Synthesis,spectral, electrochemical and catalytic studies of new Ru(III) tetradentate Schiff base complexes

The synthesis and characterization of several hexa‐coordinated ruthenium(III) Schiff base complexes of the type [RuX(EPh₃)(L)] (X = Cl or Br; E = P or As; L = dianion of the tetradentate Schiff base) are reported. IR, EPR, electronic spectra and cyclic voltammetric data of the complexes are discussed. An octahedral geometry has been tentatively proposed for all of these complexes. The new complexes have been subjected to catalytic activity in the reaction of oxidation of alcohols in the presence of N‐methylmorpholine‐N‐oxide. Copyright © 2007 John Wiley & Sons, Ltd.     

Synthesis,characterization and antibacterial activity of indium(III) complexes with adamantane-ring containing Schiff bases

Indium(III) chloride tetrahydrate and Schiff-base ligands derived from adamantaneamine and 3-/4-methoxysalicylaldehyde gave two complexes, C₂₂H₃₂Cl₃InN₂O₃ (1) and C₃₆H₄₄C_l3InN₂O₄ (2), respectively. The complexes were characterized by IR, ¹H NMR, elemental analysis, molar conductance, thermal analysis, and single-crystal X-ray diffraction. Complex 1 crystallizes in the monoclinic system, P2₁/n space group with the asymmetric unit consisting of one indium(III), one N-(3-methoxysalicylidene)-aminoadamantane (L¹), three chlorides and one N,N-dimethylformamide molecule. The indium is six-coordinate with reversed triangular-prism geometry via three oxygens and three chlorides. Complex 2 crystallizes in the triclinic system, P 1 space group; the asymmetric unit consists of one indium(III), two N-(4methoxysalicylidene)-aminoadamantane (L²), and three chlorides. The indium is five-coordinate with distorted trigonal-bipyramidal geometry via two oxygens and three chlorides. Antibacterial activities of the complexes have been investigated against Escherichia coli and Staphylococcus aureus.     

Synthesis,characterization and biological evaluation of Ru(III) mercaptopyrimidine Schiff base complexes

A new series of mercaptopyrimidine Ru(III) complexes were synthesized and characterized using various spectral techniques like single‐crystal X‐ray diffraction, Fourier transform infrared and NMR spectroscopies, thermogravimetric analysis and energy‐dispersive X‐ray analysis. The complexes were evaluated for their pharmacological activities like in vitro antimicrobial, anticancer, antituberculosis and antioxidant activities. The DNA binding of the complexes was investigated by absorption and emission spectral measurements which indicated that the complexes bind to DNA via intercalation, with molecular docking studies validating the results. DNA cleavage studies of the complexes were carried out.     

Synthesis,characterization, and in vitro antioxidant and anticancer studies of ruthenium(III) complexes of symmetric and asymmetric tetradentate Schiff bases

Ruthenium(III) complexes of three tetradentate Schiff bases with N₂O₂ donors formulated as [RuCl(LL¹)(H₂O)], [RuCl(LL²)(H₂O)] and [RuCl(LL³)(H₂O)] were synthesized and characterized by elemental analyses, molar conductance, FTIR, and electronic spectral measurements. The FTIR data showed that the tetradentate Schiff base ligands coordinate to Ru ions through the azomethine nitrogen and enolic oxygen. The antioxidant activities of the complexes were investigated through scavenging activity on 1,1-diphenyl-2-picrylhydrazyl (DPPH) and 2,2′-azinobis-3-ethylbenzothiazoline-6-sulfonic acid (ABTS) radicals. The DPPH activity for [RuCl(LL²)(H₂O)] with IC₅₀ = 0.031 mg mL^?1 was higher than the values obtained for the other Ru(III) compounds. The study revealed that the synthesized Ru(III) complexes of the tetradentate Schiff base exhibited strong scavenging activities against DPPH and moderate against ABTS radicals. In addition, the antiproliferative studies of the complexes were also tested against human renal cancer cells (TK10), human melanoma cancer cells (UACC62), and human breast cancer cells (MCF7) using the SRB assay. The results indicated that the Ru(III) complexes showed low anticancer activities against the tested human cancer cell lines.     

Inner metal complexes of tetradentate Schiff base: Synthesis,characterization, biological activity and molecular docking studies

A novel Schiff base ligand, namely 2,2′‐((1E,1′E)‐(1,3‐phenylenebis(azanylylidene))bis(methanylylidene))diphenol (H₂L), was synthesized by condensation of m‐phenylenediamine and 2‐hydroxybenzaldehyde (in 1:2 ratio). Series of complexes were obtained from the reaction of La(III), Er(III) and Yb(III) chlorides with H₂L. The ligand and complexes were characterized using elemental analysis, infrared, ¹H NMR, UV–visible and mass spectroscopies, magnetic susceptibility and conductivity measurements and thermal analysis. Infrared and ¹H NMR spectra indicated the coordination of the azomethine nitrogens and deprotonated phenolic oxygen atoms in a tetradentate manner (ONNO). The thermal behaviour of the complexes was studied from ambient temperature to 1000°C. The complexes were found to have water molecules of hydration and coordinated water molecules. The complexes were found to possess high biological activities against various organisms compared to the free ligand (Gram‐positive bacteria Staphylococcus aureus and Bacillus subtilis, Gram‐negative bacteria Salmonella sp., Escherichia coli and Pseudomonas aeruginosa and fungi Aspergillus fumigatus and Candida albicans). The more effective and probable binding modes between H₂L with different active sites of colon cancer (PDB code: 2hq6) and lung cancer (PDB code: 1x2j) receptors were investigated using molecular docking studies.     

Single-crystal electronic spectra of some quadrate chromium(III) complexes

Polarised electronic spectra of trans-[Cr(tmd)₂F₂](ClO₄), trans-[Cr(en)₂(dma)₂](ClO₄)₃, trans-[Cr(en)₂(dmf)Cl](ClO₄)₂ and trans-[Cr(en)₂(dmf)Br](ClO₄)₂ have been measured at 77 K (tmd = trimethylenediamine; dma = N,N-dimethylacetamide; dmf = N,N-dimethylformamide; en = ethylenediamine, pn = propylenediamine). The observed quartet bands have been given definitive quadrate assignments based on polarisation characteristics. The four-component quadrate quartet bands have been uncovered and assigned also in the unpolarised crystal spectrum of trans-[Cr(en)₂(dmf)₂](ClO₄)₃ at 77 K and the solution spectrum of trans-[Cr(en)(pn)F₂]⁺. The band maxima derived by gaussian analysis in these spectra have been fitted with the theoretical energy equations of d³ configuration in quadrate ligand fields including full configuration interaction. The ligand field parameters Dq, Dt, and Ds and the election correlation parameter, B, extracted by such a fitting, have been compared with those obtained for other similar systems earlier. The significance of the ligand field symmetry parameters and the translated angular overlap model parameters is discussed.     

Synthesis, X-ray crystal structures, spectroscopic and cyclic voltammetric studies of Cu(II) Schiff base complexes of pyridoxal

Two mononuclear Cu(II) complexes, [Cu(L¹H₂)](ClO₄)_1.25Cl_0.75·1.25H₂O (1) and [Cu(L²H₂)](ClO₄)₂ (2), of the pyridoxal Schiff base ligands N,N′-dipyridoxylethylenediimine (L¹H₂) and N,N′-dipyridoxyl-1,3-propanediimine (L²H₂) are reported. X-ray crystal structures of both complexes are also reported. In both complexes the pyridoxal nitrogen atoms remain protonated. In the solid state, the tetradentate Schiff base ligand is virtually planar in 1, while in 2 the ligand conformation is like an inverted umbrella. In cyclic voltammetry experiments it is found that in these complexes the Cu(III) and Cu(I) states are more easily accessible than in their salen type analogs. The pyridoxal Schiff base complexes are also found to be resistant to oxidative electro-polymerization, unlike their corresponding salicyl aldehyde Schiff base complexes.     

Synthesis,structural characterization and biological studies of neodymium(III) and samarium(III) complexes with mercaptotriazole Schiff bases

A series of neodymium(III) and samarium(III) complexes of type [Ln(L)Cl(H₂O)₃] have been synthesized with Schiff bases (LH₂) derived from 3‐(phenyl/substituted phenyl)‐4‐amino‐5‐mercapto‐1,2,4‐triazoles and isatin. The structures of the complexes were established using elemental analysis, molar conductivities, magnetic moments, infrared, NMR (¹H, ¹³C) and UV–visible spectra, X‐ray diffraction and mass spectrometry. The thermal behaviour of these compounds under non‐isothermal conditions was investigated using thermogravimetry and differential thermogravimetry. The intermediates obtained at the end of various thermal decomposition steps were identified from elemental analysis and infrared spectral studies. All the ligands and their complexes were also screened for their antibacterial activity against Staphylococcus aureus and Bacillus subtilis and antifungal activity against Aspergillus niger, Aspergillus flavus and Colletotrichum capsici. The screening results were correlated with the structural features of the compounds. Copyright © 2015 John Wiley & Sons, Ltd.     

Synthesis,crystal structure and characterization of manganese(III) complex containing a tetradentate Schiff base

N,N′-bis((2-hydroxyphenyl)(phenyl)methylidene)propane-1,2-diaminato-N,N′,O,O′)-(nitrato-O)-manganese(III) methanol solvate ([Mn(C₂₉H₂₄N₂O₂)(NO₃)CH₃OH]) was synthesized and characterized by FTIR, UV–Vis, TG–FTIR, TG/DSC, molar conductivity, magnetic moment measurement and single crystal X-ray analysis. In the structure, the Mn(III) ion adopts a distorted octahedral geometry with two nitrogen and two oxygen atoms from the Schiff base ligand in the equatorial plane, and the nitrate ion and methanol molecule in the axial position. The effects of organic solvents of various polarities on the UV–Vis spectra of the ligand and complex were investigated. The manganese(III) complex is easily dissolved in organic polar aprotic solvents and has moderate solubility in organic polar protic solvents.     

Synthesis,spectral characterization and biological studies of transition metal(II) complexes with triazole Schiff bases

New metal based triazoles (1–12) have been synthesized by the interaction of novel Schiff base ligands (L¹–L³) with the Co(II), Ni(II), Cu(II) and Zn(II) metal ions. The Schiff base ligands and their all metal(II) complexes have been thoroughly characterized using various physical, analytical and spectroscopic techniques. In vitro bacterial and fungal inhibition studies were carried out to examine the antibacterial and antifungal profile of the Schiff bases in comparison to their metal(II) complexes against two Gram‐positive, four Gram‐negative and six fungal strains. The bioactivity data showed the metal(II) complexes to have more potent antibacterial and antifungal activity than their uncomplexed parent Schiff bases against one or more bacterial and fungal species. Copyright © 2012 John Wiley & Sons, Ltd.     

Lanthanum(III) chloride complexes with heterocyclic Schiff bases

Condensation of 2-amino-3-carboxyethyl-4,5,6,7-tetrahydrobenzo[b]thiophene with carbonyl compounds such as isatin, o-hydroxyacetophenone or benzoin in 1:1 ratio in ethanol medium yielded three distinctly different heterocyclic Schiff bases viz. 2-(N-indole-2-one)amino-3-carboxyethyl-4,5,6,7-tetrahydrobenzo[b]thiophene (ISAT), 2-(N-o-hydroxyacetophenone)amino- 3-carboxyethyl-4,5,6,7-tetrahydro-benzo[b]thiophene (HAAT) or 2-(N-benzoin)amino-3-carboxyethyl-4,5,6,7-tetrahydrobenzo[b]thiophene (HBAT) respectively. These ligands formed well defined complexes with lanthanum(III) chloride under suitable conditions. The ligands and the complexes have been characterized on the basis of elemental analyses, molar conductance measurements, UV-visible, IR and proton NMR spectral studies. Kinetics and mechanism of the thermal decomposition of the ligands and the metal complexes have been studied using non-isothermal thermogravimetry. Kinetic parameters were calculated for each step of the decomposition reactions using Coats-Redfern equation. The rate controlling process for all the ligands and complexes is random nucleation with the formation of one nucleus on each particle (Mampel equation). Relative thermal stabilities of the ligands and the metal complexes have been compared.     

Organotin (IV) complexes derived from tridentate Schiff base ligands: Synthesis,spectroscopic analysis,antimicrobial and antioxidant activity

Organotin complexes of Schiff bases (derived from the condensation of hydrazides with salicylaldehyde derivatives) were prepared and their characterization was done using several spectroscopic techniques like FTIR, NMR (¹H, ¹³C, and ¹¹⁹Sn) and mass spectrometry. The spectroscopic data of the ligands and their corresponding complexes revealed that the Schiff bases chelated to the tin metal in a tridentate manner through –ONO atoms (oxygen atom of the hydroxyl group of the salicylaldehydic derivatives, the nitrogen atom of azomethine group, and the oxygen atom of enolic group present in the carboxylic acid hydrazides). Around tin atom pentacoordinated geometry was exhibited. The synthesized ligands and their complexes have been assessed for their biological potency (antibacterial, antifungal and antioxidant using Ciprofloxacin, Fluconazole and Ascorbic acid as reference compounds) and few of the compounds showed optimistic activity. The ligands having electron withdrawing group attached showed greater antimicrobial activity as compared to the other ligands. The complexes showed the better activity than the ligands. The general trend followed by the complexes was diphenyl ?> ?dibutyl ?> ?dimethyl substituted complexes. Compound 11 was the most active against microbes. The antioxidant activity increased with electron donating group. The phenyl substituted complexes showed better activity as compared to the dibutyl and dimethyl substituted complexes. Compound 20 was the best antioxidant.     

Mononuclear gallium(III) complexes based on salicylaldoximes: Synthesis,structure and spectroscopic characterization

The reactions of Ga(acac)₃ with salicylaldoxime (saoH₂) and methyl-salicylaldoxime (Me-saoH₂) in dichloromethane/hexane afforded the complexes [Ga(acac)(saoH)₂] (1) and [Ga(acac)₃][Ga(acac)(MesaoH)₂] (2), respectively, in high yields. The crystal structures of 1 and 2 have been determined by single-crystal X-ray crystallography. Both complexes are mononuclear with the Ga(III) atoms being in octahedral environments surrounded by two bidentate chelate R-saoH⁻ and one bidentate chelate acac⁻ ligands. A [Ga(acac)₃] moiety has co-crystallized along with the methylsalicylaldoximato complex. Characteristic IR as well as NMR data are discussed in terms of the nature of bonding in the structures of the two complexes. ¹H and ¹³C NMR data in CDCl₃ indicate that the salicylaldoximato complexes isomerize in solution.     

Synthesis and structural characterization of tris (methacrylato)chromium(III)

A straightforward synthetic route to produce tris(methacrylato)chromium(III), Cr(O₂C(CH₃)C=CH₂)₃, by reacting sodium methacrylate with an aqueous solution of CrCl₃ gave a blue microcrystalline powder, insoluble in most common solvents. Electronic spectroscopy (UV-Vis), electron paramagnetic resonance (EPR), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS), were employed to characterize Cr(O₂C(CH₃)C=CH₂)₃. Morphology and elemental composition of this compound were determined using scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDAX), respectively. Spherical particles of approximately 2.5 µm in diameter were obtained. Thermal stability of the product was investigated via thermogravimetric analysis (TGA). The spectroscopic studies revealed that the coordination sphere around the chromium ion corresponds to a chelating bidentate carboxylate-Cr(III) complex. Thermal stability above 350°C, and spherical shape particles of few micrometers in diameter, suggest a potential application of this novel compound as a catalyst in oxidation reactions.     

Synthesis,crystal structure,and interaction with DNA and BSA of a chromium(III) complex with naph-gly Schiff base and 1,10-phenanthroline

A new chromium(III) complex, [CrCl(naph-gly)phen]?H₂O (naph-gly = Schiff base derived from 2-hydroxy-1-naphthaldehyde and glycine, phen = 1,10-phenanthroline), has been synthesized and characterized by elemental analysis, electrospray ionization mass spectroscopy, FT-IR, and X-ray single-crystal diffraction. The chromium(III) complex belongs to the trigonal crystal system, P3(1) space group with crystallographic data: a = b = 1.97017(16) nm, c = 1.02991(7) nm, α?=?β?=?90°, γ =120°, V = 3.4621(5) nm³, D_c = 1.476 g?cm^?3, Z = 6, F(0 0 0)?=?1578, R₁ = 0.0508, wR₂ = 0.0907. There are two independent molecules in the crystallographic asymmetric unit of the chromium(III) complex. Each Cr^III is six-coordinate to form an octahedral geometry. In the crystal, a 3-D structure is formed through intermolecular hydrogen bonds. The calf thymus DNA (CT-DNA)- and bovine serum albumin (BSA)-binding properties of the complex have been studied by UV absorption, fluorescence, and circular dichroism (CD) spectroscopy. Results indicate that the chromium(III) complex binds to CT-DNA in an intercalative mode, and it can bind to BSA and cause conformational changes of BSA.     

Synthesis,spectroscopic (IR,electronic, FAB-mass,and PXRD), magnetic,and antimicrobial studies of new iron(III) complexes containing Schiff bases and substituted benzoxazole ligands

Mixed ligand complexes of iron(III), [Fe(sb)₂(py)Cl]?·?2H₂O (1–9) [where sbH?=?Schiff bases (derived from condensation of 2-aminopyridine (sapH), 2-aminophenol (saphH), o-toluidine (o-smabH), aminobenzene (sabH), p-toluidine (p-smabH), 3-nitroaniline (snabH), and anthranilic acid (saaH) with salicylaldehyde and substituted (mercapto-)benzimidazole (mbzH), {2-(o-hydroxyphenyl)}benzoxazole, (pboxH)], have been synthesized by the interactions of iron(III) chloride with corresponding ligands in 1?:?2 molar ratio in refluxing pyridine. These complexes have been characterized by elemental analyses, melting points, spectral, and magnetic studies. Powder X-ray diffraction studies of some representative complexes are also reported herein. The antibacterial and antifungal activities of the free ligands and their iron(III) complexes were found in vitro. The complexes showed good antibacterial and antifungal effect to some bacteria and fungi. Two standard antibiotics (chloromphenicol and terbinafine) were used for comparison with these complexes.     

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,characterization and biological properties of novel ON donor bidentate Schiff bases and their copper(II) complexes

Four novel ON donor Schiff bases (E)-3-((4-phenoxyphenylimino)methyl)benzene-1,2-diol (HL₁),(E)-3-((4-(4-biphenyloxy)phenyliminomethyl)benzene-1,2-diol (HL₂), (E)-3-((4-naphthoxyphenylimino)methyl)benzene-1,2-diol (HL₃), (E)-3-((4-(2-naphthoxy)phenylimino)methyl)benzene-1,2-diol (HL₄) and their copper(II) complexes bis((E)-3-((4-phenoxyphenylimino)methyl)benzene-1,2-diol) copper(II) (Cu(L₁)₂) bis((E)-3-((4-(4-biphenyloxy)phenylimino)methyl)benzene-1,2-diol) copper(II) (Cu(L₂)₂), bis((E)-3-((4-naphthoxyphenylimino)methyl)benzene-1,2-diol) copper(II) (Cu(L₃)₂), bis((E)-3-((4-(2-naphthoxy)phenylimino)methyl)benzene-1,2-diol) copper(II) (Cu(L₄)₂) have been synthesized and characterized by spectroscopic (FTIR, NMR, UV–visible) and elemental analysis. The crystal structures of HL₁, HL₂, HL_3, and HL₄ have been determined, which reveal intramolecular N-H?O (HL₁, HL₂, HL_3, and HL₄) hydrogen bonds in the solid state. Keto-amine and enol-imine tautomerism is exhibited by the Schiff bases in solid and solution states. The Schiff bases and their copper(II) complexes have been screened for their biological activities. In antimicrobial assays (antibacterial and antifungal), HL₄ showed promising results against all strains through dual inhibition property while the rest of the compounds showed activity against selective strains. On the other hand, in cytotoxic, DPPH, and inhibition of hydroxyl (OH) free radical-induced DNA damage assays, the results were found significantly correlated with each other, i.e. the ligands HL₁ and HL₂ showed moderate activity while their complexes Cu(L₁)₂ and Cu(L₂)₂ exhibited prominent increase in activity. As the results of these assays are supporting each other, it represents the strong positive correlation and antioxidant nature of investigated compounds.     

Synthesis and catalytic activity of novel heteronuclear Ln (III) -Cu(II) complexes with noncyclic polyether-amino acid Schiff base

A series of novel heteronuclear Ln(III)-CU(II) complexes with noncyclic polyether-amino acid Schiff base were synthesized. The general formula is (LnCu₂(H₂TALY) (NO₃)₅] (NO₃)₂·nH₂O (Ln= La, Nd, Sm, Gd,n = 4; Ln = Yb, Y,n = 3), where H₂TALY = tetraglycol aldehyde bis-lysine Schiff base. It is the first time to report the synthetic method for this new Cu(II) complexes and Ln(III)-Cu(II) heteronuclear complexes. The complexes were characterized by elemental analysis, IR spectra. TG-DTA, magnetic susceptibility, and especially by a 500 MHz NMR spectrometer for 2D-COSY NMR. Coordination mechanism and structures of complexes have been suggested as well. Of particular interest is the potential that the novel complexes obtained may be used as a catalyst. which prompted us to investigate them. It shows 100% conversion with the viscosity-average molecular weight 120 000 for the polymerization of methyl methacrylate (MMA) without addition of any cocatalyst. Furthermore, the complexes with such aliphatic Schiff bases can be used as a good catalyst, which has been confirmed and discussed here. They may be a new kind of catalyst system with the above speciality. Project supported by the National Natural Science Foundation of China (Grant No. 29671026) and Natural Science Foundation of Zhejiang Province (Grant No. 296062) and the Laboratory of MRAMP (Grant No. 971502).