Evidence for Ordered Layers of ${\mathrm{K}}^{+}$ in KCP (${\mathrm{K}}_2$ [Pt${\mathrm{}\left(\mathrm{CN}\right)\mathrm{}}_4$] ${\mathrm{Cl}}_{0.3}$·3${\mathrm{H}}_2$O)

We have redetermined the crystal structure of ${\mathrm{K}}_2$[Pt${\mathrm{}\left(\mathrm{CN}\right)\mathrm{}}_4$]${\mathrm{Cl}}_{0.3}$·3${\mathrm{H}}_2$O. It crystallizes in space group $P4\mathrm{mm}$, contrary to earlier assignments. The ${\mathrm{K}}^{+}$ ions occupy ordered positions in layers with a periodicity of $c=5.77\mathrm{}$ Å which are perpendicular to the $c$ axis. The same kind of superstructure was found for ${\mathrm{K}}_2$[Pt${\mathrm{}\left(\mathrm{CN}\right)\mathrm{}}_4$]${\mathrm{Br}}_{0.3}$·3${\mathrm{H}}_2$O.