A new approach towards ferromagnetic conducting materials based on TTF-containing polynuclear complexes

Abstract

Five complexes containing binuclear cation [Cu₂(LH)₂]²⁺ (LH₂ = 1 : 2 Schiff base of 1,3-diaminobenzene and butanedione monoxime) were prepared and characterized. Metathesis of one perchlorate anion in [Cu₂(LH)₂(H₂O)₂](ClO₄)₂ (1) by anionic TTF-carboxylate (TTF–CO₂⁻) leads to the complex [Cu₂(LH)₂(CH₃OH)₂](TTF–CO₂)(ClO₄)·H₂O (2). Reactions of 1 with substituted pyridines bipy, dpe and TTF–CH = CH–py result in formation of the complexes {[Cu₂(LH)₂(bipy)](ClO₄)₂}_n·2nH₂O (3), [Cu₂(LH)₂(dpe)₂](ClO₄)₂·2CH₃OH (4) and [Cu₂(LH)₂(TTF–CH = CH–py)(H₂O)](ClO₄)₂·1.5H₂O (5), where bipy = 4,4′-bipyridine, dpe = trans-(4-pyridyl)-1,2-ethylene and TTF–CH = CH–py = 1-(2-tetrathiafulvalenyl)-2-(4-pyridyl)ethylene. Whereas complex 2 is built from discrete ionic particles (with rather long Cu–S contacts), compounds 1 and 3 contain 1D polymeric chains, in which structural units are bonded through Cu–O bonds or through bridging bipy molecule, respectively. Dinuclear complexes 4 and 5 are linked though π-stacking of dpe or TTF–CH = CH–py, respectively. All complexes are characterized by dominating ferromagnetic behavior with J values in the range from +9.92(8) cm⁻¹ to +13.4(2) cm⁻¹ for Hamiltonian H = –JS₁S₂. Magnetic properties of the compounds, containing stacks of aromatic molecules in crystal structures (4 and 5), correspond to ferromagnetic intradimer and antiferromagnetic intermolecular interactions (zJ′ = −0.158(3) and −0.290(2) cm⁻¹, respectively). It was found that TTF–CH = CH–py ligand in [Cu₂(LH)₂(TTF–CH = CH–py)(H₂O)]²⁺ could be electrochemically oxidized to cation-radical form in the solution.