Role of weak hydrogen bonds in the crystal structures of phenazine, 5,10-dihydrophenazine and their 1:1 and 3:1 molecular complexes

Abstract

Phenazine (1) and 5,10-dihydrophenazine (2) form not only a 1:1 complex (3), as expected from N–H···N hydrogen bond requirements, but surprisingly also a 3:1 complex (4). Single crystal X-ray analyses of compound 2 and complexes 3 and 4 have been carried out. While the overall packing in complex 3 is as efficient as in pure 1 and 2, acidic C–H groups, which contribute actively to the structural assembly in pure 2, are not involved in hydrogen bonding in 3. It is shown that the quest for hydrogen bonding by these C–H groups steers the formation of complex 4 with an unprecedented N–H···N and C–H···N hydrogen bond mediated tape structure.