Metal–water covalency in the photo-aquated ferrocyanide complex as seen by multi-edge picosecond X-ray absorption

Abstract

In this work, we investigate the photo-aquation reaction of the ferrocyanide anion with multi-edge picosecond soft X-ray spectroscopy. Combining the information of the iron L-edge with nitrogen and oxygen K-edges, we carry out a complete characterization of the bonding channels in the [Fe(CN)₅(H₂O)]³⁻ photo-product. We observe clear spectral signatures of covalent bonding between water and the metal, reflecting the mixing of the Fe d_z² orbital with the 3a₁ and 4a₁ orbitals of H₂O. Additional fingerprints related to the symmetry reduction and the resulting loss in orbital degeneracy are also reported. The implications of the elucidated fingerprints in the context of future ultra-fast experiments are also discussed.