An iron(II) complex of 2,6-di(pyrazol-1-yl)pyrazine that crystallises in three forms, two of which exhibit an unusual angular Jahn–Teller distortion

Treatment of hydrated FeCl2 with 2 equiv. of 2,6-di(pyrazol-1-yl)pyrazine (L1H) and AgSbF6 in refluxing MeNO2 yields [Fe(L1H)2][SbF6]2 (1[SbF6]2). This compound is fully high-spin as a powder between 5 and 300 K, and exhibits a small zero-field splitting consistent with it adopting an unusual angularly distorted six-coordinate coordination geometry. Slow diffusion of Et2O into a MeNO2 solution of the compound gives varying proportions of three different crystal forms. Solvent-free 1[SbF6]2 and solvated 1[SbF6]2 · 2CH3NO2 are both high-spin at 150 K, and have undergone the proposed angular Jahn–Teller distortion to differing extents. This is the first time that this structural distortion has been observed in an iron(II) complex of a 2,6-di(pyrazol-1-yl)pyrazine derivative. In contrast 1[SbF6]2 · 3CH3NO2 is low-spin at room temperature and has a regular six-coordinate geometry.

Slow diffusion of Et2O vapour into a solution of bis[2,6-di(pyrazol-1-yl)pyrazine]iron(II) dihexafluoroantimonate 1[SbF6]2 in CH3NO2 yielded three different single crystalline phases. Solvent-free 1[SbF6]2 and solvated 1[SbF6]2 · 2CH3NO2 are both high-spin, and have undergone an unusual angular Jahn–Teller distortion to different extents. In contrast 1[SbF6]2 · 3CH3NO2 is low-spin at room temperature and has a regular six-coordinate geometry.Figure optionsDownload as PowerPoint slide