AXIAL LIGAND ORIENTATION IN IRON(II) PORPHYRINATES - PREPARATION AND CHARACTERIZATION OF LOW-SPIN BIS(IMIDAZOLE) (TETRAPHENYLPORPHYRINATO)IRON(II) COMPLEXES

The preparation of several low-spin bis(1-substituted imidazole)(tetraphenylporphyrinato)iron(II) complexes is reported (1-substituted imidazole = 1-vinylimidazole, 1-benzylimidazole, 1-methylimidazole, 1-acetylimidazole, and l-(trimethylsilyl)imidazole). These complexes have been characterized by Mössbauer and UV-vis spectroscopy. The Mössbauer isomer shifts are in the range 0.43–0.47 mm s−1 and the quadrupole splittings are in the range 0.97-1.07 mm s−1. The crystal and molecular structure of two of these complexes has been determined by single-crystal X-ray diffraction studies. The two complexes, [Fe(TPP)(l-VinIm)2] and [Fe(TPP)(l-BzlIm)2], have crystallographically imposed inversion centers that lead to parallel ligand plane orientations. Comparisons of the molecular structures of these two species with those of several analogous iron(III) derivatives reveals similar trends in the orientation of the axial imidazole ligands. However, the iron(II) derivatives do show larger axial imidazole “tilts” and “tips”. The average Fe-Np distances are 2.001 (2) Å for [Fe(TPP)(1-VinIm)2] and 1.993 (9) Å for [Fe(TPP)(1-BzlIm)2]; Fe-N(Im) bond distances are 2.004 (2) Å for [Fe(TPP)(1-VinIm)2] and 2.017 (4) Å for [Fe(TPP)(l-BzlIm)2]. Crystal data for [Fe(TPP)(l-VinIm)2]•CH2Cl2: monoclinic, FeCl2N8C55H42, a = 18.871 (4) Å, b = 11.644(3) Å, c = 22.766 (5) Å, β = 112.90 (1)°, V = 4613.2 Å3, Ζ = 4, space group C2/c, 4756 observed unique data, all measurements at 293 K. Crystal data for [Fe(TPP)(l-Bzllm)2]: triclinic, FeN8C64H48, a = 10.952 (5) Å, b = 11.402 (5) Å, c = 10.803 (9) Å, α = 104.02 (6)°, β = 105.24 (6)°, γ = 97.65 (4)°, V = 1234.6 Å3, Ζ = 1, space group P1, 3496 observed unique data, all measurements at 118 K. © 1990, American Chemical Society. All rights reserved.