Syntheses,equilibrium, and structural studies of copper(II) and nickel(II) complexes with a tripodal alanine-based ligand

A heptadentate ligand, tris[(L)-alanyl-2-carboxamidoethyl]amine (H₃trenala), has been synthesized as its tetrahydrochloride salt; its protonation constants and the stability constants of the copper(II) and nickel(II) chelates have been determined by potentiometry. Mononuclear species with protonated, neutral, or deprotonated forms of the ligand, [Cu(H₅trenala)]⁴⁺, [M(H₄trenala)]³⁺, [M(H₃trenala)]²⁺, [M(H₂trenala)]⁺, and [M(Htrenala)] (M?=?Cu²⁺ and Ni²⁺) have been detected in all cases, while only Cu²⁺ gives dinuclear [Cu₂(H₂trenala)]²⁺, [Cu₂(Htrenala)]²⁺, [Cu₂(trenala)]⁺, and [Cu₂(trenala)(OH)] species. Two dinuclear copper(II) complexes have been prepared and characterized by spectroscopic techniques (IR, UV-Vis, mass electro-spray) and thermogravimetric analysis.     

Coordination modes of histidine- or methioninehydroxamic acids in copper(II) mixed-ligand complexes with ethylenediamine in aqueous solution

The stability constants and coordination modes of the mixed-ligand complexes formed by copper(II) ion and ethylenediamine as a primary ligand and methioninehydroxamic acid (Metha) or histidinehydroxamic acid (Hisha) as a secondary ligand L were determined by potentiometric titration, UV–Vis and EPR spectroscopy. The obtained results suggest the formation of mixed-ligand species in basic solution with 4N coordination – both amine and hydroxamic nitrogens of Metha or Hisha (NH₂, N_ha) and two amine nitrogens of en (2 × NH₂) in the equatorial plane.     

Equilibrium and spectral studies of putrescine complexes with copper(II)

Summary It has been found that in the putrescine-copper system several types of complex compounds (MHL,ML,ML ₂,ML ₂OH) are formed. In thepH range of 7–9, despite a multiple excess of ligand, a precipitation occurs. When adenosine is introduced to the system, the ability to observe the complexation reaction in solution is largely increased, because the additional ligand prevents precipitation. On the basis of computer analysis of potentiometric titration data the stability constants of the compounds have been determined. The coordination mode of the complexes is discussed.

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Gleichgewichte und spektroskopische Untersuchungen an Putrescin-Komplexen mit Kupfer(II)

Zusammenfassung Es wurde festgestellt, daß sich im Putrescin-Kupfer System einige Typen von Komplexen bilden (MHL,ML,ML ₂ andML ₂OH). ImpH-Bereich von 7–9 tritt trotz eines mehrfachen Ligandenüberschusses ein Niederschlag auf. Bei Einführung von Adenosin in das System wird die Beobachtbarkeit der Komplexreaktion verbessert, da der zusätzliche Ligand die Niederschlagsbildung verhindert. Mittels Computeranalyse der potentiometrischen Titrationsdaten wurden die Stabilitätskonstanten der Verbindungen ermittelt. Die Art der Komplexierung wird ebenfalls diskutiert.

     

A tetranuclear complex from the employment of pyridine-2,6-dimethanol in copper(II) nitrate chemistry: Synthetic,structural and magnetic studies

The use of pyridine-2,6-dimethanol (pdmH₂) in copper(II) nitrate chemistry is reported. The reaction of Cu(NO₃)₂·3H₂O with one equivalent of pdmH₂ in MeCN affords the known mononuclear complex [Cu(pdmH₂)₂](NO₃)₂ (1) in high-yield. The reaction of 1 and NaOMe in an 1:1 ratio, as well as the reaction between Cu(NO₃)₂·3H₂O, pdmH₂ and NaOMe in an 1:1:1 ratio, in MeOH gives the tetranuclear complex [Cu₄(NO₃)₂(pdmH)₄(H₂O)(MeOH)](NO₃)₂ (2) in moderate yields. The cation of 2 possesses a slightly distorted tetrahedral Cu₄ topology with a [Cu₄(μ₂-OR)₄]⁴⁺ core. The pdmH⁻ ions behave as η¹:η¹:η²:μ₂ ligands. Strong intramolecular hydrogen bonds and π–π stacking interactions provide thermodynamic stability on compound 2. Variable-temperature, solid-state dc magnetic studies were carried out on complex 2 in the 2.0–300 K range. The data indicate predominant antiferromagnetic exchange interactions and a resulting S = 0 ground state, which is expected for a solely, μ₂-alkoxide-bridged system with obtuse Cu–O–Cu bond angles that magnetically behaves as a Cu₄ ring. A simplified 1 − J model was found to be adequate to describe the variable-temperature dc susceptibility data. The data were fitted to the appropriate equation derived from the Hamiltonian H = −J₁(S₁ · S₂ + S₂ · S₄ + S₃ · S₄ + S₁ · S₃), giving the parameters J₁ = −99.5 cm⁻¹ and g = 2.11(4). The combined work demonstrates the ligating flexibility of the pdmH₂ chelate and its usefulness in the synthesis of oligo- and polynuclear Cu^II_x clusters with interesting structural and magnetic properties, without requiring the co-presence of carboxylate ligands.     

Photofunctional supramolecular solution systems of chiral Schiff base nickel(II), copper(II), and zinc(II) complexes and photochromic azobenzenes

Preparations, crystal structures, electronic and CD spectra are reported for new chiral Schiff base complexes, bis(N-R-1-naphthylethyl-3,5-dichlorosalicydenaminato)nickel(II), copper(II), and zinc(II). Nickel(II) and copper(II) complexes adopt a square planar trans-[MN₂O₂] coordination geometry with Δ(R,R) configuration. While zinc(II) complex adopts a compressed tetrahedral trans-[MN₂O₂] one with Δ(R,R) configuration and exhibits an emission band around 21 000 cm⁻¹ (λ_ex = 27 000 cm⁻¹). Absorption and CD spectra were recorded in N,N′-dimethylformamide, acetone, methanol, chloroform, and toluene solutions to discuss relationships between spectral shifts of d–d and π–π^∗ bands by structural changes of the complexes and physical properties of the solvents. Moreover, we have attempted to investigate conformational changes of the complexes induced by photoisomerization of azobenzene, 4-hydroxyazobenzene, or 4-aminoazobenzene, in various solutions under different conditions. Weak intermolecular interactions between complexes and azobenzenes are important for the phenomenon by conformational changes of bulky π-conjugated moieties of the ligands.     

Synthesis of unsymmetrical compartmental oxime nickel(II) and copper(II) complexes: spectral, electrochemical and magnetic studies

A new series of binuclear unsymmetrical compartmental oxime complexes (1–5) [M₂L] [M=Cu(II), Ni(II)] have been synthesized using mononuclear complex [ML] (L=1,4-bis[2-hydroxy-3-(formyl)-5-methylbenzyl]piperazine), hydroxylamine hydrochloride and triethylamine. In this system there are two different compartments, one has piperazinyl nitrogens and phenolic oxygens and the other compartment has two oxime nitrogens and phenolic oxygens as coordinating sites. The complexes were characterized by elemental and spectral analysis. Electrochemical studies of the complexes show two step single electron quasi-reversible redox processes at cathodic potential region. For copper complexes E¹ _pc=−0.18 to −0.62 and E² _pc=−1.18 to −1.25 V, for nickel complexes E¹ _pc=−0.40 to −0.63 and E² _pc=−1.08 to −1.10 V and reduction potentials are sensitive towards the chemical environment around the copper and nickel atoms. The nickel(II) complexes undergo two electrons oxidation. The first one electron oxidation is observed around +0.75 V and the second around +1.13 V. ESR Spectra of the binuclear copper(II) complexes [Cu₂L](ClO₄), [Cu₂L(Cl)], [Cu₂L(NO₃)] shows a broad signal at g=2.1 indicating the presence of coupling between the two copper centers. Copper(II) complexes show a magnetic moment value of μ_eff around 1.59 B.M at 298 K and variable temperature magnetic measurements show a −2J value of 172 cm⁻¹ indicating presence of antiferromagnetic exchange interaction between copper(II) centres.     

Structure of Cu(II) complexes of pyridine-2,6-dithiocarbomethylamide

The crystal structure of the paramagnetic pyridine-2,6-dithiocarbomethyl-amide—copper(II) chloride (CuPDTA-Cl₂) is described: C₉H₁₁N₃S₂CuCl₂·H₂O, monoclinic, P2₁/n,a=9.163 (2),b=8.925 (5),c=17.590 (9) Å, =102.08 (1)°,Z=4,d _x =1.784g cm^–3. The structure was refined to a residual ofR=0.059, The copper is coordinated in a square—pyramidal arrangement by the pyridine nitrogen, the two thioamide sulfur atoms and the two chloride ions. The shortest Cu—Cu distance in the crystal is 5.02 Å, leading to only very weak antiferromagnetism. Spectroscopic and magnetic data are given for additional members of the CuPDTA-X [X=Cl₂, Br₂, I₂, (NO₃)₂, (SCN)₂,Py] complex type, which suggest a large degree of structural resemblance with the CuPDTA-Cl₂ complex.

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Struktur von Kupfer(II)-Komplexen des Pyridin-2,6-dithiocarbomethylamids

Zusammenfassung Die Kristallstruktur des paramagnetischen Pyridin-2,6-dithiocarbomethyl-amid Kupfer(II)-chlorids wurde bestimmt: C₉H₁₁N₃S₂CuCl₂·H₂O, monoklin, P2₁/n,a=9,163 (2),b=8,925 (5),c=17,590 (9) Å, =102,08 (1)°,Z=4,d _x =1,784g cm^–3. Die Struktur wurde bis zu einemR-Faktor vonR=0,059 verfeinert. Das Kupfer-Zentralatom zeigt quadratisch-pyramidale Koordination durch den Pyridin-Stickstoff, die beiden Thioamid Schwefelatome sowie zwei Chloridionen. Der kürzeste Cu—Cu-Abstand im Kristall beträgt 5,02 Å, was zu einem nur sehr schwachen Antiferromagnetismus führt. Spektroskopische und magnetische Größen werden für weitere Derivate vom CuPDTA-X Typ [X=Cl₂, Br₂, I₂, (NO₃)₂, (SCN)₂, Pyridin] angegeben, und im Sinne einer großen strukturellen Ähnlichkeit mit dem CuPDTA-Cl₂ interpretiert.

     

Hydrogen bonding networks and proton transfer compounds of cobalt(II) and copper(II) with pyridine-2,5-dicarboxylate

Three Co(II) and Cu(II)-pyridine-2,5-dicarboxylate (pydc) proton transfer compounds with 1,4-butanediamine (ben) and 2,2-dimethylpropane-1,3-diamine (dmpen), trans-(H₂ben)[Co(pydc)₂(H₂O)₂]·4H₂O (1), trans-(H₂dmpen)[Co(pydc)₂(H₂O)₂]·2H₂O (2) and (H₂ben)₂[Cu₂(μ-pydc)₄(H₂O)₂] (3) have been synthesized and characterized by the methods of elemental, spectroscopic (IR and UV-Vis), thermal (TG/DTG, DTA) analysis, magnetic measurement and single crystal X-ray diffraction. The crystallographic analysis revealed that the complexes consist of [Co(pydc)₂(H₂O)₂]²⁻ anion, bis(protonated) diamine cation (H₂ben for 1 and H₂dmpen for 2) and four and two crystal water molecules, respectively. The Co(II) ions are coordinated by two pydc and two aqua ligands. The bis(deprotonated) pydc ligands coordinate to the Co(II) ions through the nitrogen atom of pyridine ring and the oxygen atom of carboxylate group, creating a chelate ring. The distorted octahedral geometries are completed by two trans aqua ligands at axial positions. The molecular structure of the complex 3 consists of dinuclear [Cu₂(μ-pydc)₄(H₂O)₂]⁴⁻ units and bis(protonated) 1,4-butanediammonium cation. In the structure, each Cu(II) ion is coordinated by two nitrogen and two oxygen atoms from two pydc ligands and one oxygen atom from aqua ligand, forming a distorted square pyramidal geometry.     

Studies on mononuclear chelates derived from substituted Schiff-base ligands (part 6): synthesis and characterization of a new 3-ethoxysalicyliden- p -aminoacetophenoneoxime and its complexes with cobalt(II), nickel(II), copper(II) and zinc(II)

Schiff-base complexes of cobalt(II), nickel(II), copper(II) and, zinc(II) with 3-ethoxysalicyliden-p-aminoacetophenoneoxime (HL) were prepared and characterized on the basis of elemental analyses, IR, ¹H- and ¹³C-NMR, electronic spectra, magnetic susceptibility measurements, molar conductivity and thermogravimetric analyses (TGA). A tetrahedral geometry has been assigned to the complexes.     

Structure of the nitrosoguanidine complexes of nickel(II) and copper(II) by X-ray crystallography and computational analysis

Using the X-ray structure of solid nitrosoguanidine (ngH), potential structures of its complex with aqueous nickel(II) were surmised. A single-crystal X-ray diffraction determination of the Ni(II) complex confirmed one of these configurations. The X-ray structural parameters were compared with the most stable gaseous configurations derived from ab initio-MO calculations. The lowest energy calculated configuration of the nickel(II) complex and the X-ray crystal structure are in excellent agreement. The neutral diamagnetic, planar, red-colored [bis(nitrosoguanidate)nickel(II)] complex, [Ni(ng)₂]°, is nitrogen coordinated in the trans configuration. It is highly insoluble in all solvents investigated, and has essentially the same crystal symmetry and unit-cell dimensions as the free ligand. In ligand crystals, two molecules have four nitrogen atoms aligned in a plane such that they are suitable for coordination to a nickel ion (1.945, 2.064?Å), when it is at the 1/2,?1/2,?1/2 unit-cell position. Furthermore, the complexes stack, as in [Ni(dmg)₂]°, placing the nickel ions in nearly perfect positions for weak metal–metal bonding between adjacent layers at the near optimum distance of 3.65(1)?Å. This results in a tight, linear macromolecule having low volatility and the extremely low solubility observed. As far as we are aware this is the first instance in which a ligand crystal structure is essentially the same as the complex it forms, with minor differences in bond distances, angles and torsion angles, and suggests some potentially unique properties and applications for this material.     

A study of complex equilibria of phenylglycine with nickel(II), copper(II) and zinc(II) in water and in water - methanol solution

The complex equilibria of the systems phenylglycine — nickel(II), copper(II) and zinc(II) in water and in water — methanol solution have been studied by computer analysis of potentiometric data. The mode of coordination has been established by¹³C-NMR and IR studies.

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Gleichgewichtsuntersuchungen der Komplexbildung von Phenylglycin mit Nickel(II), Kupfer(II) und Zink(II) in Wasser und Wasser - Methanol-Lösung

Zusammenfassung Anhand einer Computer-Analyse von potentiometrischen Daten wurden die Bildungsgleichgewichte in den Systemen Phenylglycin — Nickel(II), Kupfer(II) und Zink(II) untersucht. Der Koordinationstyp wurde mittels¹³C-NMR und IR festgestellt. Die Lösungsmittel waren Wasser und Wasser — Methanol.

     

Mononuclear and homobinuclear cobalt(II), nickel(II) and copper(II) complexes with mono and bis-azocompounds derived from 2,7-dihydroxynaphthalene and anthranilic acid or o-aminophenol

Two new series of mononuclear and homobinuclear Co(II), Ni(II) and Cu(II) complexes with mono- and bis-azo compounds derived from 2,7-dihydroxynaphthalene and anthranilic acid or o-aminophenol are prepared and characterized by elemental and thermal analyses, conductance, IR, electronic, ESR spectra and magnetic moment measurements. The ligand field splitting parameters and Racah constant are calculated. The spectral and magnetic results obtained are utilized to determine the geometries around the metal(II) ion. The geometry of the complex formed depends on the structure of the ligand and the type of metal(II) ion. The mode of bonding of the ligand with the metal ions is deduced from IR spectra.     

Synthesis, structural characterization and antibacterial activity of 2,6-diacetylpyridine bis(benzenesulfonohydrazide) Schiff bases and their copper(II) complexes

2,6-Diacetylpyridine bis(benzenesulfonohydrazide) Schiff bases (L¹, L² and L³) and their Cu(II) complexes of the general formula [CuL·H₂O] were synthesized and characterized by various spectroscopic techniques. The crystal structure of [CuL³·(py)]·py was investigated by single crystal X-ray structure analysis. The Cu(II) cation has near square pyramidal, penta-coordinate geometry. The binegatively charged tetradentate Schiff base is asymmetrically coordinated to the Cu(II) ion via the pyridine N atom, the azomethine N atom, the sulfonyl O atom and the deprotonated hydrazine N atom. There is a pyridine molecule apically coordinated to the Cu(II) ion. All the Schiff bases and their copper(II) complexes were screened by the disc diffusion method against multi-drug resistant (MDR) gram-negative and gram-positive bacteria. The minimum inhibitory concentration (MIC) values were also determined. These results show that the antibacterial activity of the Schiff bases against Methicillin-resistant Staphylococcus aureus (MRSA) is enhanced when they are chelated with the copper(II) ion.     

Nickel(II), copper(II) and zinc(II) complexes withN-phenylglycine in water-methanol solution

The complex equilibria of the Ni(II), Cu(II), and Zn(II) complexes withN-phenylglycine have been studied by computer analysis of potentiometric data. The mode of coordination has been established by¹H NMR and IR studies.

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Nickel(II), Kupfer(II) und Zink(II)-Komplexe mitN-Phenylglycin in Wasser-Methanol-Lösung

Zusammenfassung Anhand der Computer-Analyse von potentiometrischen Daten wurden die Bildungsgleichgewichte von Nickel(II), Kupfer(II) und Zinc(II)-Komplexen mitN-Phenylglycin untersucht. Zur Bestätigung des Koordinationstyps wurden¹H-NMR- und IR-Messungen vorgenommen.

     

Chelating resin containing s-bonded dithizonefor the separation of copper(II), nickel(II) and zinc(II)

Analytical and physicochemical properties of a crosslinked poly (vinyl pyridine) based resin containing dithizone were examined. The resin was further used for the preconcentration of copper, nickel and zinc at batch and column level. Various conditions such as pH, equilibration time, temperature were optimised for the maximum loading of copper, nickel and zinc. The loading capacities of the resin for copper, nickel and zinc were observed to be 0.51, 0.59 and 0.65 mmol g⁻¹ of dry resin respectively. Elution of loaded copper, nickel and zinc from the resin was done by using 0.1 M HCl, 0.1 M H₂SO₄ and 0.1 M HNO₃ respectively. Separation of copper, nickel and zinc in binary and ternary mixtures was achieved without any cross contamination.     

Stabilities and coordination modes of histidine in copper(II) mixed-ligand complexes with ethylenediamine,diethylenetriamine or N,N,N′,N″,N″-pentamethyldiethylenetriamine in aqueous solution

Solution equilibrium studies on the Cu(II)–polyamine–histidine ternary systems (polyamine: ethylenediamine (en), diethylenetriamine (dien), N,N,N′,N″,N″-pentamethyldiethylenetriamine (Me₅dien)) have been performed by pH-potentiometry, UV–Vis spectrophotometry and EPR methods. The obtained results suggest the formation of the mixed-ligand complexes with [Cu(A)(His)]⁺ stoichiometry in all studied systems. Additionally, in the systems with dien and Me₅dien protonated [Cu(A)(H–His)]²⁺ species also exists in acid solution. Our spectroscopic results indicate the tetragonal geometry for the [Cu(en)(His)]⁺, the geometry slightly deviated from square pyramidal for the [Cu(dien)(His)]⁺ and strongly deviated from square pyramidal towards trigonal bipyramidal for the [Cu(Me₅dien)(His)]⁺ species. The coordination modes in these mixed-ligand complexes are discussed.     

Copper(II) ion hydrolysis in aqueous solution

A copper(II) ion-selective-electrode potentiometric method was used to determine the first and second hydrolysis constants of Cu²⁺. Special techniques prevented copper(II) hydroxide precipitation, and copper(II) carbonate and cipper(II) organic complexation during the titration of the experimental solution over the pH range 6.8–8.4. The large change in the total copper concentration during the titration due to adsorption of copper onto the vessel walls was accounted for by measuring the total copper concentration at each pH by atomic absorption spectrophotometry. The two hydrolysis constants were determined at 25°C in 0.7 and 0.05m NaClO₄ media. The measured stability constants are independent of the copper concentration and yield similar zero ionic strength values. Also, the stepwise equilibrium constants decrease as the ligand number increases.     

Complexation of copper(I) by thiourea in acidic aqueous solution

The interaction of copper(II) and copper(I) with thiourea(Tu) has been investigated by UV and visible spectrophotometry. Over the range of concentrations of copper(I) and Tu(0.1–20)×10^–3 mol-dm^–3 in acid aqueous solutions there are two complexes, CuTu₂ ⁺ (log ₂=11.1) and the other has the ratio Cu/Tu=1/1 with the likely composition Cu₂Tu₂ ²⁺ with log ₂₂=18.5. By the determination of copper(0) solubility in acid thiourea solution and potentiometric measurements it was shown that the potential of the copper electrode is that of a non-equilibrium (corrosive) electrode.     

Magnetic and spectral studies on nickel(II) and copper(II) dithiocarbazates derived from isoniazid

Some isonicotinoyldithiocarbazate complexes of nickel(II) and copper(II), of general formulae M(IN-Dtcz)₂, [M(IN-DtczH)₂]Cl₂, and [M(IN-DtczH-Sal)₂]Cl₂ (M?=?Ni(II), Cu(II); INDtcz?=?isonicotinoyldithiocarbazate; IN-DtczH?=?isonicotinoyldithiocarbazic acid; IN-DtczH-Sal?=?salicylaldehyde Schiff base of isonicotinoyldithiocarbazic acid), have been synthesized. These complexes have been investigated by elemental analyses, mass, room temperature infrared and electronic spectra, and variable temperature magnetic susceptibility measurements. The three nickel(II) dithiocarbazates and [Cu(IN-DtczH-Sal)₂]Cl₂ exhibit NS linkage of the ligands, while Cu(IN-Dtcz)₂ and [Cu(IN-DtczH)₂]Cl₂ have ONS binding of the ligands. The nickel(II) dithiocarbazates have [NiN₂S₂] chromophore. Magnetic and solution electronic absorption spectral data reveal square-planar geometry for Ni(IN-Dtcz)₂ and the existence of square-planar–tetrahedral equilibrium for [Ni(IN-DtczH)₂]Cl₂ and [Ni(IN-DtczH-Sal)₂]Cl₂. Copper(II) dithiocarbazates, namely Cu(IN-Dtcz)₂, [Cu(IN-DtczH)₂]Cl₂, with ONS ligands having dimeric or polymeric octahedral structures, and [Cu(IN-DtczH-Sal)₂]Cl₂, with NS binding having dimeric square-planar structure, exhibit antiferromagnetism. Superexchange pathway involving the bridging nitrogen and sulfur of the isonicotinoyldithiocarbazate ligands rather than direct metal–metal exchange is suggested for antiferromagnetic interactions. The spin exchange parameter, ?2J?=?202.14 and 29.26?cm^?1, has been evaluated for [Cu(IN-DtczH)₂]Cl₂ and [Cu(IN-DtczH-Sal)₂]Cl₂, respectively, while it could not be evaluated for Cu(IN-Dtcz)₂ because the slope was negative due to the non-variation of its magnetic moment with temperature. The difference in antiferromagnetic behavior and inconsistency of 2J for [Cu(IN-DtczH-Sal)₂]Cl₂ has been attributed to different electronic and steric factors of the three ligands, that is, isonicotinoyldithiocarbazate, its acid, and salicylaldehyde Schiff-base derivative.