Orbital Degree of Freedom in Conducting Platinum–Dithiolene Complex Salts

Abstract

We report experimental evidence for the orbital degrees of freedom in anion–radical salts consisting of metal–dithiolene complexes, obtained by a simple method. We observed the NIR absorption spectra of the 2D molecular conductors Me4Q[Pt(dmit)2]2 (Q = N, P, and Sb, dmit = 1,3-dithiole-2-thione-4,5-dithiolate), which shows a phase transition from the metallic phase to the semiconducting and charge-ordered phase, and analyzed the orbital levels of dimers [Pt(dmit)2]2 near the Fermi energy. The highest-energy electrons in the charge-ordered phase occupied the bonding orbitals, whereas those in the metallic phase occupied the antibonding orbitals. The redistribution of charges and the replacement of the outermost orbitals co-occurred for all dimers in Me4Q[Pt(dmit)2]2. This phenomenon differs from that in palladium analogs, in which the replacement of the outermost orbitals does not occur or occurs only for half of all dimers. Our experimental results revealed that anion–radical salts consisting of metal–dithiolene complexes have a variety of orbital distributions.