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 CN 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 CN 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) 2I 0.5, and Ni(dpg) 2I 0.14. The anomalies are explained by new pressure-induced phase transitions.