Synthesis, Crystal Structure, Fluorescence and Thermostability of Ni(II), Zn(II), Cd(II) Complexes with Schiff Base 2-Acetylpyridine-d-tryptophan

Three novel transition metal coordination polymers, [Ni(C₁₈H₁₆N₃O₂)₂·2CH₃OH] _n (1), [Zn(C₁₈H₁₆N₃O₂)₂·4CH₃OH] _n (2) and [Cd(C₁₈H₁₆N₃O₂)₂·2CH₃OH] _n (3) (C₁₈H₁₆N₃O₂=2-acetylpyridine-d-tryptophan) were synthesized and characterized by elemental analysis, IR, UV, ¹H NMR and X-ray diffraction single crystal analysis. The analyses of the structures indicate that all three materials crystallize in the tetragonal crystal system, space group P4₁2₁2. They have similar structures; i.e., the Schiff base coordinates in its deprotonated form and behaves as a hexadentate (4N+2O) coordinated ligand to form a distorted octahedron geometry. On the other hand, as a result of the alternate arrangement of chains through N–H···O intermolecular hydrogen bonds interactions, 2-D layers are formed for the three complexes. Furthermore, the luminescent properties and thermal stabilities of the three complexes were investigated.     

Reactions of cyclic and linear alkynols with a phosphinic iron(II) centre

Treatment of a MeOH solution of trans-[FeBr₂(depe)₂] (depe=Et₂PCH₂CH₂PEt₂) with HCCC₆H₁₀OH or HCC(CH₂)_nOH (n=1 or 2), in the presence of NaBPh₄, forms the cyclic allenylidene trans-[FeBr(CCC₆H₁₀)(depe)₂][BPh₄] or the alkyne trans-[FeBr{η²-HCC(CH₂)_nOH}(depe)₂][BPh₄] (n=1 or 2) complexes, respectively.     

Preparation and catalytic properties of a new dioxomolybdenum(VI) complex covalently anchored to mesoporous MCM-48

Reaction of the solvent adduct MoO₂Cl₂(THF)₂ with the 1,4-diazabutadiene ligands RNC(Ph)C(Ph)NR [R = (CH₂)₂CH₃, (CH₂)₃Si(OMe)₃] leads to complexes of the type MoO₂Cl₂(LL) in good yields at room temperature within a few minutes. The complex bearing the trimethoxysilyl groups was immobilized in the ordered mesoporous silica MCM-48 by covalent bonding. Solid state MAS NMR spectroscopy (¹³C, ²⁹Si) confirms that the structural integrity of the complex was retained during immobilization, except for loss of methoxide groups due to the reaction with surface silanols. Powder X-ray diffraction (XRD) and N₂ adsorption studies of the derivatized material indicate that the textural properties of the support were preserved during the grafting experiment and that the channels remained accessible. The modified material is active and selective in the epoxidation of cyclooctene at 55 °C using tert-butyl hydroperoxide as the oxidant. Stability was checked by recycling the solid catalyst several times. Some activity is lost from the first to second runs, but thereafter stabilizes. The catalytic behavior of the heterogenized catalyst was also compared with that observed in homogeneous phase for the complex with R=(CH₂)₂CH₃.     

Synthesis of polymer-supported metal-ion complexes and evaluation of their catalytic activities

Polymer-supported transition-metal-ion complexes of the N,N′-bis(o-hydroxy acetophenone) propylenediamine (HPPn) Schiff base were prepared by the complexation of iron(III), cobalt(II), and nickel(II) ions on a polymer-anchored N,N′-bis(5-amino-o-hydroxy acetophenone) propylenediamine Schiff base. The complexation of iron(III), cobalt(II), and nickel(II) ions on the polymer-anchored HPPn Schiff base was 83.44, 82.92, and 89.58 wt%, respectively, whereas the unsupported HPPn Schiff base showed 82.29, 81.18, and 87.29 wt % complexation of these metal ions. The iron(III) ion complexes of the HPPn Schiff base showed octahedral geometry, whereas the cobalt(II) and nickel(II) ion complexes were square planar in shape, as suggested by spectral and magnetic measurements. The thermal stability of the HPPn Schiff base increased with the complexation of metal ions, as evidenced by thermogravimetric analysis. The HPPn Schiff base showed a weight loss of 51.0 wt % at 500°C, but its iron(III), cobalt(II), and nickel(II) ion complexes showed weight losses of 27.0, 35.0, and 44.7 wt % at the same temperature. The catalytic activity of the unsupported and supported metal-ion complexes was analyzed by the study of the oxidation of phenol and epoxidation of cyclohexene in the presence of hydrogen peroxide. The supported HPPn Schiff base complexes of iron(III) ions showed a 73.0 wt % maximum conversion of phenol and 90.6 wt % epoxidation of cyclohexene, but unsupported complexes of iron(III) ions showed 63.8 wt % conversion of phenol and 83.2 wt % epoxidation of cyclohexene. The product selectivity for catechol (CTL) and epoxy cyclohexane (ECH) was 93.1 wt % and 98.1 wt % with the supported HPPn Schiff base complexes of iron(III) ions, but it was low with the supported Schiff base complexes of cobalt(II) and nickel(II) ions. The selectivity for CTL and ECH varied with the molar ratio of the metal ions but remained unaffected by the molar ratio of hydrogen peroxide to the substrate. The energy of activation for the epoxidation of cyclohexene and oxidation of phenol with the polymer-supported Schiff base complexes of iron(III) ions was 10.0 and 12.7 kJ/mol, respectively, but it was found to be higher with the supported HPPn Schiff base complexes of cobalt(II) and nickel(II) ions and with the unsupported HPPn Schiff base complexes of iron(III), cobalt(II), and nickel(II) ions. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Physicochemical Studies of 4-Substituted N-(2-Mercaptophenyl)-Salicylideneimines: Corrosion Inhibition of Mild Steel in an Acid Medium

A series of 4-substituted N-(2-mercaptophenyl)salicylideneimine Schiff bases were synthesized and investigated for corrosion inhibition of mild steel in hydrochloric acid medium. Inhibition through adsorption mechanism is proposed for these inhibitors, which is well supported by electrochemical impedance spectroscopy, the Langmuir adsorption isotherm and Scanning Electron Microscope morphologies of inhibited and uninhibited mild steel specimens. The negative ?G _ads indicates the spontaneous adsorption of the inhibitor on a mild steel surface. Among all the examined inhibitors, 5-bromo-N-(2-mercaptophenyl)salicylideneimine showed a higher inhibition efficiency. In order to reveal the usefulness of these Schiff bases as corrosion inhibitors under various circumstances, weight loss measurements were performed at various temperatures, acid concentrations and immersion times.     

Synthesis,characterization and catalytic activities of ruthenium complexes containing triphenylphosphine/triphenylarsine and tetradentate Schiff bases

Ruthenium(II) complexes of the type [Ru(CO)(B)(L)] (B=AsPh₃, pyridine, piperidine or morpholine; L=dianion of tetradentate Schiff bases) have been synthesized and characterized by physico-chemical methods. These complexes are found to be effective catalysts in the oxidation of primary and secondary alcohols using N-methylmorpholine-N-oxide as oxidant. The catalytic activity of these triphenylarsine complexes have been compared with that of triphenylphosphine complexes and with similar ruthenium(III) complexes. The formation of high valent Ruⁿ⁺²O species as catalytic intermediate is proposed for the catalytic processes.     

Synthesis and X-ray crystal structure of monomeric lanthanocene aryloxide complexes with a tridentate Schiff base ligand

Reaction of tris(cyclopentadienyl)lanthanide with the tridentate Schiff base N-1-(ortho-methoxyphenyl)salicylideneamine in THF at room temperature affords the isolation of monomeric lanthanocene Schiff base complexes, (η⁵-C₅H₅)₂Ln (OC₁₄H₁₃NO) (Ln=Sm (1), Er (2), Dy (3), Y (4)), which have been characterized by elemental analysis and mass spectra. The X-ray determination of 1 indicates that the complex is monomeric in which the metal center is coordinatively saturated by two cyclopentadienyl rings and two oxygens and one nitrogen from the Schiff base ligand. The average Sm–C bond distance is 2.723(7) Å, while those of the metal center to the Schiff base oxygens and nitrogen atoms are 2.232(4), 2.572(4) and 2.534(4) Å, respectively.     

Covalent anchoring of Mo(VI) Schiff base complex into SBA-15 as a novel heterogeneous catalyst for enhanced alkene epoxidation

Molybdenum(VI) Schiff base complexes modified mesoporous SBA-15 hybrid heterogeneous catalysts were synthesized by the reaction of MoO₂(acac)₂ with mesoporous SBA-15 functionalized by grafting procedures of 3-aminopropyl-triethoxysilane and salicylaldehyde, respectively. The physico-chemical properties of the as-synthesized catalysts were analyzed by ICP-AES, XRD, N₂ adsorption–desorption, FT-IR, SEM, TEM and EDX. The as-synthesized catalysts were effective in the catalytic epoxidation of cyclohexene. The catalytic activity can be further enhanced by silylation of the residual Si–OH groups using Me₃SiCl, which was largely due to the higher content of Mo active sites. The conversion and selectivity reached to 97.78 and 93.99 % using tert-butyl hydroperoxide as oxidant for Mo–CH₃–SA–NH₂–SBA-15, while 81.97 and 89.41 % in conversion and selectivity for Mo–SA–NH₂–SBA-15. At the same time, the catalytic performances of the hybrid materials were further systematically investigated under various reaction conditions (solvent, oxidants and alkenes, etc.). Mo–CH₃–SA–NH₂–SBA-15 catalyst can be recycled effectively and reused four cycles with little loss in activity. In addition, the results from hot filtration demonstrated that the catalytic activity mostly resulted from the heterogeneous catalytic process.     

Polystyrene anchored vanillin Schiff base—Complexation and ion removal studies

A set of six new polystyrene anchored metal complexes have been synthesized by the reaction of the metal salt with the polystyrene anchored Schiff base of vanillin. These complexes were characterized by elemental analyses, Fourier transform infrared spectroscopy, diffuse reflectance studies, thermal studies, and magnetic susceptibility measurements. The elemental analyses suggest a metal : ligand ratio of 1 : 2. The ligand is unidentate and coordinates through the azomethine nitrogen. The Mn(II), Fe(III), Co(II), Ni(II), and Cu(II) complexes are all paramagnetic while Zn(II) is diamagnetic. The Cu(II) complex is assigned a square planar structure, while Zn(II) is assigned a tetrahedral structure and Mn(II), Fe(III), Co(II), and Ni(II) are all assigned octahedral geometry. The thermal analyses were done on the ligand and its complexes to reveal their stability. Further, the application of the Schiff base as a chelating resin in ion removal studies was investigated. The polystyrene anchored Schiff base gave 96% efficiency in the removal of Ni(II) from a 20‐ppm solution in 15 min, without any interference from ions such as Mn(II), Co(II), Fe(III), Cu(II), Zn(II), U(VI), Na⁺, K⁺, NH₄⁺, Ca²⁺, Cl^?, Br^?, NO₃^?, NO₂^?,and CH₃CO₂^?. The major advantage is that the removal is achieved without altering the pH. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1536–1539, 2005     

A mononuclear copper(II) complex of a protonated unsymmetrical dinucleating Schiff base ligand

Reaction of the unsymmetrical and potentially dinucleating Schiff base ligand HL¹ with copper(II) salts has given mono- and dinuclear metal complexes. The structure of a mononuclear complex of diprotonated HL¹, [Cu(H₂L¹)(OH₂)](ClO₄)₃·H₂O·CH₃OH_, has been determined.     

Salen homonuclear and heteronuclear lanthanide(III) complexes with near-infrared (NIR) luminescence

Two lanthanide complexes are achieved by utilizing H₂salen/acac ligands (H₂salen = N,N′-ethylenebis(salicylideneimine), acac = acetylacetonate). They are homonuclear [Nd₄(μ₃-OH)₂(salen)₂(acac)₆(CH₃OH)₂]·CH₃OH (1) and heteronuclear [NdYb(salen)₂(acac)₂] (2). The structures of the two complexes were determined by X-ray crystallographic studies and their photophysical properties were investigated. The homonuclear Nd₄ complex exhibits characteristic metal-centered NIR emission. The heteronuclear NdYb shows ‘dual emission’ from both neodymium(III) and ytterbium(III) ions.     

Synthesis,Characterization and Conductivity Properties of Novel Oligomer Schiff Bases Derived from 4-Amino-3-hydrazino-5-mercapto-1, 2, 4-triazole and Their Reactions with VO(IV), Cu(II) Ions

A new Schiff base, 4-(4-hydroxysalicylidenamino)-3-hydrazino-5-mercapto-1,2,4-triazole (4HSAHMT), and novel Schiff base oligomers of 4-salicylidenamino-3-hydrazino-5-mercapto-1,2,4-triazole (SAHMT), 4-(2-hydroxynaphthylidenamino)-3-hydrazino-5-mercapto-1,2,4-triazole (2HNAHMT), 4-(4-hydroxysalicylidenamino)-3-hydrazino-5-mercapto-1,2,4-triazole (4HSAHMT) and 4-(5-bromosalicylidenamino)-3-hydrazino-5-mercapto-1,2,4-triazole (BrSAHMT) were synthesized via oxidative polymerization using NaOCl as the oxidant. The structures of the oligomers were supported by FT-IR, UV–Vis, ¹H-NMR, and ¹³C-NMR techniques. The compounds were further characterized by solubility tests, TG–DTA, and elemental analysis. The molecular weight distribution parameters of the compounds were determined by the size exclusion chromatography (SEC). According to SEC, the number average molecular weight (M _n ) values of O-SAHMT, O-BrSAHMT, O-4HSAHMT and O-2HNAHMT were 2,700, 2,100, 2,700 and 1,000 g mol^?1, respectively. The weight losses of O-SAHMT, O-BrSAHMT, O-4HSAHMT and O-2HNAHMT were 73, 76, 80 and 54 %, respectively, at 1,000 °C. TG analyses showed that the synthesized oligomers were stable toward thermal decomposition. The synthesized oligomers were converted to metal complexes with salts of VO(IV) and Cu(II). The doped and undoped electrical properties of oligomers and oligomer–metal complexes were determined by the four-point probe technique at room temperature and atmospheric pressure.     

A new trinuclear zinc(II) complex possessing five- and six-coordinated central ions and its photoluminescent property

A aromatic Schiff base ligand, N, N′-bis((4, 4′-diethylamino)salicylidene)-1, 2-phenylenediamine (H₂L), and its trinuclear zinc(II) complex, Zn₃L₂(CH₃COO)₂, were synthesized. The X-ray crystal structure of the complex reveals that two zinc ions show the coordination number of five and the third one has the coordination number of six. The complex exhibits blue-green emission as the result of the fluorescence from the intraligand emission excited state.     

Preparation and characterization of poly(styrene)/metal composites via reversible addition-fragmentation chain transfer (RAFT) polymerization

The expectant dithiocarbamate group end-functional poly(styrene) (PS) with a controlled molecular weight and low molecular weight distribution was synthesized conveniently via reversible addition-fragmentation chain transfer (RAFT) polymerization and was used to prepare polymer/metal composites with coordination chemistry. By the self-assembly technique, PS coordinated with the rare earth metal in N,N-dimethylformamide (DMF) to generate the fluorescent Eu–PS and Sm–PS complexes. Furthermore, PS-coated spherical silver nanoparticles (AgNPs) were prepared by reducing Ag⁺ to Ag⁰ under ultrasound irradiation in the presence of DMF and H₂O. The well core/shell structure of the AgNPs was characterized by transmission electron microscopy (TEM).     

Synthesis and characterization of unusual heterotrinuclear Co(III)Ni(II)Co(III) hydrotris(3,5-dimethylpyrazolyl)borate complex with mixed 1,1-azide and pyrazolate bridges

An unusual heterotrinuclear complex [LCo(μ-L₁, 1-N₃)₂(μ-L₁)Ni(μ-1, 1-N₃)₂(μ-L₁)CoL] (1) was obtained by the reaction of the precursor of half-sandwich nickel(II) complex [LNi(HL₁)₂(N₃)] (2) and CoCl₂ · 6H₂O (L = hydrotris(3,5-dimethylpyrazolyl)borate; L₁ = 3,5-dimethylpyrazolate), the complex 1 was characterized by X-ray single-crystal diffraction, elemental analysis, IR, UV–vis spectra and magnetic properties.     

NMR-spektroskopische Untersuchungen zum Komplexbildungsverhalten von Hydrazonen des Thiocarbazinsäure-O-methylesters mit Zink(II)-Ionen

Complexes of Zn(II) with Schiff Bases of Hydrazine-O-methylcarbothionates – NMR-Spectroscopic Investigations Schiff bases of hydrazine-O-methylcarbothionates react as bi- or tridentate ligands with Zn(II) ions forming neutral metal complexes ( 1a-1g ). ¹H-, ¹³C- and ¹⁵N-NMR-spectra of these complexes show the existence of configurational isomers of the CN-double bond. Furthermore, depending on the ligands 4 different coordination patterns with the donor atoms N₂S₂, N₄, N₂O₂ and NOS are demonstrated.     

Thermal routes to metal complexed polyimines; facile conversion of CoX2(NH2CH2CH{OEt}2)2 to CoX2{=NCH2CH=}2

Cobalt(II) complexes of the form CoX₂(NH₂CH₂CH{OEt}₂)₂ [X=Cl, Br, I] react hydrolytically in solution to convert hemiacetal moieties to aldehydes, the latter undergoing Schiff base condensation. Complex decomposition and the separation of metal salt and organic material occur concomitantly. In contrast, thermal reactions afford metal complexed polyimines of the form CoX₂{=NCH₂CH=}₂. Analyses are consistent with the liberation of four equivalents of ethanol per mole of CoX₂(NH₂CH₂CH{OEt}₂)₂ via an autocatalytic cycle of hemiacetal hydrolysis and Schiff base condensation. Such thermal routes offer facile access to metal complexed polyimines.     

Extraction of Lanthanides(III), U(VI), and Th(IV) from Nitric Acid Solutions with 1,5-N,N'-Bis[(diphenylphosphoryl)acetylamino]pentanes

Novel polyfunctional neutral organophosphorus ligands, namely 1,5-N,N'-bis[(diphenylphosphoryl)acetyl(alkyl)amino]pentanes [Ph₂P(O)CH₂C(O)NR]₂(CH₂)₅ (Ia, R = C₆H₁₃; Ib, R = CH₃), were studied as extractants for Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Th, and U from nitric acid solutions. The effect of both HNO₃ concentration in the aqueous phase and that of the extractant in the organic phase on the extraction of metal ions is considered. The stoichiometry of the extracted complexes was determined by the slope analysis method. Compared with the related bisaminopentane [Ph2P(O)CH₂C(O)NH]₂(CH₂)₅ (Ic), the replacement of hydrogen atoms at the amide nitrogens by alkyl radicals (compounds Ia,b) leads to an increase of metal ions extraction. Bis-CMPO ligands Ia-c were found to possess higher extraction efficiency towards U(VI), Th(IV), and Ln(III) than their monophosphorylated analogue Ph₂P(O)CH₂C(O)N(C₄H₉)₂.     

Low band gap Schiff base polymers obtained by complexation with Lewis acids

Two Schiff base polymers were prepared from the respective monomers by condensation method using toluene and N-methyl-2-pyrrolidinone as solvent. They were complexed with Al(III), In(III), and Cu(II) trifluoromethane sulfonates (triflates), and AlCl₃ Lewis acids and characterized by FT-IR, UV–Vis spectroscopy, and scanning electron microscopy (SEM). Homogeneous films were prepared by spin coating in the presence and absence of Lewis acids. Polymer–Lewis acid interaction was confirmed by FT-IR, UV–Vis spectroscopy, and SEM. Lewis acid composition in polymers was determined by FT-IR spectroscopy. Absorption spectra of these conjugated Schiff base polymer complexes exhibited smaller optical band gap than pristine polymers. These variations ranged from 2.4 to 1.4 and 3.3 to 2.0 eV. Absorption depends on the Lewis acid in the polymer and band gap on the nature of the metal incorporated in the polymeric backbone. Solubility increased by complexation. The obtained complexes were soluble in trifluoroacetic and formic acids and in m-cresol. Polymer–Lewis acid solutions in m-cresol were stable for 98 h; the others remained stable over several months. The results of this study revealed that optical, solubility, and band-gap properties of conjugated Schiff base polymers can be modified by Lewis acids and these could be studied by optoelectronics.     

Copper Complexes Obtained from the Schiff Base of Quinoline-2-Aldehyde and Aliphatic Diamines

Schiff base bis (2— quinolidene)- diamine gives a purple-red complex with copper ions with a λ_max at 530 mμ. The optimum pH for production of this complex is approximately 9.5. None of the metallic ions of the analytical groups II and III give rise to red complexes with the above Schiff base. Manganous (Mn²⁺) and stannous (Sn²⁺)ions as well as reducing agents such as hydrazine or hydroxylamine exert a catalytic effect on the rate of formation of these copper complexes. The thermal stability of the copper complex formed from the Schiff bases (2-quinoline-aldehyde with NH₂-(CH₂)_n-NH₂) is greater for diamine for which n = 4–6 than for n = 2–3.