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 1:1 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 compd. 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.
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