A
complex
of 57Fe
with
5-{4-[((4′-hydroxybenzo-15-crown-5)-5′-yl)diazo]phenyl}-10,15,20triphenylporphyrin was studied by Mössbauer spectroscopy. The presence of signals of two types in
the spectra (a doublet and an extended absorption band over a wide velocity range) suggests that
the Fe atoms occupy two structurally different positions in this complex. The dependences of the
doublet asymmetry on temperature and the angle between the normal to the sample plane and the
γ-ray beam were studied. The isomer shift δ of the doublet in the temperature range from 360 to 5 K
changes from 0.25 to 0.41 mm/s, while the quadrupole splitting remains virtually unchanged (Δ ≈
0.65 mm/s). The relaxation-type absorption over a wide velocity range, the relative area of which
strongly varies with temperature, can be described by a broad singlet with the following parameters:
δ = 0.30–0.44 mm/s and Γ = 2.8–3.38 mm/s. According to the δ values, both signals are due to
Fe(III) derivatives.
The structures and properties of metalloporphyrins (MPs), such as hemoglobin, chlorophyll, and
vitamin В12, involved in vital processes depend on the complexing metal and the peripheral
substituents. A great number of MPs are chemically inert and thermally stable, have high molar
absorption coefficients in the UV-Vis and near-IR ranges, and show reversible redox transitions. This
accounts for the interest in comprehensive study of the corresponding properties using a variety of
physicochemical techniques.
