Synthesis and metal-ion binding properties of new N2S4- and N2S5-donor macrocycles

Synthetic procedures for new N₂S₄- and N₂S₅-donor macrocycles (2 and 4) were given. The ligands were prepared by the reaction of NaBH₄ with the appropriate macrocyclic diamide in the presence of boron trifluoride ethyl etherate in dry tetrahydrofuran (THF). Solvent extraction method was used to evaluate metal-ion binding properties of the new ligands. The solvent extraction experiments suggested that the reduced macrocycles have Ag⁺ and Hg²⁺ selectivities compared to Pb²⁺, Co²⁺, Zn²⁺, Ni²⁺, Cu²⁺, Mn²⁺ and Cd²⁺ ions. The extraction constants (log K _ex) and complex compositions were determined for Ag⁺ and Hg²⁺ complex of compound (4).     

Vibrational frequencies and force constants of N2O4 in complexes with molecules of different solvents determined by Raman spectra andAb initio calculation

The Raman spectra of N₂O₄ solutions in organic solvents have been recorded. The frequencies ofv ₁,v ₂, andv ₃ bands of N₂O₄ increase with increasing solvent electron-donor properties. Especially large changes ofv ₃ N-N stretching band have been observed (254.5 cm^–1 in n-hexane, 276.5 cm^–1 in 1,4-dioxane). The ab initio calculations have shown that the interaction between N₂O₄ and electron-donor molecules causes an increase of N-N and N-O stretching and O-N-O bending force constants of N₂O₄ in agreement with the results of Raman study.     

Potential energy surfaces and vibrational spectra for isotopomers of N2O

Potential energy surfaces and vibrational spectra for the four isotopomers (^l5N¹⁴N¹⁶O,^l4N^I5N¹⁶O,¹⁵N₂ ¹⁶O and¹⁵N₂ ¹⁸O) of N₂O have been investigated with the vibrational self-consistent field-configuration interaction method. It is shown that the isotopomers with the same end atom have similar values of the potential parameters, and that substitution with different end atoms can affect the potential obviously. The calculated vibrational levels are in good agreement with the observed values by the optimization of several potential parameters (f ₁ ⁽¹⁾,f ₁₃ ⁽⁰⁾,f ₃ ⁽¹⁾ which are sensitive to isotopic substitutions. Project supported by the National Natural Science Foundation of China (Grant No. 29673029).     

Iron(III), nickel(II) and zinc(II) complexes based on acetophenone-S-methyl-thiosemicarbazone: synthesis,characterization, thermogravimetry,and a structural study

New complexes, [Fe(L)Cl], [Ni(L)], and [Zn(L)C₂H₅OH] (1–3), were synthesized by template reaction of 2-hydroxy-acetophenone-S-methyl-thiosemicarbazone with 2-hydroxy-benzaldehyde. The compounds were characterized by elemental analysis, magnetic measurements, FT-IR, ¹H NMR, UV–visible, and ESI–MS spectra. In these complexes, the ligand is coordinated to the metal ion as dinegatively charged tetradentate chelating agents via the N₂O₂ donor set. The iron(III) and zinc(II) complexes exhibit square pyramidal geometry whereas the nickel(II) complex has a square planar geometry. The crystal structure of 1, determined by X-ray diffraction method, indicates that 1 crystallizes in the monoclinic space group P21/c with Z = 4. Thermal decompositions of the compounds have been investigated using TGA in air.     

Syntheses,crystal structures,and some spectroscopic properties of zinc(II) complexes with N2O2 ligands derived from m-phenylenediamine and m-aminobenzylamine

The reaction of bis(salicylidene)-m-phenylenediamine with zinc(II) ion affords a 2?:?2 dinuclear zinc(II) complex formulated as [Zn₂(L¹)₂]. A similar 2?:?2 dinuclear zinc(II) complex, [Zn₂(L²)₂], can be obtained by reaction of bis(salicylidene)-m-aminobenzylamine with zinc(II) ion. These two dinuclear complexes slightly differ in their crystal structures, especially coordination environments around the zinc(II) centers, depending on the dissimilar flexibilities of the two ligands. The differences between the two complexes are reflected in their diffuse reflectance and photoluminescence behaviors.     

Unusual template condensation of benzophenone thiosemicarbazones and salicylaldehydes with nickel(II)

Reactions of 5-R-2-hydroxybenzophenone S-methylthiosemicarbazones (R: H, Br, Cl) and 2-hydroxy-benzaldehydes in the presence of NiCl₂ yielded template complexes by chelating with two of the ligands in the monoanionic form. The N₄O₂ complexes of the thiosemicarbazones show distorted-octahedral geometry around nickel(II). The compounds were characterized by elemental analysis, conductivity and magnetic measurements, UV-Vis, IR, ¹H-NMR, and mass spectra. Crystal structure of bis-N¹-(2-hydroxy-5-bromo-phenyl)(phenyl)methylene-N⁴-(2-hydroxy-phenyl)methylene-S-methyl-thiosemicarbazidato-Ni(II) was determined by single-crystal X-ray diffraction.     

Ion-pair extraction of transition metal cations from aqueous media using novel N2O2-macrocyclic crown ligands

Three new macrocyclic crown ether ligands containing nitrogen–oxygen donor atoms were designed and synthesized from 1,4-bis(2′-formylphenyl)-1,4-dioxabutane and 4-nitro-o-phenylenediamine. Ion-pair extraction of metal picrates such as Ag⁺, Hg²⁺, Cd²⁺, Zn²⁺, Cu²⁺, Ni²⁺, Mn²⁺, Co²⁺, and Pb²⁺ from aqueous phase to the organic phase was carried out using the novel ligands. The solvent effect over the metal picrate extractions was investigated at 25 ± 0.1 °C by using UV–visible spectrometry. The extractability and the values of the extraction constants (log K_ex) were determined for the extracted complexes.     

g-C3N4/Bi2O2CO32D纳米片复合材料的制备及可见光催化性能研究

采用自组装和化学沉淀法分别制得两种可见光驱动复合材料石墨相氮化碳/碳酸氧铋(g-C_3N_4/Bi_2O_2CO_3).采用X射线衍射光谱(XRD),紫外可见光谱、扫描电镜(SEM)、N_2吸附、电化学阻抗谱(EIS)和X射线光电子能谱(XPS)等分析手段对制备的催化剂进行了表征.结果表明,制备方法对纳米复合材料的晶相、形态及光学性能没有影响,但是影响g-C_3N_4和Bi_2O_2CO_3之间的相互作用力,导致光生电子-空穴对的分离速率存在显著差异.以可见光驱动苯酚和罗丹明B的降解实验为探针反应检测催化剂的光催化性能.实验结果表明自组装法得到的异质结催化剂中相互作用力更强,催化效果最高.O_2-是罗丹明B降解反应的主要活性物种,染料的光敏化、Bi_2O_2CO_3与g-C_3N_4综合效应,导致光生载流子电荷分离效率更高.     

On the bond order of C2 and N2

The commonly adopted bond order values of C₂ and N₂ are critically investigated with a new bond order concept. Ab initio calculations with extended basis sets suggest that C₂ can be described by a double to triple bond closer to acetylene than to ethylene and N₂ by a triple bond. The basis set dependence is discussed. Also a relation between the number of basis functions, MO's and non-vanishing eigenvalues of the bond order parts of the density matrix is presented.     

Solvation Structure and Complexation of the Manganese(II) Ion in N,N-Dimethylpropionamide and N,N,N′,N′-Tetramethylurea Studied by Means of Titration Calorimetry and Raman Spectroscopy

Aprotic N,N-dimethylpropionamide (DMPA) and N,N,N′,N′-tetramethylurea (TMU) are both strong donor solvents and coordinate to metal ions through the carbonyl oxygen atom. These solvents show a different conformational aspect in the bulk phase, i.e., DMPA exists as either a planar cis or a nonplanar staggered conformer, while TMU exists in a single planar cis conformer. It has been established that the manganese(II) ion is solvated by five molecules in both solvents. Interestingly, although the planar cis conformer of DMPA is more favorable than the nonplanar staggered one in the bulk phase, the reverse is the case in the coordination sphere of the metal ion, i.e., a conformational change occurs upon solvation. To reveal the thermodynamic aspect of this conformational change, the complexation of Mn(II) with bromide ions in DMPA and TMU has been studied by titration calorimetry at 298 K. It was found that the Mn(II) ion forms mono-, di- and tri-bromo complexes in both solvents, and their formation constants, enthalpies and entropies were obtained. The Δ H∘₁ value for MnBr⁺ strongly depends on the solvent, i.e., it is positive (19.4 kJ-mol⁻¹) in DMPA and negative (−8.7 kJ-mol⁻¹) in TMU, whereas the Δ H^∘₂ and Δ H∘₃ values for the stepwise formation of MnBr₂ and MnBr₃⁻ are both small and negative. The enthalpy of transfer Δ_tH^∘ from DMPA to TMU, which is evaluated on the basis of the extrathermodynamic TATB assumption, is 25.5 kJ-mol⁻¹ for Mn²⁺ and −3.6 kJ-mol⁻¹ for MnBr⁺. These values indicate that the difference between the formation enthalpy of MnBr⁺ in the two solvents, Δ H^∘₁ (DMPA) – Δ H∘₁ (TMU), is mainly ascribed to the value of Δ_tH^∘(Mn²⁺). It is found that the metal ion is also five-coordinated in the monobromo complex, MnBr(DMPA)₄⁺ . The enthalpy for the conformational change of DMPA from its planar cis to the nonplanar staggered form is evaluated to be −11 and −5.5 kJ-mol⁻¹ for Mn(DMPA)₅^{2 +} and MnBr(DMPA)₄⁺, respectively. Note that these values are significantly smaller than the corresponding value (5.0 kJ-mol⁻¹) in the bulk phase. We thus conclude that, although steric hindrance among solvent molecules is reduced by replacing one DMPA of Mn(DMPA)₅^{2 +} with the relatively small bromide ion, DMPA molecules are still sterically hindered in the MnBr(DMPA)₄⁺ complex.     

Synthesis and characterization of a cationic oxorhenium(V) complex containing the pentadentate N3O2-donor ligand bis ( N -methylsalicylideneiminopropyl)amine

The complex salt [ReO(bsa)]PF₆ (H₂bsa?=?bis(N-methylsalicylideneiminopropyl)amine) was prepared from the reaction of cis-[ReO₂I(PPh₃)₂] with H₂bsa in toluene. The dianionic pentadentate ligand bsa is coordinated to the ReO³⁺ moiety via one secondary amino and two imino nitrogens, and two anionic phenolate oxygens. The complex was characterized by spectroscopy and analytical data, and the structure has been determined by single-crystal X-ray diffraction analysis.     

Facile synthesis and characterization of novel benzo-fused macrocyclic dicarbonitriles and pyrazolo-fused macrocycles containing thiazole subunits

Abstract

Novel bis[2-(thiazol-2-yl)acetonitriles], linked to aliphatic cores via ethers, were prepared by the reaction of the appropriate bis(2-bromoethan-1-one) with 2-cyanothioacetamide in dioxane at reflux. Bis[2-(thiazol-2-yl)acetonitriles] were taken as key intermediates for the preparation of a new class of macrocyclic dicarbonitriles bearing two thiazole units and containing two O₂-donor sets and fused with two benzene units. The target macrocyclic dicarbonitriles were prepared by the cyclocondensation of bis[2-(thiazol-2-yl)acetonitriles] with the appropriate bis(aldehydes) in N,N-dimethylformamide in the presence of piperidine at reflux. Moreover, a new class of pyrazolo-fused macrocycles containing thiazole subunits were prepared by the reaction of macrocyclic dicarbonitriles with hydrazine hydrate in ethanol at reflux. The structures of the novel macrocycles bearing thiazole subunits were elucidated by considering their elemental analyses as well as their IR, mass, ¹H NMR and ¹³C NMR spectral data.     

A theoretical study of the relative stability of the isomeric forms of N2O3

The electronic structure, geometrical parameters and relative stability of the isomeric forms of N₂O₃ are analysed by means of ab initio calculations. Total energies of the different isomers are given. The energy difference between the most stable conformers of the symmetric N₂O₃ is 4.31 Kcal mol^–1 as provided by 6–31G basis set. The height of the rotational barrier determined by the ab initio technique is 7.12 kcal mol^–1.Member of the Carrera del Investigador CICPBA, R. Argentina.Member of the Carrera del Investigador CONICET, R. Argentina.Predoctoral fellow of CONICET, R. Argentina.     

Does application of cement kiln exhausts affect root nodule biochemistry and soil N2-fixing microbes?

The research work carried out on cement exhausts centers mostly around vegetation and crop productivity (1-3) with little or no work on root nodulation. Soil plus foliar application of exhaust dusts did not affect soil/nodule rhizobial population, nodule initiation, and possible N₂-fixing capacity inCajanus cajan, Vigna radiata, Vigna mungo,Vigna catjung, andGlycine max. The nodular biochemistry was investigated in detail. The heme protein leghemoglobin was higher compared to the control. The levels of intermediary N compounds like total ureides of the nodules, which may serve as indirect evidence of symbiotic N₂ fixation, were higher in the treated plants. There were also increments in free proline, free amino acids, soluble proteins, soluble starch, soluble sugars, total nitrogen, and phenols in the treated plants. The levels of total nitrates, soluble sucrose, and soluble SH compounds of the nodule of the control and treated plants did not show a significant difference. The activities of ascorbate peroxidase, catalase, glutathione reductase, and Superoxide dismutase were significantly higher, possibly indicating their role in alleviation of H₂O₂ and O ₂ ^- damage by the exhausts. Enzymes like nitrate reductase, nitrite reductase, and glutamine synthetase, and also the activities of acid and alkaline phosphatases were not affected. The presence of beneficial soil microbes likeAzotobacter, Azospirillum, and mycorrhizae was not affected at all.     

An 18-member dinucleating unsymmetrical [N10] macrocycle and its bimetallic complexes M2LCl2(ClO4) (M=Co,Ni, Cu,Zn, Cd or Hg)

The 18-member unsymmetrical dinucleating Shiff-base decaaza [N₁₀] macrocyclic ligand, 2,8,11,17-tetramethyl-3,5,7,12,14,16-hexaphenyl-[1,3,5,7,9,10,12,14,16,18] decaazaoctadeca-2,8,11,17-tetraene dihydroperchlorate (L · 2HClO₄) was obtained as a cream colored solid from reaction of N-acetylaniline and hydrazine in the presence of HClO₄ followed by cyclization (capping) using aniline and excess HCHO in methanol at RT. Reactions of L · 2HClO₄ with MCl₂ and [M(Ph₃P)₂Cl₂] afforded air stable complexes, M₂LCl₄(ClO₄)₂ (M = Co, Ni, Cu, Zn or Cd). The compounds have been characterized by physico-chemical and spectroscopic studies. FAB–Mass spectral data support bimetallic coordination by the macrocycle. IR studies confirm coordination/encapsulation of metal ions involving unsymmetrical aza sites. Magnetic susceptibility and UV–Visible data indicate a low-spin, five-coordinate geometry for Co(II) and Ni(II) complexes. The anisotropic EPR signals (g _∥ > g _⊥) for Cu²⁺ complex suggest an axial type tetragonality. Molecular model computations have been employed for a theoretical perspective of the ligand and complexes. The important bond lengths and bond angles have been estimated using CS Chem-3D software. The ionic association constant (K ₁) and thermodynamic free energy change (ΔG) were evaluated from the conductometric data of the complexes, which indicate presence of a strong ion-pair even in solution. Cyclic voltametric studies on solutions of M₂LCl₄(ClO₄)₂ (M = Co, Ni or Cu) in DMSO indicate reversible and quasi-reversible redox couples.     

Production of N,H, and NH active species in N2-H2 dc flowing discharges

Densities of N, H, and NH active species have been detected by laser-induced fluorescence (LIF) in N₂-xH₂ dc flowing discharges. A peak value of N atom densities far x = 0.2–0.5% and a plateau value of H atom densities between x = 1% and 90% in post-discharge conditions (0.05 sec, p = 2 torr) has been found. Comparison between LIF measurements of N atoms and the trend of the N₂(B, v = II) population shows that the emission from this state can be used for monitoring N atoms. The NH radical has only been detected inside the discharge region.On leave from Instituto Tecnológico de Aeronáutica, CNPq, Brazil.     

Synthesis,spectral characterization,catalytic and antibacterial activity of macrocyclic Cu<Superscript>II</Superscript> compounds

Macrocyclic Cu^II compounds of the type Cu(L₄)Cl₂ (where L₄ = N₄ or N₂O₂ donor macrocyclic ligand) have been synthesized by treating the corresponding macrocycles with copper chloride in methanol. These compounds were characterized with the help of elemental analysis, i.r., mass, ESR, electronic spectra, conductance, magnetic and thermal studies. Distorted octahedral geometry has been proposed for all of these compounds. These compounds were found to be efficient in the catalytic oxidation of ascorbic acid and the percentage yields of oxidation products were determined spectrophotometrically. The biological activities of these compounds have been tested against gram +ve and gram −ve bacteria and found to be more active when compared with commercially available antibacterials like streptomycin and ampicillin.     

Synthesis and Characterization of a New (E,E)-Dioxime and its Homonuclear Complexes

N′-(4′-Benzo[15-crown-5]naphthylaminoglyoxime (H₂L) and its sodium chloride complex (H₂L·NaCl) have been prepared from 2-naphthylchloroglyoxime, 4′-aminobenzo[15-crown-5] and sodium bicarbonate or sodium bicarbonate and sodium chloride. Nickel(II), cobalt(II) and copper(II) complexes of H₂L and H₂L·NaCl have a metal–ligand ratio of 1:2 and the ligand coordinates through the two N atoms, as do most of the vic-dioximes. The BF₂⁺-capped Ni(II), Co(III) and mononuclear complexes of thevic-dioxime were prepared. The macrocyclic ligands and their transition metal complexes have been characterized on the basis of IR, ¹H NMR spectroscopy and elemental analyses data.     

High resolution adsorption isotherms of N2 and Ar for nonporous silicas and MFI zeolites

The high resolution adsorption isotherms of N₂ (77.4 K) and Ar (87.3 K) have been measured for two nonporous silicas with different silanol contents (3.3 and 0.35 OH/nm²) and for two MFI zeolite with different Al contents (Si/Al=12.5 and 500). Silanol groups and Al sites (acid sites) gives the significant effect on the N₂ isotherms at submonolayer, but the Ar isotherms are independent of silanols and Al sites. The Ar isotherms, therefore, are preferable in calculation of microporosity of zeolites. The N₂ and Ar isotherms for MFI zeolite (Si/Al=500) have been measured at temperatures of 77–94 K, from which the differential adsorption energies of N₂ and Ar are calculated. The interaction of N₂ with channel surface of MFI zeolite is greater than that of Ar in the range of α _s =0.1–0.7. The hystereses are detected for the N₂ isotherm in p/p ^o=0.1–0.3 at 77.4 K and for the Ar isotherm in p/p ^o=3×10⁻⁴–2×10⁻³ at 87.3 K. However, it is difficult to explain the hysteresis phenomenon using differential adsorption energy.     

Kinetics of the thermal decomposition of [Co(NH3)6]2(C2O4)3·4H2O

The thermal decomposition of [Co(NH₃)₆]₂(C₂O₄)₃·4H₂O was studied under isothermal conditions in flowing air and argon. Dissociation of the above complex occurs in three stages. The kinetics of the particular stages thermal decomposition have been evaluated. The R_N and/or A_M models were selected as those best fitting the experimental TG curves. The activation energies,E, and lnA were calculated with a conventional procedure and by a new method suggested by Kogaet al. [10, 11]. Comparison of the results have showed that the Arrhenius parameters values estimated by the use of both methods are very close. The calculated activation energies were in air: 96 kJ mol^–1 (R_1.575, stage I); 101 kJ mol^–1 (Ain1.725 stage II); 185 kJ mol^–1 (A _2.9, stage III) and in argon: 66 kJ mol^–1 (A _1.25, stage I); 87 kJ mol^–1 (A _1.825, stage II); 133 kJ mol^–1 (A _2.525, stage III).