New Type of Neutral Binuclear Spin‐Crossover Complex of Iron(III) with Twist of Two Disulfide Bridges as a Product of Electrochemical Oxidation of [Fe^III(5Cl‐thsa)₂]⁻ Anions

Abstract

As a result of the electrochemical oxidation process, the [FeIII(5Cl‐thsa)2]− spin‐crossover (SCO) anion with N2S2O2 coordination sphere transforms into N4O2‐coordinated FeIII SCO neutral binuclear complex 2 with twist of two disulfide bridges. Each dimeric complex is a binuclear double‐stranded helicate with similar chirality of both Fe centers. The crystal structure of the complex 2 ⋅ 3H2O at 100 K has a monoclinic C2/c space group and contains large cavities (about 21.5 % of the unit cell volume) half‐filled by 3 water molecules per one dimer. The N4O2 coordination of iron(III) with two oxygen atoms (−O−) of phenoxy groups, two imine‐type (−Nim=) nitrogen atoms of azomethine groups, one amidrazone‐type (=NamidH) nitrogen atom and one ionized terminal group (−NionizH) of nitrogen has not been observed in CCDC so far. The oxidation state of the iron atoms in the dimeric complex was confirmed by 57Fe Mössbauer spectroscopy on 90 % enriched 57Fe sample. Mössbauer spectra and dc magnetic measurements demonstrated the partial HS‐HS→LS‐LS SCO in the 185–225 K temperature range. The details of the structure of complex 2 and the features of its magnetic properties were refined by theoretical analysis based on DFT calculations. The B3LYP* functional correctly predicting the energy of the spin‐crossover process was revealed.