π-d Interaction-Based Molecular Magnets: Role of Sulfur-to-Selenium Substitution

Abstract

The crystal structure and physical properties of the three conducting molecular magnets are discussed. (DMET)2FeBr4 is composed of alternating stacks of quasi-one-dimensional donor sheets and square lattice magnetic anion sheets. This salt undergoes an spin density wave (SDW) transition of the donor layer at 40 K and an antiferromagnetic transition of Fe3+ spins on the anion layer at 3.7 K. The one-to-one correspondence of the anomalies appearing on the magnetization curves with those on the magnetoresistance supports the presence of the π-d interaction. The all-sulfur analog (EDTDM)2FeBr4 shows, besides similar behaviors as the DMET salt, insulator-to-metal transition of the ground state by applying the pressure, accompanied with a large negative magnetoresistance. (EDS-TTF)2FeBr4 shows little π-d interaction despite the presence of close Se–Br contacts, showing the importance of the intermolecular orbital overlap between the π- and d-components.