Face-Sharing Homo- and Hetero-Bitetrahexahedral Superatomic Molecules M₁M₂@Li₂₀ (M₁/M₂ = Ti and W)

Superatoms, being a class of clusters with chemical behavior similar to atoms, can be used as building blocks for constructing novel functional materials. Here, superatomic molecules M₁M₂@Li₂₀ (M₁/M₂ = Ti and W) are built with our recently discovered tetrahexahedral superatoms Ti@Li₁₄ and W@Li₁₄. A low-energy face-sharing bi-tetrahexahedral structure with a high symmetry of D_{6 h} is identified by global minimum structure search and frequency calculations. The number of shared Li atoms amounts to 6, which is rarely seen before. Molecular orbital and chemical bonding analyses reveal that although isolated superatoms Ti@Li₁₄ and W@Li₁₄ are nonmagnetic, Ti₂@Li₂₀ is an open-shell superatomic molecule with a magnetic moment of 2 μ_B, whereas for W₂@Li₂₀, the electronic shell remains closed. In both Ti₂@Li₂₀ and W₂@Li₂₀, a quadruple superbonding between superatoms is found. Interestingly, an assembly of two hetero-tetrahexahedral superatoms Ti@Li₁₄ and W@Li₁₄ also gives a face-sharing bi-tetrahexahedral structure but with a notable dipole moment. This study provides a basic understanding for the superatomic bonding of Ti@Li₁₄ and W@Li₁₄, which may aid their application in developing multi-superatom molecules or even bulk crystals.