ThC2@C82 versus Th@C84: unexpected formation of triangular thorium carbide cluster inside fullerenes.

Abstract

Synthesis of the first thorium-containing clusterfullerenes, ThC2@C s (6)-C82 and ThC2@C2(5)-C82, is reported. These two novel actinide fullerene compounds were characterized by mass spectrometry, single-crystal X-ray diffraction crystallography, UV-vis-NIR spectroscopy, and theoretical calculations. Crystallographic studies reveal that the encapsulated ThC2 clusters in both C s (6)-C82 and C2(5)-C82 feature a novel bonding structure with one thorium metal center connected by a C[triple bond, length as m-dash]C unit, forming an isosceles triangular configuration, which has not been hitherto observed for endohedral fullerenes or for solid phase thorium carbides. Electronic structure calculations assign a formal electronic structure of [Th4+(C2)2-]2+@[C82]2-, with pronounced donation bonding from (C2)2- to Th4+, secondary backbonding from the fullerene to thorium and Th-C double bond character in both compounds. This work presents a new family of endohedral fullerenes, MC2@C2n-2, being unexpected isomers of MC2n , and provides broader understanding of thorium bonding.