Adsorption of Methylene Blue Dye and Analysis of Two Clays: A Study of Kinetics, Thermodynamics, and Modeling with DFT, MD, and MC Simulations.

The purpose of this research was to learn more about the primary and secondary properties of Moroccan natural clay in an effort to better investigate innovative adsorbents and gain access to an ideal adsorption system. Scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy analysis (SEM-EDX) and X-ray fluorescence were employed for identification. SEM revealed clay grains, including tiny particles and unevenly shaped sticks. First- and second-order rate laws, representing two distinct kinetic models, were applied in the kinetic approach. Adsorption of dye MB onto natural clay was studied, and the results agreed with the 2 s order model. The significant correlation coefficients support the inference that the adsorption process was governed by the Langmuir model. Subsequent DFT analyses demonstrated that the methylene blue dye's HOMO and LUMO surfaces are dispersed across most of the dye's components, pointing to a strong interaction with the clay. To determine how the dye might be adsorbed onto the clay, we employed quantum descriptors to locate its most nucleophilic and electrophilic centers. Endothermic reactions are evident during the MB adsorption process on clay, as indicated by the positive values of ΔH0 and ΔS0 (70.49 kJ mol-1of RC and 84.19 kJ mol-1 of OC and 10.45 J mol-1 K-1 of RC and 12.68 mol-1 K-1 of OC, respectively). Additionally dye molecules on the adsorbent exhibit a higher order of distribution than in the solution, indicating that the adsorption process is spontaneous.

Designed complexes combining brazilein and brazilin with betanidin for dye-sensitized solar cell application: DFT and TD-DFT study.

Dye-sensitized solar cells (DSSCs) are promising third-generation photovoltaic cell technology owing to their easy fabrication, flexibility and better performance under diffuse light conditions. Natural pigment sensitizers are abundantly available and environmentally friendliness. However, narrow absorption spectra of natural pigments result in low efficiencies of the DSSCs. Therefore, combining two or more pigments with complementary absorption spectra is considered an appropriate method to broaden the absorption band and boost efficiency. This study reports three complex molecules: brazilin-betanidin-oxane (Braz-Bd-oxane), brazilin-betanidin-ether (Braz-Bd-ether) and brazilein-betanidin-ether (Braze-Bd-ether), obtained from the etherification and bi-etherification reactions of brazilin dye and brazilein dye with betanidin dye. The equilibrium geometrical structure properties, frontier molecular orbital, electrostatic surface potential, reorganization energy, chemical reactivities, and non-linear optical properties of the studied dyes were investigated using density functional theory (DFT)/B3LYP methods, with 6-31+G(d,p) basis sets and LANL2DZ for light atom and heavy atoms respectively. The optical-electronic properties were calculated using TD-DFT/B3LYP/6-31+G(d,p) for isolated dye and TD-DFT/CAM-B3LYP/6-31G(d,p)/LANL2DZ for dyes@(TiO2)9H4. The results reveal that spectra for Braz-Bd-oxane and Braze-Bd-ether complexes red-shifted compared to the individually selected dyes. The simulated absorption spectra of the adsorbed dyes on (TiO2)9H4 are red-shifted compared to the free dye. Moreover, Braz-Bd-oxane and Braz-Bd-ether exhibit better charge transfer and photovoltaic properties than the selected natural dyes forming these complexes. Based on the dyes' optoelectronic properties and photovoltaic properties, the designed molecules Braz-Bd-oxane and Braze-Bd-ether are considered better candidates to be used as photosensitizers in dye solar cells.

Physicochemical Characterization of Clay and Study of Cationic Methylene Blue Dye Adsorption.

In an attempt to examine novel adsorbents in accessing an ideal adsorption system, this study aimed to help understand the main and secondary characteristics of a Moroccan natural clay. X-ray fluorescence, infrared, and scanning electron microscopy with energy-dispersive X-ray spectroscopy analysis (SEM-EDX) were used for the identification. The findings demonstrate that this Clay is composed of a mixture of quartz, calcite, magnetite, and Rutile in very high proportions. SEM revealed the presence of clay grains in the presence of fine particles and irregularly contoured sticks. The results of semiquantitative detection by EDX also reveal the presence of certain mineral species (Si, Al, Mg, Fe, K, Cl, S, Ca, and Na). The exploited kinetic technique was achieved using two different kinetic models: first- and second-order rate laws. Commensurate to the obtained results, the 2-sec order model better described the adsorption of dye MB onto the natural clay. The results confirmed that the adsorption process followed the Langmuir model with the high coefficient correlation obtained which are very close to 1. In the sequel, DFT results revealed that the HOMO and LUMO surfaces of the methylene blue dye are mostly distributed on all dye parts, reflecting possible strong interactions with the clay. The quantum descriptors investigated in this study identify the most nucleophilic and electrophilic centers that can be used to suggest a suitable mechanism for the adsorption of the dye by the clay. The values of enthalpy ΔH0 and entropy ΔS0 of activation were -15.88 kJ mol-1 and -0.021 J mol-1 K-1, respectively, show that the nature of the adsorption process of MB on clay is exothermic and the order of distribution of the dye molecules on the adsorbent increases with respect to that of the solution so the negative values of ΔG0 (from -9. 62 to -8.99 kJ mol-1) indicate that the adsorption process is spontaneous.

A dispersion-corrected DFT calculation on encapsulation of favipiravir drug used as antiviral against COVID-19 into carbon-, boron-, and aluminum-nitride nanotubes for optimal drug delivery systems combined with molecular docking simulations.

Favipiravir (FAV) (6-fluoro-3-oxo-3,4-dihydropyrazine-2-carboxamide) is one of the most effective antiviral drugs which is cited for action against RNA-viral infections of COVID-19. In this study, density functional theory (DFT) calculations were used to investigate three nanotubes (NTs) with FAV drug as delivery systems. The encapsulated systems (ESs) consist of FAV drug inside carbon-carbon, aluminum nitride, and boron nitride. At B3LYP-D/6-31G(d,p) and CPCM/B3LYP-D/6-31G(d,p), the optimization of NTs, FAV, and its tautomeric forms and six ESs was investigated in gas and water environments. Five tautomeric forms of FAV were investigated, two keto forms (K1 and K2) and three enol forms (E1, E2, and E3). The results revealed that E3 and K2 isomeric forms represented the most stable structures in both media; thus, these two forms were encapsulated into the NTs. The stability and the synthesis feasibility of NTs have been proven by calculating their interaction energies. Non-covalent interactions (NCIs) were investigated in the ESs to show the type of NCI with the molecular voids. The binding energies, thermochemical parameters, and recovery times were investigated to understand the mechanism of FAV encapsulation and release. The encapsulated AlNNT systems are more favorable than those of BNNTs and CNTs in gas and aqueous environments with much higher binding energies. The quantum theory of atoms in molecules (QTAIM) and recovery time analysis revealed the easier releasing of E3 from AlNNT over K2 form. Based on molecular docking simulations, we found that E3 and K2 FAV forms showed a high level of resistance to SARS-CoV-6M3M/6LU7/6W9C proteases. Supplementary Information: The online version contains supplementary material available at 10.1007/s11224-023-02182-4.

A Combined Experimental and Computational (DFT, RDF, MC and MD) Investigation of Epoxy Resin as a Potential Corrosion Inhibitor for Mild Steel in a 0.5 M H2SO4 Environment.

In this work, a tetrafunctional epoxy resin entitled 2,3,4,5-tetraglycidyloxy pentanal (TGP) was tested and investigated as a potential corrosion inhibitor for mild steel (MS) in 0.5 M H2SO4 solution. The corrosion inhibition process for mild steel was employed alongside various techniques, such as potentiodynamic polarization (PDP), electrochemical impedance spectroscopy (EIS), temperature effect (TE), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and theoretical approaches (DFT, MC, RDF and MD). Further, the corrosion efficacies obtained at the optimum concentration (10-3 M of the TGP) were 85.5% (EIS) and 88.6% (PDP), respectively. The PDP results indicated that the TGP tetrafunctional epoxy resin acted the same as an anodic inhibitor type in 0.5 M H2SO4 solution. SEM and EDS analyses found that the protective layer formed on the MS electrode surface in the presence of TGP could prevent the attack of the sulfur ions. The DFT calculation provided more information regarding the reactivity, geometric properties and the active centers of the corrosion inhibitory efficiency of the tested epoxy resin. RDF, MC and MD simulations showed that the investigated inhibitory resin have a maximum inhibition efficiency in 0.5 M H2SO4 solution.

DFT calculations of 1H- and 13C-NMR chemical shifts of 3-methyl-1-phenyl-4-(phenyldiazenyl)-1H-pyrazol-5-amine in solution.

Geometries of the 3-methyl-1-phenyl-4-(phenyldiazenyl)-1H-pyrazol-5-amine azo-dye compound and its tautomer were optimized using B3LYP and M06-2X functionals in coupling with TZVP and 6-311 + G(d,p) basis sets. The 1H- and 13C-NMR chemical shifts of all species were predicted using 13 density functional theory (DFT) approaches in coupling with TZVP and 6-311 + G(d,p) basis sets at the different optimized geometries by applying the using GIAO method using the eight geometries. The selected functionals are characterized by having different amount of Hartree-Fock exchange. The selected DFT methods were B3LYP, M06-2X, BP86, B97XD, TPSSTPSS, PBE1PBE, CAM-B3LYP, wB97XD, LSDA, HSEH1PBE, PW91PW91, LC-WPBE, and B3PW91. The results obtained were compared with the available experimental data using different statistical descriptors such as root mean square error (RMSE) and maximum absolute error (MAE). Results revealed that the prediction of the 1H-NMR chemical shifts has more significant dependence on the applied geometry than that of the prediction of the 13C-NMR chemical shifts. Among all the examined functionals, B97D and TPSSTPSS functionals were found to be the most accurate ones, while the M06-2X functional is the least accurate one. Results also revealed that the prediction of NMR chemical shifts using TZVP basis sets results is more accurate results than 6-311 + G(2d,p) basis set.

Experimental and theoretical study for removal of trimethoprim from wastewater using organically modified silica with pyrazole-3-carbaldehyde bridged to copper ions.

BACKGROUND: Human and veterinary antibiotics are typically discharged as parent chemicals in urine or feces and are known to be released into the environment via wastewater treatment plants (WWTPs). Several research investigations have recently been conducted on the removal and bioremediation of pharmaceutical and personal care products (PPCPs) disposed of in wastewater. RESULTS: SiNP-Cu, a chelating matrix, was produced by delaying and slowing 1.5-dimethyl-1H-pyrazole-3-carbaldehyde on silica gel from functionalized with 3-aminopropyltrimethoxysilane. The prepared sorbent material was characterized using several techniques including BET surface area, FT-IR spectroscopy, Scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and nitrogen adsorption-desorption isotherm. The pseudo-second-order model provided the best correlation due to the big match between the experimental and theoretical of different adsorption coefficients. The Langmuir and Freundlich adsorption models were used and the study showed a better match with the Freundlich model with a capacity of removal reached up to 420 mg g-1. The removal capacity was dependent on pH and increased by increasing pH. The removal percentage reached 91;5% at pH = 8. The adsorbent demonstrated a high percentage removal of TMP, reaching more than 94% when increased pH. The sample was simply regenerated by soaking it for a few minutes in 1 N HCl and drying it. The sorbent was repeated five times with no discernible decrease in removal capacity. The thermodynamic study also showed endothermic, increasing randomness and not spontaneous. The free energy was 2.71 kJ/mol at 320 K. The findings of the DFT B3LYP/6-31 + g (d, p) local reactivity descriptors revealed that nitrogen atoms and π-electrons of the benzene and pyrimidine rings in the TMP are responsible for the adsorption process with the SiNP surface. The negative values of the adsorption energies obtained by molecular dynamic simulation indicated the spontaneity of the adsorption process. CONCLUSION: The global reactivity indices prove that TMP is stable and it can be removed from wastewater using SiNP surface. The results of the local reactivity indices concluded that the active centers for the adsorption process are the nitrogen atoms and the π-electrons of the pyrimidine and benzene rings. Furthermore, the positive value of the maximum charge transfer number (ΔN) proves that TMP has a great tendency to donate electrons to SiNP surface during the process of adsorption.

Synthesis, identification, density functional and Hirshfeld surface studies of 2,2'-disulfanediylbis(tetrahydro-4H-cyclopenta[d][1,3,2]dioxaphosphole-2-sulfide).

The new compound 2,2'-disulfanediylbis (tetrahydro-4H-cyclo penta[d][1,3,2]dioxaphosphole 2-sulfide), the dimeric form of 2-mercaptotetrahydro-4H-cyclopenta[d] [1,3,2] dioxaphosphole 2-sulfide, has been synthesized and characterized by elemental analysis, molecular weight determination and spectral data (1 H-NMR, 13 C-NMR, 31 P-NMR, FTIR). The molecular geometry was confirmed by single X-Ray crystallography. The ground state property was examined by PBE0 and B3LYP density functionals using aug-cc-pV(Q+d)Z basis set in the gas phase and in DMSO solution. The preference of PBE0 functional was statistically established. Thermodynamic parameters and standard heat of dissociation reaction ( Δ H R 298 K o ) have been established. The calculated equilibrium constants at different temperatures reflect the stability of the dimer over the monomers at low temperatures and vice versa. Valency and Fukui indices calculations showed that the monomer is more reactive than the dimer. 2D-fingerprint revealed that, while the H…X; [X = H, O and S] nonbonding intermolecular interactions and reciprocals play a crucial role in strengthening of molecules packing in the crystal unit cell while the S…S ones contribute negatively on it.

Cellulose-Based Hectocycle Nanopolymers: Synthesis, Molecular Docking and Adsorption of Difenoconazole from Aqueous Medium.

The goal of this work was to develop polymer-based heterocycle for water purification from toxic pesticides such as difenoconazole. The polymer chosen for this purpose was cellulose nanocrystalline (CNC); two cellulose based heterocycles were prepared by crosslinking with 2,6-pyridine dicarbonyl dichloride (Cell-X), and derivatizing with 2-furan carbonyl chloride (Cell-D). The synthesized cellulose-based heterocycles were characterized by SEM, proton NMR, TGA and FT-IR spectroscopy. To optimize adsorption conditions, the effect of various variable such as time, adsorbent dose, pH, temperature, and difenoconazole initial concentration were evaluated. Results showed that, the maximum difenoconazole removal percentage was about 94.7%, and 96.6% for Cell-X and Cell-D, respectively. Kinetic and thermodynamic studies on the adsorption process showed that the adsorption of difenoconazole by the two polymers is a pseudo-second order and follows the Langmuir isotherm model. The obtained values of ∆G ° and ∆H suggest that the adsorption process is spontaneous at room temperature. The results showed that Cell-X could be a promising adsorbent on a commercial scale for difenoconazole. The several adsorption sites present in Cell-X in addition to the semi crown ether structure explains the high efficiency it has for difenoconazole, and could be used for other toxic pesticides. Monte Carlo (MC) and Molecular Dynamic (MD) simulation were performed on a model of Cell-X and difenoconazole, and the results showed strong interaction.

Benchmark calculations of proton affinity and gas-phase basicity using multilevel (G4 and G3B3), B3LYP and MP2 computational methods of para-substituted benzaldehyde compounds.

This study presents the benchmark calculations of proton affinities (PAs) and gas-phase basicities (GBs) of 8-para substituted benzaldehyde compounds using the multilevel model chemistries (G3B3 and G4), density-functional quantum model (B3LYP) and ab initio model (MP2). The results show that the computed properties are strongly correlated with the available experimental data. The PAs and the GBs of other eight para-substituted benzaldehyde compounds, for which the experimental data does not currently exist, have been calculated using G3B3 and B3LYP methods. The correlations between the experimental PAs and GBs with the computed properties such as PA, GB, chemical properties (bond lengths, electron density and δ1 H NMR chemical shift) of the investigated benzaldehydes have been studied and statistically analyzed. The influence of the substituted groups has been discussed in terms of inductive effect and electron donating and electron withdrawing effect. The results obtained show that the chemical properties of the benzaldehyde compounds are controlled by the strong coupling between the CHO group and the nature of the para-substituent groups through the benzene ring as a conducting linkage.

Synthesis of Macromolecular Aromatic Epoxy Resins as Anticorrosive Materials: Computational Modeling Reinforced Experimental Studies.

Herein, two bifunctional macromolecular aromatic epoxy resins (ERs), namely, 4,4'-isopropylidenediphenol oxirane (ERH) and 4,4'-isopropylidene tetrabromodiphenol oxirane (ERBr), are synthesized, characterized, and evaluated as anticorrosive materials for carbon steel corrosion in acidic medium. ERs were characterized using proton nuclear magnetic resonance (1H NMR) and Fourier transform infrared spectroscopy techniques. Investigated ERs acted as effective corrosion inhibitors, and their inhibition effectiveness followed the order ERBr (96.5%) > ERH (95.6%). Potentiodynamic polarization results showed that ERH and ERBr behave as predominantly anodic type and the cathodic type of corrosion inhibitors, respectively. Adsorption of both the studied ERH and ERBr molecules obeyed the Langmuir adsorption isotherm model. Density functional theory and molecular dynamics studies showed that protonated forms of ERH and ERBr contribute more to metal (carbon steel)-inhibitor (ERH/ERBr) interactions than their neutral forms.

Epoxy pre-polymers as new and effective materials for corrosion inhibition of carbon steel in acidic medium: Computational and experimental studies.

Present study is designed for the synthesis, characterization and corrosion inhibition behavior of two diamine aromatic epoxy pre-polymers (DAEPs) namely, N1,N1,N2,N2-tetrakis (oxiran-2-ylmethyl) benzene-1,2-diamine (DAEP1) and 4-methyl-N1,N1,N2,N2-tetrakis (oxiran-2-ylmethyl) benzene-1,2-diamine (DAEP2) for carbon steel corrosion in acidic medium. Synthesized DAEPs were characterized using spectral (Nuclear magnetic resonance (1H NMR) and Fourier transform infrared-attenuated total reflection (FTIR-ATR)) techniques. Viscosity studies carried out at four different temperatures (20-80 °C) increase in temperature causes significant reduction in their viscosities. The anticorrosive properties of DAEPs differing in the nature of substituents, for carbon steel corrosion in 1 M HCl solution was evaluated using several experimental and computational techniques. Both experimental and computational studies showed that inhibitor (DAEP2) that contains electron releasing methyl (-CH3) showed higher protectiveness as compared to the inhibitor (DAEP1) without substituent (-H). Electrochemical results demonstrate that DAEPs act as reasonably good inhibitors for carbon steel in 1 M HCl medium and their effectiveness followed the sequence: DAEP2 (92.9%) > DAEP1 (91.7%). The PDP results show that the diamine aromatic epoxy pre-polymers molecules (DAEPs) act as mixed type inhibitors. Electrochemical study was also supported using scanning electron microscopy (SEM) method were significant improvement in the surface morphology of inhibited (by DAEPs) metallic specimens was obtained. Results derived from computational density functional theory (DFT) and molecular dynamics (MD) simulationsand studies were consistent with the experimental results derived from SEM, EIS and PDP electrochemical studies. Adsorption of the DAEPs obeyed the Langmuir adsorption isotherm model.

Anticorrosive properties of Hexa (3-methoxy propan-1,2-diol) cyclotri-phosphazene compound for carbon steel in 3% NaCl medium: gravimetric, electrochemical, DFT and Monte Carlo simulation studies.

The corrosion inhibition performance of Hexa (3-methoxy propan-1,2 diol) cyclotriphosphazene (HMC) on carbon steel in 3% NaCl solution was investigated by weight loss (WL), potentiodynamic polarization (PDP), electrochemical impedance spectroscopy (EIS) measurements, Density functional theory (DFT) and Monte Carlo (MC) simulation. The corrosion inhibition efficiency at optimum concentration (10-3M) is 99% of HMC at 298 K. The corrosion inhibition efficiency at 10-3 M decreases with increase in temperature. The adsorption of HMC on the surface of carbon steel obeyed Langmuir isotherm. Potentiodynamic polarization study confirmed that inhibitor anodic-type. DFT and Monte Carlo (MC) simulations based computational approaches were under taken to support the experimental findings. DFT studies revealed that HMC interact with metallic surface through donor-acceptor interactions in which the anionic parts act as electron donor (HOMO) and cationic parts behaved as electron acceptor (LUMO). The MC simulations study showed that studied HMC adsorb spontaneously on Fe (110) surface.

Adsorption and anticorrosive behavior of aromatic epoxy monomers on carbon steel corrosion in acidic solution: computational studies and sustained experimental studies.

Herein, the synthesis, characterization and corrosion inhibition effectiveness of two aromatic epoxy monomers (AEMs) namely, 2-(oxiran-2-yl-methoxy)-N,N-bis(oxiran-2-yl-methyl)aniline (AEM1) and N,N-bis(oxiran-2-ylmethyl)-2-((oxiran-2-ylmethyl) thio)aniline (AEM2), in carbon steel corrosive dissolution in 1 M HCl solution is investigated using computational and experimental techniques. AEM1 and AEM2 were characterized using FT-IR, 1H NMR and 13C NMR spectroscopy techniques. Electrochemical results demonstrated that AEMs act as reasonably good corrosion inhibitors for carbon steel in 1 M HCl medium and their effectiveness followed the sequence: AEM2 (95.4%) > AEM1 (94.3%). A PDP study showed that AEMs act as mixed-type inhibitors with slight anodic predominance. Adsorption of the AEMs obeyed the Langmuir isotherm model. Interactions between AEMs and the metallic surface was further studied using DFT and MD simulations that give several computational parameters such as I, A, E HOMO, E LUMO, ΔE, δ, χ, ρ, σ, η, ΔN and E ads. The experimental and computational results were in good agreement and well complimented each other.

Rheological, electrochemical, surface, DFT and molecular dynamics simulation studies on the anticorrosive properties of new epoxy monomer compound for steel in 1 M HCl solution.

A new epoxy monomer, namely, tetraglycidyl-1,2-aminobenzamide (ER), was synthesized by condensation of the amines with epichlorohydrin in a basic medium. The obtained epoxy monomer was characterized by FT-IR and 1H NMR spectroscopy. Rheological properties of this monomer were determined using an advanced rheometer. Subsequently, the synthesized ER monomer was investigated as corrosion inhibitor for carbon steel in 1 M HCl solution. The adsorption properties of ER were analyzed by electrochemical, surface investigation and theoretical computational studies using DFT and molecular dynamics (MD). Results showed a high dependence of the viscosity of ER on temperature and concentration, and also, that ER has better inhibition performance. A good agreement between the results derived from computational (MD and DFT) and experimental methods was observed. The thermodynamic parameters, along with the kinetic parameters, showed that the adsorption of ER molecules onto carbon steel surface obeyed the Langmuir isotherm model, and the adsorption at metal-electrolyte interfaces involved both chemical and physical adsorption, but predominantly chemisorption mechanism.

Anticorrosive Effects of Some Thiophene Derivatives Against the Corrosion of Iron: A Computational Study.

It is known that iron is one of the most widely used metals in industrial production. In this work, the inhibition performances of three thiophene derivatives on the corrosion of iron were investigated in the light of several theoretical approaches. In the section including DFT calculations, several global reactivity descriptors such as EHOMO, ELUMO, ionization energy (I), electron affinity (A), HOMO-LUMO energy gap (ΔE), chemical hardness (η), softness (σ), as well as local reactivity descriptors like Fukui indices, local softness, and local electrophilicity were considered and discussed. The adsorption behaviors of considered thiophene derivatives on Fe(110) surface were investigated using molecular dynamics simulation approach. To determine the most active corrosion inhibitor among studied thiophene derivatives, we used the principle component analysis (PCA) and agglomerative hierarchical cluster analysis (AHCA). Accordingly, all data obtained using various theoretical calculation techniques are consistent with experiments.

Preference for a C3 conformation in tris-dimethylaminophosphonium cations: a comparison of the reactions of (Me2N)3P with I-X (X = Cl, Br, I, CN).

Tris-(dimethylamino)phosphine reacts with I(2) to form (Me(2)N)(3)PI(2), which when recrystallised from acetonitrile displays a structure of overall stoichiometry [{(Me(2)N)(3)PI}I](6).CH(3)CN . The asymmetric unit of consists of four different [(Me(2)N)(3)PI](+) cations, one of these exhibits a cation-anion interaction to an iodide ion, with an I-I contact distance of 3.6378(14) A, the longest yet observed for an R(3)PI(2) compound. Two of the other three cations display no interactions, whilst a cation-solvent interaction is observed for the fourth. When (Me(2)N)(3)PI(2) is recrystallised from dichloromethane the molecule abstracts chlorine from the solvent to form [(Me(2)N)(3)PCl]I this latter compound can also be synthesised directly from (Me(2)N)(3)P and ICl. The reaction of (Me(2)N)(3)P with IBr forms [(Me(2)N)(3)PBr]I, which when recrystallised from chlorinated solvents forms [(Me(2)N)(3)PCl(0.5)Br(0.5)]I. The analogous [(Me(2)N)(3)PCN]I, does not display CN-Cl exchange and can be recrystallised from dichloromethane. The structures of and have all been determined by X-ray diffraction. All of the (Me(2)N)(3)P groups in the cations in, and exhibit a C(3) conformation, in contrast to the majority of (R(2)N)(3)P systems where a C(s) conformation is usually preferred. This C(3) conformation appears to be favoured where there is increased positive charge on phosphorus, as is the case in the phosphorus(v) ionic species described herein. This conformation allows greater P-N pi-bonding, and as a result the P-N bonds are shortened, varying between 1.566(10) and 1.624(10) A in these compounds.

Gas-phase reactivity of 2,7-dimethyl-[1,2,4]-triazepine thio derivatives toward Cu+ cation: a DFT study.

The gas-phase interactions of 2,7-dimethyl-[1,2,4]-triazepine and its thio derivatives with Cu+ were studied through the use of high-level density functional theory (DFT) calculations. The structure of all possible tautomers and their conformers was optimized at the B3LYP/6-31G(d) level of theory. Final energies were obtained at the B3LYP/6-311+G(2df,2p) level. It has been found that the direct association of Cu+ occurs at the oxygen atom attached to position 3 in the case of the dioxo derivative and at the sulfur atom in all other cases. For the dithio derivatives, the global minimum of the PES corresponds to the structure in which the metal ion bridges between the heteroatom at position 3 and the nitrogen atom at position 4 of the corresponding enolic tautomer, forming a four-membered ring structure; for the dioxo derivative, this conformer competes with the ketone tautomer. Moreover, the isomerization processes leading from the most stable adduct to the other stable conformers were investigated. Among all the considered compounds, the 3,5-dithiotriazepines-Cu+ is found to be the one that associates Cu+ more tightly in the gas phase. The calculated Cu+ binding energies show a good correlation with the experimental proton affinities.