X-ray studies of three 3,6-bis(pyridin-2-yl)-1,2,4,5-tetrazine cocrystals: an unexpected molecular conformation stabilized by hydrogen bonds.

The results of the X-ray structure analysis of three novel 3,6-bis(pyridin-2-yl)-1,2,4,5-tetrazine cocrystals are presented. These are 3,6-bis(pyridin-2-yl)-1,2,4,5-tetrazine-2,4,6-tribromophenol (1/2), C 12 H 8 N 6 ·2C 6 H 3 Br 3 O, 3,6-bis(pyridin-2-yl)-1,2,4,5-tetrazine-isonicotinic acid N-oxide (1/2), C 12 H 8 N 6 ·2C 6 H 5 NO 3 , and 3,6-bis(pyridin-2-yl)-1,2,4,5-tetrazine-4-nitrobenzenesulfonamide (1/1), C 12 H 8 N 6 ·C 6 H 6 N 2 O 4 S. Special attention is paid to a conformational analysis of the title tetrazine molecule in known crystal structures. Quantum chemistry methods are used to compare the energetic parameters of the investigated conformations. A structural analysis of the hydrogen and halogen bonds with acceptor aromatic tetrazine and pyrazine rings is conducted in order to elucidate factors responsible for conformational stability.