The pattern of bifurcated hydrogen bonds in thiourea cocrystals with diazine derivatives: experimental and quantum theoretical studies

Cocrystals of thiourea with pyrazine N -oxide as thiourea–pyrazine N -oxide (2/1), C 4 H 4 N 2 O·2CH 4 N 2 S, ( I ), and with phenazine as thiourea–phenazine (6/7), 7C 12 H 8 N 2 ·6CH 4 N 2 S, ( II ), both crystallize in the monoclinic space group P 2 1 / c . In the crystalline state, molecules of both components are linked by N—H...N hydrogen bonds. In addition, there are R 2 2 (8) hydrogen-bond synthons between thiourea molecules in both crystal structures. Furthermore, bifurcated hydrogen bonds between the –NH groups in the thiourea molecule and the N and O atoms in the N -oxide ring [in ( I )], as well as the N atom in the central phenazine ring [in ( II )], play a significant role in both structures. This emerging motif was thoroughly examined using quantum chemistry methods.