Spin propensity in resonant photoemission of transition metal complexes

Resonant photoelectron spectroscopy (RPES) has been used to probe electronic structure properties of the closed-shell ${[{\mathrm{Fe}}^{\mathrm{II}}{(\mathrm{CN})}_{6}]}^{4\ensuremath{-}}$ and open-shell ${[{\mathrm{Fe}}^{\mathrm{III}}{(\mathrm{CN})}_{6}]}^{3\ensuremath{-}}$ prototype transition metal complexes in aqueous solution. Site-selective Fe $2p$ ($L$-edge) RPES maps provide new insight into spin-coupling processes at the core-excited metal centers, with autoionization of ${[{\mathrm{Fe}}^{\mathrm{III}}{(\mathrm{CN})}_{6}]}^{3\ensuremath{-}}$ showing a dramatic ($\ensuremath{\sim}4\ifmmode\times\else\texttimes\fi{}$) singlet versus triplet final-state enhancement. This shows that RPES provides unique opportunities to study spin-dependent electronic properties in transition metal based functional materials.