Electronic structure mechanism of axial ligands on itinerant electrons and negative magnetoresistance in axially-ligated iron(III) phthalocyanine molecular conductors

Abstract

Partially-oxidized Iron(III) phthalocyanine (FeIIIPc) with axial CN or Br ligands are molecular conductors with giant negative magnetoresistance. Electron conduction occurs via intermolecular overlapping of Pc π-orbitals, while negative magnetoresistance is brought about by intramolecular interaction between Fe-d and Pc-π orbitals. Aside from permitting sliπ-stacked solid-state arrangement, axial ligands can further enhance the π-d interaction of FeIII(Pc) depending on the strength of ligand field energies that proportionally leads to larger negative magnetoresistance. However, the strong ligand field of CN results in conductivity reduction due to the π-accepting nature of the ligand which enhances electron gradient in the oxidized Fe3+, thereby localizing itinerant electrons in Pc, as evidenced by charge transfers between Fe-d and CN-π orbitals. In contrast, the π-donating nature of Br ligands complements the electron deficiency of Fe3+, resulting in the delocalization of itinerant electrons in the Pc system, thus creating a highly conducting molecular system with giant negative magnetoresistance. © 2018 Oriental Scientific Publishing Company. All rights reserved