Spectroscopic characterization and electrochemical studies of ruthenium(II) carbonyl complexes containing bidentate Schiff bases and triphenylphosphine or a nitrogen heterocycle

Reactions of ruthenium(II) carbonyl complexes of the type [RuHCl(CO)(PPh₃)₂(B)] [B?=?PPh₃, pyridine (py), piperidine (pip) or morpholine (mor)] with bidentate Schiff base ligands derived from the condensation of 2-hydroxy-1-naphthaldehyde with aniline, o-, m- or p-toluidine in a 1?:?1 mol ratio in benzene resulted in the formation of complexes formulated as [RuCl(CO)(L)(PPh₃)(B)] [L?=?bidentate Schiff base anion, B?=?PPh₃, py, pip, mor]. The complexes were characterized by analyses, IR, electronic and ¹H NMR spectroscopy, and cyclic voltammetric studies. In all cases, the Schiff bases replace one molecule of phosphine and a hydride ion from the starting complexes, indicating that Ru–N bonds in the complexes containing heterocyclic nitrogenous bases are stronger than the Ru–P bond to PPh₃. Octahedral geometry is proposed for the complexes.     

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.     

Synthetic and catalytic investigations of ruthenium(III) complexes with triphenylphosphine/triphenylarsine and tridentate Schiff base

The synthesis and characterization of several hexa‐coordinated ruthenium(III) complexes of the type [RuCl(PPh₃)₂(L)] (L = dibasic tridentate ligand derived by the condensation of salicylaldehyde/o‐vanillin with o‐aminophenol/o‐aminothiophenol) are reported. IR, electronic, EPR spectral data and redox bahaviour of the complexes are discussed. An octahedral geometry has been tentatively proposed for all the complexes. The new complexes were found to be effective catalysts for the oxidation of benzyl alcohol and cyclohexanol to benzaldehyde and cyclohexanone respectively using N‐methylmorpholine‐N‐oxide as a co‐oxidant. Copyright © 2007 John Wiley & Sons, Ltd.     

Ruthenium(III) complexes with tetradentate Schiff bases containing triphenylphosphine or triphenylarsine

Ruthenium(III) complexes of Schiff bases derived from the condensation of salicylaldehyde or o-vanillin with diamines have been prepared and characterised. The complexes are of the type [RuX(EPh₃)(L)] [X=Cl or Br; E=P or As; L=bis(salicylaldehyde)tetramethylenediimine, bis(salicylaldehyde)o-phenylenediimine, bis(o-vanillin)ethylenediimine, bis(o-vanillin)propylenediimine, bis(o-vanillin)tetramethylenediimine or bis(o-vanillin)o-phenylenediimine]. The Schiff bases behave as dibasic tetradentate ligands.     

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,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.     

Synthesis,characterization and cytotoxicity of platinum(II) complexes containing reduced amino acid ester Schiff bases

Nine platinum(II) complexes containing reduced amino acid ester Schiff bases were synthesized and characterized using spectroscopy (¹H NMR, ¹³C NMR, infrared), elemental analysis and molar conductivity. The interaction of these complexes with salmon sperm DNA was investigated by means of ultraviolet and circular dichroism spectroscopies. The potential antitumor activity of all compounds was tested in vitro on HeLa and A549 tumor cell lines. Almost all the complexes exhibited better cytotoxic activity than cisplatin against these cell lines.     

Studies on DNA binding behavior of biologically active Cu(II) complexes of Schiff bases containing acyl pyrazolones and 2-ethanolamine

Pyrazolone derivatives (Z)-4-((2-hydroxyethylimino)(p-tolyl)methyl)-3-methyl-1-phenyl-1H-pyrazol-5(4H)-one [PMP-EA] (1), (Z)-1-(3-chlorophenyl)-4-((2-hydroxyethylimino)(p-tolyl)methyl)-3-methyl-1H-pyrazol-5(4H)-one [MCPMP-EA] (2), and (Z)-4-((2-hydroxyethylimino)(p-tolyl)methyl)-3-methyl-1-p-tolyl-1H-pyrazol-5(4H)-one [PTPMP-EA] (3) have been synthesized and characterized. The molecular geometry of 2 has been determined by single-crystal X-ray study. These ligands exist in amine-one tautomeric form in the solid state. Three copper(II) complexes, [Cu(PMP-EA)(H₂O)₂] (4), [Cu(MCPMP-EA)(H₂O)₂] (5), and [Cu(PTPMP-EA)(H₂O)₂] (6), respectively, have been synthesized using these ligands and characterized by microanalytical data, molar conductivity, IR, UV–Visible, FAB-Mass, magnetic measurement, TG-DTA studies, and ESR spectral studies; Cu(II) is five-coordinated with [ML(H₂O)₂] composition. The interaction of the complexes with CT-DNA (calfthymus) was investigated using different methods. The results suggest that the copper complexes bind to DNA via intercalation and can quench the fluorescence intensity of EB bound to DNA.     

The structures and cyclic voltammetry of three copper(II) complexes derived from bulky ortho-hydroxy Schiff bases

Three copper(II) complexes derived from bulky ortho-hydroxy Schiff base ligands, (1)-(3), were synthesized and characterized by chemical analysis, UV-Vis, IR, μ_eff and mass spectrometry. The solid state structures of compounds (1)-(3) were determined. The solid state X-ray diffraction studies of these compounds show that the geometry is intermediate between square planar and tetrahedral. Moreover, EPR studies in DMF solution at 77 K suggest that the geometry of these complexes in solution is different from that observed in the solid state by X-ray crystallography. Furthermore, cyclic voltammetry studies performed for (1)-(3), indicate a dependence of the cathodic potentials upon conformational and electronic effects.     

Ruthenium(II) complexes containing triphenylphosphine/triphenylarsine and bidentate Schiff bases derived from 2-hydroxy-1-naphthaldehyde and primary amines

The synthesis and characterisation of some new hexa-coordinated Schiff base complexes of the type [RuCl(CO)(EPh₃)(B)(L)] (E = P or As; B = PPh₃ or AsPh₃ or py or pip; L = anion of the Schiff bases derived from 2-hydroxy-1-naphthaldehyde and aniline, 4-chloroaniline or 2-methylaniline) are reported. I.r., electronic, ¹H-n.m.r, ³¹P-n.m.r. spectra, catalytic activity and antibacterial activity of the complexes are discussed. An octahedral structure has been tentatively proposed for all the complexes.     

Zinc(II) complexes with Schiff bases derived from ethylenediamine and salicylaldehyde: the synthesis and photoluminescent properties

The effect of the nature of organic ligands and complex formation on the photoluminescent characteristics (relative quantum yield, excited-state lifetime) and thermal stability of tetradentate Schiff bases (H₂L), derivatives of salicylaldehyde (H₂(SAL)¹, H₂(SAL)²), o-vanillin (H₂(MO)¹, H₂(MO)²) with ethylenediamine and o-phenylenediamine, and their zinc(II) complexes was studied. Zinc(II) complexes were synthesized by the reaction of H₂L with Zn(AcO)₂·2H₂O in MeOH at room temperature or under reflux. In the case of H₂L = H₂(SAL)², H₂(MO)¹, H₂(MO)², complexes of the composition ZnL·H₂O were isolated irrespective of the temperature. For H₂L = H₂(SAL)¹, the reaction results in Zn(SAL)¹·H₂O at room temperature and in anhydrous dimeric complex [Zn(SAL)¹]₂ under reflux. Density functional calculations of H₂L and ZnL confirmed that (1) luminescence of these compounds is due to the π-π* transition between orbitals of the organic ligand and (2) enhancement of conjugation of the chain and introduction of electron-donating substituents lead to a decrease of the energy gap and, there-fore, to a bathochromic shift of the emission maximum. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1846–1855, September, 2008.     

Synthesis,crystal structures and spectral studies of square planar nickel(II) complexes containing an ONS donor Schiff base and triphenylphosphine

Five mononuclear nickel(II) complexes, viz. [Ni(L1)(PPh₃)] (1), [Ni(L2)(PPh₃)] (2), [Ni(L3)(PPh₃)] (3), [Ni(L4)(PPh₃)] (4) and [Ni(L5)(PPh₃)] (5) (where L1, L2, L3, L4 and L5 are dianions of N-(2-mercaptophenyl)salicylideneimine, 5-methyl-N-(2-mercaptophenyl)salicylideneimine, 5-chloro-N-(2-mercaptophenyl)salicylideneimine, 5-bromo-N-(2-mercaptophenyl)salicylideneimine and N-(2-mercaptophenyl)naphthylideneimine, respectively), have been synthesized and characterized by means of elemental analysis, electronic, IR, ¹H, ¹³C and ³¹P NMR spectroscopy. Single crystal X-ray analysis of two of the complexes (1 and 5) has revealed the presence of a square planar coordination geometry (ONSP) about nickel. The crystal structures of the complexes are stabilized by intermolecular π–π stacking between the ligands (L) and by various C–H···π interactions.     

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.     

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,crystal structure and fluorescence properties of two dinuclear zinc(II) complexes incorporating tridentate (NNO) Schiff bases

Reactions of hydrated zinc(II) trifluoroacetate and sodium azide with two tridentate Schiff bases HL¹ (2-((E)-(2-(dimethylamino)ethylimino)methyl)-4-chlorophenol) and HL² (2-((E)-(2-(dimethylamino)ethylimino)methyl)-4-bromophenol) under the same reaction conditions yielded two dinuclear isostructural zinc(II) complexes, [Zn(L¹)(N₃)]₂ (1) and [Zn(L²)(N₃)]₂ (2), respectively. The complexes were characterized systematically by elemental analysis, UV–Vis, FT-IR, and ¹H NMR spectroscopic methods. Single-crystal X-ray diffraction studies reveal that each of the dinuclear complexes consists of two crystallographically independent zinc(II) ions connected by double bridging phenoxides. All zinc(II) ions in 1 and 2 are surrounded by similar donor sets and display distorted square–pyramidal coordination geometries. The ligands and complexes reveal intraligand ¹(π → π*) flourescence. The enhancement of the fluorescence intensities for the complexes compared to the ligands indicates their potential to serve as photoactive materials.     

Nickel(II) complexes of tridentate anthracene based Schiff bases: syntheses,properties and crystal structures

The crystal and molecular structures of Ni(II) complexes with two tridentate anthracene-containing Schiff bases are reported. The Schiff bases were prepared by condensation of 9-anthraldehyde with diethylenetriamine (adien) and with dipropylenetriamine (adipn). Complexes synthesized from Ni(O₂CCH₃)₂·4H₂O and the ligands (1?:?1 mol ratio) crystallize from methanol as [Ni(adien)(O₂CCH₃)₂(H₂O)] (1) and [Ni(adipn)(O₂CCH₃)₂]·2CH₃OH (2·2CH₃OH) in space groups P2₁/n and P2₁2₁2₁, respectively. In 1, the distorted octahedral N₃O₃ coordination sphere around the metal ion is formed by the meridional N₃-donor adien, two mutually trans unidentate acetates and one water molecule. The N₃O₃ coordination sphere constituted by the N₃-donor adipn, one unidentate acetate and one bidentate acetate in 2 can be best described as trigonal bipyramidal. The secondary amine-N of adipn, the O-atom of the unidentate acetate and the midpoint of the two O-atoms of the bidentate acetate occupy the three equatorial positions and two imine-N atoms of adipn lie in axial sites. In the crystal lattice, molecules of 1 exist as discrete dimers due to intermolecular hydrogen bonding and π–π interactions. In contrast, self-assembly of 2 via intermolecular π–π interactions leads to a one-dimensional supramolecular structure.     

Zinc(II) and mercury(II) complexes with Schiff bases: syntheses,spectral, and structural characterization

Schiff bases o-vanilidene-1-aminobenzene (HL¹) and o-vanilidene-2-methyl-1-aminobenzene (HL²) lead to the formation of mono- and bis-[(Cl)Zn(L¹)] (1), [(Cl)Zn(L²)] (2), [(Cl)Hg(L¹)] (3), [(Cl)Hg(L²)] (4), [Zn(L¹)₂] (5), [Zn(L²)₂] (6), [Hg(L¹)₂] (7), and [Hg(L²)₂] (8) complexes by reactions of zinc(II) and mercury(II) chlorides in different mole ratio(s). Complexes 1–8 have been characterized by elemental analyses (Zn, Hg, C, H, Cl, and N), melting point and spectral (IR, ¹H-NMR), PXRD, molar conductivity measurement, and TGA. Conductivity measurements suggest non-electrolytes. Structural compositions have been assigned by mass spectral studies. Four-coordinate geometry may be assigned to these complexes tentatively. Structural study reveals that in 1–4 two metal centers are held together by two bridged (μ₂-Cl) chlorides, whereas 5–8 contain two bidentate Schiff-base ligands around one metal-producing monomers.     

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.     

Ruthenium(II) complexes containing bidentate Schiff bases and their antifungal activity

The reactions of ruthenium(II) complexes, [RuHCl(CO)(PPh₃)₂(B)] [B = PPh₃, pyridine (py) or piperidine (pip)], with bidentate Schiff base ligands derived by condensing salicylaldehyde with aniline, o-, m- or p-toluidine have been carried out. The products were characterised by analytical, i.r., electronic, ¹H-n.m.r. and ³¹P-n.m.r. spectral studies and are formulated as [RuCl(CO)(L)(PPh₃)(B)] (L = Schiff base anion; B = PPh₃, py or pip). An octahedral structure has been tentatively proposed for the new complexes. The Schiff bases and the new complexes were tested in vitro to evaluate their activity against the fungus Aspergillus flavus.     

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.