The Unconventional Cadmium Borosulfates Cd[B2O(SO4)3] and Cd4[B2O(SO4)6]

Borosulfates are an expanding class of silicate-analogous materials. We report the syntheses and crystal structures of two unconventional cadmium borosulfates. Cd[B2O(SO4)(3)] crystallises in a new structure type in space group Pnma (no. 62, a=896.92(8), b=1152.0(1), c=872.75(8) pm, 1380 refl., 94 ref. param., wR(2)=0.112). Cd-4[B2O(SO4)(6)] adapts the alpha-Mg-4[B2O(SO4)(6)]-type structure with space group P3? (no. 147, a=822.22(4), c=797.88(5) pm, 1810 refl., 58 ref. param., wR(2)=0.078). Together with simultaneously elsewhere reported conventional phyllosilicate-analogous Cd[B-2(SO4)(4)], there are now in total three cadmium borosulfates with differing dimensionality of their anions, i. e. 0D, 1D and 2D. These results highlight the special position of cadmium in the periodic table and the ambiguity of its behaviour as main group or transition metal when comparing to other analogous or related borosulfates. The [B2O(SO4)(3)](2-) and [B2O(SO4)(6)](8-) anions are known from other main group and transition metal borosulfates. However, Cd2+ is the first cation for which borosulfates comprising both anions are reported for the same cation. Moreover, the optical and thermal properties of both compounds are reported using IR and UV-Vis spectroscopy as well as thermogravimetry. Both unconventional borosulfates were prepared by the thermal decomposition of the conventional borosulfate Cd[B-2(SO4)(4)] pursueing our studies on the complex thermal decomposition behaviour of such borosulfates.