Reaction of 1,1,3,3-Tetraoxa-2,2-dibromo- 4,4,5,5,6,6-hexafluoro-1,3-dithiacyclohexane with Pyrazine and Hexamethylphosphoramide:  Unexpected Cocrystals through Halogen Bonding

At room temperature, a mixture of 1,1,3,3-tetraoxa-2,2-dibromo-4,4,5,5,6,6-hexafluoro-1,3-dithiacyclohexane 2) and excess pyrazine and hexamethylphosphoramide (HMPA) in dichloromethane gave two unexpected products. The first product was the cocrystal (6), in which two bromide ions bridged two molecules of 2 via four C−Br···Br halogen bonds. The second product was the zwitterion which formed a 1:1 cocrystal with HMPA, (5), via a strong N−H···O hydrogen bond. Both products have been fully characterized by spectroscopic methods and single-crystal X-ray diffraction analysis. The reaction mechanism is discussed.