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)(2)FeBr4 are investigated. The struc tures of BMT-TTFI2. FeX4 are characterized as the sheets made of dimerized donor molecules and one-dimensional anion chains. These salts show three-di mensional Curie-Weiss behavior accompanied with antiferromagnetic transitio ns, with the highest Neel temperature (T-N = 15 K) among the pi-d interacti on based magnets for the FeBr4 salt. Within a crystal of (DMET)(2)FeBr4, th e donor molecules form one-dimensional columns, between which magnetic anio n sheets are inserted. This salt is metallic down to T-MI = 200 K, above wh ich the Curie-Weiss type magnetism is described in terms of donor and anion spins, in spite of the metallic conduction of the salt. Below T-MI the mag netism is governed by anion spins, and an antiferromagnetic phase transitio n takes place at T-N = 3.5 K.