Electronic structure of light-induced nitrosyl linkage isomers revealed by X-ray absorption spectroscopy at Ru L 3,2-edges

X-ray absorption spectroscopy (XAS) is a powerful tool for examining changes of the electronic and molecular structure following light-induced excitation of a molecule. Specifically, this method can be applied to investigate the ground (GS, RuNO) and metastable states (MS1, RuON and MS2, Ru eta(2)(NO)) of the nitrosyl ligand (NO), which differ in their coordination mode to the metal. In this work, we report for the first time experimental and theoretical (DFT) Ru L-3,(2)-edge XA spectra for the octahedral complex trans-[RuNOPy4F](ClO4)(2) (1, Py = pyridine) in both ground and metastable states. The transition from GS to MS1 using 420 nm light excitation leads to a significant downshift of the 2p -> LUMO(+1) peaks by about 0.5-0.8 eV, attributed to the destabilisation of 2p orbitals and stabilization of LUMO(+1). Subsequent irradiation of MS1 at 920 nm produces isomer MS2, for which even greater stabilization of LUMO occurs, though without a significant change in 2p energy. The change in 2p energy is attributed to a variation in the charge on the Ru atom after NO isomerization, while LUMO(+1) stabilization is related to changes in the Ru(NO) bond length and the composition of this orbital.