Cu[B₂(SO₄)₄] and Cu[B(SO₄)₂(HSO₄)]—Two Silicate Analogue Borosulfates Differing in their Dimensionality: A Comparative Study of Stability and Acidity

Abstract

Abstract Borosulfates are an ever‐expanding class of compounds and the extent of their properties is still elusive. Herein, the first two copper borosulfates Cu[B 2 (SO 4 ) 4 ] and Cu[B(SO 4 ) 2 (HSO 4 )] are presented, which are structurally related but show different dimensionalities in their substructure: While Cu[B 2 (SO 4 ) 4 ] reveals an anionic chain, [B(SO 4 ) 4/2 ] − , with both a twisted and a unique chair conformation of the B(SO 4 ) 2 B subunits, Cu[B(SO 4 ) 2 (HSO 4 )] reveals isolated [B 2 (SO 4 ) 4 (HSO 4 ) 2 ] 4− anions showing exclusively a twisted conformation. The complex anion can figuratively be obtained as a cut‐out from the anionic chain by protons. Comparative DFT calculations based on magnetochemical measurements complement the experimental studies. Calculation of the p K a values of the two conformers of the [B 2 (SO 4 ) 4 (HSO 4 ) 2 ] 4− anion revealed them to be more similar to silicic than to sulfuric acid, highlighting the close relationship to silicates.