Cd[B 2 (SO 4 ) 4 ] and H 2 [B 2 (SO 4 ) 4 ] - a phyllosilicate-analogous borosulfate and its homeotypic heteropolyacid.

Borosulfates consist of heteropolyanionic networks of corner-shared (SO 4 )- and (BO 4 )-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 H 2 [B 2 (SO 4 ) 4 ] as the first phyllosilicate analogue representative, together with the homeotypic representative Cd[B 2 (SO 4 ) 4 ]. The latter can be considered the cadmium salt of the former. Their crystal structures and crystallographic relationship are elucidated. For H 2 [B 2 (SO 4 ) 4 ], the bonding situation is examined using Hirshfeld-surface analysis. Further, the optical and thermal properties of Cd[B 2 (SO 4 ) 4 ] are investigated by FTIR and UV-Vis spectroscopy, thermogravimetry, as well as temperature-programmed powder X-ray diffraction.