Nickel(II) complex with an asymmetric tetradentate Schiff base ligand: synthesis,characterization, crystal structure,and DFT studies

Abstract

A new asymmetric tetradentate Schiff base, bis(5-methoxysalicylidene)-4-methylbenzene-1,2-diamine), H₂L, and its Ni(II) complex were prepared and characterized using elemental analyses (CHN), FTIR, UV–Vis, ¹H NMR, and ¹³C{¹H} NMR spectroscopic techniques, and crystal structures of both were determined by X-ray crystallography. For both ligand and Ni(II) complex, density functional theory calculations to find geometry parameters, IR frequencies, electronic properties, and natural bond orbital analysis (NBO) were done with M062X method and Def2-TZVP basis set. All calculated data are consistent with the experiments. NBO data for the Ni(II) complex show that the main type of transition in UV-Vis is interligand charge-transfer, which is assigned as π-π*.     

Syntheses,characterizations, crystal structures,and biological activities of two new mixed ligand Ni(II) and Cu(II) Schiff base complexes

Two mixed-ligand complexes, [Cu(L)(2imi)] (1) and [Ni(L)(2imi)]·MeOH (2) [L = 2-(((5-chloro-2-oxyphenyl)imino)methyl)phenolato) and 2imi = 2-methyl imidazole], have been prepared by the reaction of appropriate metal salts with H₂L and 2-methyl imidazole. Their structures were characterized by microanalysis, FT-IR, UV–vis, molar conductivity, and ¹H NMR for [Ni(L)(2imi)]·MeOH. The structures were determined using single crystal X-ray diffraction. Each four-coordinate metal center, Cu(II) in 1 and Ni(II) in 2, is surrounded by donors of Schiff base (L^2?) and N of 2-methyl imidazole in square planar geometries. α-Amylase activities of these compounds have also been investigated. The experimental data showed that α-amylase was inhibited by Ni(II) complex while the Cu(II) complex causes a 1.3-fold decrease in K_m value. Antimicrobial results show that these compounds, especially the Cu(II) complex, have potential for antibacterial activity against Gram negative and Gram positive bacteria and antifungal activity against Aspergillus fumigatus.     

Synthesis and characterization of Co(II), Ni(II), Zn(II) and Cu(II) complexes with a new tetraazamacrocyclic Schiff base ligand containing a piperazine moiety: X-ray crystal structure determination of the Co(II) complex

Two macrocyclic Schiff base ligands, L¹ [1+1] and L² [2+2], have been obtained in a one-pot cyclocondensation of 1,4-bis(2-formylphenyl)piperazine and 1,3-diaminopropane. Unfortunately, because of the low solubility of both ligands, their separation was unsuccessful. In the direct reaction of these mixed ligands (L¹ and L²) and the appropriate metal ions only [CoL¹(NO₃)]ClO₄, [NiL¹](ClO₄)₂, [CuL¹](ClO₄)₂ and [ZnL¹(NO₃)]ClO₄ complexes have been isolated. All the complexes were characterized by elemental analyses, IR, FAB-MS, conductivity measurements and in the case of the [ZnL¹(NO₃)]ClO₄ complex with NMR spectroscopy.     

Synthesis,structure, and biological properties of a Co(II) complex with tridentate Schiff base ligand

A new Co(II) complex of general formula [Co(L)₂] has been synthesized from a NNO tridentate Schiff base ligand, 2-[(piperidin-2-ylmethylimino)-methyl]-phenol (L). The title complex is characterized by elemental, spectroscopic, antibacterial, and single crystal X-ray structural studies. X-Ray crystallography reveals that the complex shows a distorted octahedral geometry around the Co(II) ion. The complex was tested against several bacteria and shows good antibacterial activities against almost all of the bacteria. The interactions of the title complex with calf thymus deoxyribonucleic acid (CT-DNA) have been investigated by electronic absorption and fluorescence spectroscopy, showing that the complex interacts with CT-DNA via partial intercalation. Thermogravimetric analysis (TGA) of the complex has also been reported and the result shows that the complex is thermally stable up to 134 °C.     

New copper(II) and zinc(II) complexes based on azo Schiff base ligand: Synthesis,crystal structure,photoisomerization study and antibacterial activity

Newly synthesized mononuclear copper(II) and zinc(II) complexes containing an azo Schiff base ligand (L), prepared by condensation of 2-hydroxy-5-(o-tolyldiazenyl)benzaldehyde and propylamine, were obtained and then characterized using infrared and NMR spectroscopies, mass spectrometry and X-ray diffraction. Ligand L behaves as a bidentate chelate by coordinating through deprotonated phenolic oxygen and azomethine nitrogen. The copper and zinc complexes crystallize in triclinic and orthorhombic systems, respectively, with space groups P⁻1 and Pca2₁. In these complexes, the Cu(II) ion is in a square planar geometry while the Zn(II) ion is in a distorted tetrahedral environment. The photochemical behaviors of ligand L, [Cu(L)₂] and [Zn(L)₂] were investigated. The azo group in L underwent reversible trans–cis isomerization under UV and visible irradiation. This process was inhibited for the complexes. In addition, ligand L and its copper and zinc complexes were assessed for their in vitro antibacterial activities against four pathogenic strains.     

Synthesis,characterization, crystal structure,and antibacterial evaluation of Ni (II) complex with new dithiophosphorus compound

The reaction of 2,4-bis (4-methoxyphenyl)-1,3,2,4-dithiadiphosphetane-2,4-disulfide (Lawesson^’s reagent) with phenylethylamine produced [H₃NCH₂CH₂C₆H₅]⁺ [(C₆H₅CH₂CH₂NH)(p C₆H₄OMe)PS₂]^? (1). Furthermore, reaction of 1 with NiCl₂ in dry methanol led to the novel complex 2. The compounds were characterized by ¹H and ³¹P NMR, IR spectroscopy, and elemental analysis. A single crystal X-ray structure of complex 2 showed that the nickel complex is square planar. The complex formed a supramolecular structure via intermolecular S1…H7B and O1…H2N2 hydrogen bonds. The X-ray crystallography of complex showed [R²₂](18) and R⁴₄(18) motifs in the monomers were connected to each other via S1…H7B, O1…H2N2 hydrogen bonds with donor–acceptor distance of 2.89 and 2.51 Å, respectively. The new compounds were additionally tested in view of their antibacterial properties.     

Synthesis,crystal structures,and biological properties of a new naphthalimide Schiff base and its copper(II) complex

A new naphthalimide Schiff base N-allylamine-4-(ethylenediamine-3-methoxysalicylidene)-1,8-naphthalimide (HL) and its copper(II) complex {N-allylamine-4-(ethylenediamine-3-methoxysalicylidene)-1,8-naphthalimide copper(II)} (CuL₂) have been synthesized and characterized. The crystal structure of CuL₂ has been determined by X-ray single crystal diffraction. The central Cu(II) ion is four-coordinate with an N₂O₂ donor set which is afforded by two L ligands, forming a slightly distorted square planar geometry. The interactions of HL and CuL₂ with calf thymus DNA were investigated using electronic absorption titration, fluorescence titration, and viscosity measurements. The results indicate that free HL and CuL₂ bind to DNA in an intercalation mode, and their binding affinity for DNA takes the order CuL₂ > HL. Moreover, the antioxidant assay in vitro also shows that HL and CuL₂ possess significant antioxidant activities and CuL₂ is more effective than free HL.     

Theoretical investigation on molecular structure of a new mononuclear copper(II) thiocyanato complex with tridentate Schiff base ligand

An asymmetrical Schiff base ligand, 4-bromo-2-(2-pyridylmethyliminomethyl)phenol (HL), and its copper(II) complex, [Cu(L)SCN] (1), have been synthesized. Complex 1 is experimentally characterized by elemental analysis, FT-IR and UV–vis spectroscopic techniques, and cyclic voltammetry. The structure of the complex has been established by single-crystal X-ray diffraction studies, which reveal a square planar geometry of the central copper(II) ion in 1. The neighboring molecules of the complex connect each other by π–π stacking interactions with centroid-to-centroid ring distance 3.653 Å. The ligand can display two possible tautomeric forms; therefore, 1 can have an alternate molecular structure. DFT calculations have been employed to investigate the structure and relative stabilities of the suggested tautomeric forms of the ligand and its corresponding copper(II) complex.     

Synthesis,characterization, luminescence,antibacterial, and catalytic activities of a palladium(II) complex involving a Schiff base

A new Pd(II) complex of fluorine-containing Schiff base ligand, [Pd₂(L)₂Cl₂] (1) [L?=?N-(4-fluorobenzylidene)-2,6-diethylbenzenamine], has been synthesized using solvothermal method and characterized by elemental analysis, IR-spectroscopy, thermogravimetric analysis, powder X-ray diffraction, UV–vis absorption spectra, and single-crystal X-ray diffraction. Complex 1 is a μ-chloro-bridged dinuclear cyclometallated Pd(II) complex. Thermal analysis indicates that 1 is quite stable to heat. 1 exhibits quadruple emissions in the solid state (λ _max?=?766?nm) and possesses fluorescence lifetimes (τ ₁?=?87.20?ns, τ ₂?=?190.45?ns, and τ ₃?=?1805.10?ns at 616?nm); broad structureless bands at 690–800?nm are tentatively assigned to an excimeric ³IL transition. The Schiff base (L) and its palladium(II) compound (1) have been screened for their antibacterial activity against several bacteria, and the results are compared with the activity of penicillin. Moreover, 1 has been shown to be highly effective in the Heck reaction of 4-bromotoluene with acrylic acid.     

A new Co(II) complex with N,O-donor Schiff base: Synthesis, structure and characterization

A new Co(II) complex with tridentate Schiff base ligand with a N,N,O donor set has been synthesized and characterized by single X-ray technique and spectroscopic techniques. The thermochemical properties have been studied. X-ray structure analysis of the title compound Co(II)L₂ [HL = 2-methyl-6-(2′-hydroxybenzylideneamino) pyridine] shows that the polyhedron around Co(II) is a distorted tetrahedron, and the self-assembly via intermolecular π-π interactions leads to a three-dimensional network. Crystal data for the title complex C₂₆H₂₂CoN₄O₂: Monoclinic, space group Ia, a = 11.741(7) Å, b = 8.149(5) Å, c = 22.764(16) Å, β = 98.530(12)°, V = 2154(2) ų, Z = 4.     

NMR studies on a palladium(II) complex containing an incompletely coordinated facultative pentadentate Schiff base ligand

Palladium(II) dichloride reacts with 1,10‐bis(2‐pyrrolyl)‐2,5,9‐triaza‐1,9‐decadiene to give a [Pd(C₁₅H₂₀N₅)]Cl complex in which the ligand is four‐coordinated, leaving one pyrrole group dangling. By using COSY, gHSQC, gHMBC connectivities and NOE experiments it has been concluded that one linkage isomer exists in DMSO solution, in spite of the fact that different sets of N atoms of potentially pentadentate ligand might be involved in coordination, and that the three chelate rings in the complex cation are arranged in a sequence: five‐membered, six‐membered, five‐membered which is different from that (5–5–6) found by x‐ray studies on the related [Ni(C₁₅H₂₀N₅)]Cl compound. NMR studies allowed an unambiguous assignment of all ¹H and ¹³C NMR resonances for the complex. Results of x‐ray structural analysis of [Pd(C₁₅H₂₀N₅)](CH₃COO)H₂O supported the five‐membered, six‐membered, five‐membered ring sequence in the [Pd(C₁₅H₂₀N₅)]⁺ complex cation and show an E (trans) orientation of the dangling pyrrole group with respect to the metal center. Copyright © 2002 John Wiley & Sons, Ltd.     

Spectroscopic,thermal and antimicrobial properties of the copper(II) complex of Schiff base derived from 2‐(salicylidene) aminopyridine

Schiff bases and their complex combinations with metallic ions represent a class of compounds with antimicrobial activity. A ligand was prepared by condensation of the salicylaldehyde with 2‐aminopyridine obtaining 2‐(salicylidene) aminopyridine (SB) with a high capacity for complexing Cu(II) ions. The new compound has been characterized by physical constants (melting point, solubility, stability) and the chemical structure was confirmed by elemental, spectral (IR, UV–visible, ¹H NMR and ¹³C‐NMR) and thermal analyses. The elemental analysis gives a coordination ratio of 1:2 metal:Schiff base. Lethal dose 50 (DL₅₀) values of new Schiff base and their complex with metallic ions were established. The antimicrobial activity of this complex was tested in comparison with the activity of the corresponding Schiff base on strains of Staphylococcus aureus, Bacillus cereus, Bacillus subtilis, Escherichia coli, Candida albicans, and Klebsiella. These were compared with the activity of the reference drugs (chloramphenicol, tetracycline, ofloxacin and nystatin) on the above‐mentioned strains. It has been established that all compounds tested were very active against both Gram‐positive and Gram‐negative bacteria. Copyright © 2012 John Wiley & Sons, Ltd.     

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.     

Synthesis and characterization of two Cu(II) complexes with a new pyrazole-based Schiff base ligand: crystallography,DNA interaction and antimicrobial activity of Ni(II) and Cu(II) complexes

Reaction of Cu(II) nitrate with a new pyrazole-based Schiff base ligand, 5-methyl-3-formylpyrazole-N-(2′-methylphenoxy)methyleneimine (MPzOA), afforded two types of Cu(II) complexes at different reaction temperatures, [Cu(MP_zOA)(NO₃)]₂ (1) and [Cu(3,7,11,15-tetramethylporphyrin)(H₂O)](NO₃)₂ (2), reported together with a Ni(II) complex, [Ni(MPzOA)₂(H₂O)₂]Br₂ (3). The compounds are characterized by single crystal X-ray structure analyses along with several physico-chemical and spectral parameters. Complex 1 is authenticated as a bis(μ-pyrazolato)dicopper(II), while 2 is a porphyrinogen and 3 is a distorted octahedral complex. Structural analyses of the complexes reveal that 1 crystallized in monoclinic P2₁/n space group while 2 and 3 crystallized in monoclinic C2/c space group. DNA-binding studies of the complexes have shown that the complexes interact with CT-DNA. DNA-cleavage studies with plasmid DNA have shown that 1 and 2 induce extensive DNA cleavage in the presence of H₂O₂ as an additive, whereas there is no change in degradation of super-coiled DNA by 3 in the presence of additive. The antimicrobial studies of the complexes against Escherichia coli DH5α bacteria strain indicated that all the complexes were capable of killing E. coli with different LD50 values.     

Synthesis, crystal structure and imine bond activation of a copper(II) Schiff base complex

A new copper(II) complex [Cu(HL)(ClO₄)](ClO₄) (1), where HL is a multidentate Schiff base N,N′-(2-hydroxypropane-1,3-diyl)bis(pyridine-2-aldimine), is prepared, structurally characterized by X-ray crystallography and its spectral and electrochemical properties studied. The complex forms a one-dimensional chain in the solid state structure in which the monomeric Cu(HL) units are linked by the perchlorate ligand. The complex has an axially elongated six coordinate geometry (4+2) with a CuN₄O₂ core in which the Schiff base ligand displays a tetradentate mode of bonding in the basal plane. The axial ligand is perchlorate with a significantly long Cu–O bond of ca. 2.6 Å. The one-electron paramagnetic complex displays a cyclic voltammetric response for the Cu(II)/Cu(I) couple at 0.01 V versus SCE in MeCN–0.1 M TBAP. The azomethine bond of the Schiff base in 1 on treatment with H₂O₂ undergoes oxidative conversion to form a bis(picolinato)copper(II) · dihydrate species through the formation of an amido intermediate as evidenced from the solution infrared spectral studies.     

Synthesis and crystal structure of the dinuclear copper(II) Schiff base complex μ‐hydroxido‐μ‐chlorido‐bis{[bis(trans‐2‐nitrocinnamaldehyde)ethylenediamine]chloridocopper(II)} dichloromethane sesquisolvate

Transition metal complexes of Schiff base ligands have been shown to have particular application in catalysis and magnetism. The chemistry of copper complexes is of interest owing to their importance in biological and industrial processes. The reaction of copper(I) chloride with the bidentate Schiff base N,N′‐bis(trans‐2‐nitrocinnamaldehyde)ethylenediamine {Nca₂en, systematic name: (1E,1′E,2E,2′E)‐N,N′‐(ethane‐1,2‐diyl)bis[3‐(2‐nitrophenyl)prop‐2‐en‐1‐imine]} in a 1:1 molar ratio in dichloromethane without exclusion of air or moisture resulted in the formation of the title complex μ‐chlorido‐μ‐hydroxido‐bis(chlorido{(1E,1′E,2E,2′E)‐N,N′‐(ethane‐1,2‐diyl)bis[3‐(2‐nitrophenyl)prop‐2‐en‐1‐imine]‐κ²N,N′}copper(II)) dichloromethane sesquisolvate, [Cu₂Cl₃(OH)(C₂₀H₁₈N₄O₄)₂]·1.5CH₂Cl₂. The dinuclear complex has a folded four‐membered ring in an unsymmetrical Cu₂OCl₃ core in which the approximate trigonal bipyramidal coordination displays different angular distortions in the equatorial planes of the two Cu^II atoms; the chloride bridge is asymmetric, but the hydroxide bridge is symmetric. The chelate rings of the two Nca₂en ligands have different conformations, leading to a more marked bowing of one of the ligands compared with the other. This is the first reported dinuclear complex, and the first five‐coordinate complex, of the Nca₂en Schiff base ligand. Molecules of the dimer are associated in pairs by ring‐stacking interactions supported by C—H…Cl interactions with solvent molecules; a further ring‐stacking interaction exists between the two Schiff base ligands of each molecule.     

Cu(II) complexes with 4-amino-3,5-dimethyl isoxazole and substituted aromatic aldehyde Schiff bases: synthesis,crystal structure,antimicrobial activity,DNA binding and cleavage studies

Three isoxazole Schiff bases 2-((E)-(3,5-dimethylisoxazol-4-ylimino)methyl)-6-methoxyphenol (L¹), 2-((E)-(3,5-dimethylisoxazol-4-ylimino)methyl)-4,6-diiodophenol (L²), 2-((E)-(3,5-dimethylisoxazol-4-ylimino)methyl)-6-bromo-4-chlorophenol (L³), and their Cu(II) complexes [Cu(L¹)₂] (1), [Cu(L²)₂] (2) and [Cu(L³)₂] (3) were synthesized. All the complexes have been characterized by elemental analysis, FT-IR, ESI mass, UV-Visible, ESR, TGA, magnetic moments, and single-crystal X-ray diffraction analysis. Based on analytical data, a square planar geometry is assigned to the Cu(II) complexes with N₂O₂ donors from the Schiff base ligands. The single-crystal X-ray diffraction measurements of 1 and 2 confirmed the square planar geometry. DNA binding studies from electronic absorption titrations, viscosity measurements, and fluorescence quenching studies indicated an intercalation mode of binding of Cu(II) complexes with CT-DNA. DNA cleavage experiments of Cu(II) complexes with supercoiled plasmid pBR322 DNA have also been investigated by agarose gel electrophoresis in the presence of H₂O₂ (oxidative cleavage) and UV light (photolytic cleavage). The synthesized compounds were screened for antibacterial (Escherichia coli, Pseudomonas putida, Klebsiella pneumoniae, Bacillus subtillis and Staphylococcus aureus) and antifungal (Candida albicans and Aspergillus niger) activities by the paper disk method. The Cu(II) complexes showed better activity than corresponding Schiff bases.     

Synthesis,spectral characterization and structural investigation on some 4-aminoantipyrine containing Schiff base Cu(II) complexes and their molecular association

Compounds [Cu(L₁)₂] (1) and [Cu(L₂)₂] (2), where L₁ and L₂ are Schiff base ligands of 4-aminoantipyrine and substituted salicylaldehydes, were synthesized and characterized using various spectroscopic techniques such as elemental analysis, UV–Vis, IR, and NMR. The single crystal X-ray structures for L₁, L₂, and their corresponding Cu(II) complexes assembled in a 1:2 metal to ligand ratio were analyzed for their various weak H-bonding and dimeric association. The structural analysis of compounds 1 and 2, being the first crystal structures in this series, deserves special attention to help further the understanding in this area of structure–reactivity correlation studies. Further these compounds, composed of very similar chemical composition with a small difference in the substituent on the salicylaldehyde moiety, influenced through various weak inter- and intramolecular H-bonding and C–H?π interactions, rearrange the geometry around Cu(II) from a tetrahedrally distorted square planar geometry in [Cu(L₁)₂] (1) to square planar in [Cu(L₂)₂] (2). Steric strain imposed by the methyl substitution on the 4-aminoantipyrine moiety of the Schiff base ligand, causing this small change of the Cu(II) geometry, along with various weak interactions is analyzed in detail.     

A new stepped tetranuclear copper(II) complex: synthesis,crystal structure and photoluminescence properties

Binuclear and tetranuclear copper(II) complexes are of interest because of their structural, magnetic and photoluminescence properties. Of the several important configurations of tetranuclear copper(II) complexes, there are limited reports on the crystal structures and solid‐state photoluminescence properties of `stepped' tetranuclear copper(II) complexes. A new Cu^II complex, namely bis{μ₃‐3‐[(4‐methoxy‐2‐oxidobenzylidene)amino]propanolato}bis{μ₂‐3‐[(4‐methoxy‐2‐oxidobenzylidene)amino]propanolato}tetracopper(II), [Cu₄(C₁₁H₁₃NO₃)₄], has been synthesized and characterized using elemental analysis, FT–IR, solid‐state UV–Vis spectroscopy and single‐crystal X‐ray diffraction. The crystal structure determination shows that the complex is a stepped tetranuclear structure consisting of two dinuclear [Cu₂(L )₂] units {L is 3‐[(4‐methoxy‐2‐oxidobenzylidene)amino]propanolate}. The two terminal Cu^II atoms are four‐coordinated in square‐planar environments, while the two central Cu^II atoms are five‐coordinated in square‐pyramidal environments. The solid‐state photoluminescence properties of both the complex and 3‐[(2‐hydroxy‐4‐methoxybenzylidene)amino]propanol (H₂L ) have been investigated at room temperature in the visible region. When the complex and H₂L are excited under UV light at 349 nm, the complex displays a strong blue emission at 469 nm and H₂L displays a green emission at 515 nm.     

Synthesis,spectral and antibacterial activity of Co(II), Ni(II) and Zn(II) complexes with 2‐hydroxy‐benzoic acid(3,4‐dihydro‐2H‐naphthalen‐1‐ylidene)‐hydrazide

A bioactive Schiff base HL i.e. 2‐hydroxy‐benzoic acid(3,4‐dihydro‐2H ‐naphthalen‐1‐ylidene)‐hydrazide was synthesized by reacting equimolar amount of salicylic acid hydrazide and 1‐tetralone. Co(II), Ni(II) and Zn(II) complexes of ligand HL was synthesized in 1:1 and 1:2 molar ratio of metal to ligand. The structure of the synthesized ligand and metal complexes was established by elemental analysis, molar conductance, magnetic susceptibility measurements, electronic, IR and EPR spectral techniques. For determining the thermal stability the TGA has been done. In DFT studies the geometries of Schiff bases and metal complexes were fully optimized with respect to the energy using the 6–31 + g(d,p) basis set. Spectral data reveal that ligand behave uninegative tridentate in ML complexes and uninegative bidentate in ML₂ complexes. On the basis of characterization octahedral geometry has been assigned for Co(II) and Ni(II) complexes, while tetrahedral for Zn(II) complexes. Antibacterial activity of the synthesized compounds were evaluated against Staphylococcus aureus , Bacillus subtilis, Escherichia coli , Xanthomonas campestris and Pseudomonas aeruginosa and the results revealed that metal complexes show enhanced activity in comparison to free ligand.