5:1 and 2:1 cocrystals of 2,3,4,5,6-pentafluorophenol with phenazine.

2,3,4,5,6-Pentafluorophenol (pFp), unlike phenol, forms cocrystals with the weak heteroaromatic base phenazine (phz). Two types of cocrystals were prepared, (I) with a high content of pFp, 2,3,4,5,6-pentafluorophenol-phenazine (5/1), 5C(6)HF(5)O·C(12)H(8)N(2), and (II) with a 2:1 pFp-phz molar ratio, 2,3,4,5,6-pentafluorophenol-phenazine (2/1), 2C(6)HF(5)O·C(12)H(8)N(2). In both forms, homostacks are formed by the heterocyclic base and phenol molecules and no aryl-perfluoroaryl stacking interactions occur. The arrangement of the molecules in the crystal of (I) is determined by strong O-H···N and O-H···O hydrogen bonds, weak O-H···F, C-H···F and C-H···O interactions, π-π stacking interactions between the phz molecules and C-F···π(F) interactions within the pFp stacks. Among the specific interactions in (II) are a strong O-H···N hydrogen bond, weak C-H···F interactions and π-π stacking interactions between the phz molecules. In (I) and (II), the heterocyclic molecules are located around inversion centres and one of the symmetry-independent pFp molecules in (I) is disordered about an inversion centre. Remarkably, similar structural fragments consisting of six pFp stacks can be identified in cocrystal (I) and in the known orthorhombic polymorph of pFp with Z' = 3 [Gdaniec (2007). CrystEngComm, 9, 286-288].