| Abstract
| - A new tripod N3 ligand (L), containing three imidazole rings, was synthesized in good yield. At variance with usualaromatic ligands with N2 or N3 donor sets such as pyridine or pyrazole derivatives, L stabilizes the FeIII oxidationstate. The corresponding iron(III) complexes [Fe(L)Cl3] (1) and [Fe(L)2](ClO4)3 (2) were prepared and characterizedby X-ray structural analysis and spectroscopic methods. The coordination environment around all the FeIII centershas a distorted octahedral geometry. [Fe(L)Cl3] (1) belongs to the monoclinic system, space group P21/n, a =9.7406(5) Å, b = 17.207(2) Å, c = 14.615(2) Å, β = 104.448(9)°, Z = 4, V = 2372.1(4) Å3; R = 0.044, Rw =0.055. [Fe(L)2](ClO4)3 (2) belongs to the monoclinic system, space group P21/c, a = 16.1057(15) Å, b = 11.1079(12) Å, c = 26.283(2) Å, β = 102.062(10)°, Z = 4, V = 4598.2(8) Å3; R = 0.0465, Rw = 0.0902. The Fe−N(iPrIm) bond lengths are systematically longer than the Fe−N(MeIm) ones. Compound 2 is a highly anisotropiclow-spin FeIII complex displaying a rather unusual EPR spectrum with a sharp signal at g = 3.5 and a broad oneat g ∼ 1.6. The fitting of this EPR spectrum is discussed.
- The stability of [FeL2]3+ is tentatively assigned to the stronger σ-donor character of the three imidazolyl nitrogen donors of this novel tripod ligand compared to usual aromatic N ligands such as pyridine or pyrazole derivatives.
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