Structural Organization of Dibromodiazadienes in the Crystal and Identification of Br···O Halogen Bonding Involving the Nitro Group

Nitro functionalized dibromodiazadiene dyes were prepared and fully characterized including X-ray single crystal analysis. Electron deficient dibromodiazadienes were found to be able to act as donors of halogen bonding (XB), while the nitro group acted as an acceptor of the XB. Depending on the substituents, the Br···O XB competed with other weak interactions, and for some of the dyes, they even outcompeted the XB involving the nitro group. However, the nitro functionalized dibromoalkenes 6a and 10a, which had only the nitro moiety as the most plausible acceptor of the XB, reliably formed 1D chains via Br⋯O XB. Experimental work was supported by the DFT calculations and topological analysis of the electron density distribution within the framework of Bader’s theory (QTAIM method).