Effect of penetrating groups of cations on magnetic properties in layered mixed-valence iron(II,III) compounds

Abstract A mixed-valence iron(II,III) coordination polymer bridged by 1,2-dithiooxalato (dto) has a 2D honeycomb layer and an alternating staking structure of the layer and a counter cation. Compound (nPrPh3P)[FeIIFeIII(dto)3] (2-nPr) has an eclipsed-stacking form and exhibits a ferromagnetic ordering at 11.2 K. To investigate the relationship between the interlayer distances and the ordering temperatures, we prepared two novel compounds: (AkPh3P)[FeIIFeIII(dto)3] (Ak = ethyl, 2-Et and methyl, 2-Me). The ferromagnetic ordering temperatures were found to increase with decreasing interlayer distance. Interestingly, 2-Me exhibited a charge-transfer phase transition that has not previously been seen in the eclipsed series.