Electronic and structural features of octa-coordinated yttrium–ammonia complexes: the first neutral solvated electron precursor with eight ligands and three outer electrons

Abstract

The neutral and charged yttrium metal–ammonia complexes, [Y(NH₃)₈]^0,±, are investigated using state-of-the-art quantum chemical calculations. The electronic structure of these complexes is described as an Y(NH₃)₈³⁺ core with two, three, and four electrons orbiting in its periphery. Unlike the so far reported solvated electron precursors containing alkali, alkaline earth or first-row transition metals, yttrium complexes are the only ones which can accommodate eight ammonia ligands and up to four peripheral electrons. For the neutral species, two electrons occupy the diffuse s-type orbital (1s) and one diffuse p-type orbital (1p). For the cationic counterpart one electron is removed from the 1p orbital, while for the anion another electron is added to the 1p shell. The calculated low-lying electronic states with excitation energies up to 2.0 eV populate the 1s, 1p, and 1d outer orbitals. The first ionization energy of Y(NH₃)₈ is 2.74 eV and its electron affinity is 0.64 eV. The present results suggest that saturated yttrium ammonia solutions will turn into solids (liquid or expanded metals), where a grid of Y(NH₃)₈³⁺ centers will be surrounded by “free” electrons.