Kristallstrukturen der Alkalimetall-Thiosulfate A2S2O3 nH2O (A/n = K/0, K/⅓ , Rb=1) / Crystal Structures of the Alkali Thiosulfates A2S2O3 · nH2O (A/n = K/0, K/⅓ , Rb=1)

Abstract

The potassium and rubidium thiosulfates (hydrates) considered in this work were originally obtained as by-products during several syntheses of mixed sulfido=oxido metallates. The interesting complexity of their structural chemistry has motivated us to investigate them in detail. The crystal structures of all title compounds have been determined using single-crystal X-ray data. The structure of the anhydrous potassium thiosulfate K2S2O3 (monoclinic, space group P21/c, a=1010.15(14), b=910.65(12), c=1329.4(2) pm, b =111.984(11)º, Z =8, R1=0.0665) exhibits two crystallographically different thiosulfate anions, overall coordinated by 9=10 potassium cations. Their packing in the structure leads to a complex structure with a pseudo orthorhombic unit cell. The structure of the anhydrous salt is discussed in comparison with the known even more complicated 1=3 hydrate K2S2O3·1/3H2O (monoclinic, space group P21/c, a=938.27(6), b=602.83(4), c=3096.0(2) pm, b =98.415(6)º, Z =12, R1=0.0327). Under the chosen experimental conditions, rubidium forms the monohydrate Rb2S2O3 ·H2O, which also crystallizes with a new, in this case less complex structure (monoclinic, space group C2/m, a=1061.4(1), b=567.92(4), c=1096.4(1) pm, b =97.40(1)º, Z =4, R1=0.0734). Its thiosulfate ions form double layers of equally oriented tetrahedral units. The bond lengths and angles of the thiosulfate ions in all title compounds and in the sodium salts used for comparison vary only very slightly (dS-S =199.8 - 203.0 pm, dS-O =144.8 - 147.4 pm), and the deviation from the ideal C3v symmetry is very small, despite their complex packing. The overall coordination number of the thiosulfate ions by the alkali cations (and water molecules) increases systematically with the ionic radius of the counter cations and the amount of water molecules. For all known alkali thiosulfates, both the conventional and the calculated effective coordination numbers (ECoN) of the alkali cations as well as the partial molar volumes of the cations and the water molecules are compared and discussed.