H NMR, C NMR and mass spectral studies of some Schiff bases derived from 3-amino-1,2,4-triazole

Heterocyclic Schiff bases derived from 3-amino-1,2,4-triazole and different substituted aromatic aldehydes are prepared and subjected to ¹H NMR, ¹³C NMR and mass spectral analyses. ¹H NMR spectra in DMSO exhibit a sharp singlet within the 9.35–8.90 ppm region which corresponds to the azomethine proton. The position of this signal is largely dependent on the nature of the substituents on the benzal moiety. It is observed that the shape, position and the integration value of the signal of the aromatic proton of the triazole ring (⁵C) are clearly affected by the rate of exchange, relaxation time, concentration of solution as well as the solvent used. ¹³C NMR is taken as substantial support for the results reached from ¹H NMR studies. The mass spectral results are taken as a tool to confirm the structure of the investigated compounds. The base peak (100%), mostly the M-1 peak, indicates the facile loss of hydrogen radical. The fragmentation pattern of the unsubstituted Schiff base is taken as the general scheme. Differences in the other schemes result from the effect of the electronegativity of the substituents attached to the aromatic ring.     

Crystal,molecular structure and tautomerism of (5-methyl-1H-[1,2,4]triazol-3-ylsulfanyl)-acetic acid

Molecular structure, relative stability of conformers, and tautomers of (5-methyl-1H-[1,2,4]triazol-3-ylsulfanyl)-acetic acid (MTSA) have been investigated by experimental (X-ray diffraction) and theoretical (B3LYP/aug-cc-pVDZ) methods. It was demonstrated that in the solid state MTSA exists in N1H tautomeric form. This tautomer is not the most stable in gas phase and its stabilization is provided by environment effects.     

Theoretical studies on tautomerism of tetrazole derivatives by polarisable continuum method (PCM)

Computational calculations at B3LYP/6-31++G(d,p) level were employed in the study of the predominant tautomeric forms of 1-H and 2-H tetrazole derivatives (5-NO₂, 5-CF₃, 5-F, 5-H, 5-NH₂, 5-OH, 5-CH₃) in the gas phase and solution using PCM model. For electron withdrawing derivatives in the gas phase and solution 2-H forms are more stable and dominant form. For electron releasing groups in the gas phase and solution with low dielectric constants the 2-H form is more stable but in solvents with high dielectric constants 1-H isomer is dominant form. In addition variation of dipole moments and charges on atoms in the solvents are studied.     

5-卤代1,2,3,-三唑互变异构的密度泛函理论研究

用密度泛函B3LYP/6-311 G**方法,对气相和水相中的1,2,3三,-唑及5-卤(-F、C l和-B r)代1,2,3,-三唑互变异构体进行了几何构型全自由度优化,获得了它们在气相和水相中的几何结构和电子结构。计算结果显示,在气相和水相中1,2,3三-唑和5-卤代1,2,3三-唑的N2-H型要比对应的N1-H型和N3-H型稳定。讨论了不同的取代基团和溶剂化效应对互变异构体的几何结构、能量和电荷分布以及互变异构反应活化能的影响带。并进一步研究了N1-H、N2-H和N3-H型三唑之间的互变异构机理:(a)分子内质子转移;(b)水助质子转移。计算结果表明,途径(b)所需要的活化能较小,为120.06KJ/mol,途径(a)为204.12KJ/mol。     

Experimental,DFT and Theoretical Corrosion Study for 4-(((4-ethyl-5-(thiophen-2-yl)-4H-1,2,4-triazole-3-yl)thio)methyl)-7,8-dimethyl-2H-chromen-2-one

In this work, 4-(((4-ethyl-5-(thiophen-2-yl)-4H-1,2,4-triazole-3-yl)thio)methyl)-7,8-dimethyl-2H-chromen-2-one was synthesized by acetone-mediated condensation of 4-ethyle-5-(thiophen-2-yl)-4H-1,2,4-triazole-3-thiol and 4-(chloromethyl)-7,8-dimethyl-2H-chromen-2-one. The molecule results (3) were experimentally characterized using FT-IR, ¹H-, and ¹³C NMR spectroscopy. Density Functional Theory (B3LYP/cc-pVDZ) was used to investigate the ideal molecule structure, vibrational frequencies, and ¹H with ¹³C NMR (theoretically) chemical shifts. Theoretical and experimental spectroscopy results were compared and agreed with each other, which indicated the validity of the used developed molecular structure. The Dipole moment, hardness, softnes, electronegativity, electrophilicity index, nucleophilicity index, and chemical potential as electronic structural parameters linked to corrosion inhibition efficacy were investigated for the prepared compound. Furthermore, the fraction of transferred electrons was calculated to determine the interaction between the iron surface and organic molecules. The results indicated a favorable relationship between organic-based corrosion inhibitors and quantum chemical parameters processes. The corrosion inhibitors' behavior can be predicted without the need for experimental investigation.     

Synthesis and spectral studies of organotin(IV) 4-amino-3-alkyl-1,2,4-triazole-5-thionates: in vitro antimicrobial activity

Some di- and triorganotin(IV) triazolates of general formula, R(4-n)SnLn (where n=2; R=Me, n-Bu and Ph; n=1; R=Me, n-Pr, n-Bu and Ph and HL=4-amino-3-methyl-1,2,4-triazole-5-thiol (HL-1); and 4-amino-3-ethyl-1,2,4-triazole-5-thiol (HL-2)) were synthesized by the reaction of R(4-n)SnCln with sodium salt of HL-1 and HL-2. The bonding and coordination behavior in these derivatives have been discussed on the basis of IR and 119Sn M?ssbauer spectroscopic studies in the solid state. Their coordination behavior in solution is discussed by multinuclear (1H, 13C and 119Sn) NMR spectral studies. The IR and 119Sn M?ssbauer spectroscopic studies indicate that the ligands, HL-1 and HL-2 act as a monoanionic bidentate ligand, coordinating through Sexo- and Nring. The distorted skew trapezoidal-bipyramidal and distorted trigonal bipyramidal geometries have been proposed for R2SnL2 and R3SnL, respectively, in the solid state. In vitro antimicrobial screening of some of the newly synthesized derivatives and of some di- and triorganotin(IV) derivatives of 3-amino-1,2,4-triazole-5-thiol (HL-3) and 5-amino-3H-1,3,4-thiadiazole-2-thiol (HL-4) along with two standard drugs such as fluconazole and ciprofloxacin have been carried out against the bacteria, viz. Staphylococcus aureus and Escherichia coli, and against some fungi, viz. Aspergillus fumigatus, Candida albicans, Candida albicans (ATCC 10231), Candida krusei (GO3) and Candida glabrata (HO5) by the filter paper disc method. The studied organotin(IV) compounds show mild antifungal activity as compared to that of fluconazole, however, they show almost insignificant activity against the studied Gram-positive (Staphylococcus aureas) and Gram-negative (Escherichia coli) bacteria as compared to that of standard drug, ciprofloxacin.     

Comprehensive DFT and MO studies on glyoxilic acid oxime and related ions in gas phase and solution: Conformations,basicities and acidities

Density functional (BLYP, B3LYP and BHLYP) and highly correlated MP2 and CCSD(T) calculations have been performed to investigate conformers, energy barriers, intramolecular H-bond strength, gas-phase basicity and deprotonation energies of glyoxilic acid oxime (gao) and related ions in gas phase and in aqueous solution (SCRF-PCM method). BHLYP/6-311G(d,p) and B3LYP/6-31++G(d) predictions for the global minimum conformer of gao were consistent with experiment. BLYP level overestimated the H-bond and stabilized incorrectly the H-bonded conformer. The calculations in solution indicated destabilization of H-bonded conformers due to the small polarizability and weaken of the H-bond. The same global minimum structures in gas phase and aqueous solution were found for gao-neutral (ectt) and gao-dianion (e⁻²), whereas they were different for gao-anion because of the strong decrease of the conformational energies in solution. The global minimum structures of the neutral, anion and dianion of gao, obtained in solution, are in agreement with experiment. The gas-phase basicity (GB) and molecular electrostatic potential (MEP) calculations revealed the same sites for electrophilic attack, supported by the nature of HOMO: the carbonylic oxygen for the neutral, the carboxylic oxygen for the anion and the oxime nitrogen for the dianion. MEP results in gas phase and in solution suggested a region between the two atoms, but not on one atom in accordance with bidentate binding of gao ions to a metal. The BHLYP/6-31++G(d,p) molecular properties of gao were in best consistent with CCSD(T) results. The thermodynamical properties (GB and bond deprotonation energy) of gao were better estimated at B3LYP level.     

Coordination studies of 5,6-diphenyl-3-(2-pyridyl)-1,2,4-triazine towards Cu cation. X-ray studies,spectroscopic characterization and DFT calculations

The reactions of 5,6-diphenyl-3-(2-pyridyl)-1,2,4-triazine with CuCl₂ · 2H₂O, Cu(NO₃)₂ · 3H₂O and CuSO₄ · 5H₂O have been examined, and four [CuCl₂(dppt)] (1), [CuCl₂(dppt)₂] · 2MeOH (2), [Cu(dppt)₂(H₂O)₂](NO₃)₂ (3) and [Cu(SO₄)(dppt)(H₂O)]_n · nH₂O (4) complexes have been obtained. All the complexes have been structurally and spectroscopically characterized, and compound 4 has been additionally studied by magnetic measurements. The electronic structure of 1 has been calculated with the density functional theory (DFT) method, and the time-dependent DFT calculations have been employed to calculate the electronic spectrum of 1.     

Experimental and theoretical studies on thermodynamics and properties of tautomers of 2-substituted 6(4)-methyl-1,4(1,6)-dihydropyrimidine-5-carboxylates

Experimental and theoretical studies on the thermodynamics and properties of 2-substituted 6(4)-methyl-1,4(1,6)-dihydropyrimidine-5-carboxylates were undertaken by ¹H NMR measurements and DFT (density functional theory) calculations. The ratios of tautomers a/b of dihydropyrimidines (DPs) 1, 2, and 3 were determined under various conditions to reveal the effects of temperature, solvent, and concentration on the thermodynamic data. The observed results, the free energy differences (ΔG), enthalpy differences (ΔH), and entropy differences (ΔS), are discussed in terms of the molecular structures, dipole moments (DM), and the electrostatic potential maps calculated by the DFT to clarify the nature of the DPs.     

Experimental and theoretical structural studies on 4-(2-phenylethyl)-5-(2-furyl)-2,4-dihydro-3H-1,2,4-triazole-3-thione

The structural and conformational features of 4-(2-phenylethyl)-5-(2-furyl)-2, 4-dihydro-3H-1,2,4-triazole-3-thione (1a), which can be related to the biological activity, have been investigated by X-ray diffraction and molecular modeling techniques. Ab initio method (RHF/6-31G) and density functional theory (B3LYP/6-31G(D)) have been used to calculate structural parameters, conformations, and relative energy of two tautomeric specious (1a and 1b) of the title compound. The geometry and the conformation of the thione form, 1a, is well reproduced by the DFT (B3LYP/6-31G(D)) method as compared with X-ray structure in which this form is found. The thione form is also predicted to be 14.42 kcal/mol more stable than the thiol form in the gas-phase by the DFT method.     

Synthesis,characterization and fluorescence studies of Th(IV) complexes of Schiff bases derived from 2,6-diformyl-4-methyl phenol and 3-substituted-4-amino-5-mercapto-1,2,4-triazoles

Thorium(IV) complexes have been synthesized by reacting Th(IV) nitrate with Schiff bases derived from 2,6-diformyl-4-methyl phenol and 3-substituted-4-amino-5-mercapto-1,2,4-triazoles in ethanol. These complexes have been characterized on the basis of elemental analyses, molar conductance and spectral studies. Analytical and spectral data suggest structures in which Th(IV) is six-coordinate, which is supported by coordination of seven nitrate ions with one bidentate, hydroxyl group of 2,6-diformyl-4-methyl phenol in a bidentate fashion and two azomethine groups through nitrogen atoms. The fluorescence and solid state electrical conductivity properties have been studied.     

Synergistic effect of Thiourea and HCl on Palladium (II) recovery: An investigation on Chemical structures and thermodynamic stability via DFT

This work duly investigates the recovery of Pd (II) chlorocomplexes from industrial wastewater. Chemical structures and thermodynamic stabilities of the complex formed are evaluated via density functional theory (DFT). By applying synergistic solutions of thiourea mixed with hydrochloric acid (HCl), the stripping reaction of Pd (II) in the loaded Aliquat 336 occurs and Pd (II) chlorocomplexes coordinated thiourea ligands are formed, thus 80.19% of Pd (II) chlorocomplexes can be recovered. The aim of this study is to gain a better understanding of the stripping mechanisms and the structure of the complexes formed via the synergistic system. Such an understanding is still limited since little research has been conducted in this field. Owing to their molecular geometry, ligand coordination and donor groups play a vital role in the reactivity of palladium (II) complex. Quantum models have been developed to evaluate the chemical structure and thermodynamics stability of ((NH₂)₂CS·PdCl₂) namely: (i) DFT with B3LYP/6-31g(d,p) and MP2/6-31g(d,p) basis set, (ii) MP2 with cc-pVTZ basis set and (iii) CCSD(T)/cc-pVTZ. Results demonstrate that the highest geometric stability exhibited is the structure of Pd-S bonding with 180° Cl-Pd-Cl. The distance (r) and angle (a) of the selected geometrical parameters for (NH₂)₂CS·PdCl₂ complex are reported. Additionally, FTIR and UV–vis spectroscopies have been conducted to analyze the sampling solutions. Further, the calculated vibrational frequencies and experimental spectroscopic results show good agreement with the optimized geometry.     

GIAO/DFT studies on 1,2,4‐triazole‐5‐thiones and their propargyl derivatives

Density functional theory (DFT)/Becke–Lee–Yang–Parr (B3LYP) and gauge‐including atomic orbital (GIAO) calculations were performed on a number of 1,2,4‐triazole derivatives, and the optimized structural parameters were employed to ascertain the nature of their predominant tautomers. ¹³C and ¹⁵N NMR chemical shifts of 3‐substituted 1,2,4‐triazole‐5‐thiones and their propargylated derivatives were calculated via GIAO/DFT approach at the B3LYP level of theory with geometry optimization using a 6‐311++G** basis set. A good agreement between theoretical and experimental ¹³C and ¹⁵N NMR chemical shifts could be found for the systems investigated. The data generated were useful in predicting ¹⁵N chemical shifts of all the nitrogen atoms of the triazole ring, some of which could not be obtained in solution state ¹⁵N HMBC/HSQC NMR measurements. The energy profile computed for the dipropargylated derivatives was found to follow the product distribution profile of regioisomers formed during propargylation of 1,2,4‐triazole thiones. Copyright © 2013 John Wiley & Sons, Ltd.     

5-醛基-1,2,3-三唑互变异构的理论研究

用密度泛函B3LYP/6-311++G**方法,对气相和水相中的5-醛基-1,2,3-三唑互变异构体进行了几何构型全自由度优化,获得了它们在气相和水相中的几何结构和电子结构.讨论了不同的取代基团和溶剂化效应对互变异构体的几何结构、能量以及互变异构反应活化能的影响.并进一步研究了N1-H、N2-H和N3-H型三唑之间的互变异构机理:(a)分子内质子转移;(b)水助质子转移.计算结果表明,途径(b)所需要的活化能较小,平均为101.31kJ/mol,途径(a)为211.70kJ/mol.     

A path from I(h) to C1 symmetry for C20 cage molecule

The symmetry of the C20 cage is studied based on the intrinsical relationship among point groups (Bradley, C. J.; Cracknell, A. P. The Mathematical Theory of Symmetry in Solids; Claredon Press: Oxford, 1972). The structure of the C20 cage with I(h) symmetry is constructed, as are eight other structures with subgroup symmetry. A path from I(h) symmetry to C1 symmetry is obtained for the closed-shell electronic state, and the structure with D2h symmetry is the most stable on this path. Using the D2h structure the correlation energy correction is studied on the condition of restricted excitation space at the CCSD(T) level. We obtain curves on the relation between the orbital numbers and the total energy at the CCSD(T), CCSD, and MP2 level, respectively. The results of these curves obtained from MP2 and CCSD(T) methods have the same tendency, while the results of CCSD gradually diverge with an increase in orbital numbers. When the orbitals used in the calculation reach 460, the total energy is -759.644 hartree at MP2 level and is -759.721 hartree by the CCSD(T) method. From the calculation results, we find that a large basis set can improve the reliability of the MP2 method, and to restrict excitation space is necessary when using the CCSD(T) method.     

Quantum chemical calculations of the isomer shift in iron(II) complexes of 1,2,4-triazoles with a 1 A 1 ⇔ 5 T 2 spin transition

DFT calculations have been performed to determine the isomer shift for a series of iron(II) clusters with nitrogen-containing ligands which serve as models of coordination units in Fe(II) complexes with 1,2,4-triazoles possessing a ¹ A ₁ ? ⁵ T ₂ spin transition. Good agreement has been found between the theoretical and experimental values of the isomer shift for both low-and high-spin phases. Our calculations confirmed the hypothesis about relationship between the experimentally observed differences in the isomer shift for the low-spin phases of the complexes and variations of the Fe-N mean bond length.     

Density Functional Theory studies on interactions of phosphoryl ligands with the Ca cation: Affinity and associated parameters

DFT (B3LYP/6-31G(d)) and semi-empirical (PM6) calculations of Ca²⁺ affinities on a set of substituted phosphoryl ligands were performed with complete geometry optimization. Two types of ligands were calculated: a set of trivalent [OP(R)] and a set of pentavalent [OP(R)₃] ones (R = H, F, Cl, Br, OH, OCH₃, CH₃, CN, NH₂ and NO₂), with R either directly bound to the phosphorus atom or to the para position of a phenyl ring. The affinity of the Ca²⁺ cation for the ligands was quantified in terms of interaction energy. Additionally, geometric and electronic parameters were correlated with the intensity of that interaction. Our results show that the electronic nature of the substituent mainly affects the interaction energy. Donor groups are associated with more negative interaction energies, while acceptor groups are associated with less negative interaction energies.     

A convenient one-pot synthesis of N-fused 1,2,4-triazoles via oxidative cyclization using chromium (VI) oxide

A facile one-pot synthesis of N-fused 1,2,4-triazoles from heterocyclic hydrazines and aldehydes is reported. The reaction is efficiently promoted by chromium (VI) oxide to afford the desired products mostly in high yields and in relatively short time. The high yield of the products and short reaction time are notable advantages of the developed protocol. This protocol is effective toward various substrates having different functionalities.     

Synthesis,molecular, crystal and electronic structure of [(C6H6)Ru(1,2,4-triazole)3](CF3SO3)2

[(C₆H₆)Ru(1,2,4-triazole)₃](CF₃SO₃)₂ has been prepared and studied by IR, electronic and ¹H?NMR spectroscopy and X-ray crystallography. The complex was prepared by reaction of [(C₆H₆)RuCl₂]₂ with 1,2,4-triazole in the presence of AgCF₃SO₃ in methanol. The electronic spectrum of the compound has been calculated using the TDDFT method.