Effect of organic cation A on the crystal structure and magnetisation of the layer molecular ferrimagnets AFe(II)Fe(III)(C2O4)(3)

We survey the crystal and magnetic structures and bulk magnetisation for re presentative examples of the series of ferrimagnetic tris-oxalato-ferrate(I I,III) salts with general formula AFe(II)Fe(III)(C2O4)(3) (A = quaternary a mmonium, phosphonium). The compounds all crystallise in two-dimensional hex agonal honeycomb lattices but while some show positive magnetisation at low temperature (Neel type Q) others show a large negative magnetisation below a compensation temperature T-comp (Neel type N). In compounds that exhibit negative magnetisation a discontinuity in the magnetisation is observed at T-t (T-comp < T-t < T-c) indicative of a magneto-strictive transition. In compounds that exhibit positive magnetisation, hysteresis and frequency dep endent AC susceptibility indicate a glassy magnetic order at low temperatur es, possibly arising from the frustration of random anisotropy domains belo w a blocking temperature, or imbalance and disorder of Fe(II) and Fe(III).