def2-TZVPP Level Of Theory Research Articles

Elucidation of the influence of trinitro-diazinotriazine isomerism on the energetic properties and stability: Insights from DFT approach

The exploration of isomeric energetic molecules with high nitrogen content and the examination of their structure–property relationships remains compelling areas of interest within the field of energetic materials. Energetic isomers comprising the same molecular composition but distinct molecular structures potentially lead to notable variations in performance and properties. This study focused on designing and evaluating different forms of diazinotriazine using two molecular compositions: C5H3N5 and C5N8O6, aiming to generate various isomeric structures and to guide the rational design of new molecules. The electronic configurations, energetic properties, and sensitivity prediction of the optimized structures were investigated using the M06-2X/def2-TZVPP level of theory. The trinitro-diazinotriazine isomers exhibit high heat of formation (>486 kJ/mol), high detonation properties (D > 8.7 km/s, P > 34 GPa), high density (>1.81 g/cm3), and better thermal stability (BDE > 230 kJ/mol) making them promising explosive contenders. Among the designed diazinotriazine backbones, the pyridazine-1,2,3-triazine framework is favourable for the heat of formation and detonation properties. The heats of formation, detonation velocity, pressure, and heats of detonation of A4 and B4 outperform the other trinitro-diazinotriazine isomers.

Nature of Charge Transfer Effects in Complexes of Dopamine Derivatives Adsorbed on Graphene-Type Nanostructures

Continuing the investigation started for dopamine (DA) and dopamine-o-quinone (DoQ) (see, the light absorption and charge transfer properties of the dopamine zwitterion (called dopamine-semiquinone or DsQ) adsorbed on the graphene nanoparticle surface is investigated using the ground state and linear-response time-dependent density functional theories, considering the ωB97X-D3BJ/def2-TZVPP level of theory. In terms of the strength of molecular adsorption on the surface, the DsQ form has 50% higher binding energy than that found in our previous work for the DA or DoQ cases (−20.24 kcal/mol vs. −30.41 kcal/mol). The results obtained for electronically excited states and UV-Vis absorption spectra show that the photochemical behavior of DsQ is more similar to DA than that observed for DoQ. Of the three systems analyzed, the DsQ-based complex shows the most active charge transfer (CT) phenomenon, both in terms of the number of CT-like states and the amount of charge transferred. Of the first thirty electronically excited states computed for the DsQ case, eleven are purely of the CT type, and nine are mixed CT and localized (or Frenkel) excitations. By varying the adsorption distance between the molecule and the surface vertically, the amount of charge transfer obtained for DA decreases significantly as the distance increases: for DoQ it remains stable, for DsQ there are states for which little change is observed, and for others, there is a significant change. Furthermore, the mechanistic compilation of the electron orbital diagrams of the individual components cannot describe in detail the nature of the excitations inside the complex.

Vibrational spectroscopy and structural characterization of neutral and cationic hydroxyacetone

In this study, we utilized the infrared (IR)–vacuum-ultraviolet (VUV) non-resonant ionization and fragmentation detected IR spectroscopy (NRIFD-IR) technique to explore the IR spectra (2700–7200 cm-1) and the structures of both neutral and cationic hydroxyacetone. By comparing the experimentally obtained IR spectra with the anharmonic frequencies calculated at the B2PLYP-D3/cc-pVTZ and B3LYP-D3(BJ)/def2-TZVPP level of theory, we assigned the structures of hydroxyacetone and its cation. Notably, we observed a discrepancy in the neutral spectrum within the CH stretch region, depending on whether the parent or fragment channel was monitored. This observation suggests that the near-threshold dissociative ionization process exhibits mode-selectivity, implying that certain vibrational modes play a crucial role in either facilitating or inhibiting the dissociation event.

Characterization and conformational analysis of a novel hydrazonoyltetrazole: Crystallographic and theoretical investigations of an unexpected reaction product

A new hydrazonoyltetrazole was isolated as a byproduct from a previously reported reaction, and characterized by 1H and 13C NMR spectroscopy, infrared spectroscopy, single-crystal X-ray diffraction, and high-resolution mass spectroscopy. Intermolecular interactions in the crystal state were examined by Hirshfeld surface analysis (HSA), 2D fingerprint plots, and noncovalent interaction analysis (NCI). Geometry optimization in the gaseous phase was executed at the ωB97X-D4/def2-TZVPP level of theory, and subsequent maps of molecular electrostatic potential (MEP) were generated and analyzed. The calculated MEP was in good agreement with the HSA and NCI results. Conformational analysis was performed using a CREST/CENSO protocol. Two low-energy solution conformers were obtained. To confirm the presence of the second conformer, 1H NMR spectra were calculated, the transition state connecting the two conformers was found, and their energies were obtained with the DLPNOCCSD(T) scheme. A barrier of only 4 kcal mol-1 was found between them, and their MEP maps were also created. The dispersion energies between fragments of the three structures were calculated using the local energy decomposition (LED) scheme.

Using Hybrid PDI-Fe3O4 Nanoparticles for Capturing Aliphatic Alcohols: Halogen Bonding vs. Lone Pair-π Interactions.

In this study, Fe3O4 nanoparticles (FeNPs) decorated with halogenated perylene diimides (PDIs) have been used for capturing VOCs (volatile organic compounds) through noncovalent binding. Concretely, we have used tetrachlorinated/brominated PDIs as well as a nonhalogenated PDI as a reference system. On the other hand, methanol, ethanol, propanol, and butanol were used as VOCs. Experimental studies along with theoretical calculations (the BP86-D3/def2-TZVPP level of theory) pointed to two possible and likely competitive binding modes (lone pair-π through the π-acidic surface of the PDI and a halogen bond via the σ-holes at the Cl/Br atoms). More in detail, thermal desorption (TD) experiments showed an increase in the VOC retention capacity upon increasing the length of the alkyl chain, suggesting a preference for the interaction with the PDI aromatic surface. In addition, the tetrachlorinated derivative showed larger VOC retention times compared to the tetrabrominated analog. These results were complemented by several state-of-the-art computational tools, such as the electrostatic surface potential analysis, the Quantum Theory of Atoms in Molecules (QTAIM), as well as the noncovalent interaction plot (NCIplot) visual index, which were helpful to rationalize the role of each interaction in the VOC···PDI recognition phenomena.

Predicting valence tautomerism in diverse cobalt-dioxolene complexes: elucidation of the role of ligands and solvent.

The ability of molecular switches to reversibly interconvert between different forms promises potential applications at the scale of single molecules up to bulk materials. One type of molecular switch comprises cobalt-dioxolene compounds that exhibit thermally-induced valence tautomerism (VT) interconversions between low spin Co(iii)-catecholate (LS-CoIII-cat) and high spin Co(ii)-semiquinonate (HS-CoII-sq) forms. Two families of these compounds have been investigated for decades but have generally been considered separately: neutral [Co(diox)(sq)(N2L)] and cationic [Co(diox)(N4L)]+ complexes (diox = generic dioxolene, N2L/N4L = bidentate/tetradentate N-donor ancillary ligand). Computational identification of promising new candidate compounds prior to experimental exploration is beneficial for environmental and cost considerations but requires a thorough understanding of the underlying thermochemical parameters that influence the switching. Herein, we report a robust approach for the analysis of both cobalt-dioxolene families, which involved a quantitative density functional theory-based study benchmarked with reliable quasi-experimental references. The best-performing M06L-D4/def2-TZVPP level of theory has subsequently been verified by the synthesis and experimental investigation of three new complexes, two of which exhibit thermally-induced VT, while the third remains in the LS-CoIII-cat form across all temperatures, in agreement with prediction. Valence tautomerism in solution is markedly solvent-dependent, but the origin of this has not been definitively established. We have extended our computational approach to elucidate the correlation of VT transition temperature with solvent stabilisation energy and change in dipole moment. This new understanding may inform the development of VT compounds for applications in soft materials including films, gels, and polymers.

Iridium/Zinc-Co-Catalyzed Ring-Opening Reactions of Oxabicyclic Alkenes with Indole Nucleophiles: A Combined Experimental and Theoretical Study

An experimental and theoretical investigation on the iridium/zinc-co-catalyzed ring-opening reactions of oxabicyclic alkenes with indole nucleophiles is reported. The reaction affords trans-3-indolyl-1,2-dihydronaphthalen-1-ol products in good yield with no N-alkylated products observed. The C–C bond-forming reaction does not require prior functionalization and is entirely atom-economic. The mechanism and origins of selectivity in the iridium-catalyzed ring-opening reaction have been examined at the M06-D3/Def2TZVPP level of theory. Orbital analysis and natural population analysis charges demonstrate that the Cα site of the π-allyliridium intermediate is the most electrophilic site of attack. Distortion/interaction analysis reveals that the chemoselectivity likely originates from an earlier-stage transition state between Cα and C3, which requires less distortion energy compared to Cα–N1 during the rate-determining intermolecular nucleophilic attack. Moreover, conceptual density functional theory was used to conceptualize the preferential reactive sites of the nucleophiles probed. The C–C bond-forming step is speculated to proceed through a Friedel–Crafts-type reaction.

Investigations into the flotation of molybdenite in the presence of chalcopyrite using (3S,4S,5S,6R)-3,4,5,6-tetrahydroxyoxane-2-carboxylate acid as a novel selective depressant: An experimental and theoretical perspective

(3S,4S,5S,6R)-3,4,5,6-tetrahydroxyoxane-2-carboxylate (TTC) acid was experimentally and theoretically investigated as a chalcopyrite (CPY) depressant during molybdenite-chalcopyrite (MLT-CPY) beneficiation. It was observed that the adsorption of TTC onto CPY was more than that onto MLT. The zero-point corrected complexation energies for complexes on mineral surfaces was calculated by using M06-2X/6–311++g(d,p)/def2-TZVPP level of theory in gas phase. It was established that Mo(OH)4-∙∙∙FeOH+∙∙∙TTC (S = 1) and FeOH+∙∙∙TTC (S = 0) complexes on MLT and CPY, respectively, of complexation energies of −189.0 kJ/mol and −831.0 kJ/mol, respectively, were the most stable complexes. The analyzed nature of bonding in complexes using Non-Covalent Interaction and Quantum Theory of Atoms in Molecules (QTAIM) suggested that the complexes were governed by traditional hydrogen bonding, as well as covalent, and other non-covalent interactions. Flotation tests carried out using a synthetic mixture of MLT and CPY (1:1) at pH 5.4 ± 0.1 1 in the presence an economical TTC depressant yielded a grade, recovery and separation efficiency of 58.7 %, > 97.6 % and 88.8 %, respectively. Therefore, TTC could be used as a potential depressant of CPY during the flotation of MLT.

Iron-Catalyzed Cross-Electrophile Coupling of Inert C–O Bonds with Alkyl Bromides

Iron-Catalyzed Cross-Electrophile Coupling of Inert C–O Bonds with Alkyl Bromides

The unimolecular decomposition of dimethoxymethane: channel switching as a function of temperature and pressure.

Branching ratios of competing unimolecular reactions often exhibit a complicated temperature and pressure dependence that makes modelling of complex reaction systems in the gas phase difficult. In particular, the competition between steps proceeding via tight and loose transition states is known to present a problem. A recent example from the field of combustion chemistry is the unimolecular decomposition of CH3OCH2OCH3 (DMM), which is discussed as an alternative fuel accessible from sustainable sources. It is shown by a detailed master equation analysis with energy- and angular-momentum-resolved specific rate coefficients from RRKM theory and from the simplified statistical adiabatic channel model, how channel switching of DMM depends on temperature and pressure, and under which experimental conditions which channels prevail. The necessary molecular and energy data were obtained from quantum-chemical calculations at the CCSD(F12*)(T*)/cc-pVQZ-F12//B2PLYP-D3/def2-TZVPP level of theory. A parameterization describing the channel branching over extended ranges of temperature and pressure is derived, and the model is used to simulate shock tube experiments with detection by atomic resonance absorption spectroscopy and time-of-flight mass spectrometry. The agreement between the simulated and experimental concentration-time profiles is very good. The temperature and pressure dependence of the channel branching is rationalized, and the data are presented in a form that can be readily implemented into DMM combustion models.

Examination of How Well Long-Range-Corrected Density Functionals Satisfy the Ionization Energy Theorem.

We calculated the vertical ionization energies (VIE) of 99 species in two ways to examine the accuracy of several long-range-corrected (LC) hybrid meta functionals in comparison with a gradient approximation (GA), global hybrids, and doubly hybrids. In the category of LC functionals, we examined both those with meta ingredients (i.e., that depend on the kinetic energy density) and those without them. The LC-hybrid meta functionals examined are M11, revM11, M11plus, and ωB97M-V. The reference data used to assess accuracy consist of 95 molecules and 4 atoms in the GW100 set. The two methods studied are the ΔSCF method (involving the difference of neutral and cation self-consistent field (SCF) energies) and the ionization energy theorem (involving the orbital energy of the highest occupied molecular orbital, HOMO). We calculated linear correlation coefficients (r2) and mean absolute deviations (MADs) between each approach and the reference VIE value from the CCSD(T)/def2-TZVPP level of theory. We compared the new LC-hybrid meta calculations to calculations with the 10 functionals in a previous VIE study by Brémond et al. and to the calculations with LC-BLYP (LC-Becke, Lee-Yang-Parr), CAM-B3LYP (Coulomb-attenuating-method Becke-3-parameter Lee-Yang-Parr), LC-ωHPBE, and ωB97X-D. The results show that Minnesota LC-hybrid meta functionals have the smallest mean absolute deviation of ionization energy theorem VIEs with the reference data; the LC-ωHPBE functional also does quite well in this test. This is very encouraging and indicates that LC-hybrid meta functionals would be the best starting points for the tuning strategy that has been shown to be a very good procedure for improving time-dependent density functional calculations, and it also helps explain the good success of LC-hybrid meta functionals for molecular excitation energies.

Structure of C60F36: A Gas-Phase Electron Diffraction and Quantum Chemical Computational Study of a Remarkably Distorted Fluorofullerene.

The equilibrium molecular structure of the gaseous fluorofullerene C60F36 has been determined for the first time by the electron diffraction method with the use of quantum chemical calculations up to the RI-MP2/def2-TZVPP level of theory. Vibrational amplitudes and quadratic and cubic force constants were calculated by density functional theory methods. It was found that the sample under study consists of the isomer of C1 symmetry, 81(4)%, with a small amount of the isomer of C3 symmetry, in good accordance with HPLC-MS (atmospheric pressure photoionization), HPLC-UV/vis, and NMR spectroscopic data. The presence of the isomer of T symmetry, up to 5%, cannot be completely excluded. Theoretical structural parameters of the C60F36 molecule were compared with those of the C60F48 molecule. Relative to C60, the C60F36 molecule has a remarkably distorted carbon cage because of steric, electrostatic, and orbital interactions. This results in the longest carbon-carbon bond (1.671 Å) found in free molecules. In particular, about the longest FC-CF bond, the dihedral angle is only around 20°, which leads to the very short nonbonded distance between electronegative vicinal fluorine atoms (2.531 Å) that is much shorter than the sum of van der Waals radii of fluorine atoms (2.94 Å). A natural bond orbital analysis revealed that strong nπ(F) → σ*(FC-CF) interactions delocalize the lone pair of π-type at the fluorine atoms into the antibonding orbital of the FC-CF bond. This hyperconjugation results in additional elongation of FC-CF bonds.

Temperature- and pressure-dependent kinetics of the competing C-O bond fission reactions of dimethoxymethane.

Oxymethylene ethers are often considered as promising fuel additives to reduce the emissions of soot and NOx from diesel engines. Dimethoxymethane (DMM) is the smallest member of this class of compounds and therefore particularly suitable to study the reactivity of the characteristic methylenedioxy group (O-CH2-O). In this context, we investigated the pyrolysis of DMM behind reflected shock waves at temperatures between 1100 and 1600 K and nominal pressures of 0.4 and 4.7 bar by monitoring the formation of H atoms with time-resolved atom resonance absorption spectroscopy. Rate coefficients for the C-O bond fission reactions of DMM were inferred from the recorded [H](t) profiles, and a pronounced temperature and pressure dependence of the rate coefficients was found. To rationalize this finding, we characterized the relevant parts of the potential energy surface of DMM by performing quantum chemical calculations at the CCSD(F12*)(T*)/cc-pVQZ-F12//B2PLYP-D3/def2-TZVPP level of theory. On the basis of the results, a two-channel master equation accounting for the two different C-O bond-fission reactions of DMM was set up and solved. Specific rate coefficients were calculated from the simplified Statistical Adiabatic Channel Model. The branching between the two reaction channels was modeled, and the CH3OCH2O + CH3 product channel was found to be clearly dominating. A Troe parameterization for the pressure dependence of this channel was derived. To enable implementation of both channels into kinetic mechanisms for combustion modeling, 'log p' parameterizations of the rate coefficients for both reaction channels are also given and were implemented into a literature mechanism for DMM oxidation. With this slightly modified mechanism, the results of our experiments could be adequately modeled. The role of competing molecular (i.e. nonradical) decomposition channels of DMM was also quantum-chemically checked, but no indications for such channels could be found.

Dative and electron-sharing bonding in transition metal compounds.

Quantum chemical calculations using density functional theory at the BP86-D3(BJ)/def2-TZVPP level of theory are reported for transition metal compounds [TM]-L in high and low oxidation states involving carbene, carbyne, alkene, and alkyne ligands L. The nature of the [TM]-L bond is analyzed with the energy decomposition analysis - natural orbitals for chemical valence (EDA-NOCV) method. The calculations reveal that transition metal compounds with ligands, that are typically classified as donor-acceptor complexes possessing dative bonds (Fischer-type carbenes and carbynes, alkene, and alkyne complexes) or as TM compounds with electron-sharing bonds (Schrock-type carbenes and carbynes, metallacyclopropanes, and metallacyclopropenes), exhibit significant differences between the orbital interactions when closed-shell or open shell fragments are used. Fischer-type carbene complexes have much lower orbital interaction (ΔEorb ) values when singlet fragments are employed compared to triplet fragments. In contrast, singlet and triplet fragments of Schrock-type carbene complexes give similar ΔEorb values. The best description for Fischer-type carbyne complexes is found for neutral fragments in their electronic doublet state, which engage in a mixture of dative bonding (σ donation and π backdonation) and one electron-sharing π bond. The EDA-NOCV calculations of Schrock-type carbynes using open-shell species in their quartet electronic state give similar ΔEorb values as neutral fragments in their electronic doublet state. Alkene and alkyne complexes, but also metallacyclic species, are best described with singlet fragments, but the difference between the ΔEorb values for dative bonding and electron-sharing bonding using triplet fragments becomes much smaller for molecules that are considered as metallacycles. © 2018 Wiley Periodicals, Inc.

Stabilization of group 14 tetrylene compounds by N-heterocyclic carbene: A theoretical study

The chemistry of stable tetrylenes (the heavier congeners of the group 14 elements) is an appealing target in main group chemistry because of their synthetic potential and industrial applications. The present work seeks to characterize, in the light of DFT calculations, the utilization of methylated N-heterocyclic carbene (NHC(CH3)) as a Lewis base for the stabilization of ER2 species as Lewis acids in the form of [NHC(CH3)→ER2]; (E=Ge, Sn, Pb; R=H, F, Cl, Br, CH3) complexes. The structures of the latter complexes are investigated at the M05-2X /def2-TZVPP level of theory. The nature of the C→E bonds in the complexes is analyzed with NBO, AIM, at ​M05-2X /def2-TZVPP and EDA as well as ETS-NOCV at BP86-D3/TZP(ZORA)//M05-2X/def2-TZVPP level of theory.The results confirm that the nature of the C→E bond in [NHC(CH3)→ER2]; (E=Ge, Sn, Pb; R=H, F, Cl, Br, CH3) complexes is largely electrostatic, with a contribution of about 57–67% of the total interaction energy. The orbital interaction (ΔEorb) for the considered [NHC(CH3)→ER2] complexes arises from C→E σ-donation and C←E π-back donation, which is demonstrated by ETS-NOCV schemes.

Experimental and theoretical studies on the oxidation of lomefloxacin by alkaline permanganate

The kinetic and mechanistic investigation of oxidation of emerging contaminant lomefloxacin (LMF) by alkaline permanganate was carried out spectrophotometrically. The oxidation product 7-amino-1-ethyl-6, 8-difluoro-4-oxo-quinoline-3-carboxylic acid was identified by Agilent 6130 Series Quadrupole LC/MS. The stoichiometry was found to be 1:2, that is, 1 mol of lomefloxacin reacted with 2 mol Mn(VII). Orders with respect to [LMF] and [OH−] were found to be fractional and less that one. The oxidation reaction proceeds via an alkali permanganate species that forms a complex with lomefloxacin and the complex then decomposes to give the product. The rate of reaction was found to decrease with decrease in the dielectric constant. The effects of initially added products and ionic strength have also been investigated. The kinetics of the reaction was also studied at four different temperatures, and the thermodynamic activation parameters for the reaction were evaluated and discussed. The geometry optimization of reactants and activated complex were carried out using density functional theory (DFT). The DFT calculations were accomplished with the TURBOMOLE program package (Version-6.4). The activation energy was found to be ~21 kJ/mol at RI-BP86.def 2-TZVPP level of theory.

Anion–π Interactions Involving [MXn]m−Anions: A Comprehensive Theoretical Study

In this manuscript we perform a systematic study on the geometric and energetic features of anion-π complexes, wherein the anion is a metal complex of variable shapes and charges. Such a study is lacking in the literature. For the calculations we used the ab initio RI-MP2/def2-TZVPP level of theory. A search in the Cambridge Structural Database (CSD) provides the experimental starting point that inspired the subsequent theoretical study. The influence of [MX(n)](m-) on the anion-π interaction was analyzed in terms of energetic, geometric, and charge transfer properties and Bader's theory of "atom-in-molecules" (AIM). The binding energy depends on the coordination index, geometric features and different orientations adopted by the metallic anion. The binding mode resembling a stacking interaction for linear, trigonal planar and square-planar anions is the most favorable. For tetrahedral and octahedral anions the most favorable orientation is the one with three halogen atoms pointing to the ring.

Nanodiamonds in sugar rings: an experimental and theoretical investigation of cyclodextrin–nanodiamond inclusion complexes

We report on the noncovalent interactions of nanodiamond carboxylic acids derived from adamantane, diamantane, and triamantane with β- and γ-cyclodextrins. The water solubility of the nanodiamonds was increased by attaching an aromatic dicarboxylic acid via peptide coupling. Isothermal titration calorimetry experiments were performed to determine the thermodynamic parameters (K(a), ΔH, ΔG and ΔS) for the host-guest inclusion. The stoichiometry of the complexes is invariably 1:1. It was found that K(a), ΔG and ΔH of inclusion increase for larger nanodiamonds. ΔS is generally positive, in particular for the largest nanodiamonds. β-Cyclodextrin binds all nanodiamonds, γ-cyclodextrin clearly prefers the most bulky nanodiamonds. The interaction of 9-triamantane carboxylic acid shows one of the strongest complexation constants towards γ-cyclodextrin ever reported, K(a) = 5.0 × 10(5) M(-1). In order to gain some insight into the possible structural basis of these inclusion complexes we performed density functional calculations at the B97-D3/def2-TZVPP level of theory.