Bisulfate Anion Dimers

Bisulfate Anion Dimers

Author: Angewandte Chemie International Edition

It was over two centuries ago that Coulomb first published his theory that like charges repel each other. However, recently, the concept of anti-electrostatic hydrogen bonding laid the theoretical groundwork for the existence of anion–anion dimers.  Coulomb repulsion is not the only challenge to the formation of these dimers in solution: Solvation can also separate the anions.

Amar H. Flood and colleagues, Indiana University, Bloomington, USA, could show that within a so-called cyanostar macrocycle pair (C5-symmetric macrocycles), two hydrogen-bonding HSO4 ions can form an anion–anion dimer (pictured). The complex persists in solution. 1H NMR spectroscopy results provide evidence for the bisulfate dimer’s OH⋅⋅⋅O hydrogen bonding with a peak at 13.75 ppm. The dimers in this bisulfate homodimer stabilize each other with self-complementary hydrogen bonds by encapsulation inside a pair of cyanostar macrocycles

The results demonstrate the effectiveness of a supramolecular strategy for the stabilization of reactive species in “hostile” environments, and represent the first conclusive observation of a hydrogen-bonded pair of anions.


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