CT-adduct vs. pyridinium polyhalide salt formation in the reactions between polypyridyl donors and dihalogens: reactivity of 1,4-di-(3 '-pyridylethynyl) benzene towards Br-2 and I-2

The reactions of 1,4-di-(3'-pyridylethynyl) benzene (L) with I-2 and Br-2 in CH2Cl2 afforded 1 and 2, respectively: the former compound features CT-adduct units L center dot 2I(2) connected by a third diiodine molecule to give (L center dot I-6)infinity chains, while the latter is a salt where the monocation HL'+, derived from the N-protonation of a pyridine unit and dibromination of the triple C-C bonds of L, is counterbalanced by an asymmetric tribromide. The isolation of 1 and 2 provides a striking example of how the competition between the Lewis and Bronsted-Lowry basicity of polypyridyl donors can be exploited for the rational design of either neutral or charged building blocks of supramolecular architectures.