Superatomic Chelates: The Cases of Metal Aza-Crown Ethers and Cryptands

Li, Na, and Mg+-coordinated hexaaza-18-crown-6 ([18]-aneN(6)) and 1,4,7-triazacyclononane ([9] aneN(3)), Li[1.1.1]cryptand, and Na[2.2.2]cryptand species possess a diffuse electron in a quasispherical s-type orbital. They populate expanded p-, d-, f-, and g-shape orbitals in low-lying excited states and hence are identified as superatoms. By means of quantum calculations, their superatomic shell models are revealed. The observed orbital series of M([9]aneN(3)) 2 and M[18]aneN(6) (M = Li, Na, Mg+) are identical to the 1s, 1p, 1d, 1f, 2s, and 2p. The electronic spectra of Li[1.1.1]cryptand and Na[2.2.2]cryptand were analyzed up to the 1f(1) configuration, and their transitions were found to occur at lower energies compared to their aza-crown ethers. The introduced superatomic shell models in this work closely resemble the Aufbau principle of solvated electrons precursors. All reported alkali metal complexes bear lower ionization potentials than any atom in the periodic table; thus, they can also be recognized as superalkalis.

Automated summary

The study investigated metal ion complexes like Li, Na, and Mg+, revealing their diffuse electron in quasi-spherical s-type orbitals and identifying them as superatoms. Analysis of their spectra and shell models shows unique behaviors and similarities to solvated electrons precursors, leading to the recognition of these complexes as superalkalis with lower ionization potentials than any atom in the periodic table.