Chloro(N-p-nitrobenzoylimido-meso-tetraphenylporphyrinato)iron(iii): a high-spin complex

Abstract

The crystal structures of diamagnetic (methanol)(N-p-nitrobenzoylimido-meso-tetraphenylporphyrinato)zinc(II) methanol solvate Zn(N-p-NCOC₆H₄NO₂-tpp)(MeOH)·MeOH [or 4(MeOH)·MeOH] and paramagnetic chloro(N-p-nitrobenzoylimido-meso-tetraphenylporphyrinato)iron(III) Fe(N-p-NCOC₆H₄NO₂-tpp)Cl (5), were determined. Both are pentacoordinate complexes where the p-nitrobenzoylimido (NNB) moiety is inserted into a zinc–pyrrole (or iron–pyrrole) bond. The coordination geometry of the zinc (or iron) center is best described as a distorted trigonal bipyramid with the N(2), N(5), and O(4) [or N(2), N(5), and Cl(1)] atoms lying in the equatorial plane. The plane of the three pyrrole nitrogen atoms [i.e., N(1), N(2) and N(3)] strongly bonded to Zn²⁺ in 4(MeOH)·MeOH (or Fe³⁺ in 5) is adopted as a reference plane, 3N. The porphyrin ring is severely distorted and the pyrrole ring N(4) is bonded to the NNB ligand making a dihedral angle of 30.0° (or 27.8°) with the 3N plane for 4(MeOH)·MeOH (or 5). Solid state magnetic susceptibility and the effective magnetic moment data were measured for 5 from 300 to 5 K. In the higher temperature range (T > 50 K), the effective magnetic moment is constant and is equal to 5.87 μ_B. This μ_eff value confirms that there is a high-spin ferric (S = 5/2) state for the iron atom in 5. The g values of 9.5 ± 0.4, 4.2 and 1.1 measured from X-band EPR spectra were also consistent with a high-spin ferric iron in 5. The magnitude of zero field splitting, D, and the rhombicity parameter, λ (= E/D), in 5 were determined approximately as 0.79 cm⁻¹ and 0.29, respectively, by EPR spectroscopy and paramagnetic susceptibility measurements.