Andre De La Torre Rangel, Universidad de Guadalajara

Abstract

Sensitivity of Shape Resonances in HERFD-XANES to Assess Structural Models of Transition Metal Complexes by
Fitting FEFF Simulations

Andrea de la Torre-Rangel†, Thomas Kroll‡, and Mario U. Delgado-Jaime†
†-CUCEI, University of Guadalajara, Blvd. Marcelino García Barragán 1421, 44430,
Guadalajara, México

‡-SLAC National Laboratory, Stanford University, 94025, Menlo Park, United States

Structural parameters in solids, single crystals and frozen solutions have been long investigated by EXAFS (Extended X-ray Absorption Fine Structure.1) While this technique offers ample of options to answer structural questions about transition metal complexes in general, their application on rapid reactions followed with the use of continuous-flow mixers2 or in heterogeneous
catalysis and electrocatalysis performed under in-situ conditions is undermined due to long-scanning periods; and to the possibility of having multiple contributions during the course of the reaction. Herein, we present a new methodology which involves the fitting of structural parameters based on geometrical models representing the environments of metallic sites contributing to the multiple scattering shape resonances of HERFD-XANES data. In this method, the fit parameters directly represent geometrical information such as bond distances and bond angles, in addition to energy shifts and scaling factors of the emerging FEFF simulations. Thus, the proportion of different sites in a given material or, for example, of intermediate species in relation to starting species and products during a course of a rapid reaction, can be established based on the scaling factors of the fit FEFF simulations corresponding to the contributing structural models. The fitting of FEFF simulations is performed using an adaptive grid algorithm, which we have extensively tested for the fitting of multiplet simulations to L-edge XAS data.3 We have initially explored the sensitivity of the method by fitting known FEFF simulations corresponding to structural motifs typically found in Fe and Cu proteins, from which the results will be presented and discussed.

References
(1) Cramer, S. P., X-ray Spetroscopy with Synchrotron Radiation: Fundamentals and Applications; Biological and Medical Physics, Biomedical Engineering; Springer Nature, Cham, Switzerland: 2020.
(2) Huyke, D. A.; Ramachandran, A.; Ramirez-Neri, O.; Guerrero-Cruz, J. A.; Gee, L. B.; Braun, A.; Sokaras, D.; Garcia-Estrada, B.; Solomon, E. I.; Hedman, B.; Delgado-Jaime, M. U.; DePonte, D. P.; Kroll, T.; Santiago, J. G. Millisecond timescale reactions observed
via X-ray spectroscopy in a 3D microfabricated fused silica mixer. Corrigendum. Journal
of Synchrotron Radiation 2022, 29, 930.
(3) Herrera-Yañez, M. G.; Guerrero-Cruz, J. A.; Ghiasi, M.; Elnaggar, H.; de la Torre-Rangel, A.; Bernal-Guzmán, L. A.; Flores-Moreno, R.; de Groot, F. M. F.; Delgado-Jaime, M. U. Fitting Multiplet Simulations to L-edge XAS Spectra of Transition Metal Complexes Using
an Adaptive Grid Algorithm. Inorganic Chemistry Accepted, 2023.