title: Photoemission spectra and density functional theory calculations of 3d transition metal-aqua complexes (Ti-Cu) in aqueous solution.
abstract: Photoelectron spectroscopy measurements and density functional calculations are combined to determine the lowest electron binding energies of first-row transition-metal aqua ions, titanium through copper, with 3d(1) through 3d(9) electronic configurations, in their most common oxidation states. Vertical ionization energies are found to oscillate considerably between 6.76 and 9.65 eV for the dications and between 7.05 and 10.28 eV for the respective trivalent cations. The metal cations are modeled as [M(H2O)n](q+) clusters (q = 2, 3, and 4; n = 6 and 18) surrounded by continuum solvent. The performance of 10 exchange-correlation functionals, two GGAs, three MGGAs, two HGGAs and three HMGGAs, combined with the MDF10(ECP)/6-31+G(d,p) basis set is assessed for 11 M-O bond distances, 10 vertical ionization energies, 6 adiabatic ionization energies, and the associated reorganization free energies. We find that for divalent cations the HGGA and HMGGA functionals in combination with the 18 water model show the best agreement with experimental vertical ionization energies and geometries; for trivalent ions, the MGGA functionals perform best. The corresponding reorganization free energies (λo) of the oxidized ions are significantly underestimated with all DFT functionals and cluster models. This indicates that the structural reorganization of the solvation shell upon ionization is not adequately accounted for by the simple solvation models used, emphasizing the importance of extended sampling of thermally accessible solvation structures for an accurate computation of this quantity. The photoelectron spectroscopy measurements reported herein provide a comprehensive set of transition-metal redox energetic quantities for future electronic structure benchmarks.
authors.affiliation: Departamento de Ciencias Químicas, Facultad de Ciencias Exactas, Universidad Andres Bello , Avenida Republica 275, Santiago 8370146, Chile.
authors.forename: Diana
authors.initials: D
authors.lastname: Yepes
authors.forename: Robert
authors.initials: R
authors.lastname: Seidel
authors.forename: Bernd
authors.initials: B
authors.lastname: Winter
authors.forename: Jochen
authors.initials: J
authors.lastname: Blumberger
authors.forename: Pablo
authors.initials: P
authors.lastname: Jaque
mesh_terms: D002412:Cations / Q000737:chemistry; D056831:Coordination Complexes / Q000737:chemistry*; D056951:Photoelectron Spectroscopy; D013816:Thermodynamics; D028561:Transition Elements / Q000737:chemistry*; D014867:Water / Q000737:chemistry
chemical_list: D002412:Cations; D056831:Coordination Complexes; D028561:Transition Elements; D014867:Water