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

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, [Formula: see text] [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 pK (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.