Theoretical DFT Study Research Articles

Mechanistic Insights into Ni(II)-Catalyzed Nonalternating Ethylene-Carbon Monoxide Copolymerization.

Polyethylene materials with in-chain-incorporated keto groups were recently enabled by nonalternating copolymerization of ethylene with carbon monoxide in the presence of Ni(II) phosphinephenolate catalysts. We elucidate the mechanism of this long-sought-for reaction by a combined theoretical DFT study of catalytically active species and the experimental study of polymer microstructures formed in pressure-reactor copolymerizations with different catalysts. The pathway leading to the desired nonalternating incorporation proceeds via the cis/trans isomerization of an alkyl-olefin intermediate as the rate-determining step. The formation of alternating motifs is determined by the barrier for the opening of the six-membered C,O-chelate by ethylene binding as the decisive step. An η2-coordination of a P-bound aromatic moiety axially oriented to the metal center is a crucial feature of these Ni(II) catalysts, which also modulates the competition between the two pathways. The conformational constraints imposed in a 2′,6′-dimethoxybiphenyl moiety overall result in a desirable combination of disfavoring ethylene coordination along the alternating incorporation pathway, which is primarily governed by electronics, while not overly penalizing the nonalternating chain growth, which is primarily governed by sterics.

Synthesis, characterization, and electronic structure of SrBi2S4

Black-colored crystals and a pure polycrystalline phase of SrBi2S4 were synthesized using the high-temperature sealed tube method. A single-crystal and powder X-ray diffraction studies established the crystal structure and phase purity of SrBi2S4, respectively. It crystallizes in the hexagonal C6h2−P63/m (176) space group with lattice parameters of a ​= ​b ​= ​24.9335(6) Å and c ​= ​4.0946(1) Å. The structure is made up of three-dimensional 3∞ [Bi2S4]4− anionic framework with one-dimensional tunnels which are occupied by Sr atoms. The optical bandgap and temperature-dependent resistivity studies indicated semiconducting nature for polycrystalline SrBi2S4 in agreement with the theoretical DFT study. The thermal conductivity (κ) of a cold-pressed sintered disk of SrBi2S4 decreases on heating the sample. The κ values vary from ∼0.65 ​W/mK at 300 ​K to ∼0.55 ​W/mK at 773 ​K. The COHP analysis is performed to estimate the relative strength of chemical bonding between Bi–S and Sr–S pairs.

Anode-cathode interchangeable strategy for in situ reviving electrocatalysts’ critical active sites for highly stable methanol upgrading and hydrogen evolution reactions

Surface re-construction was a common phenomenon for non-oxide compound electrocatalysts in anodic oxidation reaction in alkaline electrolyte but surface deactivation arising from excessive oxidation/hydroxylation was critical hindrance to the long-term stability. Herein, a unique anode-cathode interchangeable electrocatalysis strategy is proposed for methanol upgrading reaction (MUR) and hydrogen co-generation in membrane-free electrolyzer. A periodical electrolysis is taken place for the Ni3S2/CNTs electrode at positive/negative currents over time. Compared with the traditional chronopotentiometry mode, the MUR-HER coupled reactions by periodically switching anode/cathode per hour present an excellent long-term stability at high current densities of ± 100 mA cm−2, in which the Faradaic efficiencies for both H2 and value-added formate are greater than 95%. Substantial experimental results and deep theoretical DFT studies signify that the successful application of this strategy is mainly due to the reversible modulation of oxidation/hydroxylation status on Ni3S2 surface, which effectively prevent the surface active structures of electrocatalysts from over-oxidation.

The Role of Adsorbed Oxygen for the Ethane Oxidative Dehydrogenation on Nio(110) and (100) Surface: A Dft Theoretical Study

The Role of Adsorbed Oxygen for the Ethane Oxidative Dehydrogenation on Nio(110) and (100) Surface: A Dft Theoretical Study

Ultra-High Oxygen Evolution Potential of Cuo5-Zn1 Active Sites on Sno2(110) Surface and its Origin: Dft Theoretical Study

Ultra-High Oxygen Evolution Potential of Cuo5-Zn1 Active Sites on Sno2(110) Surface and its Origin: Dft Theoretical Study

Experimental and Theoretical DFT Study of Cu(I)/N,N-Disubstituted-N'-acylthioureato Anticancer Complexes: Actin Cytoskeleton and Induction of Death by Apoptosis in Triple-Negative Breast Tumor Cells.

Six complexes with the general formula [Cu(acylthioureato)(PPh3)2] were synthesized and characterized using spectroscopic techniques (IR, UV/visible, and 1D and 2D NMR), mass spectrometry, elemental analysis, and X-ray diffraction. Interpretation of the in vitro cytotoxicity data of Cu(I) complexes took into account their stability in cell culture medium. DFT calculations showed that NMR properties, such as the shielding of carbon atoms, are affected by relativistic effects, supported by the ZORA Hamiltonian in the theoretical calculations. Additionally, the calculation of the energies of the frontier molecular orbitals predicted that the structural changes of the acylthiourea ligands did not cause marked changes in the reactivity descriptors. All complexes were cytotoxic to the evaluated tumor cell lines [MDA-MB-231 (triple-negative breast cancer, TNBC), MCF-7 (breast cancer), and A549 (lung cancer)]. In the MDA-MB-231 cell line, complex 1 significantly altered the cytoskeleton of the cells, reducing the density and promoting the condensation of F-actin filaments. In addition, the compound caused an increase in the percentage of cells in the fragmented DNA region (sub-G0) and induced cell death via the apoptotic pathway starting at the IC50 concentration. Taken together, the results show that complex 1 has cytotoxic and apoptotic effects on TNBC cells, which is a cell line originating from an aggressive, difficult-to-treat breast cancer.

Spodium bonds and metal–halogen···halogen–metal interactions in propagation of monomeric units to dimeric or polymeric architectures

In this work we report on crystal structures of a heteroleptic coordination polymer [Hg2(HL)Cl4]n (1) where the nitrogen atom of the peripheral pyridine fragment is linked to another HgCl2 molecule and two discrete mononuclear heteroleptic complexes [Hg(HL)I2] (2) and [Mn(HL)Cl2]·MeOH (3·MeOH), which were obtained through self-assembling of N'-(1-(pyridin-2-yl)ethylidene)isonicotinohydrazide (HL) with HgCl2, HgI2 or MnCl2, respectively. HL coordinates the HgII salts in its keto-form, while MnCl2 is chelated by a zwitterionic form of HL confirmed by the solid state IR spectroscopy. The studied here ligand molecule has a tendency to involve the 4-pyridyl nitrogen atom in coordination bonding which is correlated with the ability to transfer the electric charge and production of a zwitterionic form. The crystal structure and Hirshfeld surface data analysis show a great importance of spodium bonds and metal–halogen⋯halogen–metal interactions. A prominent consequence of lack of σ- or π-hole interactions in case of MnII ion is the isolation of metal center from the external contacts. Apart form this in 3·MeOH the halogen⋯halogen interactions are absent. It seems that the σ- or π-hole regions formed at the HgII cation in 1 and 2 favor the participation of coordinated Cl or I atoms in the M–Hal⋯Hal'–M' halogen⋯halogen interactions, whereas in complex 3·MeOH there are no metal or halogen centered σ-hole interactions. Thus, the 1D coordination polymer in 1 is stabilized by the Hg⋯Cl spodium bonding. Additionally, the observed intermolecular halogen⋯halogen interactions in 1 provide cross-linking of the 1D coordination polymers, yielding a 2D supramolecular double-layered sheet. In 2 an additional contact between halogen and mercury atoms results in a dimeric unit. These dimers are linked into a 1D polymer by halogen⋯halogen interactions between metal bounded iodine atoms. The DFT theoretical studies were applied to analyze the Hg⋯X non-covalent spodium interactions that govern the formation of the 1D polymeric structure in 1 and self-assembled dimers in 2.

A study of fungicidal and anti-phenol oxidase activity of some \u03b1-amino phosphonate derivatives

BackgroundDeveloping new pesticides with multi-function may be a suitable strategy to save time and cost and reduce the emergence of resistant strains of pests and pathogens. The organophosphorus derivatives have not been widely used in agriculture as fungicides. In this work, a series of six α-amino phosphonate derivatives were prepared and tested for their fungicidal and anti-phenol oxidase activities.ResultsThe prepared compounds revealed a promising anti-fungal activity against Macrophomina phaseolina and Pythium aphanidermatum, especially M4, with MIC of 62 mg/L for M. phaseolina. M4 did not affect the fungus permeability rate of the cell membrane; however, it displayed a significant efficiency on mycelial soluble protein content. M4 and M3 with a hydroxyl group on the aniline moiety exhibited an observed anti-phenol oxidase activity. M4 inhibited the enzyme at 1 mg/mL. The DFT theoretical study revealed a significant correlation between the substituents of aniline moiety and the bioactivity of the studied compounds. The negative charge conspicuously influenced the anti-phenol oxidase activity.ConclusionsOur findings suggest the studied compounds as bases to design more effective α-amino phosphonate fungicides with additional anti-phenol oxidase activity.Graphic abstract

Theoretical DFT Study on the Mechanisms of CO/CO2 Conversion in Chemical Looping Catalyzed by Calcium Ferrite.

The CO/CO2 conversion mechanism on the calcium ferrite (CFO) surface in chemical looping was explored by a computational study using the density functional theory approach. The CFO catalytic reaction pathway of 2CO + O2 → 2CO2 conversion has been elucidated. Our results show that the Fe center in CFO plays the key role as a catalyst in the CO/CO2 conversion. Two energetically stable spin states of CFO, quintet and septet, serve as the effective catalysts. The presence of the triplet O2 molecule caused the conversion of these two spin-state structures into each other along the catalytic reaction pathway. A double release of CO2 was predicted following this reaction mechanism. The rate-determining step is the formation of the 2CO2-CFO complex (P4) in the quintet state (19.0 kcal/mol). The predicted energy barriers for all the steps suggest that the proposed pathway is plausible.

Nickel(II) complexes of two potentially heptadentate(N7) Tripodal Schiff-base ligands; X-ray crystal structure and theoretical studies

In absolute methanol, one equivalent of tripodal tetraamines bis(3-aminopropyl)(2-aminoethyl)amine, ppe or (3-aminopropyl)-bis(2-aminoethyl)amine, pee condenses with three equivalents of 2-pyridinecarboxaldehyde. Upon the addition of Ni(II) salt to the solutions of produced Schiff base ligands, two new Schiff-base complexes, [Ni(py3ppe)](ClO4)2, (1), and [Ni(py3pee)](ClO4)2, (2), were prepared. Both complexes 1 and 2 were characterized by X-ray crystal structure analysis, CHN elemental analysis and FT-IR spectroscopy. The data show that both complexes have a distorted trigonal antiprism geometry for Ni(II) ion, in which the tertiary nitrogen atom has been not coordinated to the central metal ion. A DFT theoretical study at bp86/def2-tzvp level of theory on a series of this type of Ni(II) complexes shows that, interestingly, the values of metal–ligand interaction energies are very similar and are about 510 ± 2 kcal mol−1.

Oxovanadinum (IV) complexes with bidentate ligands synthesis, characterization, and comparison between experimental and theoretical

Four oxovanadium (IV) complexes with different ligands have been prepared and characterized by different spectral techniques such as (FTIR, UV–Vis., Mass) spectra, magnetic susceptibility, and DFT theoretical studies. Ligands used in this study were 8-hydroxyquinoline (HQ), oxalate (ox), dithiooximid (DTO), and 3-aminopyridine (APY). All the spectroscopic data and the theoretical calculations confirmed that the oxovanadium (IV) complexes are paramagnetic and have distorted square pyramidal structures. The FTIR spectra explain that the ligands were bidentate by (N, O), (O, O), (N, N) ligands, and monodentate (N-donor) 3-aminopyridine ligand. The mass spectral data confirmed that the complexes are mononuclear. Theoretical calculations of the free ligands and the prepared complexes have been done by using DFT calculations with proper basis sets for each other. The complexes were very stable and their energies ranged from (−775.86 to −1164.09 a.u.) and were very different from that of the free (HQ, ox, DTO and APY) ligands. The prepared complexes are more polar (5.69 to 15.54 Debye) than the free ligands. The HOMO orbitals energies of the complexes are ranged from (−0.098 to −0.392 a.u.), whereas the ligands are ranged from (−0.216 to −0.262 a.u.), and the LUMO orbitals energies of the oxocomplexes are ranged from (−0.007 to −0.296 a.u.)

An ultrasensitive ″OFF–ON″ fluorogenic sensor based on thiazole derivative for Zn2+: Food supplement, water and bio–imaging applications

In the present study, the design of a novel turn–on fluorescent probe ((E)–5–methoxy–4–((thiazol–2–ylimino)methyl)benzene–1,3–diol) (TBD) was reported. TBD showed an excellent fluorogenic response (λex = 420 nm, λem = 530 nm) to sense Zn2+ in HEPES buffer/MeCN (5/95, v/v; pH = 7.4) media. The quantum (Φ) yield of the probe TBD increased importantly with Zn2+ and was calculated for TBD (Φ = 0.073) and TBD–Zn2+ complex (Φ = 0.78). The LOD and binding constant (Ka) of TBD were 1.29 nM and 1.102 × 106 M−1, respectively. The sensing process of TBD toward Zn2+ (1:1) was verified by the Job's plot, MALDI–TOF–MS, and 1H NMR titration studies. The ''off–on'' fluorogenic response of TBD was qualified to the photo–induced electron transfer (PET) process. The experimental outcomes were also verified by theoretical DFT studies. Furthermore, TBD had been successfully utilized to detect Zn2+ in food supplement products, drinkable water samples and living–cells for on–site analysis.

Ni-doped MoS2 modified graphitic carbon nitride layered hetero-nanostructures as highly efficient photocatalysts for environmental remediation

Highly efficient and cost-effective photocatalysts are among the most prominent targets in the field of environmental remediation and clean energy production. Here, we report that 2D/2D layer heterostructures composed of exfoliated Ni-doped MoS2 nanosheets and g-C3N4 layers can carry out photocatalytic Cr(VI) reduction in aqueous solutions with outstanding activity, exhibiting apparent QYs as high as 29.6 % and 23.7 % at 375 and 410 nm. We show that Ni doping of MoS2 markedly increases the photochemical activity, which, together with electrochemical, spectroscopic and theoretical DFT studies, arises from the enhanced carrier density and mobility at the Ni-MoS2/g-C3N4 interface. In addition to the favorable charge transport properties, delineation of the photoinduced oxidation reactions by gas monitoring techniques reveals that the high efficiency also arises from fast water oxidation kinetics. The results of this work mark an important step forward in understanding and designing low-cost and earth-abundant catalysts for detoxification of Cr(VI)-contaminated industrial effluents.

Structural, spectroscopic and DFT theoretical studies of phosphorescent CuIP2S-containing cuprous complexes.

Luminescent cuprous complexes are important coordination compounds due to their relative abundance, low cost and ability to display excellent luminescence. The structures of two CuIP2S-type cuprous complexes, namely, iodido(thiourea-κS)bis(triphenylphosphane-κP)copper(I), [CuI(CH4N2S)(C18H15P)2] or [CuI(TU)(TPP)2] (I), and (2,3-dihydrobenzimidazole-2-thione-κS)iodidobis(triphenylphosphane-κP)copper(I), [CuI(C7H6N2S)(C18H15P)2] or [CuI(DHBIT)(TPP)2] (II), are described. In these two structures, the complex molecules of both are constructed by one copper(I) centre, one iodide ion, two TPP ligands and one thione ligand (TU for I and DHBIT for II). The copper(I) centres of I and II are both located in a distorted CuIP2S tetrahedron and are coordinated by two P atoms from two TPP ligands, one S atom from the thione ligand and the I atom. The UV-Vis absorption and photoluminescence properties of these CuIP2S-type cuprous complexes have been studied using crystalline powder samples. Detailed time-dependent density functional theory (TD-DFT) calculations and wavefunction analysis reveal that the pale-blue-green phosphorescence emission should originate from intra-ligand (TPP for I and DHBIT for II) charge transfer, with a small component of the metal-to-ligand charge transfer 3(IL+ML)CT excited state.

The influence of low-temperature argon matrix on embedded water clusters. A DFT theoretical study

Computer simulations of an argon fcc crystal fragment with embedded water clusters of different sizes are performed using the quantum mechanical DFT/M06-2X method. The effect of the argon matrix on the structural, energy, and spectral parameters of individual water clusters are investigated. The formation energies of (H2O)n@Arm complexes, as well as deformation energies of water clusters and of the argon crystal involved in the embedment, are computed for n = 1–7. Matrix shifts of the IR vibrational frequencies of water clusters isolated in argon matrices are predicted based on the results of the calculations. The predictions indicate a possibility of the formation of small stable water complexes in low-temperature argon matrices.

Structural characterization, dielectric properties, optical and theoretical DFT study of (C8H14N2)(BF4)2·H2O compound

The new organic salt m-xylylenediaminium bis (tetrafluoroborate) monohydrate was prepared from a mixture of an aqueous solution of tetrafluoroborate acid and m-xylylenediamine. Crystals were grown by slow evaporation method and characterized by single-crystal X-ray diffraction. It crystallizes in the monoclinic system, space group P21/c, with a = 5.4839(2), b = 10.9453(3), c = 23.0760(6) A, β = 95.105(1)°, V = 1379.59(14) A3 and Z = 4. The intermolecular interactions were identified by Hirshfeld Surfaces analysis and their associated 2D fingerprint plots. Photoluminescence and UV–Vis absorption were carried out to identify optical properties and determine the energy gap. Dielectric and conduction mechanism were studied at different frequencies, in the temperature range of 303–390 K. A comparison of the optimized structure at the B3LYP/6-311++G(2d,2p) level, using the density functional theory, was made with the experimentally determined structure. Comprehensive experimental and theoretical structural studies were carried out by FT-IR. Molecular electrostatic potentials were also studied and discussed.

Synthesis of crystalline carbon nitride with enhanced photocatalytic NO removal performance: An experimental and DFT theoretical study

The pristine carbon nitride derived from the thermally-induced polymerization of nitrogen-containing precursors (e.g. cyanamide, dicyanamide, melamine and urea) displays low crystallinity because of the predominantly kinetic hindrance. Herein, we reported a modified molten-salts method to fabricate the crystalline carbon nitride under ambient pressure, which is expected to the large-scale production of crystalline carbon nitride. The obtained crystalline carbon nitride displayed about 3.0 times higher photocatalytic NO removal performance than that of pristine carbon nitride under visible light irradiation (λ < 400 nm). Detailed experimental characterization and theoretical calculation revealed the crucial roles of crystallinity in crystalline carbon nitride for the enhanced photocatalytic NO removal performance. This research provided deep insights into the crystallinity of carbon nitride for the enhanced photocatalytic performance.

Energetic stability and geometrical structure of variously terminated and N-doped diamond (111) surfaces – A theoretical DFT study

H-, O-, OH- and F-terminated N-doped diamond surfaces are calculated by the density functional theory in the present study. Combined effects of terminating species and substitutional N dopants in the 1st or 2nd carbon layers on several critical features (i.e., bond length, total electron density, bond population, atomic charge, Fukui function, and density-of-states) are systematically studied and discussed. The N dopant presents clear, but local, effects for all the terminating species and dopant positions. The adsorption of any individual species to the N dopant in the 1st carbon layer results in the reduction of adsorption energy (less negative), most probably owing to the full shell structure of this N dopant. The H, OH and F each provides one unpaired electron to occupy the antibonding states within the N–H, N–OH and N–F bonds, making the bonds elongated, reducing the corresponding electron densities and bond populations. On the contrary, the N dopant in the 2nd carbon layer induces slight increment of the adsorption energy for O, OH and F, attributed to the positive atomic charges of neighboring topmost C atoms. Amongst the four adsorbates, the O shows the highest reactivity to either an electrophilic or a nucleophilic attack. Besides, N dopants have slight influences on the reactivity of the adjacent adsorbates. The present results can help to understand some related chemical processes (such as the oxidation and electrochemical analysis) on N-doped diamond films.

Theoretical DFT study on metal–organic frameworks for hydrogen storage

The cluster approach has been applied to mimic metal–organic framework (MOF) structures formed by 1,4-benzenecarboxylate linkers and metal cation connectors. The geometry optimizations are carried out at B3LYP/6-31G* level followed by frequency calculations. It was found that the replacement of OBe46+ connectors with OMg46+ (or OZn46+) ones leads to an increase in both the unit-cell sizes and basicity of oxide sites making them more potential for molecular hydrogen storage applications. Within the selected secondary building units (larger cluster models), the above replacement does not lead to an alteration on conduction and valence bands as well as in the resulting bandgap values. Bottleneck point of these structures is due to the presence of the so-called “central bulk” fourfold coordinated tetrahedral oxide anion site. The latter can be efficiently removed via replacement to “distorted cubic core” by introducing ZnTi3O46+ or MgTi3O46+ connectors which can be further replaced by MgSi3O46+ units. The all threefold coordinated O3C sites formed act as potential adsorption sites for incoming hydrogen molecules. Two-layer ONIOM (MP2/6-31G*: HF/3-21G) calculations have shown that the binding energies of molecular hydrogen lie within 5.5 and 5.3 kJ/mol for the MOF structures with MgTi3O46+ and MgSi3O46+ connectors, respectively.

A size-selective method for increasing the performance of Pt supported on tungstated zirconia catalysts for alkane isomerization: a combined experimental and theoretical DFT study

A high-octane number blend was obtained with Pt/WO3–ZrO2 catalysts, synthesized by an easy alkoxide-free method for the cluster size control.