New Structural Findings from a Neutron-Diffraction Study of One-Dimensional ${\mathrm{K}}_2$Pt${\mathrm{}\left(\mathrm{CN}\right)\mathrm{}}_4$ ${\mathrm{Br}}_{0.3}$·3${\mathrm{H}}_2$O

We report a single-crystal neutron-diffraction structure study of ${\mathrm{K}}_2$Pt${\mathrm{}\left(\mathrm{CN}\right)\mathrm{}}_4$ ${\mathrm{Br}}_{0.3}$·3${\mathrm{H}}_2$O (KCP). Contrary to previous x-ray results we find that KCP is noncentrosymmetric (space group $P4\mathrm{mm}$ rather than $\frac{P4\mathrm{}}{\mathrm{mmm}}$). New water-molecule positions have been derived. The Pt${\mathrm{}\left(\mathrm{CN}\right)\mathrm{}}_4^{-2\mathrm{}}$ groups are not precisely planar, the ${\mathrm{K}}^{+}$ ions occupy ordered sites, and two crystallographically different ${\mathrm{Br}}^{-}$ ion sites are observed. The possible relationship of the ${\mathrm{Br}}^{-}$-ion disorder to the diffuse x-ray scattering previously observed is discussed.