Oxidizing Rhodium with Sulfuric Acid: The Sulfates Rh₂(SO₄)₃ and Rh₂(SO₄)₃·2H₂O

Abstract

The reaction of elemental rhodium and concentrated sulfuric acid (97 %) at 400°C leads to red plate-shaped single crystals of Rh 2 (SO 4 ) 3 [trigonal, R3, Z = 6, a = 806.8(1) pm, c = 2204.8(4) pm, V = 1242.8(4) × 10 6 pm 3 ]. The same reaction carried out at a temperature of 475°C leads to orange crystals of Rh 2 (SO 4 ) 3 ·2H 2 O [orthorhombic, Pnma, Z = 4, a = 920.46(2) pm, b = 1244.47(3) pm, c = 833.37(2) pm, V = 954.61(4) × 10 6 pm 3 ].[a]

Stabilizing the Homopolycation (I4)2+ with a Hexasulfate in (I4)[S6O19] and a Borosulfate in (I4)[B(S2O7)2]2

“…In course of our investigations of the H 2 SO 4 /SO 3 system we reported several important findings. Firstly, the extraordinary oxidation power could be shown by the oxidation of platinum metals leading to several unique compounds [20–30] . Secondly, we could demonstrate that the assumed infinite chain growth of polysulfuric acids H 2 S n O 3 n +1 , that is with increasing SO 3 content, is doubtful [31,32] .…”

“…Firstly, the extraordinary oxidation power could be shown by the oxidation of platinum metals leading to several unique compounds. [20][21][22][23][24][25][26][27][28][29][30] Secondly, we could demonstrate that the assumed infinite chain growth of polysulfuric acids H 2 S n O 3n + 1 , that is with increasing SO 3 content, is doubtful. [31,32] Nevertheless, the assumption that the Brønsted acidity of H 2 SO 4 /SO 3 mixtures increases with increasing SO 3 content seems reasonable.…”