Li₁₁Nd₁₈Fe₄O_39-δ Revisited

The structure proposed for Li ₁₁ Nd ₁₈ Fe ₄ O _39-δ (Chen et al. Inorg. Chem. 2012, 51, 8073) on the basis of diffraction and Mössbauer spectral data is compared to that determined previously for Nd ₁₈ Li ₈ Fe ₅ O ₃₉ (Dutton et al. Inorg. Chem.200847, 11212) using the same techniques. The Mössbauer spectrum reported by Chen et al. has been reinterpreted. The newly refined spectral parameters differ significantly from the published values but are similar to those reported for Nd ₁₈ Li ₈ Fe ₅ O ₃₉ . The relative areas of the three components indicate that iron cations occupy the 2a, 8e, and 16i sites in space group Pm3Ì...n, in disagreement with the model determined from neutron diffraction by Chen et al. in which only the 2a and 8e sites are so occupied. The relationship between Li ₁₁ Nd ₁₈ Fe ₄ O _39-δ and Nd ₁₈ Li ₈ Fe ₅ O ₃₉ is discussed, and it is proposed that the sample prepared by Dutton et al. is a kinetic product whereas the sample prepared by Chen et al. is the thermodynamically preferred product.