Interplay of Atomic Interactions in the Intermetallic Semiconductor Be₅ Pt

Semiconducting substances form one of the most important families of functional materials. However, semiconductors containing only metals are very rare. The chemical mechanisms behind their ground-state properties are only partially understood. Our investigations have rather unexpectedly revealed the semiconducting behaviour (band gap of 190 meV) for the intermetallic compound Be₅ Pt formed at a very low valence-electron count. Quantum-chemical analysis shows strong charge transfer from Be to Pt and reveals a three-dimensional entity of vertex-condensed empty Be₄ tetrahedrons with multi-atomic cluster bonds interpenetrated by the framework of Pt-filled vertex-condensed Be₄ tetrahedrons with two-atomic polar Be-Pt bonds. The combination of strong Coulomb interactions with relativistic effects results in a band gap.