1,3,4,5-tetrabromo-2,6-difluorobenzene has been prepared and its crystal structure has been determined via single-crystal X-ray diffraction. Infinite chains of roughly coplanar donor and acceptor molecules are held together by two crystallographically distinct and highly linear Br···N halogen bonds. Four further crystallographically distinct Br···Br halogen bonds are also observed. Each of the two Br atoms in the 3 and 5 positions on the benzene ring acts simultaneously as a halogen bond donor and acceptor to two additional bromines on two neighbouring 1,3,4,5-tetrabromo-2,6-difluorobenzene molecules. These halogen bonds are also classified as type II halogen-halogen contacts. As a result of these contacts, a staggered herringbone arrangement of the infinite chains results. These structural features are shown to be consistent with computed molecular electrostatic potential and Hirshfeld surfaces. The insights gained through this analysis imply that additional systematic variations in the substitution motifs of aromatic halogen bond donors may lead to new structures and properties. As part of this work, a single-crystal X-ray structure of 1,3,4,5-tetrabromo-2,6-difluorobenzene of moderate quality is also reported.

Graphical Abstract

The single-crystal X-ray diffraction structure of a 1:1 cocrystal of 2,3,5,6-tetramethylpyrazine and 1,3,4,5-tetrabromo-2,6-difluorobenzene is reported. Bromine-nitrogen halogen bonds link the two types of molecules together, forming infinite chains. Bromine-bromine halogen bonds (type II contacts) between aromatic molecules stabilize a herringbone-like packing arrangement.