X-Ray and Optical Study on the PtCl Chain Structure in [Pt(en)₂][Pt(en)₂Cl₂](BF₄) ₄

X-ray diffraction and optical absorption measurements were carried out on single crystals of [Pt(en)₂][Pt(en)₂Cl₂](BF₄) ₄ (en = etylenediamine). This compound has a quasi-one dimensional structure with alternating (II and IV) Pt valences along the c-axis. An orthorhombic to mono-clinic structural phase transition occurs around 255 K and the charge-transfer absorption edge was found to have a sudden shift at the transition. X-ray diffuse scattering was observed around (0 0 2n + 1) reciprocal points. While optical spectra were affected by irradiating the sample with blue light, the X-ray diffraction intensity did not change either by irradiation or by varying the sample temperature. We attribute the diffuse scattering to solitons produced during crystal growth. From measurements of thermal diffuse scattering, limited information about the phonon dispersion relation was obtained.