Influence of substituents in aromatic ring on the strength of halogen bonding in iodobenzene derivatives

Halogen bonding properties of 3,4,5-triiodobenzoic acid (1, 2), 1,2,3-triiodobenzene (3), pentaiodobenzoic acid ethanol solvate (4), hexaiodobenzene (5a, 5b, 5c), 2,4-diiodoaniline (6), 4-iodoaniline (7), 2-iodoaniline (8), 2-iodophenol (9), 4-iodophenol (10), 3-iodophenol (11) and 2,4,6-triiodophenol (12) has been studied. The results suggested that substituents other than halogen in aromatic ring affect XB properties of iodine substituents in ortho-, meta- and para-positions. The effect depends on the electron-withdrawing/electron-donating properties of the substituent. Thus, electron-withdrawing substituents with negative mesomeric effect favor m-iodines to act as XB donors and o- and p-iodines to act as XB acceptors. By contrast, electron substituents with positive mesomeric effect favor o- and p-iodines to act as XB donors and m-iodines to act as XB acceptors.