Study of [FeII(pyim)3]2+ complexes: dynamic spin equilibrium on encapsulation in zeolite Y Original Research Article

Tris complex of FeII2(2′-pyridyl)imidazole has been encapsulated in the supercages of zeolite Y and characterized by using powder XRD, FTIR, Mössbauer spectroscopy, variable temperature magnetization and MAS NMR techniques and results have been compared with those obtained for this complex with ClO4− and SO42− as anions. At room temperature, the [Fe(pyim)3](ClO4)2 complex exhibited low spin state, while [FeII(pyim)3]SO4 exhibited the existence of both low and high spin states. The encapsulated [FeII(pyim)3]2+ complex exhibited a broad quadrupole doublet characterized by isomer shift, δ=+0.55 mm/s and quadrupole splitting ΔEq=1.26 mm/s. The magnetization measurements carried out for the encapsulated [FeII(pyim)3]2+ complex showed a systematic decrease in its values with decreasing temperature down to 75 K with no indication of thermal hysteresis effects. These results suggest the existence of a dynamic spin state equilibrium between the high and low spin states for the encapsulated [FeII(pyim)3]2+ complex with time constant comparable to the characteristic Mössbauer time scale of 57Fe nuclei.