Spectroscopic, magnetic, and electrochemical studies of a dimeric N-substituted-sulfanilamide copper(II) complex. X-ray and molecular structure of the Cu2(N-(pyridin-2-yl)biphenyl-4-sulfonamidate)4 complex

A dinuclear copper(II) complex with a N-substituted sulfonamide as ligand has been investigated. The new N-(pyridin-2-yl)biphenyl-4-sulfonamide ligand has been prepared and structurally characterized. The copper(II) complex has been synthesized and its crystal structure, magnetic properties and EPR spectra were studied in detail. The metal centers are bridged by four nonlinear triatomic NCN groups. The coordination geometry of the copper(II) ions in the dinuclear entity is distorted square planar with two N-pyridyl and two N-sulfonamido atoms. Magnetic susceptibility data show a moderate antiferromagnetic coupling, with −2 J = 284 cm⁻¹. The EPR spectrum of the polycrystalline sample of the title compound has been measured at the X-band frequency at different temperatures.     

Bis-bidentate bridging ligands containing two N,O-chelating pyrazolyl-phenolate units; double helical complexes with Co(II), Cu(II) and Zn(II)

Two ligands have been prepared in which N,O-bidentate chelating pyrazolyl-phenolate units, based on 3-(2-hydroxyphenyl)pyrazole, are connected via methylene linkages to aromatic (1,4-phenylene or 3,3′-biphenylene) spacers. In each case the two N,O-donor units are too far apart to chelate to a single metal ion. Complexes of both ligands with Co(II), Cu(II) and Zn(II) were prepared and structurally characterised; in all cases the complexes are dinuclear double helicates M₂L₂, with each four-coordinate metal ion bound by a chelating unit from each of the two ligands in the complex. For Co(II) and Zn(II) the two M(NO) planes at each metal are close to perpendicular, indicative of a geometry which may be described as approximately distorted tetrahedral; for the Cu(II) complexes the angle between the two Cu(NO) planes is less, indicative of a distortion towards a more planar coordination geometry.     

Suberoylanilide hydroxamic acid, a potent histone deacetylase inhibitor; its X-ray crystal structure and solid state and solution studies of its Zn(II), Ni(II), Cu(II) and Fe(III) complexes

Reaction of the potent hydroxamate-based histone deacetylase (HDAC) inhibitor, suberoylanilide hydroxamic acid (SAHA), with hydrated metal salts of Fe(III), Cu(II), Ni(II) and Zn(II) yielded a tris-hydroxamato complex in the case of Fe(III) and bis-hydroxamato complexes in the case of Cu(II), Ni(II) and Zn(II) both in the solid state and in solution. Reaction of the secondary hydroxamic acid, N-Me-SAHA, also yielded a tris-hydroxamato complex in the case of Fe(III) and bis-hydroxamato complexes in the case of Cu(II), Ni(II) and Zn(II) in solution. These metal complexes have the hydroxamato moiety coordinated in an O,O’-bidentate fashion. Stability constants of the metal complexes formed with SAHA and N-Me-SAHA in a DMSO/H₂O 70/30%(v/v) mixture are described. A novel crystal structure of SAHA together with a novel synthesis for N-Me-SAHA are also reported.     

Free metal ion depletion by "Good's" buffers. I. N-(2-acetamido)iminodiacetic acid 1:1 complexes with calcium(ii). magnesium(II), zinc(II), manganese(II), cobalt(II), nickel(II), and copper(II).

Formation (affinity) constants for 1:1 complexes of N-(2-acetamido)iminodiacetic acid (ADAH₂) with Ca(II), Mg(II), Mn(II), Zn(II), Co(II), Ni(II), and Cu(II) have been determined. Probable structures of the various metal chelates existing in solution are discussed. Values for the deprotonation of the amide group in [Cu(ADA)] and subsequent hydroxo complex formation are also reported. The use of ADA as a buffer is considered in terms of metal buffers complexes which can be formed at physiological pH, i.e., at pH 7.0 there is essentially no free metal ion in 1:1 M²⁺ to ADA solutions.     

Equilibrium and structural studies on Co(II), Ni(II), Cu(II) and Zn(II) complexes with N-(2-benzimidazolyl)methyliminodiacetic acid: crystal structures of Ni(II) and Cu(II) complexes

Combined pH-metric, UV-Vis, ¹H NMR and EPR spectral investigations on the complex formation of M(II) ions (M=Co, Ni, Cu and Zn) with N-(2-benzimidazolyl)methyliminodiacetic acid (H₂bzimida, hereafter H₂L) in aqueous solution at a fixed ionic strength, I=10⁻¹ mol dm⁻³, at 25 ± 1 °C indicate the formation of M(L), M(H₋₁L)⁻ and M₂(H₋₁L)⁺ complexes. Proton-ligand and metal-ligand constants and the complex formation equilibria have been elucidated. Solid complexes, [M(L)(H₂O)₂] · nH₂O (n=1 for M = Co and Zn, n=2 for M = Ni) and {Cu (μ-L) · 4H₂O}_n, have been isolated and characterized by elemental analysis, spectral, conductance and magnetic measurements and thermal studies. Structures of [Ni(L)(H₂O)₂] · 2H₂O and {Cu(μ-L) · 4H₂O}_n have been determined by single crystal X-ray diffraction. The nickel(II) complex exists in a distorted octahedral environment in which the metal ion is coordinated by the two carboxylate O atoms, the amino-N atom of the iminodiacetate moiety and the pyridine type N-atom of the benzimidazole moiety. Two aqua O atoms function as fifth and sixth donor atoms. The copper(II) complex is made up of interpenetrating polymeric chains of antiferromagnetically coupled Cu(II) ions linked by carboxylato bridges in syn-anti (apical-equatorial) bonding mode and stabilized via interchain hydrogen bonds and π-π stacking interactions.     

Crystal structures and spectroscopic behavior of monomeric, dimeric and polymeric copper(II) chloroacetate adducts with isonicotinamide, N-methylnicotinamide and N,N-diethylnicotinamide

Substituted pyridines provide structural rigidity and thus permit the metal coordination geometry to guide the direction of propagation of the hydrogen-bonded links between building blocks. In this paper we present the crystal structures and spectroscopic properties of monomeric, dimeric and polymeric copper(II) chloroacetates with isonicotinamide (INA), N-methylnicotinamide (MNA) and N,N-diethylnicotinamide (DENA). The molecular structure of [Cu(ClCH₂CO₂)₂(INA)₂]₂ (1) consists of a rather interesting dinuclear molecule with copper atoms bridged by anti, anti-O,O′ bridging oxygens of two chloroacetate anions. Each copper atom is octahedrally coordinated thus forming a CuN₂O₄ core with two nitrogens, originating from two different isonicotinamide molecules, in trans positions. This complex is one of a very few examples of this rare type of structure in which both carboxylate oxygen anions are coordinated to two copper metal ions. The crystal structure of 1 revealed an infinite 1-D linear hydrogen-bonded chain formed by discrete molecules [Cu(ClCH₂CO₂)₂(INA)₂]₂ connected by strong hydrogen bonds between two amide groups. This structure is the first example, where two pairs of amide groups are involved in hydrogen bonding connecting two molecules. The X-ray structure of the complex [Cu(CCl₃CO₂)₂(INA)₂]_n (3) revealed a tetragonal bipyramidal environment about the copper(II) atom. This structure represents the first example of copper(II) complex, where isonicotinamide acts as a bridging ligand. Strong intramolecular hydrogen bonds, N-H?O, create two eight-membered metallocycle rings which stabilizes the molecular structure. The crystal structure of 3 consists of 2-D sheets of a metal-organic framework. The coordination environment of the copper(II) atom in [Cu(CCl₃CO₂)₂(MNA)₂(H₂O)₂] · 2H₂O (6 · 2H₂O) is an elongated tetragonal bipyramid. Strong intramolecular hydrogen bond interactions involving an axial coordinated water molecule and a carboxylic oxygen atom stabilize the molecular structure. The crystal structure of [Cu₂(ClCH₂CO₂)₄(DENA)]_n (7) shows that the complex is an extended zigzag coordination chain of alternating binuclear paddle-wheel units of the bridging tetracarboxylate type Cu₂(ClCH₂CO₂)₄ and N,N-diethylnicotinamide molecules. This complex represents the first example of copper(II) carboxylates where N,N-diethylnicotinamide molecule acts as a bidentate bridging ligand connecting binuclear paddle-wheel units. The variation in DENA coordination in the polymeric chain can be described by the following formula: -[Cu₂(ClCH₂CO₂)₄]-(DENA-N,O)- [Cu₂(ClCH₂CO₂)₄]-(DENA-O,N)-. All complexes were characterized by electron paramagnetic resonance (EPR) spectroscopy and IR spectroscopy. The present study shows that the pyridine-carboxyamides are very suitable molecules that can be employed as ligands in the construction of extended arrays of transition metal-containing molecules linked via hydrogen bonds.     

A fluorescent ligand rationally designed to be selective for zinc(II) over larger metal ions. The structures of the zinc(II) and cadmium(II) complexes of N,N-bis(2-methylquinoline)-2-(2-aminoethyl)pyridine

The metal ion coordinating properties of the ligands N,N-bis(2-methylquinoline)-2-(2-aminoethyl)pyridine (DQPEA) and N,N-bis(2-methylquinoline)-2-(2-aminomethyl)pyridine (DQPMA) are presented. DQPEA and DQPMA differ only in that DQPEA forms six-membered chelate rings that involve the pyridyl group, whereas DQPMA forms analogous five-membered chelate rings.These two ligands illustrate the application of a ligand design principle, which states that increase of chelate ring size in a ligand will result in increase in selectivity for smaller relative to larger metal ions. The formation constants (log K₁) of DQPEA and DQPMA with Ni(II), Cu(II), Zn(II), Cd(II) and Pb(II) are reported. As expected from the applied ligand design principle, small metal ions such as Ni(II) and Zn(II) show increases in log K₁ with DQPEA (six-membered chelate ring) relative to DQPMA (five-membered chelate ring), while large metal ions such as Cd(II) and Pb(II) show decreases in log K₁ when the chelate ring increases in size. In order to further understand the steric origin of the destabilization of complexes of metal ions of differing sizes by the six-membered chelate ring of DQPEA, the structures of [Zn(DQPEA)H₂O](ClO₄)₂ (1) [triclinic, , a = 9.2906(10), b = 10.3943(10), c = 17.3880(18) Å, α = 82.748(7)°, β = 88.519(7)°, γ = 66.957(6)°, Z = 4, R = 0.073] and [Cd(DQPEA)(NO₃)₂] (2) [monoclinic, C2/c, a = 22.160(3), b = 15.9444(18), c = 16.6962(18) Å, β = 119.780(3)°, Z = 8, R = 0.0425] are reported. The Zn in (1) is five-coordinate, with a water molecule completing the coordination sphere. The Cd(II) in (2) is six-coordinate, with two unidentate nitrates coordinated to the Cd. It is found that the bonds to the quinaldine nitrogens in the DQPEA complexes are considerably stretched as compared to those of analogous TPyA (tri(pyridylmethyl)amine) complexes, which effect is attributed to the greater steric crowding in the DQPEA complexes. The structures are analyzed for indications of the origins of the destabilization of the complex of the large Cd(II) ion relative to the smaller Zn(II) ion. A possible cause is the greater distortion of the six-membered chelate ring in (2) than in (1), as evidenced by torsion angles that are further away from the ideal values in (2) than in (1). Fluorescence properties of the DQPMA and DQPEA complexes of Zn(II) and Cd(II) are reported. It is found that the DQPEA complex of Zn(II) has increased fluorescence intensity compared to the DQPMA complex, while for the Cd(II) complex the opposite is found. This is related to the greater strain in the six-membered chelate ring of the Cd(II) DQPEA complex as compared to the Zn(II) complex, with resulting poorer overlap in the Cd-N bond, and hence greater ability to quench the fluorescence in the Cd(II) complex.     

A solution thermodynamic study of the Cu(II) and Zn(II) complexes of EBTA: X-ray crystal structure of the dimeric complex [Cu2(EBTA)(H2O)3]2

The copper(II) complex of the acyclic EBTA ligand (H₄EBTA = 1,2-bis(2-aminoethoxy)benzene-N,N,N′,N′-tetraacetic acid) has been prepared and characterized by X-ray analysis. The two copper ions of the dinuclear unit present the same distorted octahedral coordination polyhedra. The EBTA ligand is shared between two copper coordination centres, with the formation of centrosymmetric dimers, which are linked in a supramolecular tridimensional structure via additional interactions through the coordinated waters molecules with adjacent carboxylic oxygen atoms. The stability and protonation constants of EBTA with Cu(II) and Zn(II) ions indicate a higher stability of these complexes with respect to the corresponding complexes with the more flexible EGTA ligand (H₄EGTA = ethyleneglycol-bis(2-aminoethylether)-N,N,N′,N′-tetraacetic acid). On the other hand, the lower stability of [Gd(EBTA)]⁻ than [Gd(EGTA)]⁻ results in a decreased overall selectivity (lower K_sel) of EBTA towards Gd(III) and suggests that this complex may undergoes transmetallation reactions under physiological conditions.     

Ratiometric and selective fluorescent chemodosimeter for Cu(II) by Cu(II)‐induced oxidation

A new rhodamine derivative, rhodamine B 4‐N,N‐dimethylaminobenzaldehyde hydrazone (1), was designed for ratiometric sensing of Cu(II) selectively. A red‐shift from 515 to 585 nm was observed in the fluorescence spectrum when Cu(II) was added to 1 in acetonitrile. Other metal ions of interest showed no ratiometric response. The interaction between Cu(II) and 1 was found to be the Cu(II)‐induced oxidation of 1. Copyright © 2008 John Wiley & Sons, Ltd.     

A dye-binding assay for measurement of the binding of Cu(II) to proteins

We analysed the theory of the coupled equilibria between a metal ion, a metal ion-binding dye and a metal ion-binding protein in order to develop a procedure for estimating the apparent affinity constant of a metal ion:protein complex. This can be done by analysing from measurements of the change in the concentration of the metal ion:dye complex with variation in the concentration of either the metal ion or the protein. Using experimentally determined values for the affinity constant of Cu(II) for the dye, 2-(5-bromo-2-pyridylaxo)-5-(N-propyl-N-sulfopropylamino) aniline (5-Br-PSAA), this procedure was used to estimate the apparent affinity constants for formation of Cu(II):transthyretin, yielding values which were in agreement with literature values. An apparent affinity constant for Cu(II) binding to α-synuclein of ∼1 × 10⁹ M⁻¹ was obtained from measurements of tyrosine fluorescence quenching by Cu(II). This value was in good agreement with that obtained using 5-Br-PSAA. Our analysis and data therefore show that measurement of changes in the equilibria between Cu(II) and 5-Br-PSAA by Cu(II)-binding proteins provides a general procedure for estimating the affinities of proteins for Cu(II).     

Iron(III)- and copper(II) complexes of an asymmetric, pentadentate salen-like ligand bearing a pendant carboxylate group

The equilibrium and solution structural properties of the iron(III) and copper(II) complexes of an asymmetric salen-like ligand (N,N'-bis(2-hydroxybenzyl)-2,3-diamino-propionic acid, H(3)bhbdpa) bearing a pendant carboxylate group were characterized in aqueous solution by potentiometric, pH-dependent electron paramagnetic resonance (EPR) and UV-Vis (UV-Visible) measurements. In the equimolar systems the pentadentate ligand forms very stable, differently protonated mononuclear complexes with both metal ions. In the presence of iron(III) {NH, PhO(-), COO(-)}, {2NH, 2PhO(-), COO(-)} and {2NH, 2PhO(-), COO(-), OH(-)} coordinated complexes are dominant. The EPR titrations reflected the presence of microscopic complex formation pathways, leading to the formation of binding isomers in case of Cu(H(2)bhbdpa)(+), Cu(Hbhbdpa) and Cu(bhbdpa)(-). The {2NH, 2PhO(-)+COO(-)/H(2)O} coordinated Cu(bhbdpa) is the only species between pH 6-11. At twofold excess of metal ion dinuclear complexes were detected with both iron(III) and copper(II). In presence of iron(III) a mu-carboxylato-mu-hydroxo-bridged dinuclear complex (Fe(2)(bhbdpa)(OH)(3)) is formed from Fe(H(2)bhbdpa)(2+) through overlapping proton release processes, providing one of the rare examples for the stabilization of an endogenous carboxylate bridged diiron core in aqueous solution. The complex Cu(2)(bhbdpa)(+) detected in the presence of copper(II) is a paramagnetic (S=1) species with relatively weakly coupled metal ions.     

Electrochemical synthesis and crystal structures of nickel(II), copper(II), zinc(II) and cadmium(II) complexes with N,N′-bis[(4-methylphenyl)sulfonyl]ethylenediamine

The electrochemical oxidation of anodic metal (nickel, copper, zinc and cadmium) in acetonitrile solutions containing N,N′-bis[(4-methylphenyl)sulfonyl]ethylenediamine H₂L and an additional nitrogen coligand, such as 1,10-phenanthroline, yielded mixed complexes of general formula [ML(phen)₂] (M=Ni, Cu, Zn and Cd). The compounds have been characterized by microanalysis, IR and UV-Vis (Ni, Cu complexes) spectroscopy, FAB mass spectrometry, ¹H NMR spectroscopic studies (Zn, Cd complexes) and EPR spectroscopy (Cu and Ni complexes). All compounds have also been characterized by single crystal X-ray diffraction. The molecular structures of these compounds consist of individual monomeric molecules in which the metal atom is in an [MN₆] distorted octahedral environment.     

A structural study of the hydrated and the dimethylsulfoxide, N,N′-dimethylpropyleneurea, and N,N-dimethylthioformamide solvated iron(II) and iron(III) ions in solution and solid state

The structures of the solvated iron(II) and iron(III) ions have been studied in solution and solid state by extended X-ray absorption fine structure (EXAFS) in three oxygen donor solvents, water, dimethylsulfoxide (Me₂SO), N,N′-dimethylpropyleneurea (DMPU), and one sulfur donor solvent, N,N-dimethylthioformamide (DMTF); these solvents have different coordination and solvation properties. In addition, the structure of hexakis(dimethylsulfoxide)iron(III) perchlorate has been determined crystallographically to support the determination of the corresponding solvate in solution. The hydrated, the dimethylsulfoxide and N,N-dimethylthioformamide solvated iron(II) ions show regular octahedral coordination in both solution and solid state with mean Fe-O, Fe-O, and Fe-S bond distances of 2.10, 2.10, and 2.52 Å, respectively, whereas the N,N′-dimethylpropyleneurea iron(II) solvate is five-coordinated, d(Fe-O) = 2.06 Å. The compounds vary in color from light green (hydrate) to dark orange or red (DMPU). The hydrated iron(III) ion in aqueous solution and the dimethylsulfoxide solvated iron(III) ions in solution and solid state show the expected octahedral coordination, the Fe-O bond distances are 2.00 Å for both, whereas the N,N′-dimethylpropyleneurea iron(III) solvate is found to be five-coordinated with a mean Fe-O bond distance of 1.99 Å. The N,N-dimethylthioformamide solvated iron(III) ion in the solid perchlorate salt is tetrahedrally four-coordinated, the mean Fe-S bond distance is 2.20 Å. Iron(III) is reduced with time to iron(II) in N,N-dimethylthioformamide solution. The compounds vary in color from pale yellow (hydrate) to blackish red (DMPU).     

The use of solvatochromic mixed copper(II) chelates with N,N,N′,N′-tetramethylethylenediamine and tropolonato or hinokitiolato ligands, [Cu(trop/hino)(tmen)]B(C6H5)4, as indicator for Lewis basicity of solvents and low-coordinating anions

Mixed copper(II) chelates, [Cu(trop/hino)(tmen)]B(C₆H₅)₄, were prepared with a tropolonato or hinokitiolato ligands (trop/hino) and N,N,N′,N′-tetramethylethylenediamine (tmen). These chelates were, as expected, quite similar to the corresponding acetylacetonato analog [Cu(acac)(tmen)]B(C₆H₅)₄, being fairly soluble in a large number of solvents and remarkably solvatochromic in them. They were also useful as excellent Lewis basicity indicators in solution because their d-d bands continuously shift to red in wider ranges with increasing DN (donor number) of solvent. The examination on addition of various anions to these solvatochromic systems led to a quantitative view of the competition between solvent molecule and anion for coordination to metal center.     

Kinetics of the accelerator ligand effect for the complex formation of Cd(II) ion with a cationic water-soluble porphyrin

A kinetic study of the acceleration activities of inorganic and organic ligands for the incorporation of a Cd(II) ion into 5,10,15,20-tetrakis(4-N-methylpyridyl)porphine (TMPyP) has been performed. The acceleration activities of the inorganic ions decreased in the order . The logarithmic values of the rate constants of the Cd-TMPyP formation were proportional to the values of the nucleophilic constant. This fact suggests that the acceleration of the Cd(II) incorporation into TMPyP is mainly due to the enhancement of the water exchange rate in the inner coordination sphere of the Cd(II)-accelerator complex. Furthermore, the acceleration effects of organic ligands increased with the hydrophobicities of the accelerator ligands. In addition, accelerators possessing negative charges, which are capable of interacting with the positive charges of the N-methylpyridyl groups of TMPyP, significantly enhanced the incorporation of Cd(II) into TMPyP. The rate constant of the metal ion exchange reaction of Cd(II) with Pb-TMPyP in the presence of bathophenanthroline sulfonic acid was 1 400 000-fold greater than the reaction of Cd(II) with TMPyP in the absence of an accelerator. The acceleration effect of organic ligands was due to the enhancement of the hydrophobic interaction and the electrostatic interaction between the Cd(II)-accelerator complex and Pb-TMPyP in the outer coordination sphere.     

Methyl-substituted 4-nitropyridine N-oxides as ligands: structural, spectroscopic, magnetic and cytotoxic characteristics of copper(II) complexes

Seven new mono- and dinuclear Cu(II) complexes containing various methyl substituted 4-nitropyridine N-oxides as ligands were isolated and characterized physicochemically and biologically. The characterization included elemental analysis, magnetic and spectroscopic methods (diffuse reflectance and UV-visible absorption, IR, FIR). A single crystal X-ray diffraction analysis was performed for the complex with 2,5-dimethyl-4-nitropyridine N-oxide. Trans- and cis-square planar configuration around Cu ion was established for mono- and dinuclear species, respectively. In methanolic solutions the dinuclear species decompose into mononuclear ones with increasing 4 → 6 coordination number with attachment of two solvent molecules.The IR spectra showed that the strength of the Cu-ligand bond gauged by the degree of N-O elongation changed irregularly with position and number of methyl groups. Cytotoxic studies on the MCF-7 human breast cancer line revealed a structure-activity relationship: double blocking of the NO₂ group with two CH₃ groups rendered the complex completely inactive.     

A tetracopper(II) complex with N,N′-bis(picolinoyl)hydrazine

Synthesis, physical properties and X-ray structure of a hydrated tetranuclear copper(II) complex [Cu₄(μ-diph)₂(μ-H₂O)₂(O₂CCH₃)₄(H₂O)₂]·4H₂O with N,N′-bis(picolinoyl)hydrazine (H₂diph) are reported. The centrosymmetric complex has two types of copper(II) centres with distorted square-pyramidal N₂O₃ coordination spheres. The dinucleating trans planar diph²⁻ ligands are parallel to each other and act as N₂O-donor to one metal centre and N₂-donor to the other metal centre. The complex has a rectangular {Cu₄(μ-N-N)₂(μ-OH₂)₂} core with Cu···Cu distances as 4.834(1) and 3.762(1) Å. Solid state as well as solution electronic spectra show several transitions in the wavelength range 700-280 nm. The room temperature (298 K) solid state magnetic moment is 3.55 μ_B. The powder EPR spectra at 298 and 130 K are very similar and axial (g_∥ = 2.25 and g_⊥ = 2.08) in character.     

Synthesis, structural characterization and redox properties of copper(II) and manganese(II) complexes containing tridentate (N-(2-methylpyridine)-2-aminomethyl benzoate) ligand

Two new complexes, [Cu(mamba)₂] and [Mn(mamba)₂] (mamba⁻, N-(2-methylpyridine)-2-aminomethyl benzoate) were synthesized and characterized by X-ray crystallography. Whereas the [Cu(mamba)₂] complex crystallizes in a monoclinic P2₁/c space group, the [Mn(mamba)₂] complex crystallizes in a triclinic space group. The nature of the metal ion greatly influences the lattices and the molecular structures of the compounds. In the crystal lattice of the copper complex are four cocrystallized methanol solvent, which are all involved in building six strong H-bonds with the complex. However, the lattice for the manganese complex contain only one cocrystallized methanol, along with one NaClO₄, that is also involved in making one H-bond with the [Mn(mamba)₂] unit. Nevertheless, the sodium ion is coordinated to the ClO₄⁻, the methanol and two [Mn(mamba)₂] to form a stable extended chain metal complex. Electrochemical studies indicated that both complexes undergo quasi reversible one electron reduction in acetonitrile.     

Physico-chemical study of first row transition metal ions coordination compounds with N,N′-bis(2-tosylaminobenzylidene)-1,3-diaminopropanol. The crystal structure of bis-azomethine and its cobalt(II) complex

The novel Cu(II), Ni(II), Zn(II), Co(II) coordination compounds with Schiff base ligand - N,N′-bis(2-tosylaminobenzylidene)-1,3-diaminopropanol have been synthesized and studied. The structures of bis-azomethine as well as Co(II) and Zn(II) mononuclear metallochelates have been determined by X-ray analysis. The magnetic properties of all complexes were studied and interpreted in terms of HDVV theory. It was shown that exchange interaction in binuclear copper(II) complexes was affected by tosyl groups.     

Synthesis, characterization and X-ray crystal structures of dinuclear nickel(II) complexes of a novel potentially hexadentate but functionally tetradentate binucleating ligand

A binucleating potentially hexadentate chelating agent containing oxygen, nitrogen and sulfur as potential donor atoms (H₂ONNO) has been synthesized by condensing α,α-xylenebis(N-methyldithiocarbazate) with 2,4-pentanedione. An X-ray crystallographic structure determination shows that the Schiff base remains in its ketoimine tautomeric form with the protons attached to the imine nitrogen atoms. The reaction of the Schiff base with nickel(II) acetate in a 1:1 stoichiometry leads to the formation of a dinuclear nickel(II) complex [Ni(ONNO)]₂ (ONNO²⁻ = dianionic form of the Schiff base) containing N,O-chelated tetradentate ligands, the sulfur donors remaining uncoordinated. A single crystal X-ray structure determination of this dimer reveals that each ligand binds two low spin nickel(II) ions, bridged by a xylyl group. The nickel(II) atoms adopt a distorted square-planar geometry in a trans-N₂O₂ donor environment. Reaction of the Schiff base with nickel(II) acetate in the presence of excess pyridine leads to the formation of a similar dinuclear complex, [Ni(ONNO)(py)]₂, but in this case comprises five coordinate high-spin Ni(II) ions with pyridine ligands occupying the axial coordination sites as revealed by X-ray crystallographic analysis.