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 C fullerene cage, transition metal-nitrogen and lanthanide-nitrogen double bonds are costabilized simultaneously within the as-formed clusterfullerene TiCeN@C(12)-C, which is a representative heteronuclear dimetallic nitride clusterfullerene. Its molecular structure was unambiguously determined by single-crystal X-ray diffraction, revealing a slightly bent μ-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@C(12)-C. Density functional theory (DFT) calculations unveil three-center two-electron (3-2) bonds delocalized over the entire TiCeN cluster, which are responsible for costabilization of Ti=N and Ce=N double bonds. An electronic configuration of TiCeN@C is proposed featuring an intramolecular four-electron transfer, drastically different from the analogous actinide dimetallic nitride clusterfullerene (U)N@C and trimetallic nitride clusterfullerene (Sc)TiN@C , indicating the peculiarity of 4-fold negatively charged fullerene cage in stabilizing the heteronuclear dimetallic nitride cluster.