Magnetic molecular semiconductors and superconductors: BEDT-TTF tris-oxalato-metallate(III) salts

Making new compounds that combine different physical properties in the same crystal lattice is a significant goal for chemists working on synthetic metals. As part of our ongoing programme to synthesise molecular conductors containing embedded magnetic moments we have investigated charge transfer salts of BEDT-TTF with tris-oxalatometallate (III) ions M(C2O4)33− (M = Cr, Fe). The series (BEDT-TTF) ×[AM(C2O4)3]y(C6H5CN)z is especially rich and interesting since it contains semiconductors (A = K, NH4; M = Cr, Fe) and the first molecular superconductor containing paramagnetic ions (A = H2O; M = Fe; x = 4, y = z = 1). The steric and charge factors determining the geometry of cation and anion layers in these compounds are surveyed, as well as the relation between the crystal structures and physical properties.