The crystal structure determinations and refinements of K 2S 2O 7, KNaS 2O 7 and Na 2S 2O 7 from X-ray powder and single crystal diffraction data

Abstract

The crystal structures of K 2S 2O 7, KNaS 2O 7 and Na 2S 2O 7 have been solved and/or refined from X-ray synchrotron powder diffraction data and conventional single-crystal data. K 2S 2O 7: From powder diffraction data, monoclinic C 2 / c , Z = 4 , a = 12.3653 ( 2 ) , b = 7.3122 ( 1 ) , c = 7.2868 ( 1 ) Å , β = 93.0792 ( 7 ) ° , R Bragg = 0.096 . KNaS 2O 7: From powder diffraction data; triclinic P 1 ¯ , Z = 2 , a = 5.90476 ( 9 ) , b = 7.2008 ( 1 ) , c = 7.4188 ( 1 ) Å , α = 101.7074 ( 9 ) , β = 90.6960 ( 7 ) , γ = 94.2403 ( 9 ) ° , R Bragg = 0.075 . Na 2S 2O 7: From single-crystal data; triclinic P 1 ¯ , Z = 2 , a = 6.7702 ( 9 ) , b = 6.7975 ( 10 ) , c = 6.7292 ( 9 ) Å , α = 116.779 ( 2 ) , β = 96.089 ( 3 ) , γ = 84.000 ( 3 ) ° , R F = 0.033 . 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 K 2S 2O 7 and Na 2S 2O 7 the neighbouring chains are antiparallel, while in KNaS 2O 7 the chains are parallel. The differences between the K 2S 2O 7 and Na 2S 2O 7 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.