Soft x-ray absorption spectroscopy study of Prussian blue analogue ACo[Fe(CN)6]H2O nano-particles (A=Na, K)

The electronic structures of Prussian blue analogue ACo[Fe(CN)6]H2O (A=Na, K) nano-size particles has been investigated by employing soft X-ray absorption spectroscopy (XAS) at the Fe and Co L edges. Both Fe and Co ions are found to be Fe2+-Fe3+ and Co2+-Co3+ mixed-valent, with the average valence of v(Fe)∼ 2.36 and v(Co)∼ 2.41. This finding suggests that the mechanism of the photo-induced spin transition in ACo[Fe(CN)6]H2O (A=Na, K) is not a simple spin-state transition of Fe2+-Co3+ → Fe3+-Co2+. The Fe ions in ACo[Fe(CN)6]H2O are also found to have a strong covalent bonding to (CN)− ligands, but a very weak bonding to O(H2O), while Co ions have a stronger bonding to O(H2O) than to (CN)− ligands.