Rhenium(I), (III) and (V) complexes of tridentate ONX (X = O,N, S)-donor Schiff bases

The reactions of the potentially tridentate Schiff bases 2-[(2-hydroxyphenyl)iminomethyl]phenol (H₂ono) and 2-(2-aminobenzylideneimino)phenol (H₃onn) with trans-[ReOBr₃(PPh₃)₂] were studied, and the complexes [Re^IIIBr(PPh₃)₂(ono)] (1) and [Re^VBr(PPh₃)₂(onn)]Br (2) were isolated. In 1ono acts as a dianionic tridentate ligand, and in 2onn is coordinated as a tridentate trianionic imido-imino-phenolate. The complex [Re^I(CO)₃(ons)(Hno)] was isolated from the reaction of [Re(CO)₅Br] with 2-[(2-methylthio)benzylideneimino]phenol (Hons; Hno = 2-aminophenol), with ons coordinated as a bidentate chelate with a free SCH₃ group. These complexes were characterized by X-ray crystallography, NMR and IR spectroscopy.     

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.     

Synthesis,characterization and cytotoxic/cytostatic activity of Sm(III) and Gd(III) complexes

New Sm(III) and Gd(III) complexes of deprotonated 4-hydroxy-3[1-(4-nitrophenyl)-3-oxobutyl]-2H-1-benzopyran-2-one (Acenocoumarol) were synthesized and characterized using FT-IR, FT-Raman, NMR spectra, and elemental analyses. The vibrational study gave evidence for the coordination of ligand to lanthanide ions. The ligand and its lanthanide(III) complexes were tested for their cytotoxic/cytostatic activity against two tumor cell lines and peritoneal mouse macrophages. The Sm(III) and Gd(III) complexes exhibit good activity against melanoma B16 and fibrosarcoma L929 and are stronger inhibitors of tumor cell proliferation than the ligand. Besides their cytotoxicity to tumor cells, Acenocoumarol and its gadolinium(III) and samarium(III) complexes modulate NO generation in activated macrophages.     

Thermogravimetric and spectroscopic studies on La(III) and Ce(III) complexes with some thio-schiff bases

Solid complexes of five derivatives of thio-Schiff bases with La(III) and Ce(III) ions were prepared and characterized by elemental and thermogravimetric analyses. The suggested general formula of the solid complexes is [ML₂(H₂O)X]·2H₂O, whereM=trivalent lanthanide ion,L=Schiff base andX=Cl^? or ClO ₄ ^? . Information about the water of hydration, the coordinated water molecules, the coordination chemistry and the thermal stability of these complexes was obtained and is discussed. Additionally, a general scheme of thermal decomposition of the lanthanide-Schiff base complexes is proposed.     

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.     

Complexes of Oxamic Acid with La(III), Gd(III), Tb(III), Er(III), Tm(III) and Lu(III)

The preparation, for the first time, of the deprotonated complexes of oxamic acid with La(III), Gd(III), Tb(III), Er(III), Tm(III) and Lu(III) is reported. Analytical results, conductometric measurements, magnetic moments and spectral data (IR and diffuse reflectance spectra) are discussed in terms of possible structural types. The oxamate anion acts as a N, O bidentate non-bridging ligand.     

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.     

Investigation of 5-chloro-2-methoxybenzoates of La(III), Gd(III) and Lu(III) Complexes

5-Chloro-2-methoxybenzoates of La(III), Gd(III) and Lu(III) were synthesized as penta-, mono- and tetrahydrates with a metal to ligand ratio of 1:3 and with white colour typical of La(III), Gd(III) and Lu(III) ions. The complexes were characterized by elemental analysis, IR and FIR spectra, thermogravimetric and diffractometric studies. The carboxylate group appears to be a symmetrical, bidentate, chelating ligand. The complexes are polycrystalline compounds. Their thermal stabilities were studied in air and inert atmospheres. When heated they dehydrate to form anhydrous salts which next in air are decomposed through oxychlorides to the oxides of the respective metals while in inert atmosphere to the mixture of oxides, oxychlorides of lanthanides and carbon. The most thermally stable in air, nitrogen and argon atmospheres is 5-chloro-2-methoxybenzoate of Gd(III). This revised version was published online in August 2006 with corrections to the Cover Date.     

Synthesis,structure, and catalytic activity of lanthanide Gd(III) and La(III) complexes with N-(cyclohexyl)isopropyl amidate ligand

Two new lanthanide amidate complexes, {Gd₂[Cy(NCO)ⁱPr]₆} (1) and {La₂[Cy(NCO)ⁱPr]₆[Cy(HNCO)ⁱPr]} (2) (ⁱPr = isopropyl, Cy = cyclohexyl), have been synthesized in good yields by silylamine elimination reaction between Gd[N(SiMe₃)₂]₃ or La[N(SiMe₃)₂]₃ and N-(cyclohexyl)isopropyl amide. Complexes 1 and 2 have been characterized by NMR, elemental analyzes, and X-ray diffraction. The molecular structures of {[Cy(NCO)ⁱPr]Gd[μ₂-Cy(NCO)ⁱPr]₃Gd[Cy(NCO)ⁱPr]₂} (1) and {[Cy(NCO)ⁱPr]La[μ₂-Cy(NCO)ⁱPr]₃La[Cy(NCO)ⁱPr]₂[Cy(HNCO)ⁱPr]} (2) exhibit a dimer structure with three μ₂-O bridging bonds that look like a windmill. Additionally, 2 formed an intramolecular N–H···O hydrogen bond via a neutral amide. The catalytic properties of 1 and 2 for ring-opening polymerization (ROP) of ε-caprolactone have been studied. The results show that 1 and 2 are efficient catalysts for the ROP of ε-caprolactone.     

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.     

Tetradentate asymmetric Schiff bases and their Ni(II) and Fe(III) complexes

Three asymmetric Schiff-base tetradentate diimines H₂L¹, H₂L², and H₂L³ [(2-OH)C₆H₄N=CHC₆H₄2-N=CHC₆H₃(2-OH)(5-X), X?=?H, CH₃, Cl respectively] have been synthesized by a two step process. The reaction of 2-hydroxy aniline with 2-nitro-benzaldehyde in EtOH gave the starting Schiff base, 2-hydroxy-N-(2-nitrobenzylidene)aniline (SB-NO₂), which was reduced into the amino derivative (SB-NH₂) in solution. Reacting SB-NH₂ with 2-hydroxybenzaldehyde, 2-hydroxy-5-methylbenzaldehyde and 2-hydroxy-5-chlorobenzaldehyde gave the three new ligands H₂L¹, H₂L², and H₂L³ respectively. Their dimeric, binuclear metal complexes with Ni(II) and Fe(III) have also been synthesized. The ligands and their complexes were characterized by elemental analyses, LC–MS, IR, electronic, ¹H and ¹³C-NMR spectra, TGA, conductivity and magnetic measurements. All of the spectroscopic, analytical and other data indicate octahedral geometry M₂L₂(H₂O)X₂ (M: Ni,Co;X: Cl or H₂O), except for NiL² which is monomeric. Antimicrobial activities of the ligands and the complexes were evaluated against five bacteria. While the ligands and the Ni complexes are inactive towards Pseudomonas aeruginosa and Staphylococcus aureus, Fe complexes are active; only Fe complexes are inactive against Escherichia coli. All of the compounds have antimicrobial activities against Bacillus subtilis, and Yersinia enterecolitica.     

Synthesis,characterization, and crystal structure of three cobalt(II) complexes with Schiff bases derived from rimantadine

By condensation of rimantadine and substituted salicylaldehyde, three new Schiff bases, HL¹, HL² and HL³, were synthesized. Then, a mixture of one of the new ligands and cobalt(II) chloride hexahydrate in ethanol led to 1, 2, and 3, respectively. These complexes were characterized by melting point, elemental analysis, infrared spectra, molar conductance, thermal analysis, and single-crystal X-ray diffraction analysis. X-ray diffraction analysis reveals that 1 crystallizes in the orthorhombic system, Pbcn space group; each asymmetric unit consists of one cobalt(II) ion, two deprotonated ligands, and one lattice water. The central cobalt is four coordinate via two nitrogens and two oxygens from the corresponding Schiff base ligand, forming a distorted tetrahedral geometry. Complexes 2 and 3 crystallize in the monoclinic system, P2₁/c space group; each asymmetric unit consists of one cobalt(II), two corresponding deprotonated ligands, one lattice water, and one methanol. The central cobalt is also four-coordinate via two nitrogens and two oxygens from the corresponding Schiff base ligand, forming a distorted tetrahedral geometry.     

Synthesis and characterization of Ni(II) complexes of O,N-donor Schiff bases derived from acyl pyrazolone analogues

Two bidentate Schiff bases, 5-methyl-2-p-tolyl-4-(1-p-tolylimino-propyl)-2H-pyrazol-3-ol (L1) and 2-(3-chloro-phenyl)-5-methyl-4-(1-p-tolylimino-propyl)-2H-pyrazol-3-ol (L2), were synthesized by condensation of 4-acyl pyrazolones with p-toluidine in ethanol. These ligands have been characterized by elemental analysis, infrared (IR), ¹H NMR, and mass spectra. A single crystal molecular structure of ligand L2 was also solved. Nickel(II) complexes of these ligands with general formula [ML₂?·?2H₂O] have been prepared by the interaction of aqueous solution of Ni-acetate with ethanolic solution of the appropriate ligand. The complexes were separated, analyzed, and their structures were elucidated on the basis of elemental analysis, Ni(II) determination, IR, UV-Vis, conductance, mass, and TGA-DTA data. Octahedral structure was proposed for the synthesized complexes.     

Self assembly of asymmetric tetranuclear Cu(II) [2 × 2] grid-like complexes and of a dinuclear Ni(II) complex from pyridyl-phenol Schiff base ligands

Self assembly of N-salicylidene 2-aminopyridine (L1H) with Cu(NO₃)₂·3H₂O affords [Cu₄(L1)₄(NO₃)₃(CH₃OH)][Cu(L1)(NO₃)₂](2-aminopyridinium)(NO₃)·5CH₃OH (1) which is composed of an asymmetric [2 × 2] grid-like cationic complex that co-crystallizes with a Cu(II) mononuclear anion. This remarkable tetranuclear unit presents three penta-coordinated and one hexa-coordinated Cu(II) sites. This quadruple helicate structure reveals strong anti-ferromagnetic coupling (J = −340(2) cm⁻¹) between Cu(II) ions through a double alkoxo bridge. Reacting L1H with Cu(NO₃)₂·3H₂O in slightly different conditions affords however a more symmetric tetranuclear grid-like complex: [Cu₄(L1)₄(NO₃)₂(OH)₂](2-aminopyridinium)(OH)·CH₃OH) (2). A dinuclear Ni(II) complex, [Ni₂(L2)₂(L2H)₂(NCS)₂(CH₃OH)₂]·2CH₃OH (3), obtained with another related donor ligand (L2H = N-salicylidene 3-aminomethylpyridine) was also prepared.     

New chelated complexes of bis-β-carboalkoxyethyltin(IV) dichloride with S-benzyldithiocarbazate Schiff bases

The Schiff bases [H₂SBSaD], [H₂SBVD] and [H₂SBND], derived by the condensation of S-benzyldithiocarbazate and salicylaldehyde, 2-hydroxy-3-methoxybenzaldehyde and 2-hydroxy-1-naphthaldehyde respectively, react with diestertin dichlorides, R₂SnCl₂ [R=? CH₂CH₂CO₂CH₃, ? CH₂CH₂CO₂C₂H₅ or ? CH₂CH₂CO₂C₄H₉] in 1:1 molar proportion to yield chlorine-substituted complexes of the type R₂Sn(Schiff base), the base being tridentate. The complexes are characterized on the basis of their elemental analyses, IR and ¹H NMR spectral studies. The ¹³C and ¹¹⁹Sn NMR and the tin-carbon coupling constant data reveal the structures of the complexes to be octahedral with trans ester grouping, and bidentate ester linkages. The pentacoordinated complex (CH₃)₂Sn(SBSaD) was prepared by the reaction of dimethyltin oxide with H₂SBSaD in equimolar proportions.     

Ortho-metallated ruthenium(III) complexes with some acid hydrazide based Schiff bases

Ortho-metallated ruthenium(III) complexes with Schiff bases (H₂L) derived from one mole equivalent each of benzaldehyde and acid hydrazides are described. Reactions of H₂L with [Ru(PPh₃)₃Cl₂] in presence of NEt₃ (1:1:2 mole ratio) under aerobic conditions in methanol provide the complexes having the general formula trans-[Ru(L)(PPh₃)₂Cl] in 55-60% yields. The complexes have been characterized with the help of elemental analysis, magnetic susceptibility, electrochemical and various spectroscopic (infrared, electronic and EPR) measurements. The +3 oxidation state of the metal centre in these complexes is confirmed by their one-electron paramagnetic nature. Molecular structures of two representative complexes have been determined by X-ray crystallography. In each complex, the metal ion is in a distorted octahedral CNOClP₂ coordination sphere. The dianionic C,N,O-donor ligand (L²⁻) together with the chloride form a CNOCl square-plane and the P-atoms of the two PPh₃ molecules occupy the two axial sites. The electronic spectra of the complexes in dichloromethane solutions display several absorptions due to ligand-to-metal charge transfer and ligand centred transitions. In dichloromethane solutions, the complexes display a ruthenium(III) → ruthenium(IV) oxidation in the potential range 0.35-0.98 V (vs. Ag/AgCl). All the complexes in frozen (110 K) dichloromethane-toluene (1:1) solutions display rhombic EPR spectra.     

Synthesis,structural characterization,and antibacterial activity of mononuclear cobalt(III) azido complexes of two pentadentate Schiff bases derived from 2-hydroxynaphthaldehyde

The structural, spectroscopic, and electrochemical properties of [Co{(naph)₂dien}(N₃)] and [Co{(naph)₂dpt}(N₃)], where (naph)₂dien?=?bis-(2-hydroxy-1-naphthaldimine)-N-diethylenetriaminedianion and (naph)₂dpt?=?bis-(2-hydroxy-1-naphthaldimine)-N-dipropylenetriaminedianion have been investigated. These complexes are characterized by elemental analyses, IR, and UV–Vis spectroscopy. The crystal structures of these complexes have been determined by X-ray diffraction. The geometry around cobalt is distorted octahedral. The electrochemical behavior of these complexes in acetonitrile solution was also investigated. Both complexes show an irreversible Co^III–Co^II reduction at ca. ?0.8?V, accompanied by dissociation of the axial Co^II–N₃ bond. The in vitro antibacterial activities of these complexes were tested against Staphylococcus aureus and Bacillus licheniformis.     

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).     

Synthesis and characterization of reactive liquid crystalline Schiff bases,Rh(I) complexes,and their derived polymers

Two series of salicylaldimines have been synthesized that consist of model compounds with terminal methylenic chains and reactive compounds in which the terminal chains have been modified with acrylate groups. The dicarbonylrhodium(I) complexes of these systems were prepared by reacting the ligands with the dimer [RhCl(cod)]₂ and CO. Characterization of the metal‐containing acrylates by ¹H NMR spectroscopy revealed that the Rh(I) can coordinate to the terminal double bond to produce pentacoordinated complexes. Furthermore, investigation of the mesogenic properties of the complexes revealed that the bulkiness of the metallic center requires the presence of at least a three‐ring aromatic core to avoid the suppression of liquid crystallinity. The study was extended to include the side‐chain polymers obtained from the acrylate‐functionalized Schiff bases. Chelation of the preformed polyacrylate with low percentages of Rh(I) emerged as the best strategy to prepare Rh(I)‐containing polyacrylates. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4466–4477, 2000