Thermal and spectral studies of palladium(II) complexes

Palladium(II) complexes of type [Pd(L)Cl₂] [where L=2-aminopyridine-N-thiohydrazide (L¹), (2-aminopyridine-N-thio)-1,3-propanediamine (L²), benzaldehyde 2-aminopyridine-N-thiohydrazone (L³) and salicylaldehyde-2-aminopyridine-N-thiohydrazone (L⁴)] have been synthesized. The thiohydrazide, thiodiamine and thiohydrazones can exist as thione-thiol tautomer and coordinate as a bidentate N-S ligand. The ligands found to act in bidentate fashion. The complexes have been characterized by elemental analysis, IR, mass, electronic, ¹H NMR spectroscopic studies, and TG/DTA study. Antifungal studies of some complexes were also carried out. Various kinetic and thermodynamic parameters like order of reaction (n), activation energy (E _a), apparent activation entropy (S ^# ) and heat of reaction (ΔH) have also been carried out for one complex.     

Syntheses,characterization and anti‐microbial activities of palladium(II) and palladium(IV) complexes of 3,10‐C‐meso‐Me8[14]diene (L1) and its reduced isomeric anes (LA,LB and LC). Crystal and molecular structure of [PdL1][Pd(SCN)4]

The reactions of 3,10‐C‐meso‐3,5,7,7,10,12,14,14‐octamethyl‐1,4,8,11‐tetraazacyclotetradecadiene, L¹, and two isomers (L_B and L_C, differing in the orientation of methyl groups on the chiral carbon atoms) of its reduced form with PdCl₂ and K₂[Pd(SCN)₄], produce square‐planar tetrachloro‐ and tetrathiocyano‐palladium(II) complexes of general formulae [PdL′][PdCl₄] and [PdL′][Pd(SCN)₄] (L′ = L¹, L_B and L_C), respectively. By contrast, the third ane isomer, L_A, upon reaction with the same reagents, PdCl₂ and K₂[Pd(SCN)₄], formed octahedral tetrachloro‐ and tetrathiocyanato‐palladium(IV) complexes [PdL_ACl₂]Cl₂ and [PdL_A(SCN)₂](SCN)₂, respectively. The [PdL′][PdCl₄] and [PdL_ACl₂]Cl₂ complexes undergo substitution reactions with KSCN to form square‐planar and octahedral tetrathiocyanato complexes [PdL′][Pd(SCN)₄] and [PdL_A(SCN)₂](SCN)₂, respectively. All complexes have been characterized on the basis of analytical, spectroscopic, conductometric and magnetochemical data. The anti‐fungal and anti‐bacterial activities of these complexes have been studied against some phytopathogenic fungi and bacteria. The crystal structure of [PdL¹][Pd(SCN)₄] has been confirmed by X‐ray crystallography and shows with square‐planar PdN₄ and PdS₄ geometries [monoclinic, space group C2/c, a = 17.884(3) Å, b = 14.734(2) Å, c = 11.4313(18) Å, β = 104.054(5)° ]. Copyright © 2008 John Wiley & Sons, Ltd.     

两种1,2,3-三唑衍生物的配合物合成策略:晶体结构和表面分析

在不同反应条件下反应得到了两种1,2,3-三唑衍生物的配合物[Co（H₂O）₆][Co（L¹）₃]₂·4H₂O（1）和Cu（L²）₂（2）（HL¹=5-methyl-1-phenyl-1H-1,2,3-triazole-4-carboxylic acid;HL²=1-（4-iodophenyl）-5-methyl-1H-1,2,3-triazole-4-carboxylic acid）。通过X射线单晶衍射和红外光谱确定了晶体结构,同时对配合物1和2进行了表面作用分析（Hirshfeld surface analysis）,在二维指纹图谱中可以清楚的看到配合物中的主要分子间作用。     

REACTION BETWEEN [PdCl4]2- AND 5,5-DIMETHYL-2-THIOXOIMIDAZOLIDIN-4-ONE

Abstract

The reaction between 5,5-dimethyl-2-thioxoimidazolidin-4-one (H2L) and [PdCl₄]^2- has been studied in aqueous solution by potentiometric and spectrophotometric measurements. In the presence of the palladium salt, H₂L is completely monodeprotonated (HL^?); from spectrophotometric measurements, only two complexes having 1:1 and 1:2 Pd/ligand mol ratios have been identified. Potentiometric titrations, carried out on solutions with 1:1, 1:2, 1:3 and 1:4 metal/ligand mol ratios, show that these complexes must be formulated as Pd(HL)₂ and [Pd₂(HL)₂(μ-H₂O)(μ-OH)]⁺. Ionization constants of the pure ligand and formation constants of the complexes give pH distribution curves of the various species and the spectra of the two complexes. From MeOH, S-coordinated Pd(H₂L)_nCl₂ (n = 2–4) complexes have been separated in the solid state; from water, two complexes of formula Pd(H₂L)(HL)Cl and Pd(HL)Cl have been obtained with HL^? N,S-coordinated to the metal.     

Synthesis and liquid crystal properties of dinuclear cyclopalladated 5-alkyl-2-(4′-alkoxyphenyl)pyrimidine and 3-(4′-alkoxyphenyl)-6-alkoxypyridazine complexes

The dinuclear cyclopalladated complexes [Pd(L₁ or L₂)(µ-X)]₂ (HL₁=5-alkyl-2-(4′-alkoxyphenyl)pyrimidine, HL₂=3-(4′-alkoxyphenyl)-6-alkoxypyridazine, X=Cl^?, CH₂ClCOO^?, CH₂BrCOO^?, CH₃CHBrCOO^?, CH₂BrCH₂COO^?, CH₃COO^?) have been synthesized and characterized; their mesogenic properities were determined by DSC and polarizing microscopy. The effect of the bulk and the polarity of the bridging ligands on their mesogenic properties is discussed. The effect of the length of the alkyl chains on the mesogenic properties of these organometallic complexes has also been investigated.     

Synthesis,crystal structure,and antibacterial activity of mononuclear nickel(II) and cobalt(III) Schiff-base complexes

Four new mononuclear complexes, [Ni(L¹)(NCS)₂] (1), [Ni(L²)(NCS)₂] (2), [Co(L¹)(N₃)₂]ClO₄ (3), and [Co(L²)(N₃)₂]ClO₄ (4), where L¹ and L² are N,N′-bis[(pyridin-2-yl)methylidene]butane-1,4-diamine and N,N′-bis[(pyridin-2-yl)benzylidene]butane-1,4-diamine, respectively, have been prepared. The syntheses have been achieved by reaction of the respective metal perchlorate with the tetradentate Schiff bases, L¹ and L², in presence of thiocyanate (for 1 and 2) or azide (for 3 and 4). The complexes have been characterized by microanalytical, spectroscopic, single crystal X-ray diffraction and other physicochemical studies. Structural studies reveal that 1–4 are distorted octahedral geometries. The antibacterial activity of all the complexes and their constituent Schiff bases have been tested against Gram-positive and Gram-negative bacteria.     

The coordination chemistry ofN,N′-ethylenebis(2-acetylpyridine imine) andN,N′-ethylenebis(2-benzoylpyridine imine); two potentially tetradentate ligands containing four nitrogen atoms

Summary New complexes of the general formulae [ML_A(H₂O)₂]-Cl₂ (M=Ni or Cu), [ML_AX₂] (M=Co or Cu; X=Cl or Br), [NiL_ABr₂]·H₂O, [ML_A] [MCl₄] (M=Pd or Pt), [NiL_B(H₂O)₂]Cl₂·2H₂O, [ML_BCl₂] (M=Co, Ni, Cu, Pd or Pt; X=Cl or Br) and [ML_B] [MCl₄] (M=Pd or Pt), where L_A=N,N-ethylenebis(2-acetylpyridine imine) and L_B=N, N-ethylenebis(2-benzoylpyridine imine), have been isolated. The complexes were characterized by elemental analyses, conductivity measurements, t.g./d.t.g. methods, magnetic susceptibilities and spectroscopic (i.r., far-i.r., ligand field,¹Hn.m.r.) studies. Monomeric pseudo-octahedral stereochemistries for the Co^II, Ni^II and Cu^II complexes andcis square planar structures for the compounds [ML_BX₂] (M=Pd or Pt; X=Cl or Br) are assigned in the solid state. The molecules L_A and L_B behave as tetradentate chelate ligands in the Co^II, Ni^II, Cu^II and Magnus-type Pd^II and Pt^II complexes, bonding through both the pyridine and methine nitrogen atoms. A bidentateN-methine coordination of the Schiff base L_B is assigned in the [ML_BX₂] complexes (M=Pd or Pt; X=Cl or Br). The anomalous magnetic moment values of the Co^II complexes are discussed.     

First heterobimetallic MnII/MII(M = Cu,Ni) complexes with open-chain aliphatic schiff-base ligands obtained by direct template synthesis

Four new heterobimetallic complexes [CuL¹][MnCl₄] (1), [CuL²][MnCl₄] (2), [NiL¹][MnCl₄] (3), [NiL²][MnCl₄] (4) (L¹?=?4,6,6-trimethyl-1,9-diamino-3,7-di-aza-nona-3-ene; L²?=?1,15-dihydroxy-7,9,9-trimethyl-3,6,10,13-tetra-aza-pentadeca-6-ene) have been prepared from elemental metals, ethylenediamine dihydrochloride or its N-(2-hydroxyethyl) derivative and acetone by the template condensation reaction. All complexes have been characterized by elemental analysis, IR and UV-Visible spectroscopy. The structures of 2 and 3 have been determined by X-ray crystallography (2: Orthorhombic, Pna2 _1, a?=?20.136(4), b?=?11.185(2), c?=?10.251(2)Å, Z?=?4; 3: Orthorhombic, Pca2 _1, a?=?14.335(2), b?=?11.405(2), c?=?11.154(2)Å, Z?=?4 ). Both crystals consist of alternating complex cations [ML]²⁺ and anions [MnCl₄]^2? linked together by N–H···Cl–Mn and O–H···Cl–Mn hydrogen bonds forming 2D corrugated sheets in (2) and 1D helical chains in (3). Complex 2 represents the first single crystal structure elucidation of the complex containing L².     

Synthesis,crystal structure and antibacterial activity of manganese(III) and cobalt(III) complexes containing pentadentate Schiff bases of a common amine and thiocyanate

Abstract

Four new mononuclear Schiff base manganese(III) and cobalt(III) complexes viz. [Mn(L¹)(NCS)] (1), [Mn(L²)(NCS)] (2), [Co(L³)(NCS)] (3), and [Co(L⁴)(NCS)]·0.5CH₃OH·0.5H₂O (4), containing thiocyanate as a common pseudohalide ion are reported. The pentadentate Schiff base ligands H₂L¹, H₂L², H₂L³, and H₂L⁴ were obtained by the condensation of substituted salicylaldehydes with N-(3-aminopropyl)-N-methylpropane-1,3-diamine. The syntheses of the complexes have been achieved by the reaction of manganese(II) perchlorate or cobalt(II) perchlorate with the respective Schiff bases in the presence of thiocyanate in methanol medium. Complexes 1–4 have been characterized by microanalytical, spectroscopic, single-crystal X-ray diffraction and other physicochemical studies. Structural studies reveal that 1–4 adopt nearly similar structures containing the MN₄O₂ (M?=?Mn, Co) chromophore in which each central M(III) ion adopts a distorted octahedral geometry. Weak intermolecular H-bonding interactions are operative in these complexes to bind the molecular units. The antibacterial activity of 1–4 and their constituent Schiff bases has been tested against some common bacteria.     

Cyclooctenyl complexes of palladium(II) with multidentate N-heterocycles

[Pd(cod)(cotl)]ClO₄ (cod = 1,5-cyclooctadiene, cotl = cyclooctenyl, C₈H₁₃ ^–) undergoes substitutions with multidentate N-heterocycles: 1,3-bis(benzimidazolyl)benzene (L¹), 1,3-bis(1-methylbenzimidazol-2-yl)benzene (L²), 2,6-bis(benzimidazolyl)pyridine (L³) and 2,6-bis(1-methylbenzimidazol-2-yl)pyridine (L⁴) to yield mono/binuclear complexes: [Pd(cotl)(L¹)(OClO₃)], [Pd(cotl)(L)]ClO₄ (L = L² or L³) and [Pd(cotl)₂(L⁴)](ClO₄)₂. Dihalobridged binuclear complexes [PdX(cotl)]₂ (X = Cl or Br) undergo halogen bridge cleavages with the multidentate N-heterocycles to form binuclear complexes of the type [PdX(cotl)₂L] (X = Cl or Br; L = L¹, L², L³ or L⁴). The complexes were characterized by elemental analyses, ¹H-, ¹³C-n.m.r., i.r., far-i.r. and FAB-mass spectral studies.     

Synthesis,characterization, and biological activity of five new mixed-ligand palladium(II) complexes with ethylenediamine and 4-toluenesulfonyl-L-amino acid dianion

Five new palladium(II) complexes with 4-toluenesulfonyl-L-amino acid dianion and en, [Pd(en)(TsserNO)] (1), [Pd(en)(TsglyNO)] (2), [Pd(en)(TsalaNO)]?·?1.5H₂O (3), [Pd(en)(TsleuNO)]?·?H₂O (4), and [Pd(en)(TspheNO)]?·?2H₂O (5), have been synthesized and characterized by elemental analysis, IR, UV, ¹H NMR, and mass spectrometry. Crystal structure of 1 has been determined by X-ray diffraction analysis. The cytotoxicity was tested by MTT and SRB assays. The results indicate 1–5 exert cytotoxic effects against HL-60, Bel-7402, BGC-823, and KB cell lines and 5 displays the best cytotoxicity. The structure–activity relationships suggest that both amino acid and N-containing ligands have important effects on cytotoxicity.     

Self‐Assembly of Discrete Copper(I)‐Halide Complexes with Diacylthioureas

Three diacylthioureas 1,4‐C₆H₄[C(O)NHC(S)NHAr]₂ (Ar = 2,6‐iPr₂C₆H₃) ( L¹ , 1 ), 1,3‐C₆H₄[C(O)NHC(S)NHAr]₂ ( L² , 2 ), and 1,3‐C₆H₄[C(O)NHC(S)NHAr′]₂ (Ar′ = 2,6‐Me₂C₆H₃) ( L³ , 3 ) were synthesized and characterized. The Cu^I complexes from the reactions of bipodal ligands Lⁿ with CuX (X = Cl, Br, I) were structurally investigated by single‐crystal X‐ray diffraction methods. Treatment of L¹ with CuX gave the metallamacrocyclic complexes ( L¹ CuX)₂ [X = Cl ( 4 ), Br ( 5 ), I ( 6 )] with the ligand to metal in a ratio of 2:2, where both sulfur and halide anions function as terminal substituents. In contrast, when L² or L³ was reacted with CuBr, the two Lⁿ ligands coordinate to four copper atoms each in a bridging and terminal fashion to yield [ Lⁿ (CuBr)₂]₂ [n = 2 ( 7 ), 3 ( 8 )]. The obtained S₄Cu₄Br₄ core contains all four bromide anions in bridging positions. The reaction of L³ with CuX (X = Cl, I) gave the 3:3 trinuclear complexes ( L³ CuX)₃ [X = Cl ( 9 ) I ( 10 )], interconnected by halide bridges. The obtained diacylthioureas ( 1 – 3 ) and their Cu^I complexes ( 4 – 10 ) were also characterized by elemental analysis, FT‐IR, ¹H and ¹³C NMR spectroscopy.     

New diorganotin(IV) complexes with some Schiff bases derived from β-diketones: synthesis,spectral properties,thermal analysis,and antibacterial activity

The Schiff bases H₂L^a, H₂L^b, and H₂L^c have been prepared from the reaction of 2-amino-4-chlorophenol with acetylacetone, benzoylacetone, and dibenzoylmethane, respectively. Organotin(IV) complexes [SnPh₂(L^a)] (1), [SnPh₂(L^b)] (2), [SnPh₂(L^c)] (3), and [SnMe₂(L^c)] (4) have been synthesized from the reaction of SnPh₂Cl₂ and SnMe₂Cl₂ with these Schiff bases. The synthesized complexes have been characterized by elemental analysis and FT-IR, ¹H, ¹³C, and ¹¹⁹Sn NMR spectroscopy. Spectroscopic data suggest the Schiff bases are completely deprotonated and coordinated tridentate to tin via imine nitrogen and phenolic and enolic oxygen atoms; the coordination number of tin is five. Thermal decomposition of the complexes has been studied by thermogravimetry. The in vitro antibacterial activities of the Schiff bases and their complexes have been evaluated against Gram-positive (Bacillus subtilis and Staphylococcus aureus) and Gram-negative (Escherichia coli and Pseudomonas aeruginosa) bacteria. H₂L^a, H₂L^c, and all complexes exhibited good activities and have potential as drugs.     

Copper and palladium complexes with substituted pyrimidine-2-thiones and 2-thiouracils: syntheses,spectral characterization,and X-ray crystallographic study

Copper(I) and palladium(II) complexes containing 5-acetyl-6-methyl-1,2,3,4-tetrahydropyrimidine-2-thione (L¹), ethyl 4,6-dimethyl-2-thioxo-1,2,3,4-tetrahydropyrimidine-5-carboxylate (L²), cis-5-acetyl-6-ethyl-5,6-dihydro-2-thiouracil (L³), and 5,6-dihydro-2-thiouracil (L⁴) have been synthesized. All complexes were characterized by elemental analysis, IR, ¹H, and ¹³C NMR spectroscopy. To assign bands in the IR spectra of L¹ and L² and complexes with Cu(I) and Pd(II), deuterium substitution of movable protons at N-atoms was used. The crystal structures of two compounds, [Cu(L²)₂Cl] and [Pd(L⁴)₂Cl₂], were determined by X-ray single-crystal and powder diffraction, respectively. In [Cu(L²)₂Cl], copper has a rare coordination number of three and triangular surrounding of two neutral L² molecules, coordinated through sulfurs, and chloride. In [Pd(L⁴)₂Cl₂], palladium has a standard square-planar geometry, formed by two uracil molecules and two chlorides. A new method for the synthesis of 5,6-dihydro-2-thiouracil, starting from β-aminopropionic acid, was suggested.     

Organic acid effect on the structures of Cd(II) metal-organic complexes based on 2-(3-pyridyl)imidazo[4,5-<Emphasis Type="Italic">f</Emphasis>]-1,10-phenanthroline

Three new Cd(II) complexes consisting of phenanthroline derivative and organic acid ligands, formulated as [Cd₃(3-PIP)₂(L¹)₆] (I), [Cd(3-PIP)(L²)] · H₂O (II), and [Cd(3-PIP)(L³)] (III) (3-PIP = 2-(3-pyridyl)imidazo[4,5-f]-1,10-phenanthroline, HL¹ = 3,5-dinitrobenzoic acid, H₂L² = oxalic acid, H₂L³ = benzene-1,3-dicarboxylic acid), have been synthesized via the hydrothermal reaction and characterized by single-crystal X-ray diffraction, elemental analyses and FT-IR spectra. Complex I is a trinuclear structure. Complex II features a 1D zigzag chain. Complex III shows a twisted double chain of binuclear units sustained by double carboxylate bridges. Three complexes are further extended into 3D supramolecular frameworks by hydrogen bonding and π-π-stacking interactions. The structural differences among I–III show that the organic carboxylates have important effects on the structures. Furthermore, the supramolecular interactions are the critical factors in determining the final structures of the complexes. In addition, the thermal stabilities and luminescent properties of complexes I and II are also investigated.     

Substitutions of organopalladium(II) species with benzimidazole derivatives

The [Pd(cod)(cotl)]ClO₄ complex (cod = cycloocta-1,5-diene; cotl = cyclooctenyl, C₁₈H₁₃ ^–) undergoes substitutions with new Schiff base ligands containing benzimidazole L [L = 2-(2-N-n-propylidenephenyl)benzimidazole (L¹); 2-(2-N-i-propylidenephenyl)benzimidazole (L²); 2-(2-N-n-butylidenephenyl)benzimidazole (L³); 2-(2-N-i-butylidenephenyl)benzimidazole (L⁴)]. Facile displacement of cod by L occurs to produce complexes of the type [Pd(cotl)L]ClO₄· nMe₂CO (n= 0; L = L¹, L² or L³; n= 2, L = L⁴). Dihalobridge complexes of the type [Pd(cotl)X]₂(X = Cl or Br) undergo halogen-bridge cleavage with L¹–L⁴ to give mononuclear complexes of the type Pd(cotl)LX · nH₂O (n= 2, X = Cl, L = L¹; n= 0, X = Br, L = L¹; n= 0, X = Cl, L = L²; n= 0, X = Cl or Br, L = L³; n= 0, X = Cl, L = L⁴; n= 2, X = Br, L = L⁴) and a binuclear complex [Pd(cotl)Br]₂L². The complexes were characterised by physical properties, i.r., ¹H- and ¹³C-n.m.r. spectral techniques and by mass spectra. Probable structures have been proposed.     

Synthesis,crystal structures,and biological activity of oxovanadium(V) complexes with similar tridentate hydrazone ligands

Two new oxovanadium(V) complexes, [VOL¹(OEt)(EtOH)] (1) and [VOL²(OMe)(MeOH)] (2), were prepared by reaction of [VO(acac)₂] (where acac?=?acetylacetonate) with N′-(3-bromo-2-hydroxybenzylidene)-4-methylbenzohydrazide (H₂L¹) in ethanol and N′-(3-bromo-2-hydroxybenzylidene)-4-methoxybenzohydrazide (H₂L²) in methanol, respectively. Crystal and molecular structures of the complexes were determined by elemental analysis, infrared spectra, and single-crystal X-ray diffraction. The V ions have octahedral coordination. Thermal stability and the inhibition of urease of the complexes were studied.     

Synthesis,Characterization, Antimicrobial Activities,and Structural Studies of Lanthanide (III) Complexes with 1-(4-Chlorophenyl)-3-(4-fluoro/hydroxyphenyl)prop-2-en-1-thiosemicarbazone

Twelve coordinate lanthanide (III) complexes with the general composition [Ln L₃X_n(H₂O)_n] where Ln = Pr(III), Sm(III), Eu (III), Gd (III), Tb (III), Dy (III), X = Cl^?1, NO₃ ^?2, n = 2–7, and L is 1-(4-chlorophenyl)-3-(4-fluoro/hydroxyphenyl)prop-2-en-1- thiosemicarbazone have been prepared. The lanthanide complexes (5) were derived from the reaction between 1-(4-chlorophenyl)-3-(4-fluoro/hydroxyphenyl)prop-2-en-1-thiosemicarbazone (4) with an aqueous solution of lanthanide salt. Chalcone thiosemicarbazone ligand (4) was prepared by the reaction of [1-(4-chlorophenyl)-3-(4-fluoro/hydroxyphenyl)]prop-2-enone (chalcone) (3) with thiosemicarbazide in the presence of hot ethanol. All the lanthanide-ligand 1:3 complexes have been isolated in the solid state, are stable in air, and characterized on the basis of their elemental and spectral data.

Thiosemicarbazone ligands behave as bidentate ligands by coordinating through the sulfur of the isocyanide group and nitrogen of the cyanide residue. The probable structure for all the lanthanide complexes is also proposed. The chalcone thiosemicarbazone ligands and their lanthanide complexes have been screened for their antifungal and antibacterial studies. Some of the synthesized lanthanide complexes have shown enhanced activity compared with that of the free ligand.

Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.     

Palladium(II) thiohydrazone complexes: synthesis,spectral characterization and antifungal study

Palladium(II) complexes of type [Pd(L)Cl₂] [where, L?=?benzaldehyde-1,1-diphenyl-2-thiohydrazone (L¹), salicylaldehyde-1,1-diphenyl-2-thiohydrazone (L²), acetaphenone-1,1-diphenyl-2-thiohydrazone (L³) and cyclohexanone-1,1-diphenyl-2-thiohydrazone (L⁴)] have been synthesized. The thiohydrazones can exist as thione-thiol tautomers and coordinate as a bidentate N–S ligand. The ligands are found to be monobasic bidentate. The complexes have been characterized by elemental analysis, IR, mass, electronic, ¹H NMR spectroscopic studies. In vitro antifungal studies against fungi Aspergillus fumigatus, Aspergillus flavus and Aspergillus niger for some complexes have also been carried out.     

New Ni(II) complexes involving symmetrical bidentate N,O-donor Schiff base ligands: synthesis at ambient temperature,crystal structures,electrochemical study,antioxidant and cytotoxic activities

A new series of Ni(II) complexes, [Ni(L¹)₂] (1), [Ni(L²)₂] (2), [Ni(L³)₂] (3), and [Ni(L⁴)₂] (4), were synthesized at ambient temperature. The bidentate Schiff base ligands HL^1?4 have been obtained by the condensation reaction of 2-hydroxybenzaldehyde, 5-bromo-2-hydroxybenzaldehyde, 3-methoxy-2-hydroxy-benzaldehyde, and 4-methoxy-2-hydroxy-benzaldehyde, respectively, with 2-methoxyethylamine. The newly synthesized complexes were characterized by elemental analyses, FT-IR and UV–vis spectroscopy. The crystal structures of mononuclear Ni(II) complexes 2 and 3 were determined by the single-crystal X-ray diffraction technique. Electrochemical properties of the complexes were investigated in acetonitrile. The antioxidant properties of the Schiff base ligands and complexes were evaluated by two in vitro tests, DPPH radical scavenging and reducing power. The compounds were screened for their in vitro anticancer potential using gastric cancer cell lines by MTT assay. All ligands and complexes showed considerable cytotoxic activity against cancer cell lines (IC₅₀ = 0.2516–5.468 μg·mL^?1). The most promising result was achieved for complex 1 with the best IC₅₀ value of 0.2516 μg·mL^?1. It was found that the proliferation rate of MKN-45 cells decreased after treatment with the complexes in a dose-dependent way.