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...

The Role of the Lowest Excited Triplet State in Defining the Rate of Photoaquation of Hexacyanometalates

“…The LUMO, on the other hand, has strong contributions from the e g set of the 3d shell, mixed with cyanide σ orbitals. The energy levels follow the same order as seen in the isoelectronic [Fe(CN) 6 ] 4– …”

“…The second peak, slightly weaker than the first, is attributed to transitions to a set of orbitals with π character mainly centered on the ligands and with a strong contribution from the t 2g set of d orbitals in the cobalt center. As seen through the TD-DFT computation and discussed by past studies, 6,13,38 this transition intensity is proportional to the mixing of metal d orbitals and ligand π orbitals. The energy position, as also noticed in former studies on metal cyanides, 39−41 is not well reproduced at the level of TD-DFT and even higher level theories.…”

“…From our results, a rather distinct picture arose for the photoaquation dynamics in cobalt(III) hexacyanide in comparison to the isoelectronic iron(II) hexacyanide . Namely, a much longer-lived triplet state is detected in [Co(CN) 6 ] 3– with associated lower photoaquation yields for the cobalt-centered complex .…”

“…Because the only O-bearing moiety in the product is the incoming water molecule, no more peaks were observed. Since the peak lies just before the pre-edge of water, we can assign it to the creation of the relatively stable aquated [Co(CN) 5 (OH 2 )] 2– as similarly reported by Vaz da Cruz et al for [Fe(CN) 6 ] 4– . In Figure b the delay trace measured at 534.4 eV shows an analogous time-delay dependence as seen for the delay trace shown in Figure b measured at the 781.1 eV.…”

“…The energy levels follow the same order as seen in the isoelectronic [Fe(CN) 6 ] 4− . 13 The X-ray absorption spectra (XAS) at the N K-and Co L 3,2 -edges are presented in Figure 2. At the N K-edge (Figure 2a), the XAS of [Co(CN) 6 ] 3− presents a single broad peak centered at 399.5 eV with a shoulder centered at 398.6 eV.…”