Structural and equilibrium studies on mixed ligand complexes of Co(II), Ni(II), Cu(II) and Zn(II) with N-(2-benzimidazolyl)methyliminodiacetic acid and typical N, N donor ligands

Mixed ligand complexes: [Co(L)(bipy)] · 3H₂O (1), [Ni(L)(phen)] · H₂O (2), [Cu(L)(phen)] · 3H₂O (3) and [Zn(L)(bipy)] · 3H₂O (4), where L²⁻ = two -COOH deprotonated dianion of N-(2-benzimidazolyl)methyliminodiacetic acid (H₂bzimida, hereafter, H₂L), bipy = 2,2′ bipyridine and phen = 1,10-phenanthroline have been isolated and characterized by elemental analysis, spectral and magnetic measurements and thermal studies. Single crystal X-ray diffraction studies show octahedral geometry for 1, 2 and 4 and square pyramidal geometry for 3. Equilibrium studies in aqueous solution (ionic strength I = 10⁻¹ mol dm⁻³ (NaNO₃), at 25 ± 1 °C) using different molar proportions of M(II):H₂L:B, where M = Co, Ni, Cu and Zn and B = phen, bipy and en (ethylene diamine), however, provides evidence of formation of mononuclear and binuclear binary and mixed ligand complexes: M(L), M(H₋₁L)⁻, M(B)²⁺, M(L)(B), M(H₋₁L)(B)⁻, M₂(H₋₁L)(OH), (B)M(H₋₁L)M(B)⁺, where H₋₁L³⁻ represents two -COOH and the benzimidazole N₁-H deprotonated quadridentate (O⁻, N, O⁻, N), or, quinquedentate (O⁻, N, O⁻, N, N⁻) function of the coordinated ligand H₂L. Binuclear mixed ligand complex formation equilibria: M(L)(B) + M(B)²⁺ ? (B)M(H₋₁L)M(B)⁺ + H⁺ is favoured with higher π-acidity of the B ligands. For Co(II), Ni(II) and Cu(II), these equilibria are accompanied by blue shift of the electronic absorption maxima of M(II) ions, as a negatively charged bridging benzimidazolate moiety provides stronger ligand field than a neutral one. Solution stability of the mixed ligand complexes are in the expected order: Co(II) < Ni(II) < Cu(II) > Zn(II). The Δ log K_M values are less negetive than their statistical values, indicating favoured formation of the mixed ligand complexes over the binary ones.     

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.     

Synthetic, spectroscopic and X-ray crystallographic structural studies on copper(II) complexes of the aminoguanizone of pyruvic acid

Copper(II) complexes of general empirical formula, CuX(Hagpa) · nH₂O and Cu(agpa) · 2H₂O (H₂agpa = aminoguanizone of pyruvic acid, X = Cl⁻, Br⁻, , CH₃COO⁻, , n = 0, 1, 1.5, 2), have been synthesized and characterized by IR, EPR spectroscopy and X-ray crystallography. The IR spectra of the complexes showed the ONN coordination of the ligand to copper(II) ion. The crystal structures of H₂agpa · H₂O and complexes [Cu(Hagpa)Br] and [Cu₂(Hagpa)₂(H₂O)₂(SO₄)] · DMSO showed an invariable conformation and coordination mode for the uninegatively charged tridentate ligand and revealed the formation of linear polymers in which bromide or sulfate anions bridge the copper(II) ions. The EPR spectra for complexes CuX(Hagpa) · nH₂O are described by spin Hamiltonian for S = 1/2, without hyperfine structure. The g-tensor is symmetrical for Cu(agpa) · 2H₂O, has tri-axial anisotropy for sulfate complexes, and exhibits axial symmetry for the other compounds investigated.     

The structures and magnetism of trinuclear Ni(II), Co(II) and Mn(II) complexes derived from unsymmetrical compartmental ligands

Trinuclear Ni(II), Co(II) and Mn(II) complexes have been prepared from the asymmetric compartmental proligands 2-alkyliminomethyl-4-methyl-6-{[methyl-(2-pyridin-2-yl-ethyl)-amino]-methyl}-phenol(alkyl=ethyl, n-propyl and n-butyl) and 2-[(2-methoxy-ethylimino)-methyl]-4-methyl-6-{[methyl-(2-pyridin-2-yl-ethyl)-amino]-methyl}-phenol, which provide adjacent tridentate N₂O and bidentate NO donor sets. The crystal structures of [Ni₃(L⁶)₂(OAc)₂(NCS)₂] · CH₃OH · H₂O, [Co₃(L⁴)₂(OAc)₂(NCS)₂], and [Mn₃(L⁷)₂(OAc)₂(NCS)₂] · CH₃OH · H₂O were determined and show that the metals provide an isosceles triangle with M¹-M²=M¹-M³ ≈ 3.2 Å and M²-M³ ≈ 5.0 Å. The cryomagnetic properties of the complexes have been studied and indicate a weak antiferromagnetic interaction between the adjacent, M¹M² and M¹M³ ions with little magnetic interaction between the terminal M²M³ ions.     

A study on mono-, bis- and tris-N-functionalized 1,4,7-triazacyclononane with benzimidazolyl groups and their nickel(II) complexes

Three new ligands, 1-(benzimidazolyl-2-methyl)-1,4,7-triazacyclononane L¹, 1,4-bis(benzimidazolyl-2-methyl)-1,4,7-triazacyclonone L², and 1,4,7-tris-(benzimidazolyl-2-methyl)-1,4,7-triazacyclonane L³, were synthesized by a straightforward one-pot method. Their nickel(II) complexes , [NiL²CH₃CN](ClO₄)₂ · 2CH₃OH · H₂O (or [NiL²Cl] · ClO₄) and [Ni(H₋₂L³)] · H₂O were obtained and characterized by electrospray mass spectrum, ¹H NMR, CV and other physical methods. Their crystal structures were determined by X-ray analyses. The crystal structure of the nickel(II) complex of L¹ shows that two Ni(II) atoms are bridged by two Cl⁻ anions. A ferromagnetic exchange coupling and zero-field splitting effect exist in complex 1.     

Pyridyldicarboxamide-based multinuclear complexes: Syntheses, structural characterizations, and magnetic properties

Using the pyridine dicarboxamide derivative N,N′-bis(1,3,4-thiadiazol-2-yl)-2,6-pyridinedi-carboxamide (H₂-btapca) as ligand, two novel polynuclear complexes: dimeric {[Cu₂(μ₂-O₂H)(btapca)₂]·DMF·H₂O} (1) and tetrameric {[Ni₄((μ₂-O₂H)₂(btapca)₄)]·DMF·MeOH·3.5H₂O} (2) were obtained. In complex 1, two center Cu(II) ions are bounded by two btapca ligands and one aqueous molecule acting as a μ₂-H₂O bridge connect them together. Complex 2 is a tetrameric complex, in which the based backbone is an assumed Ni₄ tetrahedron with two μ₂-O₂H bridges existing inside the tetrahedron forming a basic [Ni₂(μ₂-O₂H)]₂ core, which are surrounded by four btapca ligands. The magnetic properties of the two polynuclear complexes were determined, the results show that for both of the two complexes, the overall weak ferromagnetic exchange interactions between central metal ions are evident, the best fitting parameters are: J = 7.47 cm⁻¹ (g = 2.21) for dimeric Cu(II) complex 1, and 2J₁ = 4.8 cm⁻¹, 2J₂ = −0.00204 cm⁻¹(g = 2.14, zJ′ = 0.00077 cm⁻¹) for tetrameric Ni(II) complex 2.     

Synthesis, structural and spectroscopic characterization and biomimetic properties of new copper, manganese, zinc complexes: Identification of possible superoxide-dismutase mimics bearing hydroxyl radical generating/scavenging abilities

A series of Cu(II), Zn(II) and Mn(II) coordination compounds has been synthesized by reaction of the corresponding metal salts and pyrazolyl-based ligands, i.e. the neutral 1-(2-(4-((2,2,2-tri(1H-pyrazol-1-yl)ethoxy)methyl)benzyloxy)-1,1-di(1H-pyrazol-1-yl)ethyl)-1H-pyrazole {p-C₆H₄[CH₂OCH₂C(pz)₃]₂, (L¹), and the anionic hydridotris(3-phenyl-5-methylpyrazolyl)borate (L²)⁻, bis(pyrazolyl)acetate (L³) and bis(3,5-dimethylpyrazolyl)acetate (L⁴)⁻: the species [L¹(CuCl₂)₂] (1), [L¹(Cu(OAc)₂)₂] (2), [L¹(Zn(OAc)₂)₂] (3), [(CuCl(L²)(Hpz^Ph,Me)] (4), [Mn(L³)₂]·2H₂O, (5), [ZnCl(L³)(imH)]·MeOH [CuCl(L⁴)(imH)]·2H₂O (7) have been obtained (Hpz^Ph,Me = 3-phenyl-5-methylpyrazole, imH = imidazole). Complexes 1 and 4 have been structurally characterized, also using less conventional powder diffraction methods. The superoxide scavenging activity has been characterized by indirect assays including EPR analysis. All complexes exhibit superoxide scavenging activity with IC₅₀ in the µM range and they protect against the oxidative action of peroxynitrite in different ways. 1, 4 and 7 exert both an anti- and pro-oxidant effect depending on their concentration as evaluated by EPR and fluorescence methods. The pro-oxidative effects are absent in Zn(II) and Mn(II) complexes.     

Cobalt and nickel complexes of versatile imidazole- and pyrrole-2-carbaldehyde thiosemicarbazones. Synthesis, characterisation and antimicrobial activity

Ni(II), Co(II) and Co(III) complexes of imidazole- and pyrrole-2-carbaldehyde thiosemicarbazone ligands (H₂L¹ and H₂L², respectively) have been prepared. The X-ray crystal structures of [Co(L¹)(HL¹)], [Ni(H₂L¹)₂]Cl₂ · 3.5H₂O and [Ni(HL²)₂] have been solved. The Co(III) ion assumes a slightly distorted octahedral coordination geometry, involving both N₂S binding domain of di- and monoanionic ligand molecules. Whereas in [Ni(HL²)₂] the metal ion is tetracoordinated in a square planar geometry by two pyrrole-2-carbaldehyde thiosemicarbazone molecules acting as NS-donor, the spatial array of non deprotonated H₂L¹ ligand molecules in [Ni(H₂L¹)₂]Cl₂ · 3.5H₂O is equivalent to that found for [Co(L¹)(HL¹)]. The in vitro antimicrobial properties of the ligands and their complexes were tested against representative bacterial and fungal strains in broth culture. The compounds H₂L² and [Co(L²)(HL²)(H₂L²)] · 1.5H₂O exhibit a moderate inhibitory effect on the microbial proliferation and only against some Gram positive bacteria.     

Copper(II) complexes with unsymmetrical pentadentate ed3a-type diamino-tricarboxylate ligands. Crystal structures, configurational analysis and DFT study of complexes

The O-O-N-N-O-type pentadentate ligands H₃ed3a, H₃pd3a and H₃pd3p (H₃ed3a stands ethylenediamine-N,N,N′-triacetic acid; H₃pd3a stands 1,3-propanediamine-N,N,N′-triacetic acid and H₃pd3p stands 1,3-propanediamine-N,N,N′-tri-3-propionic acid) and the corresponding novel octahedral or square-planar/trigonal-bipyramidal copper(II) complexes have been prepared and characterized. H₃ed3a, H₃pd3a and H₃pd3p ligands coordinate to copper(II) ion via five donor atoms (three deprotonated carboxylate atoms and two amine nitrogens) affording octahedral in case of ed3a³⁻ and intermediate square-pyramidal/trigonal-bipyramidal structure in case of pd3a³⁻ and pd3p³⁻. A six coordinate, octahedral geometry has been established crystallographically for the [Mg(H₂O)₆][Cu(ed3a)(H₂O)]₂ · 2H₂O complex and five coordinate square-pyramidal for the [Mg(H₂O)₅Cu(pd3a)][Cu(pd3a)] · 2H₂O. Structural data correlating similar chelate Cu(II) complexes have been used for the better understanding the pathway: octahedral → square-pyramidal ↔ trigonal- bipyramid geometry. An extensive configuration analysis is discussed in relation to information obtained for similar complexes. The infra-red and electronic absorption spectra of the complexes are discussed in comparison with related complexes of known geometries. Molecular mechanics and density functional theory (DFT) programs have been used to model the most stable geometric isomer yielding, at the same time, significant structural data. The results from density functional studies have been compared with X-ray data.     

Dinuclear terephthalato-bridged copper(II) complexes: Syntheses, spectral and structural characterization, and magnetic properties

Herein, we report the syntheses, spectral and structural characterization, and magnetic behavior of four new dinuclear terephthalato-bridged copper(II) complexes with formulae [Cu₂(trpn)₂(μ-tp)](ClO₄)₂ · 2H₂O (1), [Cu₂(aepn)₂(μ-tp)(ClO₄)₂] (2), [Cu₂(Medpt)₂(μ-tp)(H₂O)₂](ClO₄)₂ (3) and [Cu₂(Et₂dien)₂(μ-tp)(H₂O)](ClO₄)₂ (4) where tp = terephthalate dianion, trpn = tris(3-aminopropyl)-amin, aepn = N-(2-aminoethyl)-1,3-propanediamine, Medpt = 3,3′-diamino-N-methyldipropylmine and Et₂dien = N,N-diethyldiethylenetriamine. The structures of these complexes consist of two μ-tp bridging Cu(II) centers in a bis(monodentate) bonding fashion. The coordination geometry of the Cu(II) ions in these compounds may be described as close to square-based pyramid (SP) with severe significant distortion towards trigonal bipyramid (TBP) stereochemistry in 1. The visible spectra of the complexes in aqueous solutions are in complete agreement with the assigned X-ray geometry around the Cu(II) centers. Also, the solid infrared spectral data for the stretching frequencies of the tp-carboxalato groups, the ν(COO⁻) reveals the existence of bis(monodentate) coordination mode for the bridged terephthalate ligand. The susceptibility measurements at variable temperature over the range 2-300 K are reported. Despite the same bonding mode of the tp bridging ligand, there has been observed slight antiferromagnetic coupling for the compounds 1 and 4 with J values of −0.5 and −2.9 cm³ K mol⁻¹, respectively, and very weak ferromagnetic coupling for 2 and 3 with J values of 0.8 and 10.1 cm³ K mol⁻¹, respectively. The magnetic results are discussed in relation to other related μ-terephthalato dinuclear Cu(II) published compounds.     

Structural, magnetic, electrochemical, catalytic, DNA binding and cleavage studies of new macrocyclic binuclear copper(II) complexes

The macrocyclic symmetrical and a series of unsymmetrical binuclear copper(II) complexes have been synthesized by using mononuclear complex [CuL] [3,3′-((1E,7E)-3,6-dioxa-2,7-diazaocta-1,7-diene-1,8-diyl)bis(3-formyl-5-methyl-2-diolato)copper(II)]. Another compartment of the [CuL] have been condensed with various diamines like 1,2-bis(aminooxy)ethane (L¹), 1,2-diamino ethane(L^2a), 1,3-diamino propane(L^2b), 1,4-diamino butane(L^2c), 1,2-diamino benzene(L^2d), 1,8-diamino naphthalene(L^2e) and characterized by elemental, spectroscopic, and X-ray crystallographic methods. The influence of the coordination geometry and the ring size of the binucleating ligands on the electronic, redox, magnetic, catecholase activity, DNA binding and cleavage properties have been studied. The molecular structures of the symmetrical binuclear complex [Cu₂L¹(H₂O)₂](ClO₄)₂ (1) and unsymmetrical binuclear complex [Cu₂L^2b(ClO₄)(H₂O)]ClO₄ (2b) were determined by X-ray crystallography. Both of them were discrete binuclear species in which each Cu(II) ions are in distorted square pyramid. The Cu?Cu distances vary from 3.0308 (2b) to 3.0361 Å (1). Electrochemical studies evidenced that two quasi-reversible one electron-transfer reduction waves −0.91 to −1.01 V, −1.26 to −1.55 V) for binuclear complexes are obtained in the cathodic region. Cryomagnetic investigation of the binuclear complexes reveals a weak antiferromagnetic spin exchange interaction between the Cu(II) ions within the complexes (−2J = 104.4-127.5 cm⁻¹). The initial rate (V_in) for the oxidation of 3,5-di-tert-butylcatechol to o-quinone by the binuclear Cu(II)complexes are in the range 3.6 × 10⁻⁵ to 7.3 × 10⁻⁵ Ms⁻¹. The binuclear Cu(II) complexes are avid binders to calf thymus DNA. The complexes display significant oxidative cleavage of circular plasmid pBR322 DNA in the presence of mercaptoethanol using the singlet oxygen as a reactive species. The aromatic diamine condensed macrocyclic ligands of copper(II) complexes display better DNA interaction and significant chemical nuclease activity than the aliphatic diamine condensed macrocyclic Cu(II) complexes.     

Syntheses, crystal structures, and magnetic properties of two cyclic dimer M2L2 complexes constructed from a new nitronyl nitroxide ligand and M(hfac)2 (M = Cu, Mn)

Two new binuclear radical complexes derived from a new long nitronyl nitroxide ligand, 2-[4-(5-pyrimidyl)phenyl]-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (4-NITPhPyrim), and M(hfac)₂ (M²⁺ = Cu²⁺, Mn²⁺; hfac⁻ = hexafluoroacetylacetonato), [Cu(hfac)₂(4-NITPhPyrim)]₂ · 4H₂O (1) and [Mn(hfac)₂(4-NITPhPyrim)]₂ · 4H₂O (2), were synthesized as well as characterized structurally and magnetically. X-ray analysis indicates that 1 and 2 are rectangle-like centrosymmetric dimer M₂L₂ complexes. Magnetic measurements indicate that there are two types of magnetic exchanges in 1: the ferromagnetic (FM) exchange between the Cu(II) ion and the directly bonded nitroxide unit (J₁ = 24.20 cm⁻¹) and the weak FM exchange of Cu-NIT through the pyrimidine and phenyl rings (J₂ = 0.62 cm⁻¹). Besides the strong antiferromagnetic (AFM) coupling between the Mn(II) ion and the directly bonded nitroxide unit (J = −87.61 cm⁻¹), there is a weak FM interaction between the two Mn-NIT pairs (θ = 0.39 K) in 2.     

Square-planar copper(II) complexes with tetradentate amido-carboxylate ligands. Crystal structure of Na2[Cu(obap)]2 · 2H2O. Strain analysis and spectral assignments of complexes

Novel N-N-N-O-type of tetradentate ligands H₃obap (H₃obap = oxamido-N-aminopropyl-N′-benzoic acid) and H₃maeb (H₃maeb = malamido-N-aminoethyl-N′-benzoic acid) and the corresponding square-planar copper(II) complexes have been prepared and characterized. The obap³⁻ and maeb³⁻ ligands coordinate to the copper(II) ion via four ligating atoms (three deprotonated atoms: one carboxylate oxygen and two deprotonated amide nitrogens; one amine nitrogen) with in-plane square chelation. A four coordinate, square-planar geometry has been established crystallographically for the binuclear Na₂[Cu(obap)]₂ · 2H₂O complex. Structural data correlating the square-planar geometry of the [Cu(obap)]⁻ unit and an extensive strain analysis are discussed in relation to the information obtained for similar complexes. The infrared and electronic absorption spectra of the complexes are discussed in comparison to the related complexes of known geometries. Antibacterial activity of ligands and copper(II) complexes towards common Gram-negative and Gram-positive bacteria are reported as well.     

Synthesis, crystal structures and magnetic studies of terephthalato- and fumarato-bridged dinickel(II) complexes with tripodal poly-benzimidazole ligand

Two novel dinuclear nickel(II) complexes [Ni₂(ntb)₂(μ-tp)(H₂O)_1.61(CH₃OH)_0.39](NO₃)₂·5.13CH₃OH·2.25H₂O (1) and [Ni₂(ntb)₂(μ-fum)(H₂O)(CH₃OH)](NO₃)₂·6CH₃OH·H₂O (2) (tp = terephthalate dianion, fum = fumarate dianion, ntb = tris(2-benzimidazolylmethyl)amine) containing tetradentate poly-benzimidazole ligand were synthesized and structurally characterized by IR spectra, UV-Vis, elemental analysis and X-ray crystallography. The Ni(II) ions in 1 and 2 have distorted octahedral geometry with four nitrogen atoms of ntb, one oxygen atom of water and one oxygen atom supplied by the carboxylate group of the bridged dicarboxylato ligand. Complexes 1 and 2 consist of terephthalato- and fumarato-bridged dinickel(II) centers in bis(monodentate) bonding fashion. The Ni?Ni distances are 11.333 Å for 1 and 8.966 Å for 2. The magnetic susceptibility measurements at variable temperature show that two complexes exhibit weak antiferromagnetic interactions between nickel(II) ions with J values of −0.25 cm⁻¹ and −0.36 cm⁻¹, respectively.     

Structure and magnetic properties of polynuclear chloro- and hydroxo-bridged copper(II) complexes formed by a tetramacrocyclic derivative of 1,4,7-triazacyclononane

Two new copper(II) complexes of the ligand 1,2,4,5-tetrakis(1,4,7-triazacyclononan-1-ylmethyl)benzene (L^dur) have been synthesized and characterized by single crystal X-ray studies. The first, [Cu₄L^dur(μ₂-OH)₄]Cl₂(PF₆)₂ · 8H₂O (1), was isolated from a solution of L^dur and Cu²⁺ at pH 9. Under acidic conditions (pH 3), a polymeric complex, {[Cu₄L^dur(μ₂-Cl)₆](PF₆)₂ · 10H₂O}_n (2), crystallized from solution. In both complexes, each of the four triazacyclononane (tacn) rings of the L^dur ligand facially coordinate to separate metal centres. Pairs of Cu(II) centres are then doubly-bridged by hydroxo groups in 1, leading to tetranuclear complex cation units featuring pairs of isolated copper(II) dimers with Cu₂(μ₂-OH)₂ cores folded at the O?O lines. Two forms of the tetranuclear units, featuring slightly different Cu₂(μ₂-OH)₂ core geometries, are present in equal amounts within the crystal lattice. In complex 2, chloro bridging ligands link pairs of Cu(II) centres from neighbouring tetranuclear units, forming a 1D helical polymeric structure. Variable-temperature magnetic susceptibility measurements suggest that the hydroxo-bridged copper(II) centres within one of the tetranuclear units in 1 are weakly antiferromagnetically coupled (J = −27 cm⁻¹), whilst those in the other interact ferromagnetically (J = +19 cm⁻¹). Similar measurements indicate weak ferromagnetic coupling (J = +16 cm⁻¹) for the chloro-bridged copper(II) centres in 2.     

Carboxyester hydrolysis promoted by Cu(II) complexes of pyridyl-amine carboxylate-pendant ligands

Multidentate ligands containing tripodal pyridyl-amine moieties tethered to a carboxylate group by alkyl linkers of varying lengths were synthesized to obtain a series of water-soluble ligands to elucidate the effects of the differing coordination environments on the properties of the resulting metal complexes. These new, water-soluble ligands, [bis-(2-pyridin-2-yl-ethyl)-amino]-acetic acid (L¹), 3-[bis-(2-pyridin-2-yl-ethyl)-amino]-propionic acid (L²), 4-[bis-(2-pyridin-2-yl-ethyl)-amino]-butyric acid (L³), and 6-[bis-(2-pyridin-2-yl-ethyl)-amino]-hexanoic acid (L⁴), were treated with copper(II) perchlorate hexahydrate to yield the corresponding Cu(II) complexes, which have all been characterized by X-ray crystallography. L¹ binds Cu(II) to form the tetrameric complex {[Cu(μ-¹)][ClO₄] · 4H₂O}₄ (1) in the solid state, whereas the Cu(II) complexes of ligands L²-L⁴ form long-chain one-dimensional polymeric complexes {[Cu(μ-L²)][ClO₄] · H₂O}_n (2), {[Cu(μ-L³)][ClO₄] · H₂O}_n (3), and {[Cu(μ-L²)][ClO₄]  · H₂O}_n (4), respectively, in the solid state. Complexes 1-4 dissolved in 10% (v/v) CH₃CN aqueous solution were tested for their ability to promote the hydrolysis of the activated ester compound 4-nitrophenylacetate (NA), with 3 being the most active complex and 1 being the least active, possibly due to differences in the ability of the carboxylate moiety to act as either a general base or a nucleophile in the hydrolysis of NA as dictated by the tether length. The pK_a values of the copper-bound aquo ligands in solution were measured by spectrophotometric titration.     

Crystal structures and magnetic properties of tetranuclear copper(II) complexes of N-(2-hydroxymethylphenyl)salicylideneimine with a defective double-cubane core

Tetranuclear Cu(II) complexes of N-(2-hydroxymethylphenyl)salicylideneimine (H₂L1-H) and its homologues (5-CH₃: H₂L1-Me, 5-Cl: H₂L1-Cl), [Cu(L1-H)]₄ · 3H₂O (1), [Cu(L1-Me)]₄ · 2CH₂Cl₂ (2), and [Cu(L1-Cl)]₄ · 2CH₂Cl₂ (3), have been characterized by X-ray crystal structure analyses and magnetic measurements. The structure analyses revealed that the complexes 1-3 have a defective double-cubane tetra copper(II) core connected by μ₃-alkoxo bridges. The intramolecular Cu?Cu distances are in the range from 5.251(2)-5.256(3) Å for the longest to 3.0518(9)-3.092(2) Å for the shortest. Each Cu(II) ion has a square-pyramidal geometry and the dihedral angles between adjacent Cu(II) basal planes are almost right angles. Magnetic measurements of the present complexes indicate that weak antiferromagnetic interactions (J=−15 to −19 cm⁻¹) between neighboring copper(II) ions are dominant in these tetracopper cores.     

The first example of calix[4]pyrrole functionalized vic-dioxime ligand: Synthesis, characterization, spectroscopic studies and redox properties of the mononuclear transition metal complexes

Novel calix[4]pyrrole bearing vic-dioxime ligand (LH₂) of the general formula, R₁R₂C₂N₂O₂H₂ (where, R₁ = C₆H₅- and R₂ = C₃₉H₅₀N₅-) has been synthesized by the reaction of anti-chlorophenylglyoxime with 3-aminophenylcalix[4]pyrrole at room temperature. The mononuclear Cu(II), Ni(II) and Co(II)complexes of this vic-dioxime ligand were prepared and their structures were confirmed by elemental analysis, FT-IR, TGA and magnetic susceptibility measurements; the HMBC, DEPT, ¹H and ¹³C NMR spectra of the LH₂ ligand were also reported. The electrochemical property of the complexes was investigated in DMSO by cyclic voltammetry at 200 mV s⁻¹ scan rate. The cyclic voltammetric measurements clearly indicated that Co(LH)₂·2H₂O complex differs from the Ni(LH)₂ and Cu(LH)₂ complexes upon the exhibition of quasi-reversible one-electron transfer reduction process in the negative region instead of an irreversible process.     

Synthesis, structures, and magnetic properties of one-dimensional Fe-M (M = Ni, Cu) coordination polymers bridged by nitroprusside

Self-assembling [Fe(CN)₅(NO)]²⁻ and [M(L)]²⁺ (M = Ni, Cu; L = macrocycles) led to one-dimensional coordination polymers, [Ni(L1)][Fe(CN)₅(NO)] · 2H₂O (1) with parallel chains and [Cu(L2)][Fe(CN)₅(NO)] · 3H₂O (2) exhibiting a slanted chain structure. Compound 1 contains a planar macrocycle L1 coordinated to a slightly distorted octahedral Ni(II) ion in which the planarity of L1 gives rise to piling up chains in parallel. In contrast, a more flexible macrocyclic ligand L2 in 2 that surrounds a Cu center with a tetragonal elongation has bulky cyclohexyl groups together with pendant methyl side groups. The presence of the methyl groups on L2 in a chain makes the cyclohexyl groups in an adjacent chain tilted against the CuN₄ basal plane with the methyl groups, eventually resulting in the slanted chain structure. Magnetic data demonstrate that antiferromagnetic interactions (J ≈ −0.13 cm⁻¹) are operating although the paramagnetic centers are linked by the long diamagnetic [Fe(CN)₅(NO)]²⁻ anion.     

Synthesis, crystal structure and spectroscopic behaviors of Co(II) and Cu(II) complexes with Salen-type bisoxime ligands

Two Salen-type ligands (H₂L¹, 4,4′-dichloro-2,2′-[(1,3-propylene)dioxybis(nitrilomethylidyne)]diphenol and H₂L², 4,4′-dinitro-2,2′-[ethylenedioxybis(nitrilomethylidyne)]diphenol) and their corresponding complexes ({[CoL¹(MeOH)]₂(OAc)₂Co} · 2MeOH and [CuL²]₂) have been synthesized and characterized by element analyses, ¹H NMR, FT-IR and UV-Vis spectra, TG-DTA and single crystal X-ray crystallography. Crystallographic data suggests the octahedral geometry for Co(II) complex and square-pyramidal geometry for Cu(II) complex. Furthermore, the fluorescence behavior of Cu(II) complex in DMSO is discussed.