The formation of non-covalent directional interactions, such as hydrogen or halogen bonds, is a central concept of materials design, which hinges on using small compact atoms of the 2nd period, notably nitrogen and oxygen, as acceptors. Heavier atoms are much less prominent in that context, and mostly limited to sulfur. Here, we report the experimental observation and theoretical study of halogen bonds to phosphorus, arsenic and antimony in the solid state. Combining 1,3,5-trifluoro-2,4,6-triiodobenzene with triphenylphosphine, -arsine, and -stibine provides cocrystals based on I···P, I···As and I···Sb halogen bonds. The demonstration that increasingly metallic pnictogens form halogen bonds sufficiently strong to enable cocrystal formation is an advance in supramolecular chemistry which opens up opportunities in materials science, as shown by colossal thermal expansion of the cocrystal involving I···Sb halogen bonds.

Over the past several decades, halogen bonding has become a standard ‘tool’ in supramolecular chemistry and particularly in crystal engineering. Traditionally, the study of halogen bonding has primarily been focused...

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The halogen bonding proclivity of the chlorine atom coordinated to the Co(ii) metal centre has been explored by synthesis and crystal structure analysis of a family of 12 novel metal-based halogen-bonded cocrystals with iodine-based donors.

Trimorphic cocrystals, i.e. multi-component molecular crystals with three polymorphic structures, are exceedingly rare. First example of a trimorphic halogen-bonded cocrystal, reported here, shows a critical role for the interaction orthogonality.