Jordi Poater from the Universitat de Barcelona (ex-DiMoCat member) together with the DiMoCat member Miquel Solà have derived a new rule for the open-shell jellium aromaticity. Some years ago, the same two authors demonstrated that spherical compounds having a same-spin half-filled last energy level with the rest of the levels being full filled are aromatic. They showed that this situation is reached for a number of electrons equal to 2N2 + 2N + 1 with S = N + ½ and proved that, among others, C60-1 with S = 11/2 or C80-5 species with S = 13/2 are aromatic fullerenes.
Now, they have extended this finding to metal clusters. The jellium model assumes a uniform distribution of positive charge corresponding to the cluster atomic nuclei and their innermost electrons in which the interacting valence electrons move. The energy levels of valence electrons for such a model are 1S21P61D102S21F142P61G182D103S2…, where S, P, D, F, and G letters denote the angular momentum and numbers 1, 2, 3 indicate the radial nodes. The abundance found in experimental mass spectra of alkali, alkaline earth metals, and gold clusters of 2, 8, 18, 20, 34, 40… atoms are justified taken into account that these numbers correspond to closed-shell electronic structures in the jellium model. Poater and Solà have proven that if the last energy level of valence electrons for the jellium model is half-filled with same-spin electrons, the system has also some extra stability and has aromatic character. This situation is reached for the magic numbers of valence electrons of 1 (S =1/2), 5 (S = 3/2), 13 (S = 5/2), 19 (S = 1/2), 27 (S = 7/2), 37 (S = 3/2), 49 (S = 9/2)… This new set of magic numbers may become a powerful tool for researchers who work in the quest for stable single high-spin molecules for their use as single-molecule based magnets.
The paper has been published in Chem. Commun. and can be found in the following link Chem. Commun., 55 (2019) 5559-5562. Moreover, the paper has been highlighted by Chemistry World and Chem. Commun. has dedicated the inside back cover of the issue 39 of volume 55 to this work: