Isocyanide and Cyanide Entities Form Isostructural Halogen Bond- Based Supramolecular Networks Featuring Five-Center Tetrafurcated Halogen...C/N Bonding

A typical halogen bond (HaB) donor, 1,4-dibromo-2,3,5,6-tetrafluorobenzene (FBB), was cocrystallized with the isocyanide CNMes and the cyanide NCMes to give two isostructural cocrystals, (CNMes)& BULL;FBB and (NCMes)& BULL;FBB. Their solid-state architecture exhibits a close similarity between the isocyanide and cyanide groups in their HaB-accepting role. This similarity and particular bonding features of the HaBs were additionally verified by theoretical calculations (molecular electrostatic potential analysis, electron density/ electrostatic potential profiles, atoms-in-molecules charge analysis, and calculations of pKa values and binding energies). Remarkably, both cocrystals form unusual heterohexamers where one Br atom of FBB simultaneously forms four contacts with two C (or N) and two Br atoms of neighboring molecules. On the basis of the geometric parameters and the theoretical data, these contacts can be defined as five-center tetrafurcated mu 4-Br & BULL;& BULL;& BULL;(C, Br, C, Br) and mu 4-Br & BULL;& BULL;& BULL;(N, Br, N, Br) HaBs; this is the first observation of the tetrafurcated HaB involving four disunited HaB acceptors.

Automated summary

In this study, two isostructural cocrystals were synthesized, revealing the similarity of halogen bond donors in their accepting role. The similarity and unique bonding features of the halogen bonds were further verified by theoretical calculations. Additionally, the study observed for the first time a tetrafurcated halogen bond involving four disunited acceptors.