A crystalline dithorium complex with a Th–Th bond

Theoretical studies predict that homoatomic metal–metal bonds of f-block actinide elements should be ubiquitous. Surprisingly, however, the isolation and characterization of compounds featuring an actinide–actinide bond has proven challenging and the field remains undeveloped. Here we report a well-defined thorium dimer featuring a Th–Th two-centre one-electron (2c-1e) σ bond and a 2c-1e π bond. This thorium dimer was synthesized by reducing a Th(IV) chloride complex with potassium metal in tetrahydrofuran. Magnetic measurements indicate that this thorium dimer features exceedingly strong antiferromagnetic coupling between the two formal Th(III) centres with a coupling constant J ≤ −1,200 cm−1 such that the Th–Th interaction has covalent bond character. Detailed computational investigations further support the existence of the Th–Th bond in this molecule. These results demonstrate that diactinide complexes with actinide–actinide bonds are accessible but require an appropriate ligand framework to stabilize low-valent actinide centres. The isolation of compounds featuring an actinide–actinide bond is challenging. Now a well-defined Th(III) dimer with a Th–Th two-centre one-electron (2c-1e) σ bond and a 2c-1e π bond is synthesized. Theoretical and magnetic studies show that the open-shell singlet ground state and the two formal Th(III) centres exhibit strong antiferromagnetic coupling.