Bis(dimethylpyrazolyl)-aniline-s-triazine derivatives as efficient corrosion inhibitors for C-steel and computational studies.

4,6-Bis(3,5-dimethyl-1H-pyrazol-1-yl)-N-phenyl-1,3,5-triazin-2-amine (PTA-1), N-(4-bromophenyl)-4,6-bis(3,5-dimethyl-1H-pyrazol-1-yl)-1,3,5-triazin-2-amine (PTA-2) and 4,6-bis(3,5-dimethyl-1H-pyrazol-1-yl)-N-(4-methoxyphenyl)-1,3,5-triazin-2-amine (PTA-3) were synthesized and characterized. Their corrosion inhibition of carbon C-steel in 0.25 M H2SO4 was studied by electrochemical impedance. The inhibition efficiency (IE%) of triazine was superior due to the cumulative inhibition of triazine core structure and pyrazole motif. Potentiodynamic polarizations suggested that s-triazine derivatives behave as mixed type inhibitors. The IE% values were 96.5% and 93.4% at 120 ppm for inhibitor PTA-2 and PTA-3 bearing -Br and -OCH3 groups on aniline, respectively. While PTA-1 without an electron donating group showed only 79.0% inhibition at 175 ppm. The adsorption of triazine derivatives followed Langmuir and Frumkin models. The values of adsorption equilibrium constant K°ads and free energy change ΔG°ads revealed that adsorption of inhibitor onto steel surface was favoured. A corrosion inhibition mechanism was proposed suggesting the presence of physical and chemical interactions. Density functional theory computational investigation corroborated nicely with the experimental results. Monte Carlo simulation revealed that the energy associated with the metal/adsorbate arrangement dE ads/dN i, for both forms of PTA-2 and PTA-3 with electron donating groups (-439.73 and -436.62 kcal mol-1) is higher than that of PTA-1 molecule (-428.73 kcal mol-1). This aligned with experimental inhibition efficiency results.

Exploring the Sensing Potential of g-C3N4 versus Li/g-C3N4 Nanoflakes toward Hazardous Organic Volatiles: A DFT Simulation Study.

Ab initio calculations were performed to determine the sensing behavior of g-C3N4 and Li metal-doped g-C3N4 (Li/g-C3N4) quantum dots toward toxic compounds acetamide (AA), benzamide (BA), and their thio-analogues, namely, thioacetamide (TAA) and thiobenzamide (TAA). For optimization and interaction energies, the ωB97XD/6-31G(d,p) level of theory was used. Interaction energies (Eint) illustrate the high thermodynamic stabilities of the designed complexes due to the presence of the noncovalent interactions. The presence of electrostatic forces in some complexes is also observed. The observed trend of Eint in g-C3N4 complexes was BA > TAA > AA > TBA, while in Li/g-C3N4, the trend was BA > AA > TBA > TAA. The electronic properties were studied by frontier molecular orbital (FMO) and natural bond orbital analyses. According to FMO, lithium metal doping greatly enhanced the conductivity of the complexes by generating new HOMOs near the Fermi level. A significant amount of charge transfer was also observed in complexes, reflecting the increase in charge conductivity. NCI and QTAIM analyses evidenced the presence of significant noncovalent dispersion and electrostatic forces in Li/g-C3N4 and respective complexes. Charge decomposition analysis gave an idea of the transfer of charge density between quantum dots and analytes. Finally, TD-DFT explained the optical behavior of the reported complexes. The findings of this study suggested that both bare g-C3N4 and Li/g-C3N4 can effectively be used as atmospheric sensors having excellent adsorbing properties toward toxic analytes.

Theoretical Study of Dodecafluorophenylene-Based Superalkalides with Significantly High NLO Response.

Scientists are continuously trying to discover new approaches to develop materials with exceptional nonlinear optical responses. Compared with the single-ring Janus face compound (F6C6H6), the three-ring Janus face compound (C13H10F12) has a larger surface, where superalkali metals can be doped quite easily. Herein, the nonlinear optical response of Janus molecule dodecafluorophenylene (DDFP)-based superalkalides has been explored. The stability of the newly designed complexes is evident in the negative interaction energy values (ranging from -42.17 to -60.91 kcal/mol). The superalkalide nature of the complexes is corroborated through natural bond orbital (NBO) analysis, which shows negative charges on M3. This feature is further confirmed through frontier molecular orbital (FMO) analyses showing the highest occupied molecular orbital (HOMO) density over superalkalis (M3). The analysis also reveals that the H-L gap is reduced from 9.57 eV (for bare DDFP) to 2.11 eV for doped systems by adsorption of dopants on the DDFP surface. Moreover, the NLO response of the studied complexes is evaluated via static hyperpolarizabilities. The maximum value of first hyperpolarizability (ßo) among all of the designed compounds is for K3-DDFP-K3 (7.80 × 104 au) at M06-2X/6-31+G(d,p) level of theory. The ßo is also rationalized through a two-level model. Furthermore, for ßvec, the projection of hyperpolarizability on the dipole moment is calculated. The comparable results of ßvec and ßo indicate that the charge transfer in the complexes is parallel to the molecular dipole moments. These compounds, besides providing a new entry into excess-electron compounds, will also pave the way for the design and synthesis of further novel NLO materials.

A computational investigation towards substitution effects on 8π electrocyclisation of conjugated 1,3,5,7-octatetraenes.

A computational investigation using M06-2X/6-31+G(d) method is reported for the substitution effects on 8π electrocyclisation of conjugated octatetraene. This systematic study describes the mono- and di-substitution effect across the 1,3,5,7-octatetraene skeleton. A general preference of the outward substitution over the inward, at C1 position of the monosubstituted system is observed. However, mesomerically electron donating group (-NH2 and -OH) display an opposite effect with respect to secondary orbital interaction (SOI) between the lone pair on the substituent and the orbital. A comparative evaluation on the computed activation energies for the 1-, 2-, 3-, and 4-monosubstituted system showed an insignificant impact on the rate of the reaction, in contrast to the electrocyclic ring closure of the unsubstituted compound. Computations of disubstituted system are more pronounced, where a remarkable acceleration is observed for 2-NO2-7-NO2 substituted octatetraene at 4.9 kcal mol-1, and a noticeable deceleration for 4-CH3-5-CH3 substituted octatetraene at 25.4 kcal mol-1 from the parent molecule, 17.0 kcal mol-1. A visible accelerated effects are commonly exhibited by the substitution on the terminal double bonds (C1, C2, C7, and C8), that are 1,2-, 1,7-, 1,8-, and 2,7-patterns, in regard to the greater orbital interaction for the new σ-bond formation. Despite the unfavourable steric clashes of the substituents in the 1,8-system, an apparent reduction in the energy barrier up to 7.4 kcal mol-1 is computed for 1-NH2-8-NO2 system from 17.0 kcal mol-1. This is due to the synergistic effect of the electron donor and electron acceptor, enhancing the stability of the transition structure. The electrocyclic ring closure involving vicinal substitution patterns, such as 1,2-, 2,3-, 3,4-, and 4,5-systems are critically dominated by steric crowding between the adjacent functional groups. In certain cases of the 1,2-substituted system, a noticeable accelerated effects are found for 1-NH2-2-NH2-substituted compound (9.7 kcal mol-1) due to an increased in electronic density on the substituted terminal double bond (C1-C2), hence favouring the formation of the new σ-bond.

Role of Delocalization, Asymmetric Distribution of π-Electrons and Elongated Conjugation System for Enhancement of NLO Response of Open Form of Spiropyran-Based Thermochromes.

Switchable nonlinear optical (NLO) materials have widespread applications in electronics and optoelectronics. Thermo-switches generate many times higher NLO responses as compared to photo-switches. Herein, we have investigated the geometric, electronic, and nonlinear optical properties of spiropyranes thermochromes via DFT methods. The stabilities of close and open isomers of selected spiropyranes are investigated through relative energies. Electronic properties are studied through frontier molecular orbitals (FMOs) analysis. The lower HOMO-LUMO energy gap and lower excitation energy are observed for open isomers of spiropyranes, which imparts the large first hyperpolarizability value. The delocalization of π-electrons, asymmetric distribution and elongated conjugation system are dominant factors for high hyperpolarizability values of open isomers. For deep understanding, we also analyzed the frequency-dependent hyperpolarizability and refractive index of considered thermochromes. The NLO response increased significantly with increasing frequency. Among all those compounds, the highest refractive index value is observed for the open isomer of the spiropyran 1 (1.99 × 10-17 cm2/W). Molecular absorption analysis confirmed the electronic excitation in the open isomers compared to closed isomers. The results show that reversible thermochromic compounds act as excellent NLO molecular switches and can be used to design advanced electronics.

A three orders of magnitude increase in nonlinear optical response by external electric field on Cryptand[2.2.2] (C222) based alkaline earthides.

A new series of alkaline earthides based on Cryptand [2.2.2] (C222) containing nine complexes is designed by carefully placing alkali metals and alkaline earth metals inside and outside the C222 complexant, respectively i.e., M1(C222)M2 (M1 = Li, Na, K; M2 = Be, Mg, Ca). The designed complexes are reasonably stable both electronically and thermodynamically, as revealed through their vertical ionization potentials (VIPs) and interaction energies, respectively. Moreover, the true alkaline earthide nature of the complexes is confirmed through NBO and FMO analyses showing the negative charges and HOMOs over the alkaline earth metals, respectively. The further validity of true earthide characteristic is represented graphically by the spectra of partial density of states (PDOS). HOMO-LUMO gaps of the compounds are also very small (from 2.23 to 2.83 eV) when compared with pure cage's (C222) H-L gap i.e., 5.63 eV. All these features award these complexes with very small values of transition energies (ΔE) ranging from 0.68 to 2.06 eV ultimately resulting in remarkably high hyperpolarizability values up to 2.7 × 105 au (for Na+(C222)Mg-). Furthermore, applying external electric field (EEF) on the complexes enhances hyperpolarizability further. A remarkable increase of 1000 folds has been seen when hyperpolarizability of K+(C222)Ca- is calculated after EEF application i.e., from 8.79 × 104 au to 2.48 × 107 au; when subjected to 0.001 au external electric field.

[1-(Pyrazin-2-yl)ethylidene]hydrazine: a new multitopic ligand for the design of hybrid molecular frameworks.

Hydrazones and their derivatives are closely related to imine compounds and are potential antimicrobial agents. They have also found application in supramolecular chemistry as multitopic ligands to link multiple metal centres for the design of hybrid molecular frameworks. The molecule of the title compound, C6H8N4, consists of an imine linkage with an N-N bond length of 1.3540 (14) Å. This asymmetric compound is nearly planar and adopts an E configuration about the azomethine C=N double bond. In the solid state, there are two intermolecular N-H...N interactions that interconnect the molecules into a two-dimensional network. The three-dimensional arrangement of the crystal packing is further stabilized by intermolecular π-π interactions interconnecting the centroids of the heterocyclic rings.

Synthesis of cyclopropyl-substituted furans by brønsted Acid promoted cascade reactions.

Chloroacetic acid promotes an efficient and diastereoselective intramolecular cascade reaction of electron-deficient ynenones to deliver products featuring a 2,3,5-trisubstituted furan bearing a fused cyclopropyl substituent at the 5-position. Synthetically relevant polycyclic building blocks featuring rings of various sizes and heteroatoms have been synthesized in high yield using this mild acid-catalyzed reaction.

Octyl (2E)-2-[2-(di-phenyl-phosphan-yl)benzyl-idene]hydrazinecarbodi-thio-ate.

The title compound, C28H33N2S2P, adopts the thione tautomeric form, as supported by the C-S distance [1.6744 (18) Å]. The Schiff base exhibits an E conformation about the C=N bond but a Z conformation about the C-N bond. The terminal chain is disordered over two sets of sites with an occupancy ratio of 0.732 (3):0.268 (3). In the crystal, pairs of N-N-H hydrogen bonds between the thione groups link neighbouring mol-ecules into centrosymmetric dimers.

(1E,2E)-1,2-Bis(2,3,4-trimeth-oxy-benzyl-idene)hydrazine.

The title compound, C(20)H(24)N(2)O(6), was obtained as an unexpected product by the reaction of hydrazinium dithio-carbazate with 2,3,4-trimeth-oxy-benzaldehyde in refluxing ethanol. The mol-ecule lies on a center of inversion. The crystal packing is stabilized by weak inter-molecular C-H⋯O inter-actions.

Ruthenium catalysed N-alkylation of amines with alcohols.

The conversion of primary amines into secondary amines has been achieved using alcohols as the alkylating agent, catalysed by [Ru(p-cymene)Cl2]2 and a bidentate phosphine ligand.