Halogen Bonds in 2,5-Diiodo-1,4-dimethylbenezene Derivatives

1,4-Di(bromomethyl)-2,5-diiodobenzene (1), 2,5-diiodo-1,4-di(hydroxymethyl)benzene diacetate (2), and 1,1'-[(2,5-diiodo-1,4-phenylene)bis(methylene)]dipyridinium diiodide (3) were synthesized, and their crystallographic data are reported. All three crystal structures are characterized by the stacked packing of the planar molecules and the presence of halogen bonds I⋅⋅⋅Br, I⋅⋅⋅O, and I⋅⋅⋅I, respectively. The largest number of halogen bonds was found in compound 1, in which there are two I⋅⋅⋅Br bonds per halogen atom. Compounds 2 and 3 contain one halogen bond per halogen atom; however, these bonds are significantly shorter than those in compound 1. All crystals were studied by IR spectroscopy and simultaneous thermal analysis. Compound 1, which has no ionic or hydrogen bonds, melts at a higher temperature compared to ionic compound 3 (218 and 200°С, respectively) due to the presence of a larger number of intermolecular halogen bonds. Compound 2 melts at a lower temperature (151°С), which is characteristic of esters.