Crystal Structure of Bis(4-methylimidazole)tetraphenylporphyrinatoiron(III) Chloride and Related Compounds. Correlation of Ground State with Fe−N Bond Lengths

Abstract

The crystal structure of the title compound is presented and shown to be one of a class of low-spin iron porphyrin complexes having a ground-state electronic configuration of (dxy)2(dxz)2(dyz)1. If their Fe-N bond lengths (average N-porphyrin plotted against average N-axial) are considered, this class of low-spin iron(III) porphyrins of general formula [Fe(III)Por(L)2]+X- and of 2B ground state is shown to be distinctly different crystallographically from a similar class of compounds with the same general formula but with a 2E or a (dxy)2(dxz,dyz)3 ground state. A third group of compounds with the same general formula have a (dxz,dyz)4(d)1 ground state and again are in a different region of the plot. Compounds showing intermediate properties can be forecast from the simple relationship presented in this work. The electron paramagenetic resonance data are shown to be dependent on the ground state, and those of configuration (dxy)2(dxz,dyz)3 and the 2B ground state obey a correlation previously suggested in the literature.

Studies on the binding of nitrogenous bases to protoporphyrin IX iron(II) in aqueous solution at high pH values

“…Although in this work we have only studied binding to the Fe(II) oxidation state we have previously shown that in frozen solution the orientation of imidazole groups bound in [Fe(III)(PPIX)L 2 ] + is pH dependent indicating that hydrogen bonding from solvent water can influence the affinity of the imidazole to the Fe(III) atom [ 39 , 40 ]. The haem iron distance of 2.2 Å [ 99 ] is longer than those for both Fe(II) as discussed above (values around 2.00(2) Å [ 82 – 84 ] and also for those of Fe(III), we found a value of 1.975(2) Å on the structure of [Fe(III)(TPP)(4-methylimidazole) 2 ]Cl [ 100 ]; however in a protein where the resolution is around 1.5 Å it is not possible to distinguish Fe(II) from Fe(III) without supporting evidence. It is likely that imidazole and indeed triazole ligated drugs could bind the P 450 haem centre when the iron is in the reduced state as well as the low-spin Fe(III) state and thus then manifest its potential as an inhibitor.…”

Mechano‐chemical Synthesis and Spectroscopic Characterization of Hemin Complexes with Some Amino Acids

“…In hematin two high-spin iron(III) ions are antiferromagnetically coupled through a oxygen bridge and its Mössbauer spectrum is a practically a symmetric doublet. [29] As expected, the Mössbauer parameters for the hemin -His complex are similar those reported for the Fe(III)PPIX -His complex obtained in an aqueous solution at pH 10.1 (d SNP = 0.52 mm/s and D = 1.99 mm/s) [30] and also to those obtained for the hemin -Imd complexes (see Table 1). The relatively large isomer shift observed for low-spin Fe 3+ in the hemin -His complex, when compared with other low-spin ferric complexes, [31] can be attributed to the p-donor character of the imidazole residue as ligand.…”

Density functional study on geometry and electronic structure of nitrile hydratase active site model

“…It is worthwhile to note that our calculated values of the FeN bond distances (1.926 Å and 1.935 Å) are close to the value of 1.954(2) Å measured in a low MW complex structure, which was synthesized recently by Noveron et al 35 as a model of NHase. Moreover, the DFT values are not far from the range of 1.944(4)–2.031(12) Å Fe(III)‐N por distances found in a series of 23 ferric porphyrins 36.…”