The Crystal Lattice of Potassium Pyrosulphite, K2S2O5, and the Structure of the Pyrosulphite Group

Abstract

The crystal lattice of potassium pyrosulphite was examined in order to determine the structure of the pyrosulphite group. The Laue method and the oscillating crystal method were used. The dimensions of the monoclinic unit cell were found to be: $a=6.95\mathrm{}\mathrm{A}$, $b=6.19\mathrm{}\mathrm{A}$, $c=7.55\mathrm{}\mathrm{A}$, $\beta =102\mathrm{}°{41}^{\prime }$. The density determination gave 2.34 and corresponds to two molecules ${\mathrm{K}}_2$ ${\mathrm{S}}_2$ ${\mathrm{O}}_5$ in the unit cell. The space group is $\frac{P{2}_1}{m\left({C_{2h}}^2\right)}$. Two sets of four oxygen atoms are lying in general positions with coordinates $\pm \mathrm{}\left(\mathrm{xyz}\right)\mathrm{}\pm (x, \frac{1}{2}-y, z)$, while the remaining atoms are all lying in the reflection planes $\pm \left(u\frac{1}{4}v\right)$. The parameter values corresponding to the sixteen degrees of freedom were determined accurately and uniquely. No other assumptions than those underlying the theory for the diffraction of x-rays by crystals were made. The final parameters are: