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 10(15) OMEGA-cm, and Pt(bqd)2 is a semiconductor with 10(3) OMEGA-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 5d(z2) valence and 6p(z) 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 structure was observed.