Cd[B2(SO4)4] and H2[B2(SO4)4] – a phyllosilicate-analogous borosulfate and its homeotypic heteropolyacid

Abstract

Borosulfates consist of heteropolyanionic networks of corner-shared (SO₄)- and (BO₄)-tetrahedra charge compensated by metal or non-metal cations. The anionic substructures differ significantly, depending on the different branching of the silicate-analogous borosulfate building blocks. However, only one acid has been characterized by single crystal X-ray diffraction so far. Herein, we present H₂[B₂(SO₄)₄] as the first phyllosilicate analogue representative, together with the homeotypic representative Cd[B₂(SO₄)₄]. The latter can be considered the cadmium salt of the former. Their crystal structures and crystallographic relationship are elucidated. For H₂[B₂(SO₄)₄], the bonding situation is examined using Hirshfeld-surface analysis. Further, the optical and thermal properties of Cd[B₂(SO₄)₄] are investigated by FTIR and UV-Vis spectroscopy, thermogravimetry, as well as temperature-programmed powder X-ray diffraction.