A QMCF-MD investigation of the structure and dynamics of Ce4+ in aqueous solution

Cu2+ in liquid ammonia-The impact of solvent flexibility and electron correlation in ab initio quantum mechanical charge field molecular dynamics

The impact of solvent flexibility and electron correlation on the simulation results of Cu²⁺ in liquid ammonia has been investigated via an ab initio quantum mechanical charge field molecular dynamics (QMCF MD) simulation approach. To achieve this, three different simulation systems were considered in this study, namely Cu²⁺ in rigid and flexible ammonia at Hartree-Fock (HF) level of theory, as well as resolution of identity second order Møller-Plesset (MP2) perturbation theory in the rigid body case. In all cases, a stable octahedral [Cu(NH₃ )₆ ]²⁺ complex subject to dynamic Jahn-Teller distortions without the occurrence of ligand exchange was observed. The Cu²⁺  - NH₃ distance in the first shell agrees well with the experimental and other theoretical data. In all three cases, the structural data shows that the rigid-body ammonia model in conjunction with the HF level of theory provides accurate data for the first solvation shell, while at the same time, the computational demand and thus the achievable simulation time are much more beneficial. The vibrational analysis of the Cu²⁺  - NH₃ interaction yields similar force constants in the three investigated systems indicating that there is no distinct difference on the dynamical properties of the first solvation shell. In addition to the QMCF MD simulations, a number of natural bond orbital (NBO) analyses were carried out, confirming the strong electrostatic character of the Cu²⁺  - NH₃ interaction.

Structures and Free Energies of Cerium Ions in Acidic Electrolytes

The Ce³⁺/Ce⁴⁺ redox potential changes with the electrolyte, which could be due to unequal anion complexation free energies between Ce³⁺ and Ce⁴⁺ or a change in the solvent electrostatic screening. Ce complexation with anions and solvent screening also affect the solubility of Ce and charge transfer kinetics for electrochemical reactions involving waste remediation and energy storage. We report the structures and free energies of cerium complexes in seven acidic electrolytes based on Extended X-ray Absorption Fine Structure, UV-vis, and Density Functional Theory calculations. Ce³⁺ coordinates with nine water molecules as [Ce(H₂O)₉]³⁺ in all studied electrolytes. However, Ce⁴⁺ complexes with anions in all electrolytes except HClO₄. Thus, our results suggest that Ce⁴⁺-anion complexation leads to the large shifts in standard redox potential. Long range screening effects are smaller than the anion complexation energies but could be responsible for changes in the Ce solubility with acid.

Properties of the tetravalent actinide series in aqueous phase from a microscopic simulation self-consistent engine

In the context of nuclear fuel recycling and environmental issues, the understanding of the properties of radio-elements with various approaches remains a challenge regarding their dangerousness. Moreover, experimentally, some issues are also of importance; first, it is imperative to work at sufficiently high concentrations to reach the sensitivities of the analytical tools, however this condition often leads to precipitation for some of them; second, stabilizing specific oxidation states of some actinides remains a challenge, thus making it difficult to extract general trends across the actinide series. Complementary to experiments, modeling can be used to unbiasedly probe the actinide's properties in an aquatic environment and offers a predictive tool. We report the first molecular dynamics simulations based on homogeneously built force fields for the whole series of the tetravalent actinides in aqueous phase from ThIV to BkIV and including PuIV. The force fields used to model the interactions among the constituents include polarization and charge donation microscopic effects. They are built from a self-consistent iterative ab initio based engine that can be included in future developments as an element of a potential machine learning procedure devoted to generating accurate force fields. The comparison of our simulated hydrated actinide properties to available experimental data shows the model robustness and the relevance of our parameter assignment engine. Moreover, our simulated structural, dynamical and evolution of the hydration free energy data show that, apart from AmIV and CmIV, the actinide properties change progressively along the series.

Evidence for an oxygen evolving iron-oxo-cerium intermediate in iron-catalysed water oxidation

The non-haem iron complex α-[Fe(II)(CF3SO3)2(mcp)] (mcp=(N,N'-dimethyl-N,N'-bis(2-pyridylmethyl)-1,2-cis-diaminocyclohexane) reacts with Ce(IV) to oxidize water to O2, representing an iron-based functional model for the oxygen evolving complex of photosystem II. Here we trap an intermediate, characterized by cryospray ionization high resolution mass spectrometry and resonance Raman spectroscopy, and formulated as [(mcp)Fe(IV)(O)(μ-O)Ce(IV)(NO3)3](+), the first example of a well-characterized inner-sphere complex to be formed in cerium(IV)-mediated water oxidation. The identification of this reactive Fe(IV)-O-Ce(IV) adduct may open new pathways to validate mechanistic notions of an analogous Mn(V)-O-Ca(II) unit in the oxygen evolving complex that is responsible for carrying out the key O-O bond forming step.

Combined Ab Initio Computational and Infrared Spectroscopic Study of the cis- and trans-Bis(glycinato)copper(II) Complexes in Aqueous Environment

The cis- and trans-bis(glycinato)copper(II) complexes in aqueous solution have been investigated by means of a combined theoretical and experimental approach. The conducted quantum mechanical charge field molecular dynamics (QMCF-MD) studies, being the first quantum mechanical simulations of organometallic complexes by this method, yielded accurate structural details of the investigated isomers as well as novel dynamic data, which has successfully been confirmed and extended by subsequent mid-infrared measurements. The spectroscopic results, critically assessed by adjacent multivariate data analysis, indicate an isomeric stability at ambient conditions, vanishing at elevated temperatures.

Simulation of Ir(III) in Aqueous Solution: The Most Inert Ion Hydrate

The ab initio quantum mechanical charge field (QMCF) molecular dynamics (MD) approach at Hartree-Fock level was used to simulate the tripositive iridium ion in aqueous solution, evaluating structure and dynamics of its hydrate complex. The Ir-OH2 force constant was of particular interest because of the observed high inertness of Ir(iii) in aqueous solution. Iridium forms three hydration shells. Six water molecules coordinate the ion in the first hydration shell in a well defined octahedral geometry, and no exchanges took place during the simulation time of 15 ps. The second hydration shell is very flexible, however, with a mean residence time of a water molecule of 3.6 ps. The third shell can be identified only by a slight ordering effect. This investigation classified the Ir-OH2 force constant as the strongest ion-OH2 bond known to date.