title: Bonding and charge transfer in nitrogen-donor uranyl complexes: insights from NEXAFS spectra.
abstract: We investigate the electronic structure of three newly synthesized nitrogen-donor uranyl complexes [(UO2)(H2bbp)Cl2], [(UO)2(Hbbp)(Py)Cl], and [(UO2)(bbp)(Py)2] using a combination of near-edge X-ray absorption fine structure (NEXAFS) spectroscopy experiments and simulations. The complexes studied feature derivatives of the tunable tridentate N-donor ligand 2,6-bis(2-benzimidazyl)pyridine (bbp) and exhibit discrete chemical differences in uranyl coordination. The sensitivity of the N K-edge X-ray absorption spectrum to local bonding and charge transfer is exploited to systematically investigate the evolution of structural as well as electronic properties across the three complexes. A thorough interpretation of the measured experimental spectra is achieved via ab initio NEXAFS simulations based on the eXcited electron and Core-Hole (XCH) approach and enables the assignment of spectral features to electronic transitions on specific absorbing sites. We find that ligand-uranyl bonding leads to a signature blue shift in the N K-edge absorption onset, resulting from charge displacement toward the uranyl, while changes in the equatorial coordination shell of the uranyl lead to more subtle modulations in the spectral features. Theoretical simulations show that the flexible local chemistry at the nonbinding imidazole-N sites of the bbp ligand is also reflected in the NEXAFS spectra and highlights potential synthesis strategies to improve selectivity. In particular, we find that interactions of the bbp ligand with solvent molecules can lead to changes in ligand-uranyl binding geometry while also modulating the K-edge absorption. Our results suggest that NEXAFS spectroscopy combined with first-principles interpretation can offer insights into the coordination chemistry of analogous functionalized conjugated ligands.
authors.affiliation: The Molecular Foundry, ‡Chemical Sciences Division, The Glenn T. Seaborg Center, ∥Computational Research Division, and ⊥Advanced Light Source, Lawrence Berkeley National Laboratory , Berekeley, California 94720, United States.
authors.forename: C D
authors.initials: CD
authors.lastname: Pemmaraju
authors.forename: Roy
authors.initials: R
authors.lastname: Copping
authors.forename: Shuao
authors.initials: S
authors.lastname: Wang
authors.forename: Markus
authors.initials: M
authors.lastname: Janousch
authors.forename: Simon J
authors.initials: SJ
authors.lastname: Teat
authors.forename: Tolek
authors.initials: T
authors.lastname: Tyliszcak
authors.forename: Andrew
authors.initials: A
authors.lastname: Canning
authors.forename: David K
authors.initials: DK
authors.lastname: Shuh
authors.forename: David
authors.initials: D
authors.lastname: Prendergast
mesh_terms: D015394:Molecular Structure; D009584:Nitrogen / Q000737:chemistry*; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D011789:Quantum Theory; D014501:Uranium / Q000737:chemistry*; D056928:X-Ray Absorption Spectroscopy
chemical_list: D009942:Organometallic Compounds; D014501:Uranium; D009584:Nitrogen