Synthesis, structure and properties of [Hpy]2[{M(mnt)2}2](M = Co or Fe, Hpy = pyridinium, mnt = maleonitriledithiolate)

Abstract

The compounds [Hpy]₂[{M(mnt)₂}₂][M = Fe or Co, Hpy = pyridinium, mnt = maleonitriledithiolate (2,3-disulfanylmaleonitrile)] have been prepared by electrocrystallization and characterized by single-crystal X-ray diffraction, magnetic susceptibility measurements and IR and ⁵⁷Fe Mössbauer spectroscopies. The compounds are isostructural, monoclinic, space group P2₁/n with Z= 2. They both consist in alternate packing of [{M(mnt)₂}₂]^2– units, with the metal in a square-pyramidal environment co-ordinated by sulfur atoms, and pyridinium cations bridged by three-centred hydrogen bonds to the mnt ligands. Iron-57 Mössbauer spectroscopy confirmed the presence of five-co-ordinate Fe^III atoms. Magnetic susceptibility measurements on the cobalt compound showed a small (≈ 1.5 × 10^–4 emu mol^–1 at room temperature) paramagnetism, almost temperature independent below 150 K (≈ 0.7 × 10^–4 emu mol ^–1), while the iron analogue had a strong paramagnetic contribution of antiferromagnetically coupled pairs of S= 3/2; in the [{Fe(mnt)₂}₂]^2– units, with –2J/k_B= 515 K. These properties are correlated to the crystal structure and compared with other [{M(mnt)₂}₂]^2– compounds with M = Fe or Co.