Observation of the Transition from Triple Bonds to Single Bonds between Ru–Ge Bonding in RuGeO(CO)n– (n = 3–5)

This work reports the observation and characterization of heterobinuclear transition-metal main-group metal oxide carbonyl complex anions, RuGeO(CO)n– (n = 3–5), by combining mass-selected photoelectron velocity map imaging spectroscopy and quantum chemistry calculations. The experimentally determined vertical electron detachment energy of RuGeO(CO)3– surpasses those of RuGeO(CO)4– and RuGeO(CO)5–, which is attributed to distinctive bonding features. RuGeO(CO)3– manifests one covalent σ and two Ru-to-Ge dative π bonds, contrasting with the sole covalent σ bond present in RuGeO(CO)4– and RuGeO(CO)5–. Unpaired spin density distribution analysis reveals a 17-electron configuration at the Ru center in RuGeO(CO)3– and an 18-electron configuration in RuGeO(CO)4– and RuGeO(CO)5–. This work closes a gap in the quantitative physicochemical characterization of heteronuclear oxide carbonyl complexes, enhancing our insights into catalytic processes of CO/GeO on the metal surface at the molecular level.