Ag₁₃-Centered Cuboctahedral Architecture in Inorganic Cluster Chemistry: A DFT Investigation

The bonding in the [Ag₁₃{μ₃-Fe(CO)₄}₈]^3-/5- clusters, which exhibit an Ag₁₃-centered cuboctahedral core, has been analyzed and rationalized by DFT calculations. Not considering the interaction with its encapsulated atom, the empty [Ag₁₂{μ₃-Fe(CO)₄}₈]^4- cage can be considered as the assembly of 12 linearly coordinated 14-electron Ag^I metal centers. Adding a supplementary Ag⁺ at the center allows some covalent delocalized bonding which to some extent tends to reduce the electron deficiency of the 14-electron centers. Adding now two electrons strengthens the delocalized bonding between the encapsulated atom and its host, making [Ag₁₃{μ₃-Fe(CO)₄}₈]^5- a superatom with two jellium (5s-type) electrons. TDDFT calculations predict near-IR absorption for this penta-anion, because of the presence of an a_1g HOMO in the middle of an energy gap. Luminescence in the same optical range is also suggested. Other related cubococtahedral species, such as [Ag₂₃(SH)₁₆]^-, a model for the known 8-electron [Au₂₃(SR)₁₆]^- species which exhibits a bicapped centered dodecahedral kernel structure, have also been investigated.