Thorium(IV)-antimony complexes exhibiting one-, two-, and three-fold polar covalent metalmetal bonding interac

There is continued burgeoning interest in metal-metal multiple bonding to further our understanding of chemical bonding across the periodic table. However, whilst polar covalent metal-metal multiple bonding is well known for the d- and p-blocks, for actinides it is relatively underdeveloped. Homometallic examples are found in spectroscopic or fullerene-confined species, and heterometallic variants exhibiting a polar covalent σ-bond supplemented by up to two dative π-bonds are more prevalent. Hence, securing polar covalent actinide double and triple metal-metal bonds under normal experimental conditions has been a significant fundamental target. Here, exploiting the protonolysis and dehydrocoupling chemistry of the parent dihydrogen-antimonide anion, we report one, two, and three-fold thorium-antimony bonds, thus introducing polar covalent actinide-metal multiple bonding under normal experimental conditions between some of the heaviest ions in the periodic table with little or no bulky-substituent protection at the antimony centre. This provides fundamental insights into heavy element multiple bonding, in particular the tension between orbital energy- and overlap-driven covalency for the actinides in a relativistic regime.