The ubiquitous icosahedral B₁₂ in boron chemistry

Abstract

Though boranes exhibit a wide variety of polyhedral structures, all the three polymorphs of elemental boron essentially contain icosahedral B₁₂ units as the predominant building block in their unit cell. Theoretical and experimental studies on boranes show that the icosahedral arrangement leads to most stable boranes and borane anions. This paper attempts to explain the phenomenal stability associated with the icosahedral B₁₂ structure. Using fragment molecular orbital theory, the remarkable stability of B₁₂H^2-₁₂ amongcloso boranes are explained. The preferential selection icosahedral B₁₂ unit by elemental boron is explained by improvising a contrived B84 sub-unit of the β-rhombohedron, the most stable polymorph. This also leads to a novel covalent way of stuffing fullerenes with icosahedral symmetry.