Synthesis,spectroscopic characterization and catalytic activity of cis-dioxidomolybdenum (VI) complexes with chiral tetradentate Schiff bases

New chiral mononuclear cis-dioxidomolybdenum (VI) complexes, MoO ₂ L ¹ –MoO ₂ L ¹⁰ , with tetradentate Schiff bases derived from various substituted salicylaldehydes and 1S,2S-(+)-2-amino-1-(4-nitrophenyl)-1,3-propanediol were synthesized. All complexes were characterized by elemental analysis, circular dichroism, electronic and IR spectroscopy. ¹H NMR and also two-dimensional (COSY, NOESY and gHSQC) NMR measurements made for MoO ₂ L ¹ –MoO ₂ L ¹⁰ complexes show that Schiff bases are coordinated to the MoO₂²⁺ cation, creating facial (fac) and meridional (mer) types of geometrical isomers. Moreover, catalytic activity studies were also performed for all complexes in asymmetric sulfoxidation of thioanisole and epoxidation of styrene, cyclohexene and two monoterpenes, i.e. S(−)-limonene and (−)-α-pinene, using aqueous 30% H₂O₂ or tert-butyl hydroperoxide as the oxygen source.     

Synthesis,characterization and antioxidant activities of dioxomolybdenum(VI) complexes of new Schiff bases derived from substituted benzophenones

Abstract

Five novel ONS donor Schiff base ligands were synthesized by the reaction of 2-hydroxybenzophenone (L1), 2-hydroxy-4-methoxybenzophenone (L2), 2-hydroxy-4-octyloxybenzophenone (L3), 2-hydroxy-4-methoxy-4′-methylbenzophenone (L4), and 2-hydroxy-4-allyloxybenzophenone (L5) with thiocarbohydrazide. Neutral solvate dioxomolybdenum(VI) complexes with the general formula [MoO₂L(ROH)], [C1–C5] (L?=?L1, L2, L3, L4, L5 and R?=?CH₃, C₂H₅, or C₄H₉), were prepared from these Schiff bases. Characterization of all compounds was carried out by means of elemental analysis, conductivity measurements, ¹H-NMR, FT-IR, UV-Vis spectroscopy and mass spectrometry (for L1, C2, and C4) techniques. The crystal structures of ligand (L5) and complex (C1) were determined by single-crystal X-ray crystallography. Spectroscopic data and X-ray diffraction studies confirmed that the ligand is coordinated to the cis-MoO₂²⁺ core through ONS, while the sixth coordination site is occupied by solvent (ROH). The ligands and complexes were tested for in vitro antioxidant capacities. The TEAC coefficients of the ligands and complexes were found higher than reference compound. DPPH radical scavenging activities of these compounds were also investigated.     

Synthesis,characterization, optical and anti-bacterial properties of benzothiazole Schiff bases and their lanthanide (III) complexes

Two new Schiff base ligands comprising benzothiazole derivatives, namely (N,N′,E,N,N′E)-N,N′-(1,3-phenylenebis(methanylylidene))bis(5-nitrobenzo[d]thiazoL2-amine (L1) and (N,N′,E,N,N′E)-N,N′-(1,3-phenylene-bis(methanylylidene))bis(5-methylthiazo-L2-amine (L2), have been synthesized and thoroughly characterized using FTIR, ¹H NMR, mass UV/vis and fluorescence spectral techniques. Further, L1 and L2 lead to the formation of lanthanide complexes 1–6 with Ce(III), Nd(III), and Pr(III) ions in 1:2 (metal:ligand) stoichiometry. UV/vis spectra of L1, L2 and 1–6 exhibit characteristic ligand centered absorptions in the range of 230–350 nm. Besides, both ligands and complexes show significant emissions and good anti-bacterial activity against pathogenic bacteria. Ligands and complexes display anti-bacterial activity against bacteria Staphylococcus aureus (S. aureus) (MTCC 1144) causing skin infection and food poisoning and pimple-causing bacteria propionic bacteria acnes (P. acnes) (MTCC 1951).     

Green synthesis,characterization, and DFT calculations of diorganotin (IV) complexes of Schiff bases

Diorganotin (IV) complexes (1, 2, 3, 4), of the general formula R₂Sn(L)_m have been synthesized where R = n-But, n-Oct; m = 2 when L1 = N-[(Z)-(2-hydroxy-3-methoxybenzylidene)pyrazine-2-carboxamide and m = 1 when L2 = [3,4-bis-{[(E)-(2-hydroxy-3-methoxyphenyl) methylidene]amino}phenyl](phenyl)meth-anone. The prepared Schiff bases and diorganotin complexes have been characterized by elemental analysis, FTIR, and NMR (¹H, ¹³C, and ¹¹⁹Sn) spectroscopic studies. The molecular geometry, thermochemical values, and vibrational frequencies of two complexes in the ground state were calculated using the B3LYP density functional method with LANL2DZ basis set for Sn using Gaussian 09 software. A good correlation of theoretical and experimental results shows that in both the complexes the geometry around the central tin atom is tetrahedral. The studies were further extended to test and compare the in vitro cytotoxic activity of ligands and complexes against MCF-7 cell line by MTT assay. The IC50 values show that cytotoxic activity of ligands increased on complexation with tin metal.     

Synthesis and spectroscopic studies of new organotin(IV) complexes with tridentate N- and O-donor Schiff bases

The Schiff bases H₂L¹ and H₂L² have been prepared by the reaction of 2-amino-4-chlorophenol with pyrrole-2-carbaldehyde and 2-hydroxy-1-naphtaldehyde, respectively, and HL³ from reaction of 2-(aminomethyl)pyridine with 2-hydroxy-1-naphtaldehyde. Organotin complexes [SnPh₂(L¹)] (1), [SnPh₂(L²)] (2), [SnMe₂(L²)] (3) and [SnPhCl₂(L³)] (4) were synthesized from reaction of SnPh₂Cl₂ and SnMe₂Cl₂ with these Schiff bases. The synthesized complexes have been investigated by elemental analysis and FT-IR, ¹H NMR and ¹¹⁹Sn NMR spectroscopy. In complexes the Schiff bases are completely deprotonated and coordinated to tin as tridentate ligands via phenolic oxygen, pyrrolic, and imine nitrogens in 1, two phenolic oxygens and imine nitrogen in 2 and 3, and phenolic oxygen, imine and pyridine nitrogens in 4. The coordination number of tin in 1, 2, and 3 is five and in 4 is six.     

Synthesis,spectral, theoretical studies and in vitro antimicrobial activities of novel diphenyltin(IV) complexes of Schiff bases derived from phenacylamine

A series of new diphenyltin(IV) complexes of the type Ph₂SnL (L¹: N‐phenacyl‐5‐bromosalicylideneimine, Ph₂SnL¹; L²: N‐phenacyl‐3,5‐dichlorosalicylideneimine, Ph₂SnL²; L³: N–phenacyl‐4‐methoxysalicylideneimine, Ph₂SnL³) were synthesized and characterized by elemental analysis, IR, ¹H, ¹³C, ¹¹⁹Sn NMR spectroscopy and mass spectrometry techniques. The C―Sn―C angles in the complexes were calculated using equations with the ¹J(^117/119Sn―¹³C) values from ¹³C NMR spectra. The possible structures, NMR and electronic properties of the studied molecules were calculated through density functional theory and results compared with experimental data. All the complexes were found to be mildly active against several microorganisms and some fungi. Copyright © 2014 John Wiley & Sons, Ltd.     

Complexes of thorium(IV) and uranium(IV) with some Schiff bases

Complexes of thorium(IV) and uranium(IV) with Schiff bases derived from salicylaldehyde have been prepared and characterised. The metal tetrachlorides react directly with quadridentate Schiff bases in ethanol to yield the complexes but bidentate Schiff bases yield hydrolysed products under the same conditions. Complexes of the bidentate Schiff bases are obtained by reaction of ligand with metal tetraacetate in a melt or by ligand exchange with the thallium-Schiff base complex. Absorption spectra are reported and band assignments are discussed.     

Organotin(IV) complexes of dibasic tridentate Schiff bases containing ONO donor atoms

Organotin(IV) Schiff base complexes of the type (L)SnR₂ [where R?CH₃, C₆H₅ or CH₂CH₂CO₂ CH₃], (LH)Sn(C₆H₅)₃ and (L)SnCl(CH₂CH₂CO₂ CH₃) [where LH₂?2-N-salicylideneimino-2-methyl-1-propanol, derived from the condensation of salicylaldehyde and 2-amino-2-methyl-1-propanol] have been prepared and characterized on the basis of their elemental analyses, IR, ¹H, ¹³C and ¹¹⁹Sn NMR studies. In these mononuclear complexes the Schiff base acts either as a dianionic tridentate or as a monobasic bidentate moiety by coordinating through an alkoxy group, an azomethine nitrogen and a phenoxide ion to tin. Sulphur dioxide inserts in the tin–methyl/–phenyl bond in the above Schiff base complexes to give tin–O–sulphinates of formulae (L)RSn(SO₂R) and (LH)(C₆H₅)₂Sn(SO₂C₆H₅).     

Synthesis and spectroscopic characterization of cationic mononuclear oxovanadium(IV) complexes with tetradentate Schiff bases as ligands

New tetradentate Schiff-base oxovanadium(IV) complexes [VOL']SO4 (where L' = tetradentate ligands derived from 2,4-dihydroxy 5-acetyl acetophenone and substituted diamines) were prepared and characterized by physico-chemical techniques. All the complexes are monomeric in nature and a square-pyramidal geometry is proposed. Various ligand-field and molecular-orbital parameters have been calculated.     

Synthesis, characterization and structural studies of diorganotin(IV) complexes with Schiff base ligand salicylaldehyde isonicotinylhydrazone

Eight diorganotin(IV) complexes of salicylaldehyde isonicotinylhydrazone (H₂SalN) R₂Sn(SalN) R = t-Bu 1, Ph 2, PhCH₂3, o-ClC₆H₄CH₂4, p-ClC₆H₄CH₂5,m-ClC₆H₄CH₂6,o-FPhCH₂7, p-FC₆H₄CH₂8 were prepared. All complexes 1-8 have been characterized by elemental, IR, ¹H, ¹³C and ¹¹⁹Sn NMR analyses. The crystal structures of H₂SalN and complex 1 were determined by X-ray crystallography diffraction analyses. Studies show that H₂SalN is a tridentate planar ligand. For complex 1, the tin atom lies in this plane and forms a five- and six-membered chelate ring with the tridentate ligand. A comparison of the IR spectra of the ligand with those of the corresponding complexes, reveals that the disappearance of the bands assigned to carbonyl unambiguously confirms that the ligand coordinate with the tin in the enol form.     

Synthesis,characterization and biological studies of oxovanadium(IV) complexes with triazole‐derived Schiff bases

A series of triazole‐derived Schiff bases (L¹–L⁵) and their oxovanadium(IV) complexes have been synthesized. The chemical structures of Schiff bases were characterized by their analytical (CHN analysis) and spectral (IR, ¹H and ¹³C NMR and mass spectrometry) data, and oxovanadium(IV) complexes were elucidated by their physical (magnetic susceptibility and conductivity), analytical (CHN analysis), conductance measurements and electronic spectral data. The molar conductivity data indicate the oxovanadium(IV) complexes to be non‐electrolyte. The Schiff bases act as bidentate and coordinate with the oxovanadium(IV)‐forming stoichiometry of a complex as [M (L‐H)₂] where M = VO and L = L¹–L⁵ in a square‐pyramidal geometry. The agar well diffusion method was used for in vitro antibacterial screening against E. coli, S. flexenari, P. aeruginosa, S. typhi, S. aureus and B. subtilis and for antifungal activity against T. longifucus, C. albican, A. flavus, M. canis, F. solani and C. glaberata. The biological activity data show the oxovanadium(IV) complexes to be more antibacterial and antifungal than the parent Schiff bases against one or more bacterial and fungal strains. Copyright © 2009 John Wiley & Sons, Ltd.     

Synthesis,crystal structures and characterization of two Cu(II) complexes with asymmetric sulfonamide Schiff-base ligands

Reaction of the N-tosyl-1,2-diaminopropane or N-tosyl-1,2-diaminobenzene with salicylaldehyde forms two new asymmetric sulfonamide Schiff bases, N-[2-(2-hydroxybenzylideneamino)propyl]-4-methylbenzenesulfonamide (H₂L¹ ) and N-[2-(2-hydroxybenzylideneamino)phenyl]-4-methylbenzenesulfonamide (H₂L² ). Two new complexes [CuL ^x (H₂O)] (x = 1 for 1, x = 2 for 2) constructed from H₂L ^x have been prepared and characterized via X-ray single-crystal diffraction, elemental analysis, FT-IR, UV-Vis, TGA, quantum chemical calculations, and photoluminescence measurements. Weak C–H ··· π, hydrogen bonds, π–π, and Cu ··· O weak interactions lead to 3-D supramolecular architecture, 1, and 1-D double chain, 2.     

Synthesis and structural characterization of diorganotin(IV) esters with pyruvic acid isonicotinyl hydrazone and pyruvic acid salicylhydrazone Schiff bases

Eight diorganotin esters of Schiff base ligands formulated as [R₂SnLY]₂, where L₁ is 4-NC₅H₄CON₂C(CH₃) CO₂ with Y = H₂O, R = Ph (1), PhCH₂ (2), m-ClC₆H₄CH₂ (3), and L₂ is 2-HOC₆H₄CON₂C(CH₃) CO₂ with Y = CH₃OH, R = PhCH₂ (4), o-ClC₆H₄CH₂ (5), m-ClC₆H₄CH₂ (6), o-FC₆H₄CH₂ (7), p-FC₆H₄CH₂ (8) have been prepared and characterized by elemental analysis, IR, ¹H and ¹¹⁹Sn NMR spectra. The crystal structures of compounds 1, 2 and 4 have been determined by X-ray single crystal diffraction. Their structures show that the tin atoms of three compounds are all rendered seven-coordinated in distorted pentagonal bipyramid geometries with a planar SnO₄N unit and two apical aryl carbon atoms. A comparison of the IR spectra of the ligands with those of the corresponding compounds, reveals that the disappearance of the bands assigned to carbonyl unambiguously conforms that the ligands coordinate with tin in the enol form.     

Preconcentration techniques for uranium(VI) and thorium(IV) prior to analytical determination-an overview

The need for the preconcentration of trace and ultratrace amounts of uranium(VI) and thorium(IV) in conjunction with various detection techniques was clearly brought out in the introductory part. Subsequently, various off-line and on-line procedures developed for uranium(VI) and thorium(IV) prior to their analytical determination since 1990 were critically reviewed in terms of enrichment factor, retention/sorption capacity, validation using certified reference materials and application to complex real samples. The relative merits and demerits of various preconcentration and/or separation of uranium(VI) and thorium(IV) prior to quantitation by a plethora of analytical techniques are discussed in concluding part of the review article.     

Synthesis,characterization and oxygen affinity of Mn(II), Co(II) and Ni(II) complexes of diethylenetriamine Schiff bases

N,N′-diethyleneamine bis(salicylideneimine); H₂DETS and N,N′-diethyleneamine bis(o-hydroxyacetophenoneimine); H₂DETHA have been prepared to produce Mn(II), Co(II) and Ni(II) complexes by the addition of the synthesized Schiff bases to the studied ions under nitrogen. H₂DETS and H₂DETHA are neutral tridentate in the nitrato complexes and binegative pentadentate in the other complexes. A square pyramidal structure was suggested for all complexes based on elemental analysis, molar conductivity, infrared, electronic spectra and magnetic moment measurements. The oxygen absorption properties were studied for the isolated complexes by considering the solubility, oxygen affinity and stability. [Co(DETS)]·4H₂O has the highest affinity. Different concentrations for the Co(II) complex were studied.     

Synthesis and characterization of oxovanadium(IV), vanadium(IV) and oxovanadium(V) complexes of tetradentate Schiff bases. Attempted preparation of vanadium-carbon bonded compounds through desilylation

Condensation of 1,3-diaminopropane-2-ol with diacetylmonoxime, acetylacetone, salicylaldehyde and orthohydroxyacetophenone yielded the tetradentate Schiff bases N,N′-(2-hydroxy)propylenebis{(2-imino-3-oximino)butane} (H₂dampnol), N,N′-(2-hydroxy)propylenebis(acetylacetoneimine) (H₂acacpnol), N,N′-(2-hydroxy)propylenebis-(salicyalaldimine) (H₂salpnol) and N,N′-(2-hydroxy)propylenebis(7-methylsalicylaldimine) (H₂ohacpnol), respectively. The ligands form complexes with oxovanadium(IV), vanadium(IV) and oxovanadium(V) salts. Some mixed ligand complexes involving σ-bonded phenyl and benzyl radical along with tetradentate ligand, H₂L (where, H₂L stands for H₂dampnol, H₂acacpnol, H₂salpnol or H₂ohacpnol) of the types [(L)V(C₆H₅)₂]CH₃OH and [(L)V(CH₂Ph)₂]CH₃OH have been synthesized, characterized and also provide the syntheses of some new organovanadium(IV) complexes. Silylation coupled with desilylation have been employed as a route to new organovanadium(IV) complexes. All the complexes have been characterized with the help of elemental analyses, molar conductance values, molecular weights, magnetic moments and spectroscopic (IR, UV-Vis, ESR) data.     

Synthesis, characterization, and X-ray structural analysis of some half-sandwich ruthenium(II) arene complexes with new N,S-donor Schiff base ligands

A series of cationic, half-sandwich ruthenium complexes with the general formula [(η⁶-arene)RuCl(R¹S-C₆H₄-2-CHNR²)]⁺ (arene = p-cymene or hexamethylbenzene; R¹ = CH₂Ph, ⁱPr, or Et; R² = aryl) have been prepared from the reaction of [(η⁶-arene)RuCl₂]₂ with various N,S-donor Schiff base ligands derived from 2-(alkylthio)benzaldehyde and several primary amines. All of the ruthenium complexes were characterized by IR, ¹H NMR, electrochemistry, and UV/Vis spectroscopies. The p-cymene complexes undergo irreversible oxidations while the hexamethylbenzene complexes undergo quasi-reversible oxidations. The molecular structures of ligand 1a and complexes 4a, 4l, and 5e were determined by X-ray crystallography.     

Synthesis,characterization, and electrochemical study of two new macroacyclic Schiff bases and their copper(II) and zinc(II) complexes

Two new potentially octadentate N₂O₆ Schiff-base ligands 2-((E)-(2-(2-(2-((E)-2-hydroxy-3-methoxybenzylideneamino)phenoxy)phenoxy)phenylimino)methyl)-6-methoxyphenol H₂L¹ and 2-((E)-(2-(2-(2-((E)-2-hydroxy-3-methoxybenzylideneamino)phenoxy)-4-tert-butylphenoxy)phenylimino)methyl)-6-methoxyphenol H₂L² were prepared from the reaction of O-Vaniline with 1,2-bis(2′-aminophenoxy)benzene or 1,2-bis(2′-aminophenoxy)-4-t-butylbenzene, respectively. Reactions of H₂L¹ and H₂L² with copper(II) and zinc(II) salts in methanol in the presence of N(Et)₃ gave neutral [CuL¹]?·?0.5CH₂Cl₂, [CuL²], [ZnL¹]?·?0.5CH₂Cl₂, and [ZnL²] complexes. The complexes were characterized by IR spectra, elemental analysis, magnetic susceptibility, ESI–MS spectra, molar conductance (Λ_m), UV-Vis spectra and, in the case of [ZnL¹]?·?0.5CH₂Cl₂ and [ZnL²], with ¹H- and ¹³C-NMR. The crystal structure of [ZnL¹]?·?0.5CH₂Cl₂ has also been determined showing the metal ion in a highly distorted trigonal bipyramidal geometry. The electrochemical behavior of H₂L² and its Cu(II) complex, [CuL²], was studied and the formation constant of [CuL²] was evaluated using cyclic voltammetry. The logarithm value of formation constant of [CuL²] is 21.9.     

Synthesis,characterization, and thermodynamic studies of the interaction of some new water-soluble Schiff-base complexes with bovine serum albumin

Some new water-soluble Schiff-base complexes Na₂[M(5-SO₃-2,3-salpyr)(H₂O) _n ]?·?2H₂O (5-SO₃-2,3-salpyr?=?N,N′-bis(5-sulphosalicyliden)-2,3-diaminopyridine and M?=?Zn, Cu, Ni) were synthesized and characterized by elemental analysis, IR, ¹H NMR, magnetic susceptibility measurement, thermal analysis, and UV-Vis spectroscopy. The mechanism of binding of Na₂[M(5-SO₃-2,3-salpyr)(H₂O) _n ]?·?2H₂O with bovine serum albumin (BSA) was investigated by fluorescence spectroscopy. The fluorescence titration revealed that the intrinsic fluorescence of BSA was quenched by Na₂[M(5-SO₃-2,3-salpyr)], which was rationalized in terms of the static quenching mechanism. The values of the Stern–Volmer constants, quenching rate constants, binding constants, binding sites, and average aggregation number of BSA were determined by this method. Thermodynamic parameters were calculated by the van’t Hoff equation. The data clearly indicate that the binding is entropy driven and enthalpically disfavored. Based on the Förster theory of non-radiative energy transfer, the efficiency of energy transfer, and the distance between the donor (Trp residues) and the acceptor (Na₂[M(5-SO₃-2,3-salpyr)]) were evaluated. Also the synchronous fluorescence spectra showed that the microenvironment of the tryptophan residues was not changed. Finally, our results indicate that the complexes can bind to BSA and be efficiently transported in the body, which could be helpful for further drug design.     

Syntheses,characterization and X-ray crystal structures of Ni(II) complexes of tridentate monocondensed and tetradentate dicondensed Schiff bases

Two octahedral complexes [Ni(HL¹)₂](ClO₄)₂ (1) and [Ni(HL²)₂](ClO₄)₂ (2) and a square planar complex [Ni(HL³)]ClO₄ (3) have been prepared, where [HL¹ = 3-(2-amino-ethylimino)-butan-2-one oxime, HL² = 3-(2-amino-propylimino)butan-2-one oxime] and H₂L³ = 3-[2-(3-hydroxy-1-methyl-but-2-enylideneamino)-1-methyl-ethylimino]-butan-2-one oxime. All the complexes have been characterized by elemental analyses, spectral studies and room temperature magnetic moment measurements. The molecular structures of all three compounds were elucidated on the basis of X-ray crystallography; complexes 1 and 2 are seen to be the mer isomers.