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The title three-component cocrystal, C6F3I3·2C5H5NO·H2O, has been prepared as a strong candidate for multiple I...O interactions. Its crystal structure is compared with its 1:1 close relative, C6F3I3·C5H5NO [Aakeröy et al. (2014a). CrystEngComm, 16, 28-31]. The 1,3,5-trifluoro-2,4,6-triiodobenzene and water species both have crystallographic twofold axial symmetry. The main synthon in both structures is the π-π stacking of benzene rings, complemented by a number of O-H...O, C-F...π and, fundamentally, C-I...O interactions. As expected, the latter are among the strongest and more directional interactions of the sort reported in the literature, confirming that pyridine N-oxide is an eager acceptor. On the other hand, the structure presents only two of these contacts per 1,3,5-trifluoro-2,4,6-triiodobenzene molecule instead of the expected three. Possible reasons for this limitation are analyzed.

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After reporting the structure of a new polymorph of 1,3,5-trifluoro-2,4,6-triiodobenzene (denoted BzF3I3), CFI, (I), which crystallized in the space group P2/c, we perform a comparative analysis with the already reported P2/n polymorph, (II) [Reddy et al. (2006). Chem. Eur. J. 12, 2222-2234]. In polymorph (II), type-II I...I halogen bonds and I...π interactions connect molecules in such a way that a three-dimensional structure is formed; however, the way in which molecules are connected in polymorph (I), through type-II I...I halogen bonds and π-π interactions, gives rise to an exfoldable lamellar structure, which looks less tightly bound than that of (II). In agreement with this structural observation, both the melting point and the melting enthalpy of (I) are lower than those of (II).

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