Spin-orbit density functional and ab initio study of HgXn (X=F, Cl, Br, and I; n=1, 2, and 4)

Comment on "Realization of the Zn3+ oxidation state" by H. Fang, H. Banjade, Deepika and P. Jena, Nanoscale, 2021, , 14041-14048

Two zinc-boron clusters (ZnBeB₁₁(CN)₁₂ and ZnBeB₂₃(CN)₂₂) reported in a theoretical study by P. Jena and co-workers are reinvestigated using quantum chemistry calculations. The results prove that the zinc atoms in these two clusters retain a normal oxidation state of +2, overturning the conclusion reached in the previous study that a +3 oxidation state is present. The semi-empirical LOBA method points out this contrast, which is demonstrated via various wavefunction analysis approaches. No unpaired electrons are observed on zinc atoms nor is there a spin density difference distribution, revealing that the zinc atoms have a fully occupied 3d¹⁰ electron shell. Density of states studies give the same conclusion, and they further show that zinc atoms adopt an sp²-hybrid type during bonding. From the perspective of energy, we advise that the electron affinity energy is not a reliable way of evaluating the oxidation state. Instead, binding energy calculations and constrained DFT are applicable, and these also support the presence of Zn²⁺. The simulated XPS peaks are consistent with the experimental data for Zn(II) measured in ZnS. Lastly, the ETS-NOCV method is adopted to give insights into the bonding structures between zinc atoms and boron clusters. It is suggested that future theoretical research into similar problems is analyzed more cautiously to avoid potentially misleading other researchers.

Nitrogen Reduction by Multimetallic trans-Uranium Actinide Complexes: A Theoretical Comparison of Np and Pu to U

There is recent interest in organometallic complexes of the trans-uranium elements. However, preparation and characterization of such complexes are hampered by radioactivity and chemotoxicity issues as well as the air-sensitive and poorly understood behavior of existing compounds. As such, there are no examples of small-molecule activation via redox reactivity of organometallic trans-uranium complexes. This contrasts with the situation for uranium. Indeed, a multimetallic uranium(III) nitride complex was recently synthesized, characterized, and shown to be able to capture and functionalize molecular nitrogen (N₂) through a four-electron reduction process, N₂ → N₂^4-. The bis-uranium nitride, U-N-U core of this complex is held in a potassium siloxide framework. Importantly, the N₂^4- product could be further functionalized to yield ammonia (NH₃) and other desirable species. Using the U-N-U potassium siloxide complex, K₃U-N-U, and its cesium analogue, Cs₃U-N-U, as starting points, we use scalar-relativistic and spin-orbit coupled density functional theory calculations to shed light on the energetics and mechanism for N₂ capture and functionalization. The N₂ → N₂^4- reactivity depends on the redox potentials of the U(III) centers and crucially on the stability of the starting complex with respect to decomposition into the mixed oxidation U(IV)/U(III) K₂U-N-U or Cs₂U-N-U species. For the trans-uranium, Np and Pu analogues of K₃U-N-U, the N₂ → N₂^4- process is endoergic and would not occur. Interestingly, modification of the Np-O and Pu-O bonds between the actinide cores and the coordinated siloxide framework to Np-NH, Pu-NH, Np-CH₂, and Pu-CH₂ bonds drastically improves the reaction free energies. The Np-NH species are stable and can reductively capture and reduce N₂ to N₂^4-. This is supported by analysis of the spin densities, molecular structure, long-range dispersion effects, as well as spin-orbit coupling effects. These findings chart a path for achieving small-molecule activation with organometallic neptunium analogues of existing uranium complexes.

Ab initio quantum-chemical computations of the absorption cross sections of HgX2 and HgXY (X, Y = Cl, Br, and I): molecules of interest in the Earth's atmosphere

The electronic-structure properties of the low-lying electronic states and the absorption cross sections of mercury halides have been determined within the UV-vis spectrum range (170 nm ≤ λ_photon ≤ 600 nm).

The dynamics of the Hg + Br2 reaction: elucidation of the reaction mechanism for the Br exchange reaction

In spite of its importance in the Hg atmospheric chemistry, the dynamics of the Hg + Br₂ → HgBr + Br reaction is poorly understood. In this article, we have carried out a comprehensive study of the reaction mechanism of this reaction by means of quasiclassical trajectories (QCTs) on an existing ab initio potential energy surface (PES). The reaction has a non trivial dynamics, as a consequence of its large endothermicity, the presence of a deep potential well, and the competition between the Br exchange and the collision induced dissociation processes. Our calculations demonstrate that insertion is only relevant at energies just above the reaction threshold and that, at energies above 2.3 eV, HgBr formation typically takes place via a sort of frustrated dissociation. In order to compare directly with the results obtained in extensive cross molecular beam experiments for the homologous reaction with I₂, angular distributions in the laboratory frame for Hg + Br₂ have been simulated under similar experimental conditions. The lack of agreement at the highest energies considered suggests that either the two reactions have substantially different mechanisms or that calculations on a single PES cannot account for the dynamics at those energies.

Ab initio quantum-chemical computations of the electronic states in HgBr2 and IBr: Molecules of interest on the Earth's atmosphere

The electronic states of atmospheric relevant molecules IBr and HgBr₂ are reported, within the UV-Vis spectrum range (170nm≤λ_photon≤600 nm) by means of the complete-active-space self-consistent field/multi-state complete-active-space second-order perturbation theory/spin-orbit restricted-active-space state-interaction (CASSCF/MS-CASPT2/SO-RASSI) quantum-chemical approach and atomic-natural-orbital relativistic-correlation-consistent (ANO-RCC) basis sets. Several analyses of the methodology were carried out in order to reach converged results and therefore to establish a highly accurate level of theory. Good agreement is found with the experimental data with errors not higher than around 0.1 eV. The presented analyses shall allow upcoming studies aimed to accurately determine the absorption cross sections of interhalogen molecules and compounds with Hg that are relevant to better comprehend the photochemical processes taking place in the atmosphere.

Spin-Orbit Effect on the Molecular Properties of TeXn (X = F, Cl, Br, and I; n = 1, 2, and 4): A Density Functional Theory and Ab Initio Study

Density functional theory (DFT) and ab initio calculations, including spin-orbit coupling (SOC), were performed to investigate the spin-orbit (SO) effect on the molecular properties of tellurium halides, TeXn (X = F, Cl, Br, and I; n = 1, 2, and 4). SOC elongates the Te-X bond and slightly reduces the vibrational frequencies. Consideration of SOC leads to better agreement with experimental values. Møller-Plesset second-order perturbation theory (MP2) seriously underestimates the Te-X bond lengths. In contrast, B3LYP significantly overestimates them. SO-PBE0 and multireference configuration interactions with the Davidson correction (MRCI+Q), which include SOC via a state-interaction approach, give the Te-I bond length of TeI2 that matches the experimental value. On the basis of the calculated thermochemical energy and optimized molecular structure, TeI4 is unlikely to be stable. The use of PBE0 including SOC is strongly recommended for predicting the molecular properties of Te-containing compounds.

A theoretical study on the reaction of ozone with aqueous iodide

Atmospheric iodine chemistry plays a key role in tropospheric ozone catalytic destruction, new particle formation, and as one of the possible sinks of gaseous polar elemental mercury. Moreover, it has been recently proposed that reaction of ozone with iodide on the sea surface could be the major contributor to the chemical loss of atmospheric ozone. However, the mechanism of the reaction between aqueous iodide and ozone is not well known. The aim of this paper is to improve the understanding of such a mechanism. In this paper, an ab initio study of the reaction of aqueous iodide and ozone is presented, evaluating thermodynamic data of the different reactions proposed in previous experimental studies. In addition, the structures, energetics and possible evolution of the key IOOO(-) intermediate are discussed for the first time.

How Accurate Can a Local Coupled Cluster Approach Be in Computing the Activation Energies of Late-Transition-Metal-Catalyzed Reactions with Au, Pt, and Ir?

To improve the accuracy of local coupled cluster (LCC) methods in computing activation energies, we propose herein a new computational scheme. Its applications to various types of late-transition-metal-catalyzed reactions involving Au, Pt, and Ir indicate that the new corrective approach for LCC methods can downsize the mean unsigned deviation and maximum deviation, from the CCSD(T)/CBS reference, to about 0.3 and 0.9 kcal/mol. Using this method, we also calibrated the performance of popular density functionals, with respect to the same test set of reactions. It is concluded that the best functional is the general-purpose double hybrid functional B2GP-PLYP. Other well-performing functionals include the "kinetic" functionals M06-2X and BMK, which have a large percentage of HF exchange, and general-purpose functionals like PBE0 and wB97X. Comparatively, general-purpose functionals like PBE0 and TPSSh perform much better than the tested "kinetic" functionals for Pt-/Ir-catalyzed reactions, while the opposite is true for Au-catalyzed reactions. In contrast, wB97X performs more uniformly in these two classes of reactions. These findings hint that even within the scope of late transition metals, different types of reactions may require different types of optimal DFT methods. Empirical dispersion correction of DFT was found to have a small or no effect on the studied reactions barriers.