Inorganic Chemistry - Wickleder
Non-metal compounds with oxo anions
In this project synthetic routes to a so far scarcely investigated class of non-metal oxo anionic compounds are developed. In the course of our investigations we were able to show that by reactions with highly concentrated mineral acids under harsh conditions compounds with unprecedented properties may be obtained. A fine example is the novel tris-(disulfato)-silicate anion [Si(S2O7)3]2- (Fig. 1, left), which showed octahedral silicon coordination by three inorganic ligands for the first time. This leads to a very large chemical shift in the solid state NMR spectrum (Fig. 1, right).
Fig. 1 The tris-(disulfato)-silicate anion [Si(S2O7)3]2- (left) and the 29Si MAS-NMR spectrum of (NH4)2[Si(S2O7)3] (right)
A further concise example is the novel boron sulfate B2S2O9, which could be obtained via hydrolysis of HSO3Cl with B(OH)3. In this compound the [BO4]- and [SO4]- tetrahedra are linked to a double layer, analogous to the topology of well known phyllosilicates (Fig. 2). In contrast to the respective silicate compounds these layers are not charged. The electric neutrality may offer interesting properties of such type of compounds. Analogously to Phyllosilicates, which are important materials in consequence of their manifold intercalation probabilities, B2S2O9 should also be able to host guest compounds in between the double layers. Due to the electric neutrality it should be possible to intercalate also neutral and non polar molecules.
Further actual research in the field of non metals point at the synthesis of Phosphorus compounds. Following our hitherto knowledge of the elements Silicon and Boron the generation of phosphorus sulfates with widespread tetrahedral networks should be possible, as well as the synthesis of a "disulfato phosphate" with octahedral Phosphor coordination which is completely unknown up to now.
Fig. 2 Phyllosilicate analoguous structure of B2S2O9