Metal-to-metal electron transfer and magnetic interactions in a mixed-valence Prussian Blue analogue

In search of a new Prussian Blue analogue exhibiting fascinating magnetic properties, potassium manganese hexacyanoferrate, K0.2Mn0.66IIMn1.44III[Fe0.2IIFe0.8III(CN)6]O0.66(CH3COO)1.32], 7.6H2O, has been synthesized. This compound undergoes a paramagnetic to ferrimagnetic transition at 10 K. Temperature and magnetic field-dependent magnetization studies of this compound have revealed different spin alignments below and above 3 K. The nature of possible magnetic interactions between the nearest neighbor magnetic centers has been discussed in order to explore the origin of the observed magnetic interactions. Mössbauer spectroscopic study at different temperatures demonstrates the presence of both FeIII and FeII in low-spin states in this compound. Quantitative analysis of the FeIII and FeII ions, and their temperature dependence exhibits the existence of an electron transfer phenomenon between Mn and Fe ions [FeIII (t2g5, S=1/2S=1/2)–CN–MnII (t2g3eg2, S=5/2S=5/2)]⇔[FeII (t2g6, S=0S=0)–CN–MnIII (t2g3eg1, S=2S=2)]. This electron transfer has been remarkably enhanced in the magnetically ordered region.