Rubidium trithionate

Rubidium trithionate, Rb2S306.—When rubidium persulphate reacts with somewhat more than twice the molecular proportion of strontium thiosulphate in solution, rubidium tetrathionate is formed ... 

Until 1950 the only X-ray crystallographic work on polythionates was Zachariasen s structure determination of potassium trithionate (239) published in 1934, a partial structure analysis of thallium trithionate by Ketelaar and Sanders (151) in 1936, and unit cell and space group determinations of rubidium trithionate (161) and potassium tetrathionate (218). Since then, surveys of unit cells and space groups of tetra-, penta-, and hexathionates and selenotrithionates, selenopentathionates, and telluropentathionates have been made, and structure determinations of two tetrathionates, three pentathionates, one selenopentathionate, two telluropentathionates, and two hexathionates have been carried out. 

The strontium sulphite produced by decomposition of the excess of strontium thiosulphate then reacts with the rubidium tetrathionate, forming trithionate ... 

Caesium trithionate, Cs2S306.—The trithionate has been prepared by a method analogous to that employed for the rubidium salt. It crystallizes in the triclinic system as an efflorescent monohydrate. The anhydrous salt has a density of 3-3 (approx.). 

Potassium trithionate is orthorhombic bipyramidal, space group D -Pnma with four formula units per unit cell. From Zachariasen s (239) structure analysis, carried out in the early thirties by trial and error methods, the trithionate ion has mirror plane symmetry in the crystals, lying with all three sulfur atoms and two of the oxygen atoms in the mirror plane. The rubidium salt (161) is isomorphous with the potassium salt. The third trithionate for which data are available, the thallium salt, is monoclinic prismatic, space group Ca ,6-C2/c with four formula units per unit cell (151). Here, the trithionate ion has a twofold axis as symmetry element. 

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