Impact of finite-temperature and condensed-phase effects on theoretical X-ray absorption spectra of transition metal complexes

Detection and Characterization of Hydride Ligands in Copper Complexes by Hard X-Ray Spectroscopy

Transition metal complexes, particularly copper hydrides, play an important role in various catalytic processes and molecular inorganic chemistry. This study employs synchrotron hard X-ray spectroscopy to gain insights into the geometric and electronic properties of copper hydrides as potential catalysts for CO2 hydrogenation. The potential of high energy resolution X-ray absorption near-edge structure (HERFD-XANES) and valence-to-core X-ray emission (VtC-XES) is demonstrated with measurement on Stryker's reagent (Cu6H6) and [Cu3(μ3-H)(dpmppe)2](PF6)2 (Cu3H), alongside a non-hydride copper compound ICu(dtbppOH) (Cuy-I). The XANES analysis reveals that coordination geometries strongly influence the spectra, providing only indirect details about hydride coordination. The VtC-XES analysis exhibits a distinct signal around 8975 eV, offering a diagnostic tool to identify hydride ligands. Theoretical calculations support and extend these findings by comparing hydride-containing complexes with their hydride-free counterparts.

Scrutinizing "Ligand Bands" via Polarized Single-Crystal X-ray Absorption Spectra of Copper(I) and Copper(II) Bis-2,2'-bipyridine Species

High-energy resolution fluorescence-detected Cu K-edge X-ray absorption spectroscopy (XAS) and single-crystal polarized XAS data are presented toward refining the assignments of bands assigned as excitations from Cu 1s to ligand-localized molecular orbitals. These have been previously dubbed "XAS-metal-ligand charge transfer" (XAS-MLCT) bands. Data are presented for a series of [Cu(xbpy)₂]ⁿ⁺ complexes (xbpy = 2,2'-bipyridine (1ⁿ⁺), 4,4'-bisamino-2,2'-bipyridine (2ⁿ⁺), and 4,4'-dimethoxy-2,2'-bipyridine (3ⁿ⁺); n = 1 and 2). Dipolar dependencies of these "XAS-MLCT" bands in both Cu¹⁺ and Cu²⁺ species lead to reassignment of these features as owing their intensities primarily to Cu 1s → Cu 4p excitations. The transition densities are Cu-localized, highlighting that XAS-MLCT features in Cu XAS spectra are not "charge transfer" transitions but rather quasi-atomic transitions. Although scrutiny of the acceptor orbitals supports assignment as Cu 1s → ligand π* transitions, it ultimately appears that while the ligand orbital energetics govern the positions of these bands the intensity is conferred through a small degree of metal 4p mixing into otherwise ligand-dominated acceptor molecular orbitals.

CP2K: An electronic structure and molecular dynamics software package - Quickstep: Efficient and accurate electronic structure calculations

CP2K is an open source electronic structure and molecular dynamics software package to perform atomistic simulations of solid-state, liquid, molecular, and biological systems. It is especially aimed at massively parallel and linear-scaling electronic structure methods and state-of-the-art ab initio molecular dynamics simulations. Excellent performance for electronic structure calculations is achieved using novel algorithms implemented for modern high-performance computing systems. This review revisits the main capabilities of CP2K to perform efficient and accurate electronic structure simulations. The emphasis is put on density functional theory and multiple post-Hartree-Fock methods using the Gaussian and plane wave approach and its augmented all-electron extension.

Tumbling with a limp: local asymmetry in water's hydrogen bond network and its consequences

Ab initio molecular dynamics simulations of ambient liquid water and energy decomposition analysis have recently shown that water molecules exhibit significant asymmetry between the strengths of the two donor and/or the two acceptor interactions.