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

Abstract

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 metallanthanide heteronuclear dimetallic nitride into a C 84 fullerene cage, transition metal−nitrogen and lanthanide-nitrogen double bonds are costabilized simultaneously within the as-formed clusterfullerene TiCeN@C 1 (12)-C 84 , 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 2 -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 1 (12)-C 84 . 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 Ti 4+ Ce 3+ N 3− @C 84 4− is proposed featuring an intramolecular four-electron transfer, drastically different from the analogous actinide dimetallic nitride clusterfullerene (U 2 ) 9+ N 3− @C 80 6− and trimetallic nitride clusterfullerene (Sc 2 ) 6+ Ti 3+ N 3− @C 80 6−, indicating the peculiarity of 4-fold negatively charged fullerene cage in stabilizing the heteronuclear dimetallic nitride cluster.