Enhanced stability of the Nb3O6− and Nb4O6+ clusters: the nxcπ rule versus superatomic nature†

This study examines the chemical reactivity of niobium clusters with carbon dioxide (CO₂), with an emphasis on the analysis of the ensuing products Nb₄O₆⁺ and Nb₃O₆⁻, which show up in the cationic and anionic mass spectra, respectively. Using density functional theory (DFT) calculations, we demonstrate the reactivity of the Nb_n^± clusters with CO₂ and reveal distinct stabilization mechanisms for the two prominent products. The stability of Nb₃O₆⁻ is determined by the existence of ten π bonds pertaining to π-electron delocalization, which conforms to the nxcπ electron configuration model. Despite having only a one-atom distinction, Nb₄O₆⁺ exhibits superatomic electron shells embodying superatom stability. The divergent stabilizing mechanisms found in Nb₄O₆⁺ and Nb₃O₆⁻ illustrate the intricate nature of cluster chemistry and the significance of electronic structure in governing cluster stability and reactivity.