The geometries, electronic structures, and bonding properties of the title endohedral Zintl clusters have been studied by using ab initio calculations. [Fe@Ge10 ]4- and [Co@Ge10 ]3- have D5h -symmetric pentagonal prismatic structure and [Fe@Sn10 ]4- adopts the C2v -symmetric structure as their ground-state structures, whereas all the other clusters possess D4d bicapped square antiprismatic structures, in consistent with the experimental values when available. Natural bonding orbital and electron localization function disclosed that the negative charges are localized on the central atoms rather than the cages while the TME ionic bonding interactions increase in the order of Ge < Sn < Pb. The energy decomposition analysis revealed that the total bonding energy ∆Eint between central TM and E10 cage is above 150 kcal/mol. The ionic bonding interaction termed as electrostatic interaction ∆Eelstat increases in the order of Ge < Sn < Pb and becomes higher than the covalent bonding interactions termed as total orbital interactions ∆Eorb . Among the total orbital interactions, the π back donations from the TM-d orbitals to the empty cage orbitals consisting of E-p orbitals, the magnitude of which is importantly affected by the cage symmetry, are dominant contributions.
Keywords: Group-14 elements; Zintl Cluster; chemical bonding; density functional theory calculations; electronic structures.
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