Laplacian of the Hamiltonian Kinetic Energy Density as an Indicator of Binding and Weak Interactions

Screening diluents to optimize cesium contaminant separation using t-BAMBP extractant

The widespread use of nuclear energy has raised concerns about nuclear safety and radioactive waste management, particularly due to the release of radioactive cesium. This study investigates the use of t-BAMBP (4-tert-butyl-2-(α-methylbenzyl) phenol) for the extraction and separation of cesium from simulate high concentration cesium containing wastewater, focusing on the selection of suitable diluents to enhance the efficiency of the process. We performed a systematic study using density functional theory (DFT) calculations to evaluate the intrinsic properties and interactions of various common diluents with t-BAMBP. The diluents studied include aromatic hydrocarbons (benzene, toluene, xylene), alkanes (cyclohexane, hexane, heptane), and alcohols (hexanol, octanol). Our computational results revealed that cyclohexane is the most suitable diluent due to its moderate solvation-free energy, high nonpolarity, and optimal balance between solubility and reactivity. Experimental validation confirmed the computational findings. The cyclohexane-diluted t-BAMBP system achieved the highest cesium extraction efficiency of over 94 %, with a separation factor (βCs/K) of 767.67. Cyclohexane demonstrated the lowest toxicity and cost among the diluents evaluated, making it a safer and more economical choice for practical applications. The results of this study provide a comprehensive theoretical and experimental basis for the selection of diluents in the t-BAMBP extraction system, offering insights for the sustainable utilization of cesium resources and effective management of radioactive waste.

Spin Energy Contributions of the Kinetic Energy Density in the Stabilization of the Metal-Ligand Interactions

The kinetic energy (KE) density plays an essential role in the stabilization mechanism of covalent, polar covalent, and ionic bondings; however, its role in metal-ligand bindings remains unclear. In a recent work, the energetic contributions of the spin densities α and β were studied to explain the geometrical characteristics of a series of metal-ligand complexes. Notably, the KE density was found to modulate/stabilize the spin components of the intra-atomic nucleus-electron interactions within the metal in the complex. Here, we investigate the topographic properties of the spin components of the KE density for a family of high-spin hexa-aquo complexes ([M(H2O)6]2+) to shed light on the stabilization of the metal-ligand interaction. We compute the Lagrangian, G(r), and Hamiltonian, K(r), KE densities and analyze the evolution of its spin components in the formation of two metal-ligand coordination complexes. We study Kα/β(r) along the metal-oxygen (M-O) internuclear axis as a function of the metal. Our results indicate that K(r) is a more distance-sensitive quantity compared to G(r) as it displays topographic features at larger M-O distances. Furthermore, K(r) allows one to identify the predominant interaction mechanism in the complexes.

The determinants of effective defluorination by the LiAl-LDHs

Millions of people in poor areas are still under the threat of fluoride contamination. How to effectively separate fluorine in water is an important step to reduce the ecological risk. In this paper, we performed a systematic DFT calculation focused on the defluorination behavior between the LiAl- and MgAl-LDHs. The results indicated that the LiAl-LDHs exhibited high chemical activity before the defluorination, because of the better electronic structure. After the defluorination, the LiAl-LDHs with adsorbed-F^- were also more stable than the MgAl-LDHs. In addition, the existence of coordination covalent bond for the adsorbed-F^- attached to the LiAl-LDHs was confirmed. This is an important reason for the high defluorination efficiency by the LiAl-LDHs. In addition, a series of weak interaction, including hydrogen bond and van der Waals interaction were also observed. Finally, a LiAl-LDHs with excellent fluoride removal properties were synthesized well by simple hydrothermal method. The results showed that our synthesized LiAl-LDHs with the capacity of 156.09 mg/g, could be effectively defluorinated in water. Notably, it surpasses most materials and has potential applications.

The role of doped-Mn on enhancing arsenic removal by MgAl-LDHs

To meet the challenges posed by global arsenic water contamination, the MgAlMn-LDHs with extraordinary efficiency of arsenate removal was developed. In order to clarify the enhancement effect of the doped-Mn on the arsenate removal performance of the LDHs, the cluster models of the MgAlMn-LDHs and MgAl-LDHs were established and calculated by using density functional theory (DFT). The results shown that the doped-Mn can significantly change the electronic structure of the LDHs and improve its chemical activity. Compared with the MgAl-LDHs that without the doped-Mn, the HOMO-LUMO gap was smaller after doping. In addition, the -OH and Al on the laminates were also activated to improve the adsorption property of the LDHs. Besides, the doped-Mn existed as a novel active site. On the other hand, the MgAlMn-LDHs with the doped-Mn, the increased of the binding energy, as well as the decreased of the ion exchange energy of interlayer Cl^-, making the ability to arsenate removal had been considerably elevated than the MgAl-LDHs. Furthermore, there is an obvious coordination covalent bond between arsenate and the laminates of the MgAlMn-LDHs that with the doped-Mn.

Chalcogen Bonding in the Molecular Dimers of WCh2 (Ch = S, Se, Te): On the Basic Understanding of the Local Interfacial and Interlayer Bonding Environment in 2D Layered Tungsten Dichalcogenides

Layered two-dimensional transition metal dichalcogenides and their heterostructures are of current interest, owing to the diversity of their applications in many areas of materials nanoscience and technologies. With this in mind, we have examined the three molecular dimers of the tungsten dichalcogenide series, (WCh₂)₂ (Ch = S, Se, Te), using density functional theory to provide insight into which interactions, and their specific characteristics, are responsible for the interfacial/interlayer region in the room temperature 2H phase of WCh₂ crystals. Our calculations at various levels of theory suggested that the Te···Te chalcogen bonding in (WTe₂)₂ is weak, whereas the Se···Se and S···S bonding interactions in (WSe₂)₂ and (WS₂)₂, respectively, are of the van der Waals type. The presence and character of Ch···Ch chalcogen bonding interactions in the dimers of (WCh₂)₂ are examined with a number of theoretical approaches and discussed, including charge-density-based approaches, such as the quantum theory of atoms in molecules, interaction region indicator, independent gradient model, and reduced density gradient non-covalent index approaches. The charge-density-based topological features are shown to be concordant with the results that originate from the extrema of potential on the electrostatic surfaces of WCh₂ monomers. A natural bond orbital analysis has enabled us to suggest a number of weak hyperconjugative charge transfer interactions between the interacting monomers that are responsible for the geometry of the (WCh₂)₂ dimers at equilibrium. In addition to other features, we demonstrate that there is no so-called van der Waals gap between the monolayers in two-dimensional layered transition metal tungsten dichalcogenides, which are gapless, and that the (WCh₂)₂ dimers may be prototypes for a basic understanding of the physical chemistry of the chemical bonding environments associated with the local interfacial/interlayer regions in layered 2H-WCh₂ nanoscale systems.

Bonding and metastability for Group 12 dications

Electronic structure and bonding properties of the Group 12 dications M₂ ²⁺ (M = Zn, Cd, Hg) are investigated and electron density-derived quantities are used to characterize the metastability of these species. Of particular interest are the complementary descriptions afforded by the Laplacian of the electron density ∇² ρ(r) and the one-electron Bohm quantum potential (Q =  ∇ 2 ρ r / 2 ρ r ) along the bond path. Further, properties derived from the pair density including the localization-delocalization matrices (LDMs) and the interacting quantum atoms (IQA) energies are analyzed within the framework of the quantum theory of atoms in molecules (QTAIM). From the crossing points of the singlet (ground) and triplet (excited) potential energy curves, the barriers for dissociation (BFD) are estimated to be 25.2 kcal/mol (1.09 eV) for Zn₂ ²⁺ , 22.8 kcal/mol (0.99 eV) for Cd₂ ²⁺ , and 26.4 kcal/mol (1.14 eV) for Hg₂ ²⁺ . For comparison and benchmarking purposes, the case of N₂ ²⁺ is considered as a texbook example of metastability. At the equilibrium geometries, LDMs, which are used here as an electronic fingerprinting tool, discriminate and group together Group 12 M₂ ²⁺ from its isoelectronic Group 11 M₂ . While "classical" bonding indices are inconclusive in establishing regions of metastability in the bonding, it is shown that the one-electron Bohm quantum potential is promising in this regard.

Covalent vs Charge-Shift Nature of the Metal-Metal Bond in Transition Metal Complexes: A Unified Understanding

We present here a general conceptualization of the nature of metal-metal (M-M) bonding in transition-metal (TM) complexes across the periods of TM elements, by use of ab initio valence-bond theory. The calculations reveal a dual-trend: For M-M bonds in groups 7 and 9, the 3d-series forms charge-shift bonds (CSB), while upon moving down to the 5d-series, the bonds become gradually covalent. In contrast, M-M bonds of metals having filled d-orbitals (groups 11 and 12) behave oppositely; initially the M-M bond is covalent, but upon moving down the Periodic Table, the CSB character increases. These trends originate in the radial-distribution-functions of the atomic orbitals, which determine the compactness of the valence-orbitals vis-à-vis the filled semicore orbitals. Key factors that gauge this compactness are the presence/absence of a radial-node in the valence-orbital and relativistic contraction/expansion of the valence/semicore orbitals. Whenever these orbital-types are spatially coincident, the covalent bond-pairing is weakened by Pauli-repulsion with the semicore electrons, and CSB takes over. Thus, for groups 3-10, which possess (n - 1)s²(n - 1)p⁶ semicores, this spatial-coincidence is maximal at the 3d-transition-metals which consequently form charge-shift M-M bonds. However, in groups 11 and 12, the relativistic effects maximize spatial-coincidence in the third series, wherein the 5d¹⁰ core approaches the valence 6s orbital, and the respective Pauli repulsion generates M-M bonds with CSB character. These considerations create a generalized paradigm for M-M bonding in the transition-elements periods, and Pauli repulsion emerges as the factor that unifies CSB over the periods of main-group and transition elements.

Photophysical and electrochemical properties of two trans-A2B-corroles: differences between phenyl or pyrenyl groups at the meso-10 position

The photophysical properties of two meso–trans-A₂B-type corroles containing phenyl or pyrenyl units were reported in this study. TD-DFT calculations and electrochemical analysis were conducted to better understand the corrole molecular structures.