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

Borosulfates are an ever-expanding class of compounds and the extent of their properties is still elusive. Herein, the first two copper borosulfates Cu[B2(SO4)4] and Cu[B(SO4)2(HSO4)] are presented, which are structurally related but show different dimensionalities in their substructure: While Cu[B2(SO4)4] reveals an anionic chain, (Formula presented.) [B(SO4)4/2]−, with both a twisted and a unique chair conformation of the B(SO4)2B subunits, Cu[B(SO4)2(HSO4)] reveals isolated [B2(SO4)4(HSO4)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 pKa values of the two conformers of the [B2(SO4)4(HSO4)2]4− anion revealed them to be more similar to silicic than to sulfuric acid, highlighting the close relationship to silicates.