Investigation Of Iron(III) Complex With Crown-Porphyrin. Pankratov D.A., Dolzhenko V.D., Kiselev Y.M., Stukan R.A., Al Ansari Y.F., Savinkina E.V. //Hyperfine Interactions. 2013. V.222. Is.1 (Suppl). P. S1-S11
Iron complex of 5-(4-(((4′-hydroxy-benzo-15-crown-5)-5′-yl)diazo)phenyl)-10,15,20-triphenylporphyrin was investigated by 57Fe Mössbauer spectroscopy and EPR. Two Fe sites were identified; they give two differing signals, doublet and wide absorption in a large velocity interval. EPR spectra of solutions of the complex in chloroform at room temperature also show two signals with g = 2.064, AFe = 0.032 cm− 1; g = 2.015, AFe = 0.0034 cm− 1. The doublet asymmetry is studied vs. temperature and normal angle to the sample plane and gamma-beam. The isomer shift δ in the doublet varies from 0.41 to 0.25 mm/s in the 5÷360 K temperature range, whereas quadruple splitting value is constant, Δ ∼ 0.65 mm/s. The relax absorption may be described as a wide singlet (δ = 0.30 ÷ 0.44 mm/s and Γ = 2.83 ÷ 3.38 mm/s); its relative area strongly depends on temperature. According to δ, both signals are assigned to Fe(III).
Structures and properties of metal porhyrins (MPs) (hemoglobin, chlorophyll, vitamin B12, etc.) participating in vital processes depend on a central metal and peripheral substituents. Most MPs possess chemical and thermal stability, high extinctions coefficients in UV, visible and near IR ranges and reversible red-ox transitions. Therefore, detail study of their properties with the use of various physicochemical methods is of interest.
Varying peripheral substituents and central metal give unusual stable supramolecular assembles with channels for electronic and ionic conductivity which are sensitive to weak effects. This is a new way for creating new materials, e.g. luminescent, which can be used in modern equipments.
An actual direction of the MP chemistry is introduction of additional fragments, e.g. crown ethers (which can assume various metal atoms), into porphyrin molecules. It increases possibilities of formation of supramolecular metal-complex systems with specified properties. Stabilization of peroxo- and superoxo-derivatives in an iron complex of a crown-porphyrin was shown by Mössbauer spectroscopy.
This work considers properties of the iron complex with a benzo-15-crown-5-substituted meso-tetraphenylporphyrin.
According to the Mössbauer and EPR spectroscopy, the amorphous 57Fe complex of 5-(4-(((4’-hydroxy-benzo-15-crown-5)-5’-yl)diazo)phenyl)-10,15,20-triphenylporphyrin contains iron atoms in two sites, porphyrin and crown-ether rings. In the Mössbauer spectra, iron atoms in hard porphyrin surrounding show the asymmetric doublet line with the parameters corresponding to the high-spin Fe(III).
The iron(III) atoms in the large crown-ether ring show the wide absorption band of relaxation origin.
The Mössbauer spectra of 1 show unusual features, such as absence of temperature dependence for doublet asymmetry and extremely low temperature of locking relaxation effects. These features of the Mössbauer spectra were not found yet.
According to the EPR data, iron atoms are also distributed between porphyrin and crown-ether fragments of the ligand, since HFS for the metal–nitrogen and metal–oxygen bonds must differ strongly as observed in the corresponding EPR spectrum.
Therefore, the structure of the complex may be described by the formula shown in Fig.