Planar tetracoordinate oxygen stabilized within triel–chalcogen dicationic frameworks

Abstract

Planar tetracoordinate oxygen (ptO) challenges oxygen's intrinsic preference for two-coordinate bonding. We present a systematic investigation of dicationic triel–chalcogen clusters O©X₄E₄²⁺ (X = Al, Ga, In; E = S, Se, Te), identifying 9 D_4h ptO global minima. The oxygen atom is best described as a formally O²⁻ dianion electrostatically embedded within a charge-delocalized X₄E₄ tetracationic framework sustained by a robust X–E σ-scaffold, with negligible X–X interactions. Bonding analysis indicates predominantly electrostatic O–X interactions, whereas the X₄E₄ crown is stabilized by localized 2c–2e X–E σ-bonds and delocalized 3c–2e X–E–X π-bonds. Magnetic response calculations reveal localized diatropic vortices around the ptO center and the X–E–X regions, but no global ring current, consistent with the nonaromatic character. Born–Oppenheimer molecular dynamics simulations confirm dynamic stability at 500 K. π-Anion complexation with cyclooctatetraenide (COT²⁻) demonstrates that retention of the planar geometry depends on intrinsic framework rigidity and is preserved in the aluminum derivatives. These results establish electrostatic embedding within a rigid X₄E₄ scaffold as an effective strategy for stabilizing ptO in main-group clusters.