Optical properties of the cation-deficient platinum chain salt K1.75Pt(CN)4¢1.5H2O

The room-temperature polarized reflectance of a potassium-deficient platinum chain salt K1.75Pt(CN)4.1.5Hz[K0 (def)CP] has been measured in the infrared and visible. The reflectance is strongly anisotropic, with a plasma edge in the red and high reflectance in the infrared for light polarized parallel to the Pt chain axis and almost frequency-independent reflectance for the transverse polarization. Analysis of the plasma edge indicates a nearly-free-electron mass for the conduction electrons. The data show the existence of an energy gap at room temperature and suggest a Peierls transition above room temperature: The parallel polarized reflectance has structure in the infrared which is the first direct evidence for strong coupling of the conduction electrons to the C - N stretching vibration of the tetracyanoplatinate unit in quasi-one-dimensional platinum chain conductors.