Conducting Behavior and Valence Ordering of a One‐Dimensional MMX‐Type Coordination Polymer under High Pressure

One‐dimensional (1D) halogen‐bridged mixed‐valent binuclear metal compounds, the so‐called MMX chains, are well known as highly conductive coordination polymers because of the high electronic flexibility within their metal‐dimer unit. Herein, we report on the conducting behavior and electronic state of a highly conductive MMX‐chain compound, Pt 2 (dta) 4 I (dta: CH 3 CS 2 – ) under high pressure. Electrical resistivity measurements showed that this compound exhibits semiconducting behavior in a broad pressure region, despite metallic conduction under ambient pressure. Raman spectra provided clear information about the semiconducting state of this compound under pressure, which was also supported by X‐ray diffraction (XRD) studies. Moreover, we successfully clarified the pressure–temperature phase diagram of this material. By comparing with an analogous material, we found that the difference in the alkyl chain length of the terminal ligand plays an important role for the conducting behavior and the electronic phase under pressure.