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

Iron phthalocyanine (FePc) has been studied using Fe-57 Mossbauer spectroscopy, to obtain information which helps in understanding the gas-sensing properties of phthalocyanines. The isomer shift values of the alpha and beta phases (0.46 and 0.49 with respect to alpha-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 (theta(D)) and recoil fractions at room temperature (f(300)) for the alpha and beta phases, respectively: theta(D) = 143 and f(300) = 0.14; theta(D) = 199 and f(300) = 0.36. This indicates a more rigid structure for the beta-phase, consistent with the presence of the two additional nitrogen interactions, absent in the alpha-phase, giving an octahedral structure.