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Hyperhalogens Amp Up Electronegativity

A step up in complexity from “superhalogens,” gold-boron clusters now have the highest electron affinities observed

by Elizabeth K. Wilson
October 18, 2010 | A version of this story appeared in Volume 88, Issue 42

Credit: Angew. Chem. Int. Ed.
Neutral (left) and anionic structural models of the hyperhalogen AuO(BO2).
Credit: Angew. Chem. Int. Ed.
Neutral (left) and anionic structural models of the hyperhalogen AuO(BO2).

Chemists have synthesized a class of gold-and-boron-based molecules that have ultrahigh electronegativities. If the molecules can be tamed, they could possibly be used as superoxidizing agents (Angew. Chem. Int. Ed., DOI: 10.1002/anie.201002212). Using both theoretical methods and gas-phase photoelectron spectroscopy experiments, Puru Jena of Virginia Commonwealth University and colleagues studied the properties of Aun (BO2) clusters, which they call hyperhalogens. These molecules are a step up in complexity from superhalogens, which are highly electronegative molecules with electron affinities even greater than those of elements like fluorine. Superhalogens are typically made from a central metal atom surrounded by halogen or oxygen atoms; they include MnO4 and PtF6 , but also species such as ClO4 and BO2 . Jena and coworkers found that surrounding a gold atom with two BO2 super­halogen groups produced a species that has an electron affinity of 5.7 eV—almost 2.5 eV larger than that of AuF2. The researchers hypothesize that even more powerful hyperhalogens could be created by tailoring the central metal atom and surrounding superhalogen building blocks. They also suggest that if the central atom is a transition-metal atom, hyperhalogen clusters could have magnetic moments, forming a rare ferromagnetic insulator if the moments align in parallel.


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