Ionic Character Of Bond Research Articles

Electronic modification of NaCrO2 via Ni2+ substitution as efficient cathode for sodium-ion batteries

The feature of high theoretical capacity, long thermal stability, and low-cost fabrication offers the layered transition metal oxide NaCrO2 as an excellent candidate for sodium-ion batteries. Here, we show an effective method for electronic modulation of NaCrO2 by partial substitution of Cr3+ with low-valent Ni2+ to produce NaCr0.95Ni0.05O2 as an efficient cathode for these batteries. We found that Ni2+ substitution plays a critical role in the ionic character of transition metal-oxygen bonds, which increases the interlayer separation and thus improves sodium-ion diffusion kinetics. Furthermore, Ni2+ substitution reduces the deterioration of NaCrO2 throughout charge-discharge processes and thus boosts the cycle performance of the materials. The resultant NaCr0.95Ni0.05O2 cathode displays a remarkable rate performance with specific capacities of 91.2 mAh g-1 at 50 C and a high retention (~80%) of the initial capacity after cycling for 1,000 cycles at 10 C.

Complexation of trivalent Eu and Am ions with phenanthroline-derived ligands tuned by rotating thiazole/oxazole substituents

The reprocessing of spent nuclear fuels is greatly challenging, as the current separation technique of lanthanide (Ln) and actinide (An) suffers too many difficulties. In this paper, selective ligands of phenanthroline derivatives modified by thiazole/oxazole were designed by relativistic density functional theory calculations. Their complexation of Eu3+ and Am3+ and the mechanism of selective separation were comprehensively examined. The spatial rotation against the CC bond between phenanthroline and thiazole/oxazole has access to six ligands. It is shown that Looo with oxazole substituents and their oxygens being opposite is the best electron donor for metal ions. The results of WBIs and MBO unravel that Am-L bond has more covalency than respective Eu-L bond. From topological analyses, it is found that these metal–ligand bonds are dominated by electrostatic interaction and largely of ionic bond character. Thermodynamically, all ligands prefer binding Eu3+ to Am3+.

Doping of large amount tetravalent Ge ions into Fe2O3 structure and experimental results on modified structural, optical and electronic properties

We report the doping of high concentration of tetravalent Ge4+ ions (5 mol % for x = 0.05–30 mol % for x = 0.30) at the Fe3+ sites of Fe2-xGexO3 system by chemical coprecipitation route. The charge state of Fe and Ge ions has been modified into lower values, in addition to their normal +3 and + 4 states, to stabilize the rhombohedral phase of hematite (α-Fe2O3) structure. X-ray photoelectron spectra and optical band gap measurements indicated a combination of ionic and covalence character of metal-oxygen bonds as an effect of Ge doping in the hematite structure. The Ge doped hematite samples have exhibited semiconductor properties with band gap of 1.50–4.70 eV and remarkably enhanced electrical conductivity (σ ∼ 10−4 S/m) in comparison to α-Fe2O3 (10−11 S/m). The results confirmed the strategy of enhancing electrical conductivity in hematite structure by doping of tetravalent cations. The thermo-conductivity measurements using warming and cooling modes showed highly irreversible feature at higher temperatures. Some of the samples indicated metal-like state at lower temperature, in addition to semiconductor state at higher temperatures. It has been understood that combination of ionic and covalence character of the metal-oxygen bonds has played an important role in modifying the semiconductor properties in Ge doped Fe2O3 system.

Fluorine chemistry in lithium-ion and sodium-ion batteries

As the peculiar element in the Periodic Table of Elements, fluorine gas owns the highest standard electrode potential of 2.87 V vs. F-, and a fluorine atom has the maximum electronegativity. Benefiting from the prominent property, fluorine plays an important role in the development of lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs) in terms of cathode materials (transition metal fluorides, fluorinated polyanionic compounds), electrolytes, and interfaces. In cathode materials, the highly electronegative renders enhanced ionic character of transition metal fluorine bonds and correspondingly high working potential in electrolytes; fluorinated electrolytes possess good antioxidant ability and flame retardance, which can significantly improve the thermal safety of a battery. On an electrode-electrolyte interface, the fluorine-rich inorganic component (such as LiF and NaF) is essential for the formation of a robust and stable solid electrolyte interface on anodes. Despite the remarkable advances achieved in fluorinated cathodes, electrolytes, and interfaces, there is still a lack of comprehensive understanding of the function of fluorides in LIBs and SIBs. Accordingly, this review briefly summarized the recent progress of fluorine-based electrodes, electrolytes, and interfaces and highlighted the correlation between the composition, property, and function to reveal the fluorine chemistry in LIBs and SIBs. This review will provide guidance for the rational design and targeted regulation of fluorine-dominated high-performance electrode materials, functionalized electrolytes, and consolidated interfaces.

Cr-doped Sb2Te materials promising for high performance phase-change random access memory

Transition metal doping is an effective strategy to improve the properties of phase-change random access memory (PCRAM), while the underlying mechanism remains to be sufficiently investigated. Herein, a Cr-doped Sb2Te film is fabricated by co-sputtering and the enhancement mechanism of Cr-doping is deeply investigated by experiments and first-principles calculations. The CrxSb2Te film exhibits excellent performances involving high crystallization temperature (238.9 °C) and good data retention (10 years @161.7 °C) for Cr0.56Sb2Te, low density change rate (3.8%) and high reversible switching speed (5 ns) for Cr0.29Sb2Te, providing a variety of options for different applications. The calculated results show that Cr atoms preferentially substitute the Sb1 site and the CrTe bonds display a stronger ionic bond character in contrast to the covalent bonded SbTe, thus improving the crystalline phase stability and crystallization temperature. Moreover, ab initio molecular dynamics simulations demonstrate that in the amorphous phase Cr atoms locate in defective octahedral coordination. Meanwhile, the homopolar SbSb wrong bond increased with Cr doping and the Cr atoms tend to form tight cluster in the amorphous phase which could benefit for the fast phase-change speed. Our present findings of Cr0.29Sb2Te PCRAM device clearly reveal the enhancement mechanism by Cr doping which provides guidance for developing high-performance PCRAM devices.

Lanthanides Toxicity in Zebrafish Embryos Are Correlated to Their Atomic Number.

Rare earth elements (REEs) are critical metallic materials with a broad application in industry and biomedicine. The exponential increase in REEs utilization might elevate the toxicity to aquatic animals if they are released into the water due to uncareful handling. The specific objective of our study is to explore comprehensively the critical factor of a model Lanthanide complex electronic structures for the acute toxicity of REEs based on utilizing zebrafish as a model animal. Based on the 96 h LC50 test, we found that the majority of light REEs display lower LC50 values (4.19–25.17 ppm) than heavy REEs (10.30–41.83 ppm); indicating that they are atomic number dependent. Later, linear regression analyses further show that the average carbon charge on the aromatic ring (aromatic Cavg charge) can be the most significant electronic structural factor responsible for the Lanthanides’ toxicity in zebrafish embryos. Our results confirm a very strong correlation of LC50 to Lanthanide’s atomic numbers (r = 0.72), Milliken charge (r = 0.70), and aromatic Cavg charge (r = −0.85). This most significant correlation suggests a possible toxicity mechanism that the Lanthanide cation’s capability to stably bind to the aromatic ring on the residue of targeted proteins via a covalent chelating bond. Instead, the increasing ionic bond character can reduce REEs’ toxicity. In addition, Lanthanide toxicity was also evaluated by observing the disruption of photo motor response (PMR) activity in zebrafish embryos. Our study provides the first in vivo evidence to demonstrate the correlation between an atomic number of Lanthanide ions and the Lanthanide toxicity to zebrafish embryos.

Quantitative Account of the Bonding Properties of a Rubredoxin Model Complex [Fe(SCH3)4]q, q = −2, −1, +2, +3

Iron-sulfur clusters play important roles in biology as parts of electron-transfer chains and catalytic cofactors. Here, we report a detailed computational analysis of a structural model of the simplest natural iron-sulfur cluster of rubredoxin and its cationic counterparts. Specifically, we investigated adiabatic reduction energies, dissociation energies, and bonding properties of the low-lying electronic states of the complexes [Fe(SCH3)4]2-/1-/2+/3+ using multireference (CASSCF, MRCISD), and coupled cluster [CCSD(T)] methodologies. We show that the nature of the Fe-S chemical bond and the magnitude of the ionization potentials in the anionic and cationic [Fe(SCH3)4] complexes offer a physical rationale for the relative stabilization, structure, and speciation of these complexes. Anionic and cationic complexes present different types of chemical bonds: prevalently ionic in [Fe(SCH3)4]2-/1- complexes and covalent in [Fe(SCH3)4]2+/3+ complexes. The ionic bonds result in an energy gain for the transition [Fe(SCH3)4]2- → [Fe(SCH3)4]- (i.e., FeII → FeIII) of 1.5 eV, while the covalent bonds result in an energy loss for the transition [Fe(SCH3)4]2+ → [Fe(SCH3)4]3+ of 16.6 eV, almost half of the ionization potential of Fe2+. The ionic versus covalent bond character influences the Fe-S bond strength and length, that is, ionic Fe-S bonds are longer than covalent ones by about 0.2 Å (for FeII) and 0.04 Å (for FeII). Finally, the average Fe-S heterolytic bond strength is 6.7 eV (FeII) and 14.6 eV (FeIII) at the RCCSD(T) level of theory.

Acid-base properties of hydroxyapatite(0001) by the adsorption of probe molecules: An ab initio investigation

The presence of both acidic and basic adsorption sites on the surface of hydroxyapatite [${\mathrm{Ca}}_{10}{({\mathrm{PO}}_{4})}_{6}{(\mathrm{OH})}_{2}$; HAP] is an interesting property for catalytic applications. Here, we report a density functional theory investigation of the adsorption properties of $\mathrm{CO}, {\mathrm{CO}}_{2}, {\mathrm{C}}_{2}{\mathrm{H}}_{2}, {\mathrm{CH}}_{4}, {\mathrm{H}}_{2}, {\mathrm{H}}_{2}\mathrm{O}, {\mathrm{NH}}_{3}, {\mathrm{SO}}_{2}$, and ${\mathrm{BCl}}_{3}$ on the $\mathrm{HAP}(0001)$ surface. All probe molecules have a lower energy when they are adsorbed in the region between the most exposed ${\mathrm{Ca}}^{2+}$ ion (electron acceptor) and a neighboring $\mathrm{PO}{{}_{4}}^{3\ensuremath{-}}$ group, where the $\mathrm{O}$ atoms (electron donor) contribute to the stabilization of the adsorbed molecule. By evaluating the redistribution of the electron density and the change of the atomic charges, the ${\mathrm{Ca}}^{2+}$ and $\mathrm{PO}{{}_{4}}^{3\ensuremath{-}}$ sites were identified as Lewis acidic and Lewis basic adsorption sites, respectively, which indicates that simultaneous acid-base interactions occur upon adsorption of all studied probe molecules. All adsorbates interact with the surface via atoms of opposing charges, which enhances the ionic character of molecular bonds by increasing the distinction between cationic and anionic charges within the molecule. Furthermore, molecules with greater ionic character show stronger interaction with the substrate and greater geometric deformation. Although most adsorbed molecules ($\mathrm{CO}, {\mathrm{CO}}_{2}, {\mathrm{C}}_{2}{\mathrm{H}}_{2}, {\mathrm{CH}}_{4}, {\mathrm{H}}_{2}, {\mathrm{H}}_{2}\mathrm{O}$, and ${\mathrm{NH}}_{3}$) do not show substantial net charge transfer, polarization effects due to the redistribution of charge are observed upon adsorption of all probe molecules. The change in the work function increases linearly with the total change in the surface dipole moment for ${\mathrm{H}}_{2}\mathrm{O}, {\mathrm{NH}}_{3}, {\mathrm{SO}}_{2}$, and ${\mathrm{BCl}}_{3}$, while for the remaining systems, the magnitude of the work function change remains more uniform. By identifying the type of interaction between each probe molecule and the $\mathrm{HAP}(0001)$ surface, the present study contributes to the understanding of the acid-base properties of the $\mathrm{HAP}(0001)$ surface, which we elaborated in a short discussion based on the individual bond orders for the acidic and basic sites.

From Electronegativity towards Reactivity-Searching for a Measure of Atomic Reactivity.

Pauling introduced the concept of electronegativity of an atom which has played an important role in understanding the polarity and ionic character of bonds between atoms. We set out to define a related concept of atomic reactivity in such a way that it can be quantified and used to predict the stability of covalent bonds in molecules. Guided by the early definition of electronegativity by Mulliken in terms of first ionization energies and Pauling in terms of bond energies, we propose corresponding definitions of atomic reactivity. The main goal of clearly distinguishing the inert gas atoms as nonreactive is fulfilled by three different proposed measures of atomic reactivity. The measure likely to be found most useful is based on the bond energies in atomic hydrides, which are related to atomic reactivities by a geometric average. The origin of the atomic reactivity is found in the symmetry of the atomic environment and related conservation laws which are also the origin of the shell structure of atoms and the periodic table. The reactive atoms are characterized by degenerate or nearly degenerate (several states of the same or nearly the same energy) ground states, while the inert atoms have nondegenerate ground states and no near-degeneracies. We show how to extend the use of the Aufbau model of atomic structure to qualitatively describe atomic reactivity in terms of ground state degeneracy. The symmetry and related conservation laws of atomic electron structures produce a strain (energy increase) in the structure, which we estimate by use of the Thomas-Fermi form of DFT implemented approximately with and without the symmetry and conservation constraints. This simplified and approximate analysis indicates that the total strain energy of an atom correlates strongly with the corresponding atomic reactivity measures but antibonding mechanisms prevent full conversion of strain relaxation to bonding.

Identifying Ionic and Polar Covalent Bonds in Superionic Metal Halides

Solid state batteries are the future of energy storage due to their improved stability and energy density. Before they can rival the liquid-based batteries of today, however, significant improvement in ionic conductivity must be achieved. In pursuit of these improvements the bond character of AgI and other metal halides were simulated and analyzed. Maximally localized Wannier Functions from Quantum Espresso and Wannier 90 were used to calculate the electronic structure of AgBr, AgI, CuCl, CuI, and CuBr with four different crystal structures at multiple temperatures. Python and the Atomic Simulations Environment were used to identify diffusing cations, the angles between each interacting cation-anion bond and their bond types, ionic or polar-covalent. To illustrate the correlation between ionic diffusion and bond character, the angles and bond type of only the diffusing cations were isolated for graphical analysis. Understanding this correlation will lend insight into conductivity and enable the engineering of faster conductive crystals.

The Structures of ZnCl2-Ethanol Mixtures, a Spectroscopic and Quantum Chemical Calculation Study.

We report in this article the structural properties, spectral behavior and heterogeneity of ZnCl2-ethanol (EtOH) mixtures in a wide-composition range (1:3 to 1:14 in molar ratios), using ATR-FTIR spectroscopy and quantum chemical calculations. To improve the resolution of the initial IR spectra, excess spectroscopy and two-dimensional correlation spectroscopy were employed. The transformation process was suggested to be from EtOH trimer and EtOH tetramer to EtOH monomer, EtOH dimer and ZnCl2-3EtOH complex upon mixing. The theoretical findings showed that increasing the content of EtOH was accompanied with the flow of negative charge to ZnCl2. This led to reinforcement of the Zn←O coordination bonds, increase of the ionic character of Zn‒Cl bond and weakening and even dissociation of the Zn‒Cl bond. It was found that in some of the ZnCl2-EtOH complexes optimized at the gas phase or under the solvent effect, there existed hydroxyls with a very special interactive array in the form of Cl‒Zn+←O‒H…Cl−, which incredibly red-shifted to wavenumbers <3000 cm−1. This in-depth study shows the physical insights of the respective electrolyte alcoholic solutions, particularly the solvation process of the salt, help to rationalize the reported experimental results, and may shed light on understanding the properties of the deep eutectic solvents formed from ZnCl2 and an alcohol.

Delocalized Bonding in Li2X2 Rings: Probing the Limits of the Covalent and Ionic Bonding Models.

In spite of the highly ionic character of most lithium-element bonds, the bonding within Li2X2 rings presents similarities with that found in analogous transition metal systems. They obey simple framework electron counting rules that allow us to predict whether they will form a regular ring or a squeezed one with short Li-Li or X-X distances. A combined computational and structural database analysis discloses the orbital conditions that determine the framework electron counting rules. These systems probe the borderline between the covalent and ionic bonding models since, paradoxically, a non-negligible covalent contribution of the two Li atoms (formally Li+ ions in the ionic model) to the Li-X framework bonding favors them approaching each other within bonding distance.

Elastic anisotropy, electronic and magnetic behaviours of ferromagnetic Europium Niobate EuNbO3 in orthorhombic structure: DFT + U, MFA and QTAIM studies

ABSTRACT Recently, previous studies have shown that at room temperature, EuNbO3 adopts an orthorhombic structure of Imma space group with a ferromagnetic behaviour. The relevant idea of ⁣this work is to provide a new insight into some electronic and magnetic behaviours of EuNbO3 in orthorhombic structure, which are still unknown, based on the results already found previously. The structural properties have been determined using two functionals (GGA-PBE and GGA-PBEsol) and the found results are in good agreement with the previous ones. Mechanical behaviour and elastic anisotropy have also been studied in detail from which, it has been confirmed that EuNbO3 is mechanically stable in Imma orthorhombic perovskite structure. The directional analysis of Young’s modulus has shown that it is elastically anisotropic. For the electronic properties, many approaches have been used in order to take all the considerations that are not taken into account by GGA semilocal functional, hence, spin–orbit coupling effect (SOC), Hubbard correction (GGA + U) and Modified Becke–Johnson exchange potential (mBJ) have been adopted. The two adopted mBJ parameterizations gave different results, hence, for that of TB-mBJ, the studied compound is almost halfmetallic, while that of Radi A. Jishi et al. showed a semiconductor behaviour. To estimate Curie temperature, we have employed the mean field approximation (MFA), hence, its estimated value is higher than that of transition to the tetragonal I4/mcm structure, which has been determined previously. The ionic character of Eu-O and Nb-O bonds has been confirmed by The Quantum Theory of Atoms in Molecules (QTAIM).

Tailoring doping effect in olivine-type NaMnPO4: insights from density functional theory

On the basis of spin density functional theory, this paper comparatively investigates the electronic properties of NaMnPO4 doped with As, N and Sb using the generalized gradient approximation (GGA) with the functional parameterized by Perdew–Burke–Ernzerhof correction (PBE). Such doped ions significantly alter the lattice parameters and cell volumes. Density of states (DOS) demonstrates that the dopants introduce impurity states near the edge of the conduction bands. The band gaps are obviously reduced in the presence of the dopants, indicating the better electronic conductivity. According to Mulliken Population Analysis, the ionic character of Na-O bond is reduced by the dopants, leading to the flexible sodium diffusivity. Due to the calculations, Sb ion enhances more electronic conductivity and diffusion of NaMnPO4 in comparison with As and N atom. Finally, we expect that this work will be supportive to design these materials for rechargeable batteries based on sodium ion.

Structures and adhesion of hcp thin film coating interfaces on a single-crystal bcc substrate by PVD: Ti/Mo and Zr/Mo

Polycrystalline hcp Ti and Zr thin films were developed on single-crystal bcc-Mo (110) substrate using PVD method. XRD analysis suggests the preferred facet relation of (0001)hcp//(110)bcc. Sandwich supercell models were then constructed to evaluate the interface energy, adhesion strength and bonding nature from the first principles. The Burgers and Pitsch-Schrader orientation relation (OR) were predicted as the most energy-favored for the PVD Ti and Zr thin film interfaces on the Mo (110), respectively. Interface adhesion was predicted to be fairly strong for both interfaces. The d-d orbital interaction between Ti/Zr and Mo is found closely associated with the spatial redistribution of Bader valence charges. The resulting new bonds across the interfaces are rather delocalized, showing a mixed covalent and weak ionic bond character. These results strongly suggest that single-crystal Mo (110) is a promising substrate for developing high quality hcp Ti or Zr thin films through PVD.

Optical properties of (Se80Te20)100-xZnx (2 ≤ x ≤ 6) amorphous thin films

The (Se80Te20)100-xZnx (2 ≤ x ≤ 6)thin film compositions have been prepared by melt quenching technique followed by electron-beam physical vapour deposition. X-ray diffraction pattern and SEM micrographs ascertain the amorphous nature of prepared thin films. The transmission spectra from UV/VIS/NIR double beam spectrophotometer (500 ≤ λ (nm) ≤ 2600) is used for optical characterization of thin films. The absorption coefficient and energetic parameter (A) for various compositions indicate that the absorption mechanism in Se-Te-Zn glassy system occur via allowed indirect transitions. The optical band gap for thin films lies at the edge of near infrared region in A-band (λ~900 nm).The average heat of atomization has no essential influence on the optical band gap energy values. The refractive index (n) for thin films exhibit normal dispersion in the wavelength range 800 nm ≤ λ ≤ 1100 nm (IR-A), and is nearly constant at longer wavelength λ ≥ 1400 nm (IR-B). The dispersion of refractive index below the band gap energy region is studied using the Wemple-DiDomenico (WDD) single oscillator model. It is found that, to a good approximation the single-oscillator energy scales with the optical band gap (Eo≈1.4Egopt). The deduced value of parameter β = 0.24 ± 0.01 corresponds to ionic character of bonds in the Se-Te-Zn system. The dielectric parameters (ε’, ε”,ɛ∞, ɛL), optical conductivity (σ1,σ2), ratio of carrier concentration to the effective mass (N/m*) have also been deduced for thin films. The calculated values of plasma frequency ωP and Nopt are in good agreement with carrier concentration of semiconductors. The energy loss occurred in the interior of the Se-Te-Zn thin films is found to be due to the interband electronic transitions.

First-principles investigation of Sn doping on the geometric and electronic structures of V2O5

The influence of Sn doping on the geometric and electronic structures of V2O5 were investigated by the plane-wave pseudopotential technique based on density functional theory (DFT) with LDA/CA-PZ functional. After Sn doping, the unit cell volume of V2O5 increases slightly and the system changes from intrinsic semiconductor to n-type semiconductor. In the Sn doped V2O5, the V-O bonds show a significant covalent bond character, while the Sn-O bonds exhibits mainly ionic bond character; the V = O bonds from the vanadium and terminal oxygen have the strongest bond strength among all the V-O bonds in the system; in addition, the bond strength of the terminal/apical V-O bonds adjacent to Sn atom weakens obviously.

Characterisation of superalkaline-earth-metal halides, hydroxide and chalcogenides

ABSTRACTA new series of superalkaline-earth-metal compounds Al14X (X = F2, Cl2, Br2, I2, (OH)2, O, S) has been investigated at the TPSS/Def2-TZVPP level. It is found that both interaction position and mode between Al14 and X ligands influence isomer stability of the resulting superatom compounds. On the one hand, the top and bottom sites of Al14 have higher reactivity relative to middle ones. On the other hand, different ligands favour different binding patterns when combining with Al14. For example, the halogen ligands prefer to occupy on-top sites of Al14. In contrast, the end-on bound configurations are the least favourable ones for Al14 oxide. Natural population analysis indicates that the Al14 cluster donates electrons to X ligands. Atoms in molecules analysis also suggests ionic bond character of the connection(s) between Al14 and X moieties. Thus, the Al14X compounds are much like divalent salts where superatom Al14 behaves just like an alkaline-earth-metal atom. Furthermore, considerable dissociation energies and large highest occupied molecular orbital and lowest unoccupied molecular orbital gaps confirm stability of these superatom compounds.

Thermo-mechanical properties of cubic lanthanide oxides

This contribution investigates the effect of the addition of the Hubbard U parameter on the electronic structural and mechanical properties of cubic (C-type) lanthanide sesquioxides (Ln2O3). Calculated Bader's charges confirm the ionic character of LnO bonds in the C-type Ln2O3. Estimated structural parameters (i.e., lattice constants) coincide with analogous experimental values. The calculated band gaps energies at the Ueff of 5 eV for these compounds exhibit a non-metallic character and Ueff of 6.5 eV reproduces the analogous experimental band gap of cerium sesquioxide Ce2O3. We have thoroughly investigated the effect of the O/Ce ratios and the effect of hafnium (Hf) and zirconium (Zr) dopants on the reduction energies of CeOx configurations. Our analysis for the reduction energy of CeO2, over a wide range of temperatures displays that, shuffling between the two +4 and +3 oxidation states of Ce exhibit a temperature-independent behaviour. Higher O/Ce ratios necessitate lower reduction energies. Our results on CeHfZrO alloys are in reasonable agreements with analogous fitted values pertinent to lowering reduction energies and shrinkage in lattice parameters when contrasted with pure CeO2. Structural analysis reveals that Hf and Zr atoms in the solid solution are shifted towards the nearest vacancies upon reduction. It is hoped that values provided herein to shed an atomic-base insight into the reduction/oxidation thermodynamics of increasingly deployed catalysts for environmental applications.

Vibrational Characterization of Microsolvated Electrocatalytic Water Oxidation Intermediate: [Ru(tpy)(bpy)(OH)]2+(H2O)0–4

The infrared predissociation spectra of the mass-selected electrocatalytic water oxidation intermediate [Ru(tpy)(bpy)(OH)]2+(H2O)0-4 are reported. The [Ru(tpy)(bpy)(OH)]2+ species is generated by passing a solution of [Ru(tpy)(bpy)(H2O)](ClO4)2 through an electrochemical flow cell held at 1.2 V and is immediately introduced into the gas phase via electrospray ionization (ESI). The microsolvated clusters are formed by reconstructing the water network in a cryogenic ion trap. Details of the hydrogen bonding network in these clusters are revealed by the infrared predissociation spectra in the OH stretch region. This improved method for capturing microsolvated clusters yielded colder complexes with much better resolved IR features than previous studies. The analysis of these spectra, supported by electronic structure calculations and compared to previous results on [Ru(tpy)(bpy)(H2O)]2+(H2O)0-4 clusters, reveals the nature of the Ru-OH bond and the effect of hydrogen bonding on facilitating the subsequent oxidation to [Ru(tpy)(bpy)(O)]2+ in the proposed catalytic cycle. Particularly, the hydrogen bonding interaction in [Ru(tpy)(bpy)(OH)]2+(H2O)1 is much weaker than that in the corresponding [Ru(tpy)(bpy)(H2O)]2+(H2O)1 and thus is less effective at activating the hydroxyl ligand for further oxidation via proton coupled electron transfer (PCET). Furthermore, the results here reveal that the Ru-OH bond, though formally described as an Ru3+/OH- interaction, has more covalent bond character than ionic bond character.