Ferrimagnetic Mixed-Valency and Mixed-Metal Tris(oxalato)iron(III) Compounds:  Synthesis, Structure, and Magnetism

• Published in: Inorganic chemistry 1996-02, Vol.35 (5), p.1201-1206
• Main Authors: Mathonière, Corine, Nuttall, Christopher J, Carling, Simon G, Day, Peter
• Format: Article
• Language: English
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/ic950703v

The synthesis and structural and magnetic characterization of 16 compounds AMIIFeIII(C2O4)3 (A = N(n-C3H7)4, N(n-C4H9)4, N(n-C5H11)4, P(n-C4H9)4, P(C6H5)4, N(n-C4H9)3(C6H5CH2), (C6H5)3PNP(C6H5)3, As(C6H5)4; MII = Mn, Fe) are reported. X-ray powder diffraction profiles are indexed in R3c or its subgroup P6522 or P6/mmm to derive unit cell constants. The structures of all the compounds consist of two-dimensional honeycomb networks [MIIFeIII(C2O4)3 -]∞. The MII = Fe compounds behave as ferrimagnets with T c between 33 and 48 K, but five exhibit a crossover from positive to negative magnetization near 30 K when cooled in a field of 10 mT. The compounds exhibiting this unusual magnetic behavior are those that have the highest T c. Within the set N(n-C n H2 n +1)4FeIIFeIII(C2O4)3 (n = 3−5), T c increases with interlayer separation and the low-temperature magnetization changes from positive (n = 3) to negative (n = 4, 5). In the M = MnII compounds, the in-plane cell parameter a 0 is ∼0.03 Å greater than in the corresponding M = FeII ones while the interlayer separation (c 0/6) is on average 0.08 Å smaller. All members of the MII = Mn series have magnetic susceptibilities showing broad maxima at 55 K characteristic of two-dimensional antiferromagnetism, but the magnetization of several of the salts increases sharply below 27 K due to the onset of spin canting, the magnitude of which varies significantly with A.