Characterization of a strong covalent Th3+-Th3+ bond inside an Ih(7)-C80 fullerene cage

The nature of the actinide-actinide bonds is of fundamental importance to understand the electronic structure of the 5f elements. It has attracted considerable theoretical attention, but little is known experimentally as the synthesis of these chemical bonds remains extremely challenging. Herein, we report a strong covalent Th-Th bond formed between two rarely accessible Th3+ ions, stabilized inside a fullerene cage nanocontainer as Th-2@I-h(7)-C-80. This compound is synthesized using the arc-discharge method and fully characterized using several techniques. The single-crystal X-Ray diffraction analysis determines that the two Th atoms are separated by 3.816 angstrom. Both experimental and quantum-chemical results show that the two Th atoms have formal charges of +3 and confirm the presence of a strong covalent Th-Th bond inside I-h(7)-C-80. Moreover, density functional theory and ab initio multireference calculations suggest that the overlap between the 7s/6d hybrid thorium orbitals is so large that the bond still exists at Th-Th separations larger than 6 angstrom. This work demonstrates the authenticity of covalent actinide metal-metal bonds in a stable compound and deepens our fundamental understanding of f element metal bonds. Studying the nature of actinide-actinide bonds is important for understanding the electronic structure of the 5f elements, but the synthesis of these chemical bonds remains extremely challenging. Here, the authors report a strong covalent Th-Th bond formed between two rarely accessible Th3+ ions, stabilized inside a fullerene cage.

Automated summary

Studying the nature of actinide-actinide bonds is crucial for understanding the electronic structure of the 5f elements, but the synthesis of these chemical bonds remains highly challenging. In this study, a strong covalent Th-Th bond formed between two rarely accessible Th3+ ions is reported.