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

The crystal structures of K{sub 2}S{sub 2}O{sub 7}, KNaS{sub 2}O{sub 7} and Na{sub 2}S{sub 2}O{sub 7} have been solved and/or refined from X-ray synchrotron powder diffraction data and conventional single-crystal data. K{sub 2}S{sub 2}O{sub 7}: From powder diffraction data, monoclinic C2/c, Z=4, a=12.3653(2), b=7.3122(1), c=7.2868(1)A, {beta}=93.0792(7){sup o}, R{sub Bragg}=0.096. KNaS{sub 2}O{sub 7}: From powder diffraction data; triclinic P1-bar , Z=2, a=5.90476(9), b=7.2008(1), c=7.4188(1)A, {alpha}=101.7074(9), {beta}=90.6960(7), {gamma}=94.2403(9){sup o}, R{sub Bragg}=0.075. Na{sub 2}S{sub 2}O{sub 7}: From single-crystal data; triclinic P1-bar , Z=2, a=6.7702(9), b=6.7975(10), c=6.7292(9)A, {alpha}=116.779(2), {beta}=96.089(3), {gamma}=84.000(3){sup o}, R{sub 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{sub 2}S{sub 2}O{sub 7} and Na{sub 2}S{sub 2}O{sub 7} the neighbouring chains are antiparallel, while in KNaS{sub 2}O{sub 7} the chains are parallel. The differences between the K{sub 2}S{sub 2}O{sub 7} and Na{sub 2}S{sub 2}O{sub 7} structures, with double-, respectively single-sided chain connections and straight, respectively, corrugated structural layers can be understood in terms of the differences in sizemore » and coordinating ability of the cations.« less