Cluster-Geometry-Associated Metal-Metal Bonding in Trimetallic Carbide Clusterfullerenes.

Geometry configurations of the metallic clusters play a significant role in the involved bonding nature. Herein, we report the crystallographic characterization of unprecedented erbium-based trimetallic clusterfullerenes, namely, Er 3 C 2 @ I h (7)-C 80 , in which the inner Er 3 C 2 cluster presents a lifted bat ray configuration with the C 2 unit elevated by ∼1.62 Å above the Er 3 plane. Within the plane, the Er···Er distances for Er1···Er2, Er1···Er2A, and Er2···Er2A are 3.4051(15), 3.4051(15), and 3.3178(15) Å, respectively, falling into the range of the metal-metal bonding. Density functional theory calculations unveil the three-center-one-electron Er-Er-Er bond in Er 3 C 2 @ I h (7)-C 80 with one electron shared by three metals, and thus, its exceptional electronic structure can be expressed as (Er 3 ) 8+ (C 2 ) 2- @C 80 6- . Interestingly, with the further observation on the geometry configurations of the encapsulated clusters in M 3 C 2 @C 2 n (M = Sc, Y, and Lu) series, we find that the lifted bat ray configuration of the inner cluster is explicitly associated with the formation of the bonding interactions between the inner metals. This finding provides insights into the nature of metal-metal bonding and gives guidelines for the design of the single-molecule magnet.