Ligand-Field Effects in a Ruthenium(II) Polypyridyl Complex Probed by Femtosecond X-ray Absorption Spectroscopy

Abstract

We employ femtosecond X-ray absorption spectroscopy of [Ru­(m-bpy)3]2+ (m-bpy = 6-methyl-2,2′-bipyridine) to elucidate the time evolution of the spin and charge density upon metal-to-ligand charge-transfer (MLCT) excitation. The core-level transitions at the Ru L3-edge reveal a very short MLCT lifetime of 0.9 ps and relaxation to the lowest triplet metal-centered state (3MC) which exhibits a lifetime of about 300 ps. Time-dependent density functional theory relates ligand methylation to a lower ligand field strength that stabilizes the 3MC state. A quarter of the 3MLCT population appears to be trapped which may be attributed to intramolecular vibrational relaxation or further electron transfer to the solvent. Our results demonstrate that small changes in the ligand field allow control of the photophysical properties. Moreover, this study underscores the high information content of femtosecond L-edge spectroscopy as a probe of valence charge density and spin-state in 4d transition metals.

Uncovering the 3d and 4d Electronic Interactions in Solvated Ru Complexes with 2p3d Resonant Inelastic X-ray Scattering

“…The findings from this study present a framework for analyzing and understanding the 2p3d RIXS spectra for solvated 4d transition metal complexes, that are being actively studied with timeresolved X-ray spectroscopy at synchrotrons and X-ray free electron laser facilities. 30,32,39 Inorganic Chemistry…”

“…This suggests that calculations may need to include multireference methodology to completely describe the electronic structure of these, and similar, transition metal complexes. The findings from this study present a framework for analyzing and understanding the 2p3d RIXS spectra for solvated 4d transition metal complexes, that are being actively studied with time-resolved X-ray spectroscopy at synchrotrons and X-ray free electron laser facilities. ,, …”

Tracking C–H activation with orbital resolution

“…In this work, we demonstrate a distinct way to experimentally evaluate metal-ligand charge-transfer interactions during C-H activation by metal complexes. Using time-resolved x-ray absorption spectroscopy (XAS) at the metal L-edge (11,(25)(26)(27)(28)(29)(30), we probe the short-lived reaction intermediates from the vantage point of the reactive metal site to interrogate the decisive charge-transfer interactions that determine the overall reaction. In two ultraviolet (UV)-pump and x-ray-probe experiments at the Swiss Free Electron Laser facility (SwissFEL) and the Swiss Light Source synchrotron radiation facility (SLS), we track s-complex formation and oxidative addition using CpRh(CO) 2 (where Cp is cyclopentadienyl) (10,(18)(19)(20) in octane solution.…”

Femtosecond x-ray absorption spectroscopy of pyrazine at the nitrogen K-edge: on the validity of the Lorentzian limit

“…In the case of a fast core-hole decay, one may approximate the commutator [e i Ĥv t , μvc ] to zero in equation (18), and thus invert the order of the two operators without substantially altering the integral in equation ( 16) [39]. In practice, this approximation means that the wavepacket propagation after the probe pulse is neglected and results in the Lorentzian limit or short-time approximation,…”