Novel Molecular Magnets Based on Organic Complexes

The crystal structure and the physical properties of the radical ion salts BMT-TTFI2·FeX4 (X ˭ Br, Cl) and (DMET)2FeBr4 are investigated. The structures of BMT-TTFI2·FeX4 are characterized as the sheets made of dimerized donor molecules and one-dimensional anion chains. These salts show three-dimensional Curie-Weiss behavior accompanied with antiferromagnetic transitions, with the highest Neel temperature (T N= 15 K) among the π-d interaction based magnets for the FeBr4 salt. Within a crystal of (DMET)2FeBr4, the donor molecules form one-dimensional columns, between which magnetic anion sheets are inserted. This salt is metallic down to T MI = 200 K, above which the Curie-Weiss type magnetism is described in terms of donor and anion spins, in spite of the metallic condaction of the salt. Below T MI the magnetism is governed by anion spins, and an antiferromagnetic phase transition takes place at T N=3.5 K.