Trithorium superatom confounds with its unexpected and ‘mind-blowing’ diamagnetism

Amazing stuff! The Trithorium was apparently already discovered as early as 2021.

"Superatoms are unusual structures first discovered 40 years ago, where clusters of atoms exhibit the properties of elemental atoms due to quantum confinement effects. This can result in radically different behaviour than would otherwise be expected; for example, a cluster of Al13 acts in a similar manner to elemental chlorine. This unique shifting of how the clusters react has meant superatoms can be used as nanoscale building blocks, with chemists able to fine-tune the properties of structures as required. ...

Actinides are difficult to work with. They are radioactive and compounds are often thermally unstable, with powdered samples decomposing in days and solutions rapidly decomposing at over 35°C.

Previously, the group created a σ-aromatic thorium, the first aromatic ring made solely from actinides and the first time an actinide–actinide bond had been created. This earlier work overturned previous predictions, which suggested that actinide–actinide bonds would be weak, rather than the strong bonds typically seen in delocalised aromatic structures.

This new paper pushes the boundaries of actinide chemistry even further. The superatom structure is based around a trithorium nanocluster – three thorium atoms forming an aromatic ring – supported by a scaffold of chlorine, with each thorium atom also supporting a wing-like aromatic ring. ...

molecule also comes with a ‘mind-blowing’ twist, Liddle says. ‘Although [the electron structure is] unambiguously paramagnetic, [the molecule’s] magnetism is diamagnetic.’ ...

Although diamagnetic molecules are common (the best example is water), the result indicates that the actinide bonds are causing ‘exalted’ diamagnetism – greater than expected diamagnetism due to an aromatic ring. ..."

From the abstract:

"Quantum-confined nanoclusters can be described by the jellium model, which emphasizes closed-shell electron configurations, but an open-shell variation with jellium aromaticity has been proposed.

Such clusters are termed superatoms because they behave like an atom, and they exhibit unusual properties. Superatoms feature metal–metal bonding; hence, since their discovery 40 years ago, superatoms have exclusively involved main group or transition metals, with actinides only considered computationally as dopants owing to actinide–actinide bonding being exceedingly rare.

Here we report trithorium nanoclusters exhibiting three-centre-one-electron actinide–actinide bonding. Experimental and computational analysis demonstrates Robin–Day Class III 6d-orbital valence delocalization in these clusters. These S = 1/2 clusters are paramagnetic, but in external applied magnetic fields they exhibit exalted diamagnetism, evidencing actinide open-shell jellium aromaticity superatom character.

Exalted diamagnetism is not normally associated with a single unpaired electron, but with a 1S1 magic number, the valence delocalization enables exalted diamagnetism, which is aromaticity, via superatom ring currents."

Trithorium superatom confounds with its unexpected and ‘mind-blowing’ diamagnetism | Research | Chemistry World "The first superatoms made using actinides have been created, continuing to upend our understanding of how f-block elements form bonds and adding a new dimension to one of the strangest chemical phenomena."

Valence-delocalized trithorium nanocluster superatoms with open-shell exalted diamagnetism (open access)

Fig. 1: Synthesis of 3 and 4M (M = K, Rb and Cs).

In previous work (ref. 21), treatment of 1 with 2 afforded 3, which contains a three-centre-two-electron trithorium bonding interaction. In this work, treatment of 1 and 2.2.2-cryptand with MC8 reducing agents affords complexes 4M (M = K, Rb, Cs). The fate of the excess M and 2.2.2-cryptand component was not determined.