Extended d-Electron State of Fe(CN)₆Unit in Prussian Blue Analogue

Abstract

The Prussian blue analogue, AxM[Fe(CN)6]yzH2O (A and M are an alkali metal and a transition metal, respectively), is one of the candidates for a positive electrode material of a lithium-ion secondary battery. For further development of the electrode material, deeper understanding of the redox states of the constituents, i.e., M and the Fe(CN)6 unit, is indispensable. Here, we investigated the electronic state of the redox constituents of K0.34Co[Fe(CN)6]0.753.6H2O by means of the electrostatic potential method combined with the maximum entropy method combined with the Rietveld analysis (MEM/Rietveld). The electrostatic potential U(r) revealed that both the reduced and oxidixed states of Fe extend to the surrounding CN groups, which may cause the robustness of the cyano-bridged transition metal network.

Visualizing charge densities and electrostatic potentials in materials by synchrotron X-ray powder diffraction

“…These findings indicate that the transferred electrons from Mn to Fe spreads over the hexacyanoferrate ([Fe(CN) 6 ]) via the strong Fet 2g − CNπ* hybridization at the low-temperature tetragonal phase [55]. The similar phenomenon has been observed in a transition metal cyanide containing water, K 0.34 Co [Fe(CN) 6 ] 0.75 3.6H 2 O by charge density [30] and electrostatic potential analyses [56].…”

Evidence of electronic polarization of the As ion in the superconducting phase of F-doped LaFeAsO

“…1d). At low temperatures, this fascinating feature is supposedly caused by the accumulation of electrons in the Fe layer and was confirmed by the electrostatic potential analysis of the MEM results (Tanaka et al, 2006;Kim et al, 2011;Fujiwara et al, 2012). Figs.…”

Complex Magnetic Phases in Nanosized Core@Shell Prussian Blue Analogue Cubes: Rb0.48Co[Fe(CN)6]0.75[(H2O)6]0.25·0.34H2O@K0.36Ni[Cr(CN)6]0.74[(H2O)6]0.26·0.11H2O

“…For the Co–Fe component, the Fe–C bond length (1.821 Å at 80 K) of the present compound is ∼4% smaller than the reported ones (1.91–1.93 Å at 300 K), and the Co–N bond length (1.929 Å at 80 K) is ∼7% smaller (2.07–2.12 Å at 300 K). Nevertheless, much smaller FeC 6 octahedra with a Fe–C bond length of ∼1.79 Å at 90 K have also been reported . The compact CoN 6 and FeC 6 octahedra formed in the present compound resulted in a relatively larger separation (1.29 Å at 80 K) between the N and C ions, where capability in mediating charge transfer between Fe and Co ions can be limited.…”