Yoji Hara

Electrical conduction of bis(1,2-diondioximato)metals(II) and their partially oxidized complexes at high pressures

The resistivity of one-dimensional d8-metal complexes with various kinds of 1,2-diondioxime(dimethylglyoxime, nioxime, and diphenylglyoxime) ligands has been measured at high pressures. The resistivity of M(dmg)2 and M(niox)2 decreased with increasing pressure. The resistivity of M(dmg)2 is much lower than that of M(niox)2 at high pressure, though M-M distances and optical energy gaps in both salts are almost the same at atmospheric pressure. An anomalous low resistivity has been observed in Pt(dmg)2 at about 40 kbar. The electrical resistivity of M(niox)2 and M(dmg)2, oxidized by oxidizing agents, decreased with increasing pressure. The resistivity of partially oxidized Pt complexes is significantly higher than that of the parent compounds at high pressure. On the contrary, partially oxidized Ni and Pd complexes are more conductive than unoxidized compounds at high pressures. The electrocal resistivity of unoxidized and partially oxidized Pt complexes increased with increasing pressure at higher pressures. The resistivity minimum at high pressure has been observed only in Pt complexes. The infrared spectra of the d8-metal complexes and their partially oxidized complexes have been investigated. The frequency of the CN stretching vibration in M(dmg)2 and M(niox)2 salts increases in the order Ni > Pd > Pt; on the other hand, the frequency of M(niox)2Xn increases in the order Ni < Pd < Pt. The frequency of the CN stretching vibration is closely related to the effect of metal-ligand π∗ back bonding in d8-metal complexes. Some anomalies in the resistance-pressure curve have been found in Ni(dpg)2, Ni(dpg)2I, Ni(dpg)2I0.5, and Ni(dpg)2I0.14. The anomalies are explained by new pressure-induced phase transitions.

On the electronic structures of some conductive one-dimensional metal-glyoximes at high pressures

Abstract Bis(dimethylglyoximato)Pt(II)(PtDMG) 2 ) and its related complexes exhibit a remarkable decrease in electrical resistance at high pressures. The least resistivity and the activation energy observed for Pt(DMG) 2 are 10 −1 Ω-cm and 5 × 10 −3 eV, respectively. These low values are tentatively attributed to the effect of hyperconjugation to methyl substituent on the electric polarizability in the ligand.

A resistance minimum and the electronic structures of some one-dimensional Pt-complexes at high pressures

Abstract The effect of pressure has been measured up to 650 kbar on the electrical resistance in six one-dimensional Pt-complexes, including two mixed valence ones. SrPt(CN) 4 ·2H 2 O, MgPt(CN) 4 ·7H 2 O and BaPt(CN) 4 ·4H 2 O do not show a resistance minimum, contrary to other d 8 -metal complexes, suggesting a considerable contribution of π ∗ orbitals of CN - ligands to the conduction.

Changes of the electronic states of a mixed‐valence compound at high pressures‐insoluble Prussian blue, Fe4[Fe(CN)6]3

The effect of pressure has been measured on the abosrption spectra, x‐ray diffraction, and electrical resistance in the mixed‐valence compound ferric ferrocyanide or insoluble Prussian blue (ISPB). In the optical measurements, the charge transfer band from Fe(II) to Fe(III) showed a blue shift and decrease in intensity with pressure. The x‐ray diffraction measurements up to 90 kbar showed that Fe(II)–Fe(III) distance decreased continuously. The electrical resistance was found to decrease by a factor of 10−2 up to 130 kbar at 297°K, but was found to have a resistance minimum at 333°K. The ξp2 value which indicates the delocalization of an electron between Fe(II) and Fe(III) was introduced. By using the results from the optical and the x‐ray diffraction measurements at high pressures, this ξp2 value was estimated as a function of pressure.

Effect of Ultrahigh Pressure on Some Quasi-One-Dimensional Conductors

The electrical behavior of quasi-one-dimensional conductors at high pressure has been of considerable interest in recent years. Square-planar complexes of transition metals [1–7] and salts of 7,7,8,8-tetracyanoquinodimethane (TCNQ) anion radical [8–17] have been investigated most extensively. Studies have also been carried out on phthalocyanines [18] and polymeric sulfur nitride, (SN)x [19].