Structure and bonding of γ-B(28): is the high pressure form of elemental boron ionic?

The recently characterized crystal structure of metastable γ-B(28) is analyzed from a crystal chemical point of view, and the electron requirement of its building units and that of their linkage is determined. The structure consists of unique B(2) dumbbells and B(12) icosahedra, which are connected through two-center and three-center, two-electron bonds. The different bonding motifs are ascertained by theoretical calculations of difference charge distributions. Chemical bonding in high pressure γ-B(28) bears great resemblance to α-B(12) which is the simplest boron modification. The previously made description of γ-B(28) as ionic in terms of (B(2))(δ+) and (B(12))(δ-) is not supported.