New Form Of Boron

High-pressure tactics have uncovered a never-before-seen form of the element boron. The new entity has significant ionic character, a first for a material made from a single element.

"Boron seems to break all the rules and stereotypes of chemical bonding," says Artem R. Oganov, a theoretical crystallographer at the State University of New York, Stony Brook. Wedged between metals and nonmetals on the periodic table, boron adopts a range of structures, all of which are sensitive to impurities. As a result, researchers don't have a complete picture of boron's elemental forms.

Oganov led a multi-institution team that synthesized the new entity (Nature, DOI: 10.1038/nature07736). Although it takes shape only at elevated pressure, this new form remains stable under a wide range of temperatures and pressures.

The structure of the all-boron lattice is shown to the left. The team determined through computer simulations that it comprises clusters of 12 boron atoms interspersed with pairs of boron atoms. Each piece of the lattice transfers charges to the other, with the B₁₂ units (purple) carrying a partial negative charge and the B₂ (orange) units a partial positive charge.

"The work not only enriches our understanding of boron chemistry, it also strengthens parallels with gallium chemistry—the new structure's B₂ units are reminiscent of Ga₂ units found in gallium," comments François P. Gabbaï, a boron chemistry expert at Texas A&M University.