The crystal structure determinations and refinements of K2S2O7, KNaS2O7 and Na2S2O7 from X-ray powder and single crystal diffraction data

The crystal structures of K2S2O7, KNaS2O7 and Na2S2O7 have been solved and/or refined from X-ray synchrotron powder diffraction data and conventional single-crystal data. K2S2O7: From powder diffraction data, monoclinic image, image, image, image, image, image, image. KNaS2O7: From powder diffraction data; triclinic image, image, image, image, image, image, image, image, image. Na2S2O7: From single-crystal data; triclinic image, image, image, image, image, image, image, image, image. The disulphate anions are essentially eclipsed. All three structures can be described as dichromate-like, where the alkali cations coordinate oxygens of the isolated disulphate groups in three-dimensional networks. The K–O and Na–O coordinations were determined from electron density topology and coordination geometry. The three structures have a cation-disulphate chain in common. In K2S2O7 and Na2S2O7 the neighbouring chains are antiparallel, while in KNaS2O7 the chains are parallel. The differences between the K2S2O7 and Na2S2O7 structures, with double-, respectively single-sided chain connections and straight, respectively, corrugated structural layers can be understood in terms of the differences in size and coordinating ability of the cations.