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

Phenazine (1) and 5,10-dihydrophenazine (2) form not only a 1 : I 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.