Copper and Silver Cuboctahedron Cavities in Halide Encapsulation: Evaluation of Interaction Energy and Optical Properties Given by the Inclusion of Halides as Non-Innocent Templates

The formation of anion-templated molecular clusters offers the encapsulation of different anions, enabling further understanding of the interaction between the inner anion and the resulting metal cavity. Here, we evaluated two prototypical isostructural copper and silver clusters with a halide anion embedded into a cuboctahedron cage featured in [M₁₂(μ₁₂-X){S₂P(O<i>ⁿ</i>Pr)₂}₆{C≡CPh}₄]⁺ clusters (M = Cu, Ag; X═Cl^-, Br^-, I^-), elucidating the structural, electronic, and optical properties variation owing to the favorable cluster-halide interaction. Our results show that Ag₁₂ clusters exhibit larger, more adaptable cavities and diminished steric repulsion compared to Cu₁₂, facilitating enhanced halide accommodation. Energy decomposition analysis reveals that electrostatic forces (∼75.6%) predominantly stabilize halide inclusion, complemented by orbital (∼20.2%) and dispersion (∼4.2%) interactions, with an ionic character diminishing from Cl^- to I^- in accordance with HSAB theory. Charge-transfer pathways identified via EDA-NOCV underscore the donor-acceptor orbital interactions contributing to complex stabilization. The frontier orbital manyfold and optical properties vary upon inclusion of the halide anion, revealing a non-innocent character of the endohedral atom template. These findings advance fundamental understanding of noncovalent interactions and structural flexibility in metal cluster hosts incorporating inner anions, favoring the rational design of a tunable host building up nanoscaled materials for catalysis, sensing, and molecular recognition.