Strategy to Probe the Local Atomic Structure of Luminescent Rare Earth Complexes by X-ray Absorption Near-Edge Spectroscopy Simulation Using a Machine Learning-Based PyFitIt Approach

Latif U Khan; Zahid U Khan; Lucca Blois; Lubna Tabassam; Hermi F Brito; Santiago J A Figueroa

doi:10.1021/acs.inorgchem.2c03850

Strategy to Probe the Local Atomic Structure of Luminescent Rare Earth Complexes by X-ray Absorption Near-Edge Spectroscopy Simulation Using a Machine Learning-Based PyFitIt Approach

Inorg Chem. 2023 Feb 13;62(6):2738-2750. doi: 10.1021/acs.inorgchem.2c03850. Epub 2023 Jan 30.

Authors

Latif U Khan^{1

2}, Zahid U Khan^{2

3}, Lucca Blois², Lubna Tabassam⁴, Hermi F Brito², Santiago J A Figueroa⁵

Affiliations

¹ Synchrotron-light for Experimental Science and Applications in the Middle East (SESAME), P.O. Box 7, Allan19252, Jordan.
² Department of Fundamental Chemistry, Institute of Chemistry, University of São Paulo (USP), 05508-000São Paulo, SP, Brazil.
³ Department of Biochemistry, Institute of Chemistry, University of São Paulo (USP), 05508-000São Paulo, SP, Brazil.
⁴ Optoelectronic Research Lab, COMSATS University Islamabad, Park Road Chak Shahzad, Islamabad45550, Pakistan.
⁵ Brazilian Synchrotron Light Laboratory (LNLS), Brazilian Center for Research in Energy and Materials (CNPEM), 13083-970Campinas, São Paulo, Brazil.

PMID: 36714953
DOI: 10.1021/acs.inorgchem.2c03850

Abstract

Rare earth(III) β-diketonates are highly remarkable luminophores in the visible spectral region among the rare earth compounds, owing to the efficient contribution from the 4f-4f intraconfigurational transitions. To get detailed structural insight into the RE³⁺ sites (RE = Eu, Gd, and Sm), X-ray absorption near-edge spectroscopy (XANES) can be very potent in probing the local chemical environment around the RE³⁺ ion. In this work, a PyFitIt machine learning approach was employed as a new strategy to simulate the Eu, Gd, and Sm L₃-edge XANES and thereby determine the local atomic structure of the luminescence RE³⁺ β-diketonate complexes, [Eu(tta)₃(H₂O)₂], [C₄mim][Eu(dbm)₄], [Gd(tta)₃(H₂O)₂], and [Sm(dbm)₃(phen)] (tta, 3-thenoyltrifluoroacetonate; dbm, dibenzoylmethane; phen, phenanthroline; and C₄mim, 1-butyl-3-methylimidazolium bromide). Continuous Cauchy wavelet transform validated the PyFitIt calculated XANES by visualizing very efficiently the coordination geometries, composed of O and O/N backscatterers around the RE³⁺ (RE = Eu and Gd) and Sm³⁺ ions, respectively, as a pinkish-red color map in the two-dimensional images of the corresponding complexes. Extended X-ray absorption fine structure fit in Artemis also corroborated the three-dimensional structures generated by PyFitIt XANES simulation for all the compounds. Though, relatively slightly higher bond distance values for the Sm³⁺ complex are due to the higher atomic radius of the Sm³⁺ ion when compared to the Eu³⁺ and Gd³⁺ complexes. Meanwhile, higher Debye-Waller factor (σ²) values for the [C₄mim][Eu(dbm)₄] when compared to the [Eu(tta)₃(H₂O)₂] indicated the structure disorder, owing to the distortion in the local geometry. It is noteworthy that the optical properties, described mainly by the Ω_λ (λ = 2 and 4) 4f-4f intensity parameters, are very sensitive to the local coordination environment around the Eu³⁺ ion. Thus, a close agreement between the experimental and theoretically calculated Ω_λ parameter values confirmed that the PyFitIt calculated square antiprismatic structures are precisely similar to the real structures of the Eu³⁺ complexes.