Comprehensive Experimental and Computational Spectroscopic Study of Hexacyanoferrate Complexes in Water: From Infrared to X-ray Wavelengths

Abstract

We present a joint experimental and computational study of the hexacyanoferrate aqueous complexes at equilibrium in the 250 meV to 7.15 keV regime. The experiments and the computations include the vibrational spectroscopy of the cyanide ligands, the valence electronic absorption spectra, and Fe 1s core hole spectra using element-specific-resonant X-ray absorption and emission techniques. Density functional theory-based quantum mechanics/molecular mechanics molecular dynamics simulations are performed to generate explicit solute-solvent configurations, which serve as inputs for the spectroscopy calculations of the experiments spanning the IR to X-ray wavelengths. The spectroscopy simulations are performed at the same level of theory across this large energy window, which allows for a systematic comparison of the effects of explicit solute-solvent interactions in the vibrational, valence electronic, and core-level spectra of hexacyanoferrate complexes in water. Although the spectroscopy of hexacyanoferrate complexes in solution has been the subject of several studies, most of the previous works have focused on a narrow energy window and have not accounted for explicit solute-solvent interactions in their spectroscopy simulations. In this work, we focus our analysis on identifying how the local solvation environment around the hexacyanoferrate complexes influences the intensity and line shape of specific spectroscopic features in the UV/vis, X-ray absorption, and valence-to-core X-ray emission spectra. The identification of these features and their relationship to solute-solvent interactions is important because hexacyanoferrate complexes serve as model systems for understanding the photochemistry and photophysics of a large class of Fe(II) and Fe(III) complexes in solution.

High seebeck coefficient in middle-temperature thermocell with deep eutectic solvent

“…The high S e of the ethaline thermocell can be attributed to the large entropy difference, specifically solvation entropy, between [Fe(CN) 6 ] 3− and [Fe(CN) 6 ] 4− . [Fe(CN) 6 ] 4− has a higher surface charge density compared to that of [Fe(CN) 6 ] 3− , which further regulates the orientation of solvent molecules 4 , 23 , 24 . The solvation effect of these redox species was investigated by FT-IR spectroscopy (Fig.…”

“…[Fe(CN) 6 ] 4− shows a broader C≡N stretching vibration peak with a full width at half maximum (FWHM) of 22.5 cm −1 against [Fe(CN) 6 ] 3− with an FWHM of 9.8 cm −1 . The broader peak corresponds to more substantial structural heterogeneity in the solvation environment of [Fe(CN) 6 ] 4− , which is originated from the stronger hydrogen bond interaction between the solute and the solvent 23 , 24 . This enhanced interaction, in turn, leads to a tightly-packed solvation shell surrounding [Fe(CN) 6 ] 4− than that of [Fe(CN) 6 ] 3− .…”

Manipulating valence and core electronic excitations of a transition-metal complex using UV/Vis and X-ray cavities

“…We investigate the ferricyanide complex in water, which serves as a prototypical model system for the structure and spectroscopy of Fe( iii ) octahedral transition metal complexes. 38–40 We consider cavities with resonance frequencies in the UV/Vis and X-ray regimes and develop the formalism for signals involving non-Hermitian polariton Hamiltonians, which include cavity dissipation and exciton decay.…”

Probing Solute–Solvent Interactions of Transition Metal Complexes Using L-Edge Absorption Spectroscopy

“…The study highlighted the importance of explicitly treating the solvent in quantum chemical simulations in order to ensure an accurate modeling of the electronic structure of iron cyanides. 15 Both studies particularly found a strong hydrogen-bonding interaction between protic solvents and the cyanide (CN – ) ligands, which impacts intramolecular covalency. More specifically, the hydrogen bond has been reported to withdraw charge from the CN – ligands, which is compensated for by a concomitant increase in π-backdonation.…”