Structural Insights into Chalcogen Polycations and Their Stabilization via (Hydrogen)polysulfates

Abstract

We report the preparation and characterization of the cations [Se₄]²⁺, [Te₄]²⁺ and [Te₆]⁴⁺, stabilized as polysulfates, namely [Se₄][S₂O₇], [Se₄][HS₂O₇]₂, [Se₄][HS₃O₁₀]₂, [Te₄][HS₃O₁₀]₂, [Te₆][HS₃O₁₀]₄ and [Te₆][S₄O₁₃]₂. In case of the tellurium compounds, this represents the first stabilization and solid-state investigations of the species from chlorosulfuric acid / sulfur trioxide-based media, although the respective colorful solutions are known for over 200 years. The unusual cation–anion interaction was investigated via Density functional theory (DFT) calculations, i.e. MEP surface plots, QTAIM and NBO analyses. The non-covalent interactions (chalcogen bonding (ChB)) within the novel species reveal different binding modes, namely bifurcated (Ch⋯O,O or Ch,Ch⋯O) as well as standard (Ch⋯O) σ-hole interactions. We show that the [Se₄]²⁺ dication exhibits an electrophilic duality, engaging in σ- as well as π-hole interactions and that the stabilization of polycationic chalcogens with oxoanions is enhanced by auxiliary Ch⋯O contacts.