Transition Metal/Lanthanide-Nitrogen Double Bonds Co-stabilized in a Carbon Cage

Metal–nitrogen double bonds have been commonly reported for conventional metal complexes, but the coexistence of both transition metal–nitrogen and lanthanide–nitrogen double bonds bridged by nitrogen within one compound has never been reported. Herein, by encapsulating a ternary transition metal-lanthanide heteronuclear dimetallic nitride into a C84 fullerene cage, transition metal–nitrogen and lanthanide-nitrogen double bonds are costabilized simultaneously within the as-formed clusterfullerene TiCeN@C1(12)-C84, which is a representative heteronuclear dimetallic nitride clusterfullerene. Its molecular structure was unambiguously determined by single-crystal X-ray diffraction, revealing a slightly bent μ2-bridged nitride cluster with short Ti–N (1.761 Å) and Ce–N (2.109 Å) bond lengths, which are comparable to the corresponding Ti═N and Ce═N double bonds of reported metal complexes and consistent with the theoretically predicted values, confirming their coexistence within TiCeN@C1(12)-C84. Density functional theory (DFT) calculations unveil three-center two-electron (3c-2e) bonds delocalized over the entire TiCeN cluster, which are responsible for costabilization of Ti═N and Ce═N double bonds. An electronic configuration of Ti4+Ce3+N3–@C844– is proposed featuring an intramolecular four-electron transfer, drastically different from the analogous actinide dimetallic nitride clusterfullerene (U2)9+N3–@C806– and trimetallic nitride clusterfullerene (Sc2)6+Ti3+N3–@C806–, indicating the peculiarity of 4-fold negatively charged fullerene cage in stabilizing the heteronuclear dimetallic nitride cluster.