Study of spin crossover phenomenon in dimethylsulfoxide solutions of an iron(ii) perrhenate complex with 2,6-<i>bis</i>(benzimidazol-2-yl)piridine

By methods of static magnetic susceptibility, conductometry and spectrophotometry measurements in UV and visible spectra ranges, there were studied physicochemical properties of solutions of perrhenate iron(II) complexes with 2,6-bis(benzimidazol-2-yl)pyridine (L) of composition [FeL2](ReO4)2 ⋅ 1.5H2O (1) in dimethylsulfoxide (DMSO). As it was established previously, 1 provides a sharp high-temperature spincrossover (SCO) 1А1 ↔ 5Т2. The study of the temperature dependence of meff(Т) of complex 1 in DMSO showed that the SCO also reveals itself in solution. According to the electrical conductivity of solutions in DMSO at 298 K, the complex 1 in the studied concentration range 3.6 × 10–6 — 9.12 × 10–4 M is almost completely dissociated. An absorption peak was found in the UV region of the spectrum, which is practically independent on temperature. In the visible region, two combined absorption peaks are observed at 520–560 nm, which are responsible for the complex formation of FeL2+ and FeL22+ and vary with temperature and L concentration.