Compounds featuring unsupported metal–metal bonds between actinide elements remain highly sought after yet confined to inert gas matrix studies. Notwithstanding this paucity, actinide–actinide bonding has been the subject of significant computational effort. In this contribution, density functional theory, CASPT2 and CCSD(T) calculations at both the scalar and spin orbit levels are used to survey the Th–Th bonding in a range of systems of general formula LTh–ThL, where L is one of a range of neutral p block donor ligands. Several of these are found to have very short Th–Th bonds arising from a new type of Th–Th quadruple bond with a previously unreported electronic configuration featuring two unpaired electrons in 6d based δ bonding orbitals. H3AsThThAsH3 is found to have the shortest Th–Th bond yet reported (2.590 Å). The Th2 unit is a highly sensitive probe of the L ligand’s electron donor/acceptor ability; we can tune the Th–Th bond from quadruple to triple, double and single by judicious choice of L, up to 2.888 Å for singly bonded ONThThNO.

Shortest Th–Th distance from a new type of quadruple bond

253rd National Meeting (2017)

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