Synthesis,characterization and thermodynamics of some novel tertiary phosphine cobalt(III) unsymmetrical tetradentate Schiff Base complexes

The [Co(salpyren)PBu₃]ClO₄ · H₂O, [(N-salicylidene-N′-pyrrolidene)-1,2-ethylenediaminato] tributylphosphineCo(III)perchlorate · monohydrate; [Co(Mesalpyren)PBu₃]ClO₄ · H₂O, [(7-methyl-N-salicylidene-N′-pyrrolidene)-1,2-ethylenediaminato] tributylphosphineCo(III)perchlorate · monohydrate; [Co(Phsalpyren)PBu₃]ClO₄ · H₂O [(7-phenyl-N-salicylidene-N′-pyrrolidene)-1,2-ethylenediaminato] tributylphosphineCo(III) perchlorate · monohydrate, were synthesized and characterized. The equilibrium constants and the thermodynamic parameters were measured spectrophotometrically for the 1:1 adduct formation of [Co(chel)PBu₃]ClO₄ · H₂O, where (chel = salpyren, Mesalpyren, Phsalpyren) as acceptors with phosphites [P(OR)₃ (R = Me, Et and i-Pr)] as donors, in acetonitrile (CH₃CN) and dimethylformamide (DMF) solvents, in constant ionic strength (I = 0.1 m NaClO₄) and at various temperatures T = 283 to 313 K. The trend of the equilibrium constants of the donors (phosphites) toward a given cobalt(III) Schiff base complex is as follows: P(OEt)₃ > P(Oi-Pr)₃ > P(OMe)₃. The trend of the equilibrium constants of the cobalt(III) Schiff base complexes toward a given phosphite is as follows: 7-Mesalpyren > salpyren > 7-Phsalpyren. The trend of the equilibrium constants with a given donor toward a given acceptor with respect to the solvent is as follows: CH₃CN > DMF.     

Kinetic Studies of the Ligand Substitution Reaction of Some New Uranyl Schiff Base Complexes with Tri‐n‐butylphosphine

Kinetics of the substitution reaction of solvent molecule in uranyl(VI) Schiff base complexes by tri‐n‐butylposphine as the entering nucleophile in acetonitrile at 10–40°C was studied spectrophotometrically. The second‐order rate constants for the substitution reaction of the solvent molecule were found to be (8.8 ± 0.5) × 10^?3, (5.3 ± 0.2) × 10^?3, (7.5 ± 0.3) × 10^?3, (6.1 ± 0.3) × 10^?3, (13.5 ± 1.6) × 10^?3, (13.2 ± 0.9) × 10^?3, (52.9 ± 0.2) × 10^?3, and (88.1 ± 0.6) × 10^?3 M^?1 s^?1 at 40°C for [UO₂(Schiff base)(CH₃CN)], where Schiff base = L1–L8, respectively. In a temperature dependence study, the activation parameters ΔH^# and ΔS^# for the reaction of uranyl complexes with PBu₃ were determined. From the linear rate dependence on the concentration of PBu₃, the span of k₂ values and the large negative values of the activation entropy, an associative (A) mechanism is deduced for the solvent substitution. By comparing the second‐order rate constants k_2, it was concluded that the steric and the electronic properties of the complexes were important for the rate of the reactions.     

A green,efficient and recyclable poly(4-vinylpyridine)-supported copper iodide catalyst for the synthesis of coumarin derivatives under solvent-free conditions

Poly(4-vinylpyridine)-supported copper iodide is reported as a green, efficient and recyclable catalyst for the synthesis of coumarin derivatives by the Pechmann reaction under solvent-free conditions. This catalyst can be recovered by simple filtration and recycled up to eight consecutive runs without any loss of their efficiency.     

Z-Scan and Absorption Study of Crocin and Rhodamine B Decolorization by Bacterial Laccase

Dye decolorization is currently measured by the reduction of dye absorption, based on its linear optical properties in solution. However, this method is not suitable for high dye concentrations with linear attributes in the absorption spectra. In this work, nonlinear optical properties are used to study dye decolorization of Crocin and Rhodamine B treated with a bacterial laccase. For this purpose, the Z-scan was used to obtain the nonlinear refractive indices and nonlinear absorption coefficient of Rhodamine B and Crocin in the presence and absence of the bacterial laccase enzyme. The results showed that nonlinear optical properties could be used to study dye decolorization in solutions.     

Ultrasonic and bio‐assisted synthesis of Ag@HNTs‐T as a novel heterogeneous catalyst for the green synthesis of propargylamines: A combination of experimental and computational study

A novel heterogeneous catalyst is prepared through functionalization of halloysite nanotube with 1H‐1,2,3‐triazole‐5‐methanol and subsequent immobilization of silver nanoparticles through bio‐assisted approach using Arctiumplatylepis extract. The resulting catalyst, Ag@HNTs‐T, was characterized by using SEM/EDX, BET, XRD, FTIR, ICP‐AES, TGA, DTGA and elemental mapping analysis. Moreover, we computationally assessed metal‐ligand interactions in Ag@HNTs‐T complex model to interpret the immobilization behavior of silver nanoparticles on HNTs surface via quantum chemistry computations. The catalytic activity of the catalyst was studied for the synthesis of propargylamines via A³ and KA² coupling reactions under ultrasonic irradiation. The results demonstrated that Ag@HNTs‐T could efficiently promote these reactions to furnish the corresponding products in high yields and short reaction times. The study of the recyclability of the catalyst and Ag(0) leaching confirmed that the catalyst was recyclability up to four reaction runs with slight Ag(0) leaching.     

Kinetic Studies of Substitution Reactions of Uranyl(VI) Schiff Base Complexes with Tributylphosphine

The kinetics of the substitution reaction of uranyl Schiff base complexes with tributylphosphine was studied spectrophotometrically in acetonitrile. Uranyl complexes have a pentagonal bipyramidal structure with a trans‐UO₂ moiety at the axial positions. In uranyl tetradentate Schiff base complexes, the fifth position of the equatorial plane is occupied by the solvent molecule, which weakly coordinates to the U center. In a substitution reaction, tributylphosphine can easily replace the solvent molecule. By considering the excellent linearity of k_obs versus the molar concentration of tributylphosphine, the large negative values of Δ S^#, and the small values of Δ H^#, an associative (A) mechanism has been suggested. By comparing the rate constants (k₂) and the activation parameters, it is obvious that two parameters are effective in the rate of substitution reactions; The first parameter is the steric effect that the rate of reaction has been decreased by increasing this factor, and the other parameter is the electronic property that the electron‐withdrawing group leads to increase the rate of reaction and the electron donor group decreases it. © 2013 Wiley Periodicals, Inc. Int J Chem Kinet 45: 168–174, 2013     

Feasibility of least-square support vector machine in predicting the effects of shear rate on the rheological properties and pumping power of MWCNT–MgO/oil hybrid nanofluid based on experimental data

Journal of Thermal Analysis and Calorimetry - The main objective of the present paper was to investigate the feasibility of the least-square support vector machine (LSSVM) in predicting the effects...     

Evaluating the efficiency of the GO‐Fe3O4/TiO2 mesoporous photocatalyst for degradation of chlorpyrifos pesticide under visible light irradiation

In this work, the photocatalytic activity of the synthesized graphene oxide (GO)‐Fe₃O₄/TiO₂ mesoporous photocatalysts was evaluated using chlorpyrifos (CP) as a contaminant. The nano‐photocatalyst was characterized by X‐ray diffraction, field emission scanning electron microscopy with energy‐dispersive X‐ray spectroscopy, transmission electron microscopy, and specific surface area by the Brunauer–Emmett–Teller method. Using visible light, the GO‐Fe₃O₄/TiO₂ mesoporous photocatalyst was investigated on the degradation of CP pesticide. The GO‐Fe₃O₄/TiO₂ photocatalyst displayed a good photocatalytic activity, which was achieving 97% of CP degradation after 60 min. Finally, experiments were performed to evaluate GO‐Fe₃O₄/TiO₂ mesoporous nanocatalyst activity on repeated applications; after several uses, its photocatalytic activity was retained, which indicated stability.     

A highly efficient protocol for the synthesis of N-aryl nucleobases using zinc oxide in ionic liquids

A highly efficient and simple method for the synthesis of N-aryl derivatives of pyrimidine and purine nucleobases via Narylation of nucleobases using zinc oxide in 1-butyl-3-methylimidazolium bromide ([bmim]Br) under microwave as well as thermal conditions is described. In both conditions, the title compounds were produced in high to excellent yields and in short reaction times.