Lanthanide-Nitrogen Triple Bonds.

Lanthanide-ligand multiple bonds are difficult to stabilize due to the dominating ionic bonding nature of lanthanide metals, and solid-state synthesis of a lanthanide complex bearing a lanthanide-nitrogen triple bond has long been expected but never been reported. Here, we stabilize the lanthanide-nitrogen triple bond in solid state for the first time, in the form of a diatomic monocation CeN+ captured in a nitrogen-substituted carbon cage C81N-, namely, CeN@C81N with two cage isomers. Single-crystal X-ray diffraction results reveal the existence of Ce≡N triple bonds with bond lengths of 1.76 Å, which is much shorter than the shortest Ce═N double bond ever recorded (2.04 Å). Quantum-chemical studies reveal the formal Ce4+ valence state with enhanced 4f electron contribution to the Ce≡N triple bond, resulting in an electronic structure of [Ce4+≡N3-]+@[C81N]- featuring an unprecedented intramolecular single-electron transfer.