A paramagnetic metal complex, [Cu(TTF-Salphen)], in which a tetrathiafulvalene (TTF) moiety is conjugated with a Salphen coordination site, was synthesized as a potential candidate for a new π-d system. Its radical salt, [Cu(TTF-Salphen)]₂PF₆, exhibits high electrical conductivity with semiconducting behavior, attributed to its columnar stacking structure. Weak antiferromagnetic interactions are observed between itinerant π-electrons and localized d-spins via π-d interactions.

Abstract

A paramagnetic metal complex, [Cu^II(TTF-Salphen)], in which a TTF (tetrathiafulvalene) ligand is coordinated through a Salphen coordination site, was synthesized as a potential candidate for a new π-d system. Electrochemical oxidation afforded its cation radical salt, [Cu^II(TTF-Salphen)]₂PF₆, as black, block-shaped crystals. X-ray crystallographic analysis revealed that both the neutral and cationic complexes possess planar structures and stack in a head-to-tail manner to form dimers. The 2:1 stoichiometry of the TTF-complex to the anion in [Cu^II(TTF-Salphen)]₂PF₆ indicates a partial oxidation state of +0.5 for the TTF moiety. Electrical conductivity measurements of [Cu^II(TTF-Salphen)]₂PF₆ revealed semiconducting behavior, reflecting its one-dimensional columnar structure, yielded a room-temperature conductivity of σ_RT = 1.8 S·cm⁻¹ and an activation energy of E _a = 0.14 eV. [Cu^II(TTF-Salphen)]₂PF₆ exhibits weak antiferromagnetic interactions between the π-spins of the TTF moieties and the d-spins of Cu(II) centers upon cooling, followed by the formation of singlet states by the π-spins in the TTF moieties below 20 K. Electron spin resonance (ESR) measurements on the powder sample of [Cu^II(TTF-Salphen)]₂PF₆ support the magnetic behavior observed in the magnetic susceptibility measurements.