Effect of sterically inhibited axial azaferrocene ligands on the physical properties of iron(III) porphyrins. Crystal structures of bis(azaferrocene) complexes of iron(III) and cobalt(III) porphyrinates

Abstract

The crystal structures of [Fe(oep)L 2 ][O 3 SCF 3 ] and [Co(oep)L 2 ][ClO 4 ] [H 2 oep = 2,3,7,8,12,13,17,18octaethylporphyrin, L = [Fe(C 5 H 5 )(C 4 H 4 N)] have been determined. The azaferrocene ligands L in both compounds are seen to be parallel. The axial M᎐N (azaferrocene) bonds are longer than those found in analogous imidazole and pyridine complexes. Rhombic EPR spectra for bis(azaferrocene) complexes of iron() porphyrins are postulated to be a result of steric interactions of the azaferrocene H 2,5 atoms splitting the degeneracy of the d xz and d yz orbitals. The Mössbauer spectra of these iron complexes were recorded and interpreted as evidence for σ bonding of the azaferrocene nitrogen atom to the porphyrin iron core with little or no π back bonding from the porphyrinic iron to the N atom. This is in agreement with the long bond lengths found in the structures. The rhombic EPR spectra observed are in keeping with a parallel arrangement of the ligand planes, as are the magnitudes of the Mössbauer quadrupole splittings. It is shown that the large g z values of the complexes are not unusual and must relate to long axial bonds and to steric effects splitting the d xz and d yz orbitals.

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

“…The plot of average Fe−N por distance (average of all four Fe−N porphyrin distances) against Fe−N ax distance (Figure ) is instructive. The compounds on the plot can be divided into four groups except for compound 21 (which is discussed below). Compounds 1 − 13 and 22 5-7,9,11,13,14,16,19 have all been shown to have a (d xy ) 2 (d xz , d yz ) 3 ground state, which is an orbital singlet ( 2 B), and the unpaired electron is localized in the d yz orbital. , Of these compounds, 1 − 13 are within the same area (presented with an arbitrary oval line) of the plot.…”

Intramolecular Quenching of Porphyrin Fluorescence by a Covalently Linked Ferrocene in DNA Scaffolding

“…The ferrocenyl porphyrins in this study are the first designed to be water-soluble. However, a number of groups have synthesized covalently linked porphyrin−ferrocene species, − including more elaborate triads , and systems designed to undergo molecular self-assembly. − Substituted ferrocenes have also been used as axial ligands to the metal center in metalloporphyrins. , …”

“…However, a number of groups have synthesized covalently linked porphyrin-ferrocene species, [57][58][59][60][61][62][63] including more elaborate triads 64,65 and systems designed to undergo molecular self-assembly. [66][67][68] Substituted ferrocenes have also been used as axial ligands to the metal center in metalloporphyrins. 69,70 Absorption Spectra and Salt-Induced Stacking Interactions.…”

Electronic structures of methylated azaferrocenes and their borane adducts: Photoelectron spectroscopy and electronic structure calculations

“…Earlier work in this area studied [bis (azaferrocene)iron(III)porphyrin] complexes and azaferrocene-M (CO) 5 complexes (M = Cr, Mo, W) using 57 Fe Mössbauer spectroscopy and other techniques. 15,16 Questions of interest are: How does the π-coordination of a heterocycle (e.g., pyrrolyl) to a metal affect the nitrogen lone pair properties as compared to related non-coordinated heterocycles such as pyridine? Also, how does coordination of the lone pair to a Lewis acid affect the metal-ligand binding?…”