Partial Covalency Research Articles

Effect of order-disorder transition and lattice distortion on the mechanical properties of W-X (X = V, Nb, Ta) solid solutions

With the prosperity of high entropy alloys, short-range ordering is getting more and more attentions and regarded as the deciding role in the hardening or softening of solid solutions. In this work, the phase stability and mechanical properties of short-range ordered and disordered body-centered cubic (BCC) structures of W-X solid solutions (X = V, Nb, and Ta) are systematically investigated through a combination of first-principles calculation, cluster expansion and quasi-harmonic Debye formula. Based on the calculated heat of formation (ΔHf), W-X solid solutions show a strong short-range ordering tendency, as those ordered structures have a lower ΔHf than the disordered ones. Generally, short-range ordering results in the decrease of the shear modulus to bulk modulus ratio (G/B) and hardness for W-V and W-Ta systems, while an increase for W-Nb system, manifesting solid-solution softening and hardening effect, respectively. The short-ranged ordered C11b W2X phase exhibits a singularity in mechanical properties characterized by a higher G/B than solid solution phases compared to other ordered phases. The lattice distortion breaks the symmetric W-W bonds and leads to partial covalency in the W2X phases. Besides the increased brittleness, this distortion also causes the increase of ideal strength and the reduction of maximum tensile elongation of W2X. The effect of short-range ordering and lattice distortion on the hardening or softening of the W-X systems disappears after the order-disorder transition. The W-V and W-Ta phases have higher order-disorder transition temperature than W-Nb phase. Nevertheless, the transition temperature is relatively low in comparison to their melting points, signifying the important role in controlling the solute concentration at lower temperature.

A comparison of structure, bonding and non-covalent interactions of aryl halide and diarylhalonium halogen-bond donors.

Halogen bonding permeates many areas of chemistry. A wide range of halogen-bond donors including neutral, cationic, monovalent, and hypervalent have been developed and studied. In this work we used density functional theory (DFT), natural bond orbital (NBO) theory, and quantum theory of atoms in molecules (QTAIM) to analyze aryl halogen-bond donors that are neutral, cationic, monovalent and hypervalent and in each series we include the halogens Cl, Br, I, and At. Within this diverse set of halogen-bond donors, we have found trends that relate halogen bond length with the van der Waals radii of the halogen and the non-covalent or partial covalency of the halogen bond. We have also developed a model to calculate ΔG of halogen-bond formation by the linear combination of the % p-orbital character on the halogen and energy of the σ-hole on the halogen-bond donor.

Enhanced Am/Eu separation ability of disulfonated diamide N-heterocyclic ligands by adjusting N-, O-donor affinity: A theoretical comparative study

Separation of minor actinides (MAs) from lanthanides (Ln) is a vital and challenging stage in advanced nuclear waste treatment. Development of water-soluble back-extraction ligand is regarded as a feasible alternative method for high efficiency An(III)/Ln(III) separation. Therefore, theoretical investigating on the deep mechanism behind the selective back-extraction of An(III) is very important. In this work, Am- and Eu-complexes with three water-soluble disulfonated N-heterocyclic ligands, disulfonated N,N’-diphenyl-2,9-diamide-1,10-phenanthroline (DS-Ph-DaPhen, L1), disulfonated N,N’-diphenyl-2,9-diamide-2,2′-Dipyridine (DS-Ph-DADipy, L2), and disulfonated N,N’-diphenyl-2,9-diamide 5H-cyclopenta[2,1-b:3,4-b’]-Dipyridine (DS-Ph-Da-5H-Cyclo-PentaDipy, L3) were systematically investigated using quasi-relativistic density functional theory (DFT) method. Electrostaic potential (ESP) and restrained electroStatic potential (RESP) atomic charge on donor atoms indicate that N atoms’ affinity toward metal ions in L2 and L3 was increased by replaceing the phenanthroline ring with dipyridine ring and 5H-Cyclo-PentaDipyridine ring, while the affinity of O atoms seem to decrease from L1 to L2 and L3. Through Wiberg bond indices and quantum theory of atoms in molecule (QTAIM) analyses, three ligands’ Am(III) preference may be attributed to the weak but different extend partial covalency in Am-N and Eu-N bonds. Based on the NBO population and PDOS analyses, slightly more overlap of Am-5f and N/O-2p orbitals than those between Eu-4f and N/O-2p orbitals. Based on the theoretical calculation, the covalency difference between Am-N and Eu-N bonds seems to have inverse correlation with the intensity of M−N bonds. However, all the theoretical results suggest that, by increasing N’s affinity and weakening O’ affinity at the same time, ligand’s Am(III)/Eu(III) separation ability can be improved. This work offers some useful information for changing ligands’ An(III)/Ln(III) back-extraction and separation abilities by adjusting the affinity of donor N and O atoms in its central N-heterocyclic skeleton, and may shed light for future designing of more efficient An(III)/Ln(III) back-extraction ligands.

Atomistic Simulations of the Crystalline-to-Amorphous Transformation of γ-Al2O3 Nanoparticles: Delicate Interplay between Lattice Distortions, Stresses, and Space Charges

The size-dependent phase stability of γ-Al2O3 was studied by large-scale molecular dynamics simulations over a wide temperature range from 300 to 900 K. For the γ-Al2O3 crystal, a bulk transformation to α-Al2O3 by an FCC-to-HCP transition of the O sublattice is still kinetically hindered at 900 K. However, local distortions of the FCC O-sublattice by the formation of quasi-octahedral Al local coordination spheres become thermally activated, as driven by the partial covalency of the Al-O bond. On the contrary, spherical γ-Al2O3 nanoparticles (NPs) (with sizes of 6 and 10 nm) undergo a crystalline-to-amorphous transformation at 900 K, which starts at the reconstructed surface and propagates into the core through collective displacements of anions and cations, resulting in the formation of 7- and 8-fold local coordination spheres of Al. In parallel, the reconstructed Al-enriched surface is separated from the stoichiometric core by a diffuse Al-depleted transition region. This compositional heterogeneity creates an imbalance of charges inside the NP, which induces a net attractive Coulombic force that is strong enough to reverse the initial stress state in the NP core from compressive to tensile. These findings disclose the delicate interplay between lattice distortions, stresses, and space-charge regions in oxide nanosystems. A fundamental explanation for the reported expansion of metal-oxide NPs with decreasing size is provided, which has significant implications for, e.g., heterogeneous catalysis, NP sintering, and additive manufacturing of NP-reinforced metal matrix composites.

Therapeutic Potential of B12N12-X (X = Au, Os, and Pt) Nanostructured as Effective Fluorouracil (5Fu) Drug Delivery Materials.

In view of the research-substantiated comparative efficiency of nontoxic and bioavailable nanomaterials synergic with human systems for drug delivery, this work was aimed at studying the comparative efficiency of transition metal (Au, Os, and Pt)-decorated B12N12 nanocages in the adsorption of fluorouracil (5Fu), an antimetabolite-classed anticarcinogen administered for cancers of the breast, colon, rectum, and cervix. Three different metal-decorated nanocages interacted with 5Fu drug at the oxygen (O) and fluorine (F) sites, resulting in six adsorbent-adsorbate systems whose reactivity and sensitivity were investigated using density functional theory computation at the B3LYP/def2TZVP level of theory with special emphasis on the structural geometry, electronic, and topology analysis as well as the thermodynamic properties of the systems. While the electronic studies predicted Os@F as having the lowest and most favorable Egp and Ead of 1.3306 eV and -11.9 kcal/mol, respectively, the thermodynamic evaluation showed Pt@F to have the most favorable thermal energy (E), heat capacity (Cp), and entropy (ΔS) values as well as negative ΔH and ΔG while the adsorption studies showed that the greatest degree of chemisorption with Ead magnitude of -204.5023 kcal/mol was observed in energies ranging from -12.0 to 138.4 kcal/mol with Os@F and Au@F at the lower and upper borders. The quantum theory of atoms in molecules results show that the six systems had noncovalent interactions as well as a certain degree of partial covalency but none showed covalent interaction while the noncovalent interaction analysis corroborated this by showing that the six systems had favorable interactions, though of varying degrees, with very little trace of steric hindrance or electrostatic interactions. Overall, the study showed that notwithstanding the good performance of the six adsorbent systems considered, the Pt@F and Os@F showed the most favorable potential for the delivery of 5Fu.

Non-covalent interactions in the monohydrated complexes of 1,2,3,4-tetrahydroisoquinoline.

The eleven monohydrates of 1, 2, 3, 4-tetrahydroisoquinoline (THIQ) are analyzed through natural bond orbital (NBO) analysis and QTAIM methods employing M06-2X functional in DFT and MP2 methods. Here, the role of OH bonds as an acceptor and donor is critically analyzed. The role of lone pairs of O is critically monitored in two of the complexes, where N-H···O hydrogen bonds are present. The relative contributions of rehybridisation and hyperconjugation are compared in detail. Popelier criteria are satisfied in all the complexes barring a few exceptions involving weak hydrogen bonds. At the bond critical points (BCP), four monohydrates show higher values of electron density (ρC) and negative values of total electron energy density (HC), while Laplacian [Formula: see text] remains positive. These complexes satisfy the criteria of partial covalency. All these are O-H⋅⋅⋅N-type bonds. Remaining h-bonds are weaker in nature. These are also confirmed by the smaller values of ρC at the respective BCP. The variation of potential energy density (VC) among the complexes seems to be the most important factor in determining the nature of non-covalent interactions.

Theoretical and experimental approaches to the use of benzoyl carbamothioyl alanine as a new ionophore for development of various mercury selective electrodes

Benzoyl carbamothioyl alanine (BCA) was prepared, characterized, and applied as an ionophore to fabricate three new mercury-selective potentiometric sensors. First, the molecular mechanic-based MMFF94 technique was used to determine the most stable BCA’s conformer and its isosteric complexes with some cations. The reaction’s Gibbs free energy results indicated the acceptable thermodynamic complexation reactivity of the ligand and Hg2+. The quantum theory of atoms in molecules revealed that the interaction of Hg2+ with oxygen and sulfur atoms corresponded to electrostatic nature and partial covalency, respectively. FTIR spectra indicated that the Hg2+ ion could coordinate with a BCA molecule through sulfur, oxygen, and nitrogen atoms. The theoretical thermodynamic parameters calculated in the solvent phase and the experimental selection pattern extracted from UV–visible spectroscopy showed excellent agreement. The morphology of the PVC membrane was studied using field emission-scanning electron microscopy and the presence of Hg2+ ions in the membrane matrix was confirmed by the analysis of EDX spectra. Overall, using the mentioned ligand, three different liquid membrane mercury selective electrodes were constructed: liquid internal electrolyte-ion selective electrode (LIE-ISE), coated wire-ISE (CW-ISE), and solid state-ISE (SS-ISE). Responses were Nernstian for all of the electrodes. The detection limit was improved for CW-ISE (7 × 10-6 M) and SS-ISE (7 × 10-9 M) compared to LIE-ISE (1 × 10-5 M). Also, the response time of LIE-ISE was approximately 15 s, while it was 5 s for both CW-ISE and SS-ISE. The sensors were applied as indicator electrodes in the potentiometric titration of Hg2+ with ethylenediaminetetraacetic acid.

Thermodynamic non-ideality and disorder heterogeneity in actinide silicate solid solutions

Non-ideal thermodynamics of solid solutions can greatly impact materials degradation behavior. We have investigated an actinide silicate solid solution system (USiO4–ThSiO4), demonstrating that thermodynamic non-ideality follows a distinctive, atomic-scale disordering process, which is usually considered as a random distribution. Neutron total scattering implemented by pair distribution function analysis confirmed a random distribution model for U and Th in first three coordination shells; however, a machine-learning algorithm suggested heterogeneous U and Th clusters at nanoscale (~2 nm). The local disorder and nanosized heterogeneous is an example of the non-ideality of mixing that has an electronic origin. Partial covalency from the U/Th 5f–O 2p hybridization promotes electron transfer during mixing and leads to local polyhedral distortions. The electronic origin accounts for the strong non-ideality in thermodynamic parameters that extends the stability field of the actinide silicates in nature and under typical nuclear waste repository conditions.

Ca–Li substitution driven structural, dynamics of electron density, magnetic and optical properties of BiFeO3 nanoparticles

Ca and Ca–Li substitution dependent modification in structural, electron density, vibrational, magnetic and optical properties of BiFeO3 nanoparticles synthesized by tartaric acid based sol–gel route are reported. X-ray diffraction and transmission electron microscopy techniques revealed the phase purity and nanocrystalline nature of BiFeO3, Bi0·95Ca0·05FeO3, Bi0·95Ca0·05Fe0·95Li0·05O3 samples. The electron density plots indicated the displacement of Bi and Fe ions and partial covalency of Bi–O and Fe–O the bonds. The Ca and Ca–Li ions substitution induced distortion in rhombohedral structure resulting in enhanced magnetization of BiFeO3 nanoparticles. The magnetization is highest for Ca–Li substituted BiFeO3 nanoparticles with saturation magnetization of 0.036 emu/g due to the canted spin structure and uncompensated surface spins. The enhanced magnetic properties are also endorsed by the electron spin resonance and Raman studies. The band-gap of BiFeO3 nanoparticles can be tuned by aliovalent ions substitution from 2.26 eV for BiFeO3 to 2.20 and 2.17 eV for Ca, and Ca–Li substituted BiFeO3 nanoparticles respectively.

Direct Spectroscopy for Probing the Critical Role of Partial Covalency in Oxygen Reduction Reaction for Cobalt-Manganese Spinel Oxides.

Nanocrystalline multivalent metal spinels are considered as attractive non-precious oxygen electrocatalysts. Identifying their active sites and understanding their reaction mechanisms are essential to explore novel transition metal (TM) oxides catalysts and further promote their catalytic efficiency. Here we report a systematic investigation, by means of soft X-ray absorption spectroscopy (sXAS), on cubic and tetragonal CoxMn3-xO4 (x = 1, 1.5, 2) spinel oxides as a family of highly active catalysts for the oxygen reduction reaction (ORR). We demonstrate that the ORR activity for oxide catalysts primarily correlates to the partial covalency of between O 2p orbital with Mn4+ 3d t2g-down/eg-up, Mn3+ 3d eg-up and Co3+ 3d eg-up orbitals in octahedron, which is directly revealed by the O K-edge sXAS. Our findings propose the critical influences of the partial covalency between oxygen 2p band and specific metal 3d band on the competition between intermediates displacement of the ORR, and thus highlight the importance of electronic structure in controlling oxide catalytic activity.

Correlation of sintering temperature with structural and multiferroic properties of un-doped and cobalt doped bismuth ferrite

The crystal structure and physical properties of BiFeO3 and BiFe0.95Co0.05O3 sintered at various sintering temperature were studied using x-ray diffraction, scanning electron microscopy (SEM), electric and magnetic measurements. All the samples crystallize in a distorted perovskite structure with space group R3c and show minor impurity phase. An influence of various structural parameters and electronic states over physical properties of all the compounds were investigated. Partial covalency of the Bi–O bonds was confirmed using electron density calculation. Density functional theory (DFT) calculation has supported the validity of the experimental results. Moreover, microstructural investigation using the SEM shows that Co substitution in BiFeO3 increases the grain growth and increases the average grain size when sintered at 800 °C. P–E loop confirmed the ferroelectric behavior of synthesized compounds. The remnant magnetization Mr of BiFe0.95Co0.05O3 compound sintered at 850 °C was enhanced significantly, which provides potential applications of the material in information storage.

Theoretical investigation on the covalence in AgRnX and XAgRn (X = F - I).

CCSD(T) calculations were performed to investigate the stabilities and interaction mechanisms of the AgRnX and XAgRn (X = F - I) series. Dissociation energies and frontier orbital properties demonstrate an increased trend of stabilities. Ag spd hybrids and Rn/X sp hybrids come into the σAg-Rn and σAg-X bonding orbital. The nature of Ag-Rn, Ag-X and Rn-X interactions were investigated by atoms in molecules (AIM) theory. The negative energy density and positive Laplacian values, as well as small electron densities at bond critical points (BCPs), characterize the moderate strength with partial covalence of interactions. BCP properties (-G/V and G/ρ), electron density deformations and natural resonance theory (NRT) results display increased covalence down the periodic table.

π⋅⋅⋅H+ ⋅⋅⋅π Hydrogen Bonds and Their Lithium and Gold Analogues: MP2 and CASPT2 Calculations.

Molecular systems in which two simple π-electron species, acetylene and ethylene, are linked by a cation located between them are analyzed in this study. In particular, the C2 H2 ⋅⋅⋅M+ ⋅⋅⋅C2 H2 , C2 H4 ⋅⋅⋅M+ ⋅⋅⋅C2 H2 , and C2 H4 ⋅⋅⋅M+ ⋅⋅⋅C2 H4 complexes (M+ =H+ , Li+ , Au+ ) are calculated with the use of MP2 and CASPT2 methods. The Quantum Theory of Atoms in Molecules (QTAIM), energy decomposition analysis (EDA), and Natural Bond Orbital (NBO) approaches are applied to deepen the understanding of the nature of M+ ⋅⋅⋅π interactions in these complexes. It is found that the interactions in gold and proton complexes are characterized by at least partial covalency, whereas interactions in lithium complexes are rather electrostatic in nature.

Stabilities and interactions of CuRnX and XCuRn (X = F – I): ab initio calculations

ABSTRACTTheoretical investigations on the CuRnX and XCuRn (X = F – I) series have been performed at the CCSD(T) theoretical level. Analyses on dissociation energy and frontier orbital show a decreased trend of stabilities down the periodic table. NBO analyses show the existence of σCu-Rn and σCu-X bonding orbital resulted from the overlap between Cu spd hybrid and Rn/X sp hybrid. The Cu–Rn, Cu–X and Rn–X interactions characterised by negative energy density values, positive Laplacian values and small electron densities at bond critical point (BCP) can be described as interactions of moderate strength with partial covalence. Analyses on electron localisation functions, electron density deformations, BCP properties (−G/V and G/ρ) and natural resonance theory demonstrate an increased covalence down the periodic table.

AuRnX and XAuRn (X=F ‐ I and OH)

AbstractSystematic theoretical investigations on the AuRnX and XAuRn (X=F‐I and OH) have been performed at B3LYP, MP2 and CCSD(T) theoretical levels. The linear structures, stretching frequencies and IR intensities were predicted. Analyses on dissociation energies and frontier orbitals show a decreased trend of stability down the periodic table for halogens. Natural bond orbital analyses show the σAu‐Rn and σAu‐X bonding occured between Au spd hybrids and Rn/X sp hybrids. The Au−Rn,Au−X and Rn−X interactions, characterized by negative energy densities and positive Laplacian values together with relative small electron densities at BCPs, can be described as interactions of moderate strength with partial covalence. Analyses on electron localization functions, electron density deformations and bonding orbital coefficients found an increased covalence trend down the periodic table for halogens.

Anion-π Interactions in Flavoproteins Involve a Substantial Charge-Transfer Component.

Anion-π interactions have been shown to stabilize flavoproteins and to regulate the redox potential of the flavin cofactor. They are commonly attributed to electrostatic forces. Herein we show that anion-flavin interactions can have a substantial charge-transfer component. Our conclusion emanates from a multi-approach theoretical analysis and is backed by previously reported observations of absorption bands, originating from charge transfer between oxidized flavin and proximate cysteine thiolate groups. This partial covalency of anion-flavin contacts renders classical simulations of flavoproteins questionable.

Multiple Weak C–H Intramolecular Hydrogen Bonding as an Aid to Minimizing Bond Rotation Flexibility

The presence of 14 intramolecular interactions relevant to bond rotational flexibility in coordination compounds important in the context of crystal engineering were identified by density functional theory calculations in the crystal structure of the highly crystalline oxoimido complex [Mo(NC6H4CMe3-2)(O)Cl2(bipy)] (1). A combination of computational techniques including noncovalent interaction index properties and Quantum Theory of Atoms analysis which are based on the computed electron density as well as natural bond orbitals analysis, were used to uncover the nature of the interactions. Weakly stabilizing intramolecular interactions involving electrostatic contributions were found for O····HC, N····HC, and CH····HC, close separations involving the bipy ligand where coordination does not allow flexibility and for O····HC, N····HC, Cl····HC, CH····HC, and C····HC close contacts where C–N and C–C rotations of the imido ligand would allow flexibility. Partial covalency is not a significant feature of these...

Room temperature synthesis and spectral characterization of Cu2+-doped CdO powder

In the present study, we have synthesized undoped and Cu2+-doped CdO nanopowders by a mild solution method at room temperature. Powder X-ray diffraction, optical absorption, electron paramagnetic resonance and Fourier transform infrared measurements are used to characterize prepared powders. The powder X-ray diffraction patterns reflect the cubic crystal structure for undoped and Cu2+-doped CdO powders. Surface morphology images and compositional features are studied by scanning electron microscopy and energy-dispersive X-ray techniques, respectively. The optical absorption spectra exhibit a single absorption band for Cu2+-doped sample, which is the characteristic absorption band of distorted octahedral site symmetry. By correlating the electron paramagnetic resonance and optical results for Cu2+-doped CdO nanopowder, bonding parameters are evaluated. These values indicate the partial covalency of in-plane σ (α2) and in-plane π bonding (\( \beta_{1}^{2} \)) between copper ions and their ligands. The FT-IR spectra indicate the fundamental vibrations of Cd–O.

Embedding covalency into metal catalysts for efficient electrochemical conversion of CO2.

CO2 conversion is an essential technology to develop a sustainable carbon economy for the present and the future. Many studies have focused extensively on the electrochemical conversion of CO2 into various useful chemicals. However, there is not yet a solution of sufficiently high enough efficiency and stability to demonstrate practical applicability. In this work, we use first-principles-based high-throughput screening to propose silver-based catalysts for efficient electrochemical reduction of CO2 to CO while decreasing the overpotential by 0.4-0.5 V. We discovered the covalency-aided electrochemical reaction (CAER) mechanism in which p-block dopants have a major effect on the modulating reaction energetics by imposing partial covalency into the metal catalysts, thereby enhancing their catalytic activity well beyond modulations arising from d-block dopants. In particular, sulfur or arsenic doping can effectively minimize the overpotential with good structural and electrochemical stability. We expect this work to provide useful insights to guide the development of a feasible strategy to overcome the limitations of current technology for electrochemical CO2 conversion.

Pure and Zn-doped Pt clusters go flat and upright on MgO(100).

Pure and doped sub-nanoclusters can exhibit superb catalytic activity, which, however, strongly depends on their size, shape, composition, and the nature of the support. This work is about surface-deposited sub-nano Pt-based clusters, which are promising catalysts for the reactions of dehydrogenation. Using density functional theory and ab initio calculations, and an ab initio genetic algorithm for finding the global minima of clusters, we found a peculiar effect that Pt5 and Pt4Zn clusters exhibit upon deposition on MgO(100). Both of them change shapes from the gas phase 3-D form to a planar form, and they stand upright on the support. Several reasons are responsible for this behaviour. In part, clusters go flat due to the electron transfer from the support. Indeed, the anionic Pt5(-) and Pt4Zn(-) species are flat also in the gas phase. Charging induces the second-order Jahn-Teller effect (or partial covalency) facilitated by the recruitment of the higher-energy 6p atomic orbitals on Pt into the valence manifold, and that is the reason for the planarization of the anions. Secondly, clusters maximize interactions with the surface O atoms (resulting in further favouring of 2-D structures over 3-D), and avoid contacts with surface Mg atoms (resulting in upright morphologies).