Variable magnetotransport properties in the TPP[Fe(Pc)L2]2 system (TPP = tetraphenylphosphonium, Pc = phthalocyaninato, L = CN, Cl, and Br)

Abstract

A series of one-dimensional conductors, TPP[Fe^III(Pc)L₂]₂ with L = CN, Cl, and Br, have been prepared. These compounds show giant negative magnetoresistance due to the interaction between conduction π-electrons and localized Fe-centered d-spins, but the magnitude is found to vary based on the axial ligand, suggesting that the strength of the π–d interactions is sensitively influenced by the axial substituent. The magnetic susceptibility also shows the difference in the magnetic interactions by the axial substituent. The ab initio calculation of the isolated molecules has revealed that the Jahn–Teller effect in this system induces splitting of d_xz and d_yz orbitals, and that the energy shift of the d-orbital accommodating an unpaired electron is varied by the axial substituent. The axial-ligand dependence of the intramolecular π–d interaction is found to correlate with the magnitude of the magnetoresistance.