Experimental Evidence for Jahn-Teller Transition in a Fe(II)Fe(III) Bimetallic Oxalate

Bimetallic oxalate ${[N-(n-C_4H_9)_4][FeFe(C_2O_4)_3]}_{n}$ has been investigated by the Mössbauer spectroscopy. The Mössbauer studies confirm that high-spin Fe(III) (S=5/2) and Fe(II) (S=2) ions are present in the compound. These spectra above 60 K consist of three quadrupole doublets, indicating that there are three different Fe sites in the material. The Mössbauer results reveal that spontaneous magnetization of Fe(II) sublattices increases more steeply than that of Fe(III) sublattices as the temperature decreases from $T_{C}$. Great increase of quadrupole splitting at 50 K provides compelling evidence for the predicted Jahn-Teller transition.