Insulator-to-Metal-to-Semiconductor Transitions of One-Dimensional Bis(1,2-dione dioximato)Pt(II) Complexes at High Pressures

The electrical resistivities and absorption spectra of one-dimensional bis(1,2-dione dioximato)Pt(II) have been studied at high pressures. The resistivities of needle crystals of Pt(dmg)2 and Pt(bqd)2 were measured in detail under a quasi-hydrostatic pressure of up to 7 GPa. Pt(dmg)2 is an insulator with a resistivity of 1015 Ω cm, and Pt(bqd)2 is a semiconductor with 103 Ω cm at atmospheric pressure. A pressure-induced insulator (semiconductor)-to-metal transition was observed for both complexes. This transition arises from a crossing of the 5dz2 valence and 6pz conduction bands. When the pressure was further increasued, a metal-to-semiconductor transition took place at around the pressure that showed a resistivity minimum. A new pressure-induced absorption band was found in the visible region for the Pt complexes. The new band did not shift with pressure; the intensity of the band, however, increased with pressure over a narrow pressure region. The pressure-induced band may be due to intramolecular d–d transitions. The metal-to-semiconductor transition may arise from a change in the electronic states at high pressure, since no anomaly in the strucutre was observed.