Temperature dependence of the mِssbauer parameters in the iron(II) ethyl phosphonate Fe(II)(PO3C2H5)·H2O

57Fe Mössbauer measurements have been performed on the lamellar iron (II) ethylphosphonate Fe(II)(C2H5PO3)·H2O. Mössbauer parameters have been studied as a function of temperature in the paramagnetic state (above 28 K). In the temperature range 150–200 K this compound has been found to undergo a phase transition resulting in a discontinuity in the quadrupole splitting ΔE. This unusual behavior was ascribed to a structural change and not to a transition from an ordered to a quasi-liquid state of the water molecule and/or CH2CH3 moieties. Results of a preliminary infrared study supports this hypothesis.