Are Ba11Cd6Sb12 and Sr11Cd6Sb12 Zintl phases or not? A density-functional theory study.

The chemical bonding and the electronic band structures of two isoelectronic and isostructural Zintl compounds, Sr(11)Cd(6)Sb(12) and Ba(11)Cd(6)Sb(12), have been studied on the basis of the density-functional theory (DFT) using the tight-binding linear-muffin-tin-orbital (TB-LMTO-ASA) approach and the local-density approximation (LDA). These results reveal that the classic Zintl reasoning and the concept of two-center two-electron bonds cannot explain the subtleties of this complex structure type. The computations also suggest that the antimony dimers present in these structures play an important role and allow for a greater flexibility in optimization of the bonding with the surrounding d-metal atoms.