Structure and bonding analysis of the polar intermetallic compounds ScZn12 and YZn12

ScZn 12 and YZn 12 were synthesized by solution growth from Zn-rich melts and their body-centered tetragonal ThMn 12 structure ( I 4/ mmm ) characterized from single crystal X-ray diffraction. Both compounds can be classified as polar intermetallics featuring a framework of slightly reduced Zn atoms as a consequence of partial charge transfer from Sc (Y). A structural analysis of this framework highlights a biface-capped tetrahedron Zn 6 moiety as fundamental building unit. The connectivity of these units generates a rigid and regular 20-atom Zn cage that accommodates the rare-earth (RE) atoms. Electronic structure calculations based on density functional theory (DFT) revealed pronounced hybridization between Zn sp bands and high-lying, formally unoccupied RE d states. This interaction enhances a pseudogap at the Fermi level in the electronic density of states. Consequently, ScZn 12 and YZn 12 , along with isostructural lanthanoid zincides, can be regarded as electron compounds with an optimal electron-per-atom (e/a) ratio of 2.08 (or 2.25 when expressed as electrons per Zinc atom). The rigidity of the Zn framework suggests that the size of the 20-atom Zn polyhedron is ideally matched by formally trivalent middle-to-late lanthanides as well as for Y, whose size is comparable to that of Dy, whereas Sc is comparatively undersized. Despite the seemingly loose coordination environment of Sc, phonon calculations confirm the dynamic stability of ScZn 12 . The calculated formation energies for REZn 12 (RE = Sc, Y, Sm) are −13.1, −18.0, and −18.9 kJ/mol-atom, respectively, consistent with a lower thermodynamic stability of ScZn 12 .