Pressure‐Induced Metal–Semiconductor–Metal Transitions in an MMX‐Chain Complex, Pt 2 (C 2 H 5 CS 2 ) 4 I

The electrical conductivity and X‐ray diffraction measurements were performed for a highlyconductive halogen‐bridged binuclear‐metal mixed‐valence complex (the so‐called MMX chain), Pt 2 (C 2 H 5 CS 2 ) 4 I, under high pressure up to 2.5 GPa. The complex exhibited pressure‐induced metal–semiconductor–metal transitions at 0.5 and 2.1 GPa. The X‐ray diffuse scatterings were observed at k = n  + 0.5 ( n : integer) under ambient pressure, which are derived from the charge‐density wave (CDW: ··· Pt 2+ –Pt 2+ ··· I–Pt 3+ –Pt 3+ –I ··· ) fluctuation in the MMX chain. Above 0.5 GPa, where the pressure‐induced metal–semiconductor transition occurred, these scatterings disappeared. The electronic phases under high pressure ( P ) were found to be attributable to the metallic averaged‐valence state (AV: –Pt 2.5+ –Pt 2.5+ –I–Pt 2.5+ –Pt 2.5+ –I–) with CDW fluctuation of P < 0.5 GPa, semiconducting charge‐polarization state (CP: ··· Pt 2+ –Pt 3+ –I ··· Pt 2+ –Pt 3+ –I ··· ) of 0.5 < P < 2.1 GPa, and metallic AV state of P > 2.1 GPa. The electronic state of Pt 2 (C 2 H 5 CS 2 ) 4 I is very sensitive to pressure, which implies that the phase competition among the CP, CDW, and AV phases is present in the MMX chain. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)