Formation constants of binary chelates of Cu(II)/Ni(II) with 4-chloro and 4-amino picolinic acid N-oxide in aquo organic media

The proton ligand constants of 4-chloro and 4-amino picolinic acid N-oxide and the formation constants of corresponding binary chelates of Cu(II) and Ni(II) have been measured at 30°C and 0.1M ionic strength in varying percentages of dioxane-water, acetone-water, ethanol-water and isopropanol-water. The results are discussed with reference to the change in dielectric constants of water in the presence of organic solvent, change in the structuredness of water, change in hydrogen bonding ability of the organic solvent in water, solvent basicity and proton solvation by organic solvent. The values have been compared with aqueous and mixed aqueous systems of picolinic acid N-oxide and 4-methoxy picolinic acid N-oxide.     

The determination of the stability constants of mixed ligand complexes of adenine and amino acids with Ni(II) by potentiometric titration method

A potentiometric titration technique has been used to determine the stability constants for the various complexes of Ni(II) with adenine (A) as primary ligand and selected amino acids (L) as secondary ligands. Ternary complexes of amino acids are formed in a stepwise mechanism, whereby (A) binds to Ni(II), followed by interaction with ligand (L), whereas thiol-containing ligands form ternary complexes through a simultaneous mechanism. The formation constants of the complexes were determined at 25 °C and ionic strength 0.1 M NaNO₃. The relative stabilities of the ternary complexes are compared with those of the corresponding binary complexes in terms of Δlog K values. The concentration distribution of the complexes are evaluated.     

In vitro antimicrobial-activity studies on the mixed ligand complexes of Hg(II) with 8-hydroxyquinoline and salicylic acids

A series of mixed ligand complexes of Hg(II) with the general formula Hg (OX) (SA) (where OX: 8-hydroxyquinoline, SA: salicylic, 5-chloro-, 3,5-dibromo, 3,5-diiodo, 3,5-dinitro, acetyl thiosalicylic acids) are isolated in pure state and characterised by elemental analysis and infrared data. The low molar conductance of the complexes in dimethylformamide indicates non-electrolyte nature. The antimicrobial activity of these complexes against various bacteria and fungi is studied which indicates that in several cases, the mixed ligand complexes possess fairly highly antimicrobial activity than the binary mercury-oxinate. The lipophilic tendency of these complexes and its influence on the antimicrobial activity is critically examined. A probable mechanism for the toxic action of these complexes against various organisms is discussed.     

Potentiometric studies of binary and ternary complexes of Zn(II) with triethylenetetramine as primary ligand and selected amino acids and DNA units as secondary ligands

The acid-base equilibria of triethylenetetramine. (Trien) and the formation equilibria of binary and ternary complexes of Zn(II) with Trien as primary ligand and some selected arnino acids and DNA units as secondary ligands have been investigated. The results showed the formation of a 11 Zn (Trien)²⁺ complex. At higher pH, the Zn (Trien)²⁺ complex is hydrolysed to give Zn (Trien) (OH)⁺ and Zn(Trien)(OH)₂ complexes. The fraction of the monohydroxo species attains a maximum of 81.3% at pH 10. The stability constantsK _Zn(Trien)A ^Zn(Trien) for the ternary complexes were determined. Histidine coordinates in a histamine-like way. Lysine and ornithine ligate by the two amino groups. Serine and methionine are bound in a glycine-like mode. However, penicillamine, cysteine and glutathione ligate partly like mercaptoethylamine and partly like mercaptopropionic acid. In the case of DNA complexes, inosine is bound through the n₁ atom. However, uracil, undine, thymine and thymidine ligate through the N₃ atom. The relative stabilities of ternary complexes are compared with those of the corresponding binary complexes in terms of logK values. The concentration distribution diagrams of the complexes are evaluated.     

Characterisation and antimicrobial activity studies of the mixed ligand complexes of Cu(II) With 8-hydroxyquinoline and salicylic acids

Mixed ligand complexes of copper(II) with 8-hydroxyquinoline and various salicylic acids were isolated. Elemental analysis, conductometric andIR data of these complexes were recorded. The esr and electronic spectral data of these complexes indicate distorted square planar coordination for central copper ion. The σ bond and inplane π bond coefficients α² and β² respectively, of these complexes indicate partial covalency in the metal ligand bonding. The antimicrobial activity studies show that the mixed ligand complexes act as more effective toxic agents thanbis (8-hydroxyquinolinato) copper(II) against certain bacteria and fungi. The lipophilic tendency of these complexes is determined and its influence on their antimicrobial activity is critically examined. A probable mechanism for the antimicrobial activity of these complexes is discussed Presented at theXXII International Conference on Coordination Chemistry held at Budapest, Hungary, Aug 23–27, 1982     

Complexation and ligand exchange in aqueous of Cu(II) and Ni(II) with hydrazides of some aromatic acids

Solvation and complexation of Cu(II) and Ni(II) with benzoic (L′), p-methoxybenzoic (L″), and isonicotinic (L) acid hydrazides in aqueous-ethanol solutions (ethanol mole fraction 0.07–0.68) were studied by pH-metry, spectrophotometry, and nuclear magnetic relaxation. The formation constants of the species M(L′)²⁺, M(L′) ₂ ²⁺ , M(L″)²⁺, M(L″) ₂ ²⁺ , M(LH)³⁺, M(L)²⁺, M(L)(LH)³⁺, and M(L) ₂ ²⁺ , where M = Cu²⁺ and Ni²⁺, were determined. With isonicotinic acid hydrazide, a change in the coordination mode was observed in an isomer of Cu(L) ₂ ²⁺ , with one of the ligands coordinating in the bidentate fashion, and the other, in the monodentate fashion via the pyridine nitrogen atom. The suggested structures were confirmed by analysis of the parameters of the ESR and electronic absorption spectra of the complexes. The rate constants of ligand exchange and formation of the complexes Cu(L′)²⁺, Cu(L′) ₂ ²⁺ , Cu(L″)²⁺, and Cu(L″) ₂ ²⁺ in aqueous solutions were determined from nuclear magnetic relaxation measurements; the reactions occur by the associative mechanism. A cyclic process of reduction of Cu(II) to colloidal copper in the presence of L″ and atmospheric oxygen is described.     

Coordination compounds of Co(II), Ni(II) and Cu(II) with capric acid hydrazide

The reaction of aquo-ethanolic solutions of Co(II), Ni(II) and Cu(II) salts and ethanolic solution of capric acid hydrazide (L) yielded paramagnetic, high-spin bis- and tris(ligand) chelate complexes. The tris(ligand) complexes, [ML ₃]X ₂·nH₂O [M=Co(II), Ni(II);X=NO ₃ ^– , ClO ₄ ^– , 1/2SO ₄ ^2– ], have an octahedral structure formed on account of the bidentate (NO) coordination of three neutral hydrazide molecules. In the bis(ligand) complexes,ML ₂(NCS)₂ [M=Co(II), Ni(II)] and CuL ₂ X ₂·nH₂O (X=NO ₃ ^– , ClO ₄ ^– and 1/2SO ₄ ^2– ), the oxoanions and NCS^– take also part in coordination. The complexes have been characterized by elemental analysis, IR spectra, magnetic measurements, molar conductivity and TG analysis.

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Caprinsäurehydrazid-Komplexe von Co(II), Ni(II) und Cu(II)

Zusammenfassung Durch die Reaktion von wäßrig-ethanolischen Lösungen von Co(II)-, Ni(II)-und Cu(II)-Salzen mit einer ethanolischen Lösung von Caprinsäurehydrazid (L) wurden paramagnetische high-spin Bis- und Tris-Ligand-Chelatkomplexe erhalten. Tris-Ligand-Komplexe des Typs [ML ₃ X ₂·nH₂O [M=Co(II), Ni(II);X=NO ₃ ^– , ClO ₄ ^– , 1/2SO ₄ ^2– ], die eine oktaedrische Struktur besitzen, entstehen durch die Koordination von drei neutralen zweizähnigen (NO)-Hydrazidmolekülen. Bei den Bis-Ligand-KomplexenML ₂(NCS)₂ [M=Co(II), Ni(II)], sowie bei den Bis-Ligand-Komplexen CuL ₂ X ₂·nH₂O (X=NO ₃ ^– , ClO ₄ ^– , 1/2SO ₄ ^2– ) nehmen bei der Koordination außer Hydrazid auch die Säurereste teil. Die Komplexe wurden durch Elementaranalyse, IR-Spektren, magnetische Messungen, molare Leitfähigkeit und TG-Analysen charakterisiert.

     

Synthesis,spectral studies,and antimicrobial activity of binary and ternary Cu(II), Ni(II), and Fe(III) complexes of new hexadentate Schiff bases derived from 4,6-diacetylresorcinol and amino acids

Two new hexadentate N₂O₄ donor Schiff bases, H₄L¹ and H₄L², were synthesized by condensation of 4,6-diacetylresorcinol with glycine and alanine, respectively. The structures of the ligands were elucidated by elemental analyses, IR, ¹H NMR, electronic, and mass spectra. Reactions of the Schiff bases with copper(II), nickel(II), and iron(III) nitrates in 1 : 2 molar ratio gave binuclear metal complexes and, in the presence of 8-hydroxyquinoline (8-HQ) or 1,10-phenanthroline (Phen) as secondary ligands (L′), mixed-ligand complexes in two molar ratios 1 : 2 : 2 and 1 : 2 : 1 (L¹/L² : M : L′). The complexes were characterized by elemental and thermal analyses, IR, electronic, mass, and ESR spectral studies, as well as conductivity and magnetic susceptibility measurements. The spectroscopic data reveal that the Schiff-base ligands were dibasic or tetrabasic hexadentate ligands. The coordination sites with the metal ions are two azomethine nitrogens, two oxygens of phenolic groups, and two oxygens of carboxylic groups. Copper(II) complexes were octahedral and square planar while nickel(II) and iron(III) complexes were octahedral. The Schiff bases, H₄L¹ and H₄L², and some of their metal complexes showed antibacterial activity towards Gram-positive (Staphylococcus aureus and Streptococcus pyogenes) and Gram-negative (Pseudomonas fluorescens and Pseudomonas phaseolicola) bacteria and antifungal activity towards the fungi Fusarium oxysporium and Aspergillus fumigatus.     

Theoretical study of inner and outer mononuclear complexes of Co(II), Ni(II), and Cu(II) with a compartmental hexadentate Schiff base derived from 3-formylsalicylic acid

Density functional theory (B3LYP/6-31G(d)) has been applied for optimization and calculation of the vibrational spectra of the compartmental hexadentate Schiff base derived from 3-formylsalicylic acid and 4,5-dichloro-1,2-phenylenediamine and 12 of its mononuclear complexes with Co(II), Ni(II), and Cu(II). Six of these complexes have the metal ion occupying the inner, N₂O₂, or the outer, O₂O₂, coordination sites in square planar geometry. The other six complexes possess octahedral geometry, occupying the inner or the outer coordination sites coordinating, additionally, to two waters. Significant changes in the ligand geometry have been observed in all complexes to permit efficient complexation with the metal. Assignments of the infrared bands are proposed based on calculations. Vibrational frequencies that are important for assignment and confirmation of the coordination sites are reported. Comparison of the total energies of the complexes reveals that inner complexes are more stable than corresponding outer complexes. Selectivity of metal ions to the coordination sites is also discussed.     

Studies on the mixed-ligand complexes of copper(II) with gallic acid and pyridine carboxylic acids and their benzologues

Summary The ternary complex formation of copper(II) with gallic acid (gal) and 2-hydroxy nicotinic acid (hyna), 2-mercapto nicotinic acid (mena), salicylic acid (sa) or thiosalicylic acid (tsa) as a second ligand in a 1:1:1 molar ratio has been investigated in 40% (v/v) ethanol using spectrophotometric andpH titration methods. The solution equilibria of the ternary systems have been determined and the stability constants of the mixed complexes has been evaluated. Considering all parameters, the Cu-gal-sa ternary system was proved as a suitable, rapid, and sensitive spectrophotometric indicator for determining traces of copper.The ternary system containingsa obeysBeer's law up to 3.4 µg·ml^–1 copper. The optimum range for the determination of copper (Ringbom) atpH 6.0 ranges from 0.63 to 1.74 µg·ml^–1 of copper. The molar absorptivity of the ternary complex is 1.3×10⁴l·mol^–1·cm^–1.

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Untersuchungen anmixed-ligand — Komplexen von Kupfer(II) mit 3,4,5-Trihydroxybenzoesäure und Pyridincarbonsäuren und ihren C-Homologen

Zusammenfassung Die Bildung ternärer Komplexe von Kupfer(II) mit 3,4,5-Trihydroxybenzoesäure (gal) und 2-Hydroxynicotinsäure (hyna), 2-Mercaptonicotinsäure (mena), Salicylsäure (sa) oder Thiosalicylsäure (tsa) in einem molaren Verhältnis von 1:1:1 wurde mittels spektrophotometrischer und potentiometrischer Methoden in 40% (v/v) Ethanol untersucht. Die Lösungsgleichgewichte der termären Systeme und die Stabilitätskonstanten der gemischten Komplexe wurden bestimmt. Unter Berücksichtigung aller Parameter erwies sich das termäre System Cu-gal-sa als geeigneter schneller und empfindlicher Indikator zur Spurenanalyse von Kupfer.Dassa enthaltende ternäre System gehorcht demBeerschen Gesetz bis zu einer Kupferkonzentration von 3.4 µg·ml^–1. Der optimale Bereich zur Bestimmung von Kupfer (Ringbom) beipH 6.0 erstreckt sich von 0.63 bis 1.74 µg Cu pro ml. Die molare Extinktion des ternären Komplexes beträgt 1.3×10⁴l·mol·cm^–1.

     

Binding interactions of mixed ligand copper(II) amino acid Schiff base complexes with biological targets: Spectroscopic evaluation and molecular docking

Three mixed ligand copper(II) complexes [Cu(o ‐vanillin‐l ‐tryptophan Schiff base)(diimine)] (diimine =2,2′‐bipyridine ( 1 ), 1,10‐phenanthroline ( 2 ) and 5,6‐dimethyl‐1,10‐phenanthroline( 3 )) were synthesized and characterized using analytical and spectral methods. The molecular structures of 1 – 3 were optimized using density functional theory (DFT) at B3LYP/LanL2DZ levels in the gas phase. Spectral and DFT studies suggest a distorted square pyramidal geometry around the copper ion. Binding interactions of 1 – 3 with calf thymus DNA and bovine serum albumin protein were studied using UV–visible and fluorescence spectroscopies, viscometric titrations and cyclic voltammetry and also using molecular docking analysis. Studies of the binding of the complexes with calf thymus DNA reveal intercalation, which is supported by molecular docking simulation. The DNA cleavage nature of 1 – 3 with pUC19 DNA shows that the complexes can cleave DNA without any external agents, and the efficiency follows the order 1  >  3  >  2 . Synchronous and three‐dimensional fluorescence spectral studies suggest that the secondary structures of the protein are altered by the complexes. Antioxidant studies reveal that the complexes have significant radical scavenging activity against DPPH. In vitro cytotoxic activity of the complexes was evaluated against breast cancer cells (MCF‐7), revealing that complex 2 exhibits higher cytotoxicity than the other complexes. Nuclear chromatin condensation and fragmentation were observed with DAPI staining assay. The mitochondrial membrane potential damage was studied by FITC staining assay. Flow cytometric analysis suggests that all the metal complexes induce cell apoptosis.     

Complexes of Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) with 4-chloro-2-methoxybenzoic acid anion

The complexes of 4-chloro-2-methoxybenzoic acid anion with Mn²⁺, Co²⁺, Ni²⁺, Cu²⁺ and Zn²⁺ were obtained as polycrystalline solids with general formula M(C₈H₆ClO₃)₂·nH₂O and colours typical for M(II) ions (Mn – slightly pink, Co – pink, Ni – slightly green, Cu – turquoise and Zn – white). The results of elemental, thermal and spectral analyses suggest that compounds of Mn(II), Cu(II) and Zn(II) are tetrahydrates whereas those of Co(II) and Ni(II) are pentahydrates. The carboxylate groups in these complexes are monodentate. The hydrates of 4-chloro-2-methoxybenzoates of Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) heated in air to 1273 K are dehydrated in one step in the range of 323–411 K and form anhydrous salts which next in the range of 433–1212 K are decomposed to the following oxides: Mn₃O₄, CoO, NiO and ZnO. The final products of decomposition of Cu(II) complex are CuO and Cu. The solubility value in water at 293 K for all complexes is in the order of 10^–3 mol dm^–3. The plots of χ_M vs. temperature of 4-chloro-2-methoxybenzoates of Mn(II), Co(II), Ni(II) and Cu(II) follow the Curie–Weiss law. The magnetic moment values of Mn²⁺, Co²⁺, Ni²⁺ and Cu²⁺ ions in these complexes were determined in the range of 76−303 K and they change from: 5.88–6.04 μ_B for Mn(C₈H₆ClO₃)₂·4H₂O, 3.96–4.75 μ_B for Co(C₈H₆ClO₃)₂·5H₂O, 2.32–3.02 μ_B for Ni(C₈H₆ClO₃)₂·5H₂O and 1.77–1.94 μ_B for Cu(C₈H₆ClO₃)₂·4H₂O.     

Structure,energetics and reactivity of ternary complexes of amino acids with Cu(II) and 2,2'-bipyridine by density functional theory. A combination of radical-induced and spin-remote fragmentations

The structures, electron distributions and dissociation energies of gas-phase ternary complexes of Cu(II) with 2,2'-bipyridine and leucine, isoleucine and lysine were addressed by density functional theory using the hybrid B3LYP functional, effective core potentials and the 6-31 + G(d) and LANL2DZ basis sets. The calculations confirm the previously suggested structures, in which amino acid carboxylates coordinate to the Cu atom by the carboxylate and alpha-amino groups in square-planar complexes. The dissociation energies for consecutive eliminations of CO(2) and alkyl radicals from isomeric singly charged complexes of leucine and isoleucine correlate with the ion relative abundances observed in collisionally activated dissociation mass spectra. Doubly charged lysine complexes show extremely low dissociation energies that are consistent with the <1 eV center-of-mass collision energies that were used in previous CAD studies. The calculated charge and spin densities point to radical-induced dissociations of singly charged complexes with an open-electron shell. In contrast, the unpaired electron is virtually inert in doubly charged, open-shell complexes that undergo charge-induced, spin-remote dissociations in the amino acid residues.     

Complexing tendencies of UO 22+ and Th4+ in their mixed ligand complexes with aminopolycarboxylates and resorcinol or its derivatives

Formation contants (log K _MAL ^MA ) of mixed ligand complexes MAL, where M = UO ₂ ²⁺ or Th⁴⁺, A = IMDA, NTA, HEDTA, EDTA, CDTA or DTPA, and L = resorcinol (res), 2-methyl resorcinol (2-Me-res), 5-methyl resorcinol (5-Me-res) or 4-chloro resorcinol (4-Cl-res), have been determined pH-metrically by the Irving-Rossotti approach at 25°C and at an ionic strength,I = 0.2(moldm⁻³KNO₃). The observed stability sequences are IMDA > NTA > HEDTA > EDTA > CDTA > DTPA, and 4-Cl-res > 5-Me-res > 2-Me-res > res with respect to primary and secondary ligands, respectively. Th⁴⁺ forms more stable mixed complexes than UO ₂ ²⁺ . The A ΔlogK values are negative due mainly to the charge repulsion involved in the complexation MA + L⇋MAL.     

Complexation of N-bis[2-(1,2-dicarboxyethoxy)ethyl]aspartic acid with Fe(II), Co(II), and Ni(II) in aqueous solution

In a search for environment-friendly metal chelating ligands for industrial applications, the protonation and complex formation equilibria of N-bis[2-(1,2-dicarboxyethoxy)ethyl]aspartic acid (BCA6) with Fe(II), Co(II), and Ni(II) ions in aqueous 0.1 M NaCl solution were studied at 25°C by potentiometric titration. The model for complexation and the stability constants of different complexes were determined for each metal ion using SUPERQUAD. In all cases, complex formation was dominated by stable ML^4? complexes.     

Synthesis of the first mixed ligand Mn (II) and Cd (II) complexes of 4-methoxy-pyridine-2-carboxylic acid,molecular docking studies and investigation of their anti-tumor effects in vitro

The first mixed ligand Mn (II) and Cd (II) complexes containing 4-methoxy-pyridine-2-carboxylic acid (4-mpic) and 4,4′-dimethyl-2,2′-bipyridine (dmbpy) were synthesized in this study. The geometric structures of [Mn(4-mpic)₂(dmbpy)] (complex 1 ) and [Cd(4-mpic)₂(dmbpy)] (complex 2 ) were determined by single crystal X-Ray diffraction method. FT-IR and UV–Vis spectra were also recorded to investigate vibrational and electronic properties of complexes 1 and 2 . Density functional theory (DFT) calculations were also carried out to provide a deep understanding in geometric, spectroscopic, electronic and nonlinear optical (NLO) properties of complexes 1 and 2 . The first-order hyperpolarizibility (β) parameter calculated as 332.9736 × 10⁻³⁰ esu demonstrated that complex 1 is an extremely promising candidate to NLO materials. Natural bond orbital (NBO) analysis not only verified the distorted octahedral geometries of central metal ions, but also found out the high-energy interactions responsible for biological activities for complexes 1 and 2 . Anti-cancer activities of complexes 1 and 2 were tested on human breast carcinoma cell line MCF-7 (ER and PR positive, HER2 negative) and the triple negative breast carcinoma cell line MDA-MB 231 (ER, PR and HER2 negative). Dose–response relationship derived from MTT assays indicates that complexes 1 and 2 are showing concentration-dependent effects, which could suggest a potential use for these drug combinations in cancer cell lines.     

Synthesis,characterization and antibacterial activity of some new complexes of Cu(II), Ni(II), VO(II), Mn(II) with Schiff base derived from 4-amino-2,3-dimethyl-1-phenyl-3-pyrazolin-5-one

Coordination compounds of Cu(II), VO(II), Ni(II), and Mn(II) with the Schiff base obtained through the condensation of 4-amino-2,3-dimethyl-1-phenyl-3-pyrazolin-5-one with 3-formyl-6-methyl-chromone were synthesized. The characterization of the newly formed compounds was done by ¹H NMR, UV–Vis, IR, ESR spectroscopy, elemental analysis and molar electric conductibility. The crystal structure of 1-phenyl-2,3-dimethyl-4-(N-3-formyl-6-methyl-chromone)-3-pyrazolin-5-one (HL) has been determined by X-ray diffraction studies, as well as the one of its copper(II) complex [CuL(OAc)]·CH₃OH which contains an anionic ligand and an acetate in the coordination sphere of the metal. The single crystal X-ray structure for (HL) was analyzed for its various weak H-bonding and dimeric association.     

Unusual co-ordination behaviour of imidazole-4-acetic acid. Synthesis, crystal structure and vibrational studies of one-dimensional co-ordination polymer of zinc(II) with two different ligand forms

This work is devoted to structural and vibrational studies of novel 1D polymeric zinc(II) complex [ZnCl(ia)(Hia)]·H₂O (infinity) [Hia=imidazole-4-acetic acid]. It has been found for the first time that the ia anion is acting as bidentate bridging ligand with N1 and carboxylate oxygen atoms as binding centres. The quasi-tetrahedral coordination polyhedron is completed by one chloride anion and monodentate Hia ligand bonded with zinc(II) cation via carboxylate oxygen atom. The compound crystallise in the triclinic P space group with Z=2. The polymer chains are held together by hydrogen bonding network involving the N---H and carboxylate groups, chloride ions and water molecules. The differences between normal vibrations of two ligand forms present in the complex are discussed on the basis of the density functional calculations (DFT) performed for natural and N-deuterated isotopomers. The assignment of the observed MIR and Raman bands is given in terms of potential energy distribution (PED).     

Complexation of [S,S,S]- and [R,S,R]-isomers of N-bis [2-(1,2-dicarboxyethoxy)ethyl] aspartic acid with Mg(II), Ca(II), Mn(II), Fe(III), Cu(II) and Zn(II) ions in aqueous solution

In a search for environmentally friendly metal chelating ligands for industrial applications, the protonation and complex formation equilibria of [S,S,S]- and [R,S,R]-isomers of N-bis[2-(1,2-dicarboxyethoxy)ethyl] aspartic acid (BCA6) with Mg(II), Ca(II), Mn(II), Fe(III), Cu(II) and Zn(II) ions in aqueous 0.1 M NaCl solution were studied at 25°C by potentiometric titration. The model for complexation and the stability constants of the different complexes were determined for each metal ion using the computer program SUPERQUAD. With all metal ions (M ⁿ⁺), stable ML ^n?6 complexes dominated complex formation for both isomers. Differences in complexation models were found for binuclear species.     

Functionalization of superparamagnetic Fe3O4@SiO2 nanoparticles with a Cu(II) binuclear Schiff base complex as an efficient and reusable nanomagnetic catalyst for N‐arylation of α‐amino acids and nitrogen‐containing heterocycles with aryl halides

Fe₃O₄@SiO₂ nanoparticles was functionalized with a binuclear Schiff base Cu(II)‐complex (Fe₃O₄@SiO₂/Schiff base‐Cu(II) NPs) and used as an effective magnetic hetereogeneous nanocatalyst for the N‐arylation of α‐amino acids and nitrogen‐containig heterocycles. The catalyst, Fe₃O₄@SiO₂/Schiff base‐Cu(II) NPs, was characterized by Fourier transform infrared (FTIR) and ultraviolet‐visible (UV‐vis) analyses step by step. Size, morphology, and size distribution of the nanocatalyst were studied by transmission electron microscopy (TEM), scanning electron microscopy (SEM), and dynamic light scatterings (DLS) analyses, respectively. The structure of Fe₃O₄ nanoparticles was checked by X‐ray diffraction (XRD) technique. Furthermore, the magnetic properties of the nanocatalyst were investigated by vibrating sample magnetometer (VSM) analysis. Loading content as well as leaching amounts of copper supported by the catalyst was measured by inductive coupled plasma (ICP) analysis. Also, thermal studies of the nanocatalyst was studied by thermal gravimetric analysis (TGA) instrument. X‐ray photoelectron spectroscopy (XPS) analysis of the catalyst revealed that the copper sites are in +2 oxidation state. The Fe₃O₄@SiO₂/Schiff base‐Cu(II) complex was found to be an effective catalyst for C–N cross‐coupling reactions, which high to excellent yields were achieved for α‐amino acids as well as N‐hetereocyclic compounds. Easy recoverability of the catalyst by an external magnet, reusability up to eight runs without significant loss of activity, and its well stability during the reaction are among the other highlights of this catalyst.