Variable-temperature ⁵⁷Fe Mössbauer studies of the α and β phases of iron phthalocyanine

Abstract

Iron phthalocyanine (FePc) has been studied using Fe-57 Mössbauer spectroscopy, to obtain information which helps in understanding the gas-sensing properties of phthalocyanines. The isomer shift values of the α and β phases (0.46 and 0.49 with respect to α-Fe) occur between high-spin and low-spin iron(II) ion. The quadrupole values (2.50 and 2.62) are characteristic of high-spin iron(II). The variable-temperature studies have determined different Debye temperatures (θ_D) and recoil fractions at room temperature (f₃₀₀) for the α and β phases, respectively: θ_D = 143 and f₃₀₀ = 0.14; θ_D = 199 and f₃₀₀ = 0.36. This indicates a more rigid structure for the β-phase, consistent with the presence of the two additional nitrogen interactions, absent in the α-phase, giving an octahedral structure.