The Crystal Lattice of Anhydrous Sodium Sulphite,Na2SO3

The crystal structure of ${\mathrm{Na}}_2$S${\mathrm{O}}_3$ has been investigated by means of the Laue, the ionization, the rotation and the powder methods. The hexagonal unit cell containing two molecules was found to have dimensions: $a=5.441\mathrm{}\mathrm{A} c=6.133\mathrm{}\mathrm{A}$. The observations seemed to be in conflict with all hexagonal and trigonal space groups. The difficulty was, however, overcome by assuming the crystals to be twins with the $c$-axis as twinning axis. The space group ${C_{3i}}^1$ was under this assumption found to be the only possible one. All parameters involved were determined from the observed intensities with the following result: 4 atoms Na in position $1a \mathrm{}\left(000\right)\mathrm{}$, $1b \left(00\mathrm{} \frac{1}{2}\right)$ and $2d \left(\frac{1}{3} \frac{2}{3} u_1\right)$, ($\frac{2}{3} \frac{1}{3} {\overline{u}}_1$) with $u_1=0.67\mathrm{}$ 2 atoms S in positions $2d \left(\frac{1}{3} \frac{2}{3} u_2\right)$, ($\frac{2}{3} \frac{1}{3} {\overline{u}}_2$) with $u_2=0.17\mathrm{}$ 6 atoms O in positions $6g\left(\mathrm{xyz}\right)\mathrm{}$, ($y-x, \overline{x}, z$), ($\overline{y}, x-y, z$), ($\overline{x}\overline{y}\overline{z}$), ($x-y, x, \overline{z}$), ($y, y-x,\overline{z}$) with $x=0.14\mathrm{}$, $y=0.40\mathrm{}$, $z=0.25\mathrm{}$. Two of the Na atoms are surrounded by 6 oxygens at a distance 2.469A; while the remaining two sodium atoms are surrounded by 3 oxygens at a distance 2.461A and by 3 at 2.870A. The structure shows the presence of groups S${\mathrm{O}}_3$. The distance from sulphur to the 3 surrounding oxygens is 1.39A, while the oxygens in the equilateral triangle have a distance of 2.24A. The sulphur atom has a displacement of 0.51A out of...