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

Abstract

Treatment of hydrated FeCl 2 with 2 equiv. of 2,6-di(pyrazol-1-yl)pyrazine (L 1H) and AgSbF 6 in refluxing MeNO 2 yields [Fe(L 1H) 2][SbF 6] 2 ( 1[ SbF 6 ] 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 Et 2O into a MeNO 2 solution of the compound gives varying proportions of three different crystal forms. Solvent-free 1[ SbF 6 ] 2 and solvated 1[ SbF 6 ] 2 · 2CH 3NO 2 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[ SbF 6 ] 2 · 3CH 3NO 2 is low-spin at room temperature and has a regular six-coordinate geometry.