Observation of Structurally Diverse Complexes OCeNi(CO) ₃ ^– and CeNi(CO) ₃ ^– with the Shortest Ce–Ni Bond and Ce≡O Triple Bond

Gas-phase heteronuclear cerium–nickel carbonyl complexes, OCeNi(CO) 3 – and CeNi(CO) 3 –, were successfully synthesized and characterized via mass-selected infrared photodissociation spectroscopy in combination with global minimum energy searches. The agreement between experimental and theoretical spectra reveals the coexistence of multiple isomers, different from single-structured iron carbonyl analogues. Besides, these complexes possess the shortest Ce–Ni bond and a relatively higher bond order reported to date, along with a previously unobserved Ce≡O triple bond. Detailed chemical bonding analyses unravel the formation of multicenter covalent bonds or dative bonds between Ce-based moieties and the Ni(CO) 3 – fragment, highlighting that the Ni 4p (rather than 3d) orbital plays a key role in bonding with the Ce 6s or 5d orbital. Such diverse bonding modes are found to arise from the singly occupied molecular orbital (SOMO) of the Ni(CO) 3 – fragment, whose amphiphilic nature and multiple active sites facilitate interactions with Ce-based moieties. These findings advance the scope of metal–metal bond between f-block elements and transition metals, paving a way for exploring novel heterobimetallic interactions.