Temperature effects on prevalent structures of hydrated Fe+ complexes: Infrared spectroscopy and DFT calculations of Fe+(H2O)n (n = 3–8)

Size-dependent H and H2 formation by infrared multiple photon dissociation spectroscopy of hydrated vanadium cations, V+(H2O)n, n = 3-51

Infrared spectra of the hydrated vanadium cation (V⁺(H₂O)_n; n = 3–51) were measured in the O–H stretching region employing infrared multiple photon dissociation (IRMPD) spectroscopy. Spectral fingerprints, along with size-dependent fragmentation channels, were observed and rationalized by comparing to spectra simulated using density functional theory. Photodissociation leading to water loss was found for cluster sizes n = 3–7, consistent with isomers featuring intact water ligands. Loss of molecular hydrogen was observed as a weak channel starting at n = 8, indicating the advent of inserted isomers, HVOH⁺(H₂O)_n−1. The majority of ions for n = 8, however, are composed of two-dimensional intact isomers, concordant with previous infrared studies on hydrated vanadium. A third channel, loss of atomic hydrogen, is observed weakly for n = 9–11, coinciding with the point at which the H and H₂O calculated binding energies become energetically competitive for intact isomers. A clear and sudden spectral pattern and fragmentation channel intensity at n = 12 suggest a structural change to inserted isomers. The H₂ channel intensity decreases sharply and is not observed for n = 20 and 25–51. IRMPD spectra for clusters sizes n = 15–51 are qualitatively similar indicating no significant structural changes, and are thought to be composed of inserted isomers, consistent with recent electronic spectroscopy experiments.

Infrared multiple photon dissociation spectra of V⁺(H₂O)_n depend on experiment conditions, with strong kinetic shift effects for large clusters.

Infrared Multiple Photon Dissociation Spectroscopy Confirms Reversible Water Activation in Mn+(H2O)n, n ≤ 8

Controlled activation of water molecules is the key to efficient water splitting. Hydrated singly charged manganese ions Mn⁺(H₂O)_n exhibit a size-dependent insertion reaction, which is probed by infrared multiple photon dissociation spectroscopy (IRMPD) and FT-ICR mass spectrometry. The noninserted isomer of Mn⁺(H₂O)₄ is formed directly in the laser vaporization ion source, while its inserted counterpart HMnOH⁺(H₂O)₃ is selectively prepared by gentle removal of water molecules from larger clusters. The IRMPD spectra in the O-H stretch region of both systems are markedly different, and correlate very well with quantum chemical calculations of the respective species at the CCSD(T)/aug-cc-pVDZ//BHandHLYP/aug-cc-pVDZ level of theory. The calculated potential energy surface for water loss from HMnOH⁺(H₂O)₃ shows that this cluster ion is metastable. During IRMPD, the system rearranges back to the noninserted Mn⁺(H₂O)₃ structure, indicating that the inserted structure requires stabilization by hydration. The studied system serves as an atomically defined single-atom redox-center for reversible metal insertion into the O-H bond, a key step in metal-centered water activation.

Infrared spectroscopic and computational studies of Co(ClO4)2 dissolved in N,N-dimethylformamide (DMF). Vibrations of DMF influenced by Co2+ or ClO4- or both

Infrared (IR) spectroscopy for N,N-dimethylformamide (DMF) shows that the OCN bend (δ_OCN) and the CO stretch (ν_CO) vibrations undergo an upshift and a downshift, respectively, on the dissolution of Co(ClO₄)₂. Quantum chemical calculations are performed for optimizing the structures and predicting the IR spectra of model complexes for solute species. The calculations reveal that Co²⁺ exerts a much larger influence than ClO₄^- on the vibrations of DMF. For Co²⁺(DMF)₆, in which each DMF molecule is coordinated to Co²⁺ via the O atom, the Co²⁺⋯DMF interaction upshifts the δ_OCN frequencies (+24 cm^-1 on average) while the dipole coupling gives rise to splitting (12 cm^-1) of the modes. On the other hand, the Co²⁺⋯DMF interaction downshifts the ν_CO frequencies (-15 cm^-1 on average) while the splitting of the modes amounts to 37 cm^-1. As a result, one of the ν_CO modes is located at an upshifted position (+13 cm^-1) despite the O-atom coordination. For six-coordinated isomers of Co²⁺(DMF)₇, the δ_OCN and ν_CO frequencies of the second-sphere DMF are close to those of bulk DMF in neat liquid. The calculations indicate that it is difficult to prove or exclude the formation of contact ion pairs [Co(DMF)₅ClO₄]⁺ and solvent-shared ion pairs [Co(DMF)₆ClO₄]⁺ by IR spectroscopy in the δ_OCN and ν_CO regions. However, asymmetric ClO stretches of the ClO₄^- moiety suggest that conceivable is the coexistence of solvent-shared ion pairs only.

Microsolvation of Zn cations: infrared multiple photon dissociation spectroscopy of Zn+(H2O)n (n = 2-35)

The structures, along with solvation evolution, of size-selected Zn⁺(H₂O)_n (n = 2-35) complexes have been determined by combining infrared multiple photon photodissociation (IRMPD) spectroscopy and density functional theory. The infrared spectra were recorded in the O-H stretching region, revealing varying shifts in band position due to different water binding motifs. Concordant with previous studies, a coordination number of 3 is observed, determined by the sudden appearance of a broad, red-shifted band in the hydrogen bonding region for clusters n > 3. The coordination number of 3 seems to be retained even for the larger clusters, due to incoming ligands experiencing significant repulsion from the Zn⁺ valence 4s electron. Evidence of spectrally distinct single- and double-acceptor sites are presented for medium-sized clusters, 4 ≤n≤ 7, however for larger clusters, n≥ 8, the hydrogen bonding region is dominated by a broad, unresolved band, indicative of the increased number of second and third coordination sphere ligands. No evidence of a solvated, six-fold coordinated Zn²⁺ ion/solvated electron pair is present in the spectra.

Structures of the solvated copper(ii) ion in ammonia at various temperatures

We investigated theoretically the structures and relative stabilities of the solvated copper(ii) ion in ammonia, Cu²⁺(NH₃)_n, n = 1–10.

Photochemistry of Fe:H2O Adducts in Argon Matrixes: A Combined Experimental and Theoretical Study in the Mid-IR and UV-Visible Regions

The photochemistry of Fe:H₂O adducts is of interest in fields as diverse as catalysis and astrochemistry. Industrially, iron can be used as a catalyst to convert H₂O to H₂, whereas in the interstellar medium it may be an important component of dust grains, influencing the chemistry on their icy surfaces. This study consisted of the deposition and spectral characterization of binary systems of atomic iron with H₂O in cryogenic argon matrixes. In this way, we were able to obtain information about the interaction of the two species; we observed the formation of adducts of iron monomers and dimers with water molecules in the mid-IR and UV-visible spectral domains. Upon irradiation with a UV radiation source, the iron species were inserted into the water molecules to form HFeOH and HFe₂OH, leading in some cases to the formation of FeO possibly accompanied by the production of H₂. DFT and correlated multireference wave function calculations confirmed our attributions. This combination of IR and UV-visible spectroscopy with theoretical calculations allowed us to determine, for the first time, the spectral characteristics of iron adducts and their photoproducts in the UV-visible and in the OH stretching region of the mid-IR domain.

Hydrogen bond network structures of protonated short-chain alcohol clusters

Protonated alcohol clusters enable extraction of the physical essence of the nature of hydrogen bond networks.

Quantitative Temperature Dependence of the Microscopic Hydration Structures Investigated by Ultraviolet Photodissociation Spectroscopy of Hydrated Phenol Cations

To discuss the temperature effect on microscopic hydration structures in clusters, relative populations of the isomers having different hydration structures at well-defined temperatures are quite important. In the present study, we measured ultraviolet photodissociation spectra of the temperature-controlled hydrated phenol cation [PhOH(H₂O)₅]⁺ trapped in the 22-pole ion trap. Two isomers having a distinct hydration motif with each other are identified in the spectra, and a clear change in the relative populations is observed in the temperature range from 30 to 150 K. This behavior is quantitatively interpreted by statistical mechanical estimation based on density functional theory calculations. A ring with tail-type hydration motif is dominant in cold conditions, whereas a chain-like motif is dominant in hot conditions. The present study provides very quantitative information about the temperature effect on the microscopic hydration structures.

Influence of hydration on ion-biomolecule interactions: M(+)(indole)(H2O)(n) (M = Na, K; n = 3-6)

The indole functional group can be found in many biologically relevant molecules, such as neurotransmitters, pineal hormones and medicines. Indole has been used as a tractable model to study the hydration structures of biomolecules as well as the interplay of non-covalent interactions within ion-biomolecule-water complexes, which largely determine their structure and dynamics. With three potential binding sites: above the six- or five-member ring, and the N-H group, the competition between π and hydrogen bond interactions involves multiple locations. Electrostatic interactions from monovalent cations are in direct competition with hydrogen bonding interactions, as structural configurations involving both direct cation-indole interactions and cation-water-indole bridging interactions were observed. The different charge densities of Na(+) and K(+) give rise to different structural conformers at the same level of hydration. Infrared spectra with parallel hybrid functional-based calculations and Gibbs free energy calculations revealed rich structural insights into the Na(+)/K(+)(indole)(H2O)3-6 cluster ion complexes. Isotopic (H/D) analyses were applied to decouple the spectral features originating from the OH and NH stretches. Results showed no evidence of direct interaction between water and the NH group of indole (via a σ-hydrogen bond) at current levels of hydration with the incorporation of cations. Hydrogen bonding to a π-system, however, was ubiquitous at hydration levels between two and five.

Hydrogen-bonded ring closing and opening of protonated methanol clusters H+(CH3OH)n (n = 4–8) with the inert gas tagging

Temperature dependence of hydrogen bond network structures of protonated methanol clusters is explored by IR spectroscopy and DFT simulations.

Coordination structure and charge transfer in microsolvated transition metal hydroxide clusters [MOH]+(H2O)1–4

Infrared vibrational predissociation spectra of transition metal hydroxide clusters, [MOH]⁺(H₂O)_1–4·D₂ with M = Mn, Fe, Co, Ni, Cu, and Zn, are presented and analyzed, showing solvent driven changes in coordination and charge transfer.