Trivalent acid radical-centered YLi4+ (Y = PO4, AsO4, VO4) cations: new polynuclear species designed to enrich the superalkali family

Abstract

A new series of polynuclear superalkali cations YLi₄⁺ (Y = PO₄, AsO₄, VO₄) has been characterized using ab initio methods. The central Y³⁻ (PO₄³⁻, AsO₄³⁻, VO₄³⁻) acid radicals preserve their structural and electronic integrity in the first several lowest-lying isomers of YLi₄⁺. Meanwhile, the introduction of Li⁺ cations can also dissociate an O²⁻ ion from the Y³⁻ groups. Besides, the AsO₄³⁻ group is discerned to be separated into AsO₂⁻ and O₂²⁻ fragments other than AsO₃⁻ and O²⁻ units. This is why the AsO₄Li₄⁺ cation has been found to possess more diverse structures. The vertical electron affinities (EA_vert) of the YLi₄⁺ cations range from 2.44 to 4.67 eV, which are low enough to validate the superalkali or pseudoalkali identity of the title species. It is also noteworthy that the YLi₄⁺ conformer with T_d symmetry allows a more even distribution of the excess positive charge, and consequently exhibits the lowest EA_vert value of ca. 2.45 eV.