Synthesis, structure and magnetic characterization of decamethylmetallocenium ethyl tricyanoethylenecarboxylate charge-transfer salts

Abstract: Ethyl tricyanoethylenecarboxylate (ETCE) is a one-electron acceptor related to tetracyanoethylene that can serve as a building block for the construction of molecule-based magnets. The reactions of ETCE with decamethylmetallocenes, (M=Cr, Mn, Fe) give three new charge-transfer salt magnets, [ETCE] 1, [ETCE] 2 and [ETCE] 3. The expected mixed pi stacking of anions and cations is obtained, with the ETCE radical anion exhibiting typical disorder over two nearly equivalent footprints. Powder diffraction supports the belief that all three compounds are isomorphous. Magnetic measurements indicate that 1 is a soft ferromagnet, ordering below a critical temperature, T c, of 3.8K. Compound 2 exhibits complex magnetic behavior consisting of two frequency-dependent peaks in the ac susceptibility, the first at about 11.2K and the second at about 7K. At 1.8K, the compound is hysteretic and exhibits a coercive field of 10kG. Compound 3 is a glassy, apparently canted, ferromagnet displaying an out-of-phase ac susceptibility signal below about 3K. [Copyright &y& Elsevier]