Sulfate 387 oxidation states lower than

In oxidation states lower than -t-4, only Ti forms a sulfate and this gives rise to the alums, MTi(S04)2-12H20 (M = Rb, Cs), containing the octahedral hexaaquotitanium(III) ion. 

The toxicity of chromium is dependent on the oxidation state of the chromium atom, with chromium(VI) being significantly more toxic than chromium(III). One of the factors believed to contribute to this increased toxicity is the greater ability of chromium(VI) to enter cells, compared to chromium(III). Chromium(VI) exists as the tetrahedral chromate anion at physiological pH, and resembles the forms of other natural anions, such as sulfate and phosphate, which are permeable across nonselective membrane channels. Chromium(III), however, forms octahedral complexes and cannot easily enter through these channels. Therefore, the lower toxicity to chromium(III) may be due in part to lack of penetration through cell membranes. It follows that extracellular reduction of chromium(VI) to chromium(III) may result in a decreased penetration of chromium into cells, and therefore, a decreased toxicity. 

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