Novel Cu, Co and Pb supramolecular networks of pyridine-2,6-dicarboxylate (pydc) in cooperation with a bent dipyridyl spacer via coordinative, hydrogen-bonding and aromatic stacking interactions

Reaction of M(OAc)₂ (M^II = Cu^II for 1, Co^II for 2, and Pb^II for 3) with pyridine-2,6-dicarboxylic acid (H₂pydc) in presence of a dipyridyl spacer 2,5-bis(4-pyridyl)-1,3,4-oxadiazole (bpo) affords three novel metal-organic supramolecular networks [Cu₂(bpo)(pydc)₂(H₂O)₃] · 2.75H₂O(1), [Co(bpo)(pydc)(H₂O)₂] · (H₂O) (2) and [Pb(pydc)]_n (3), which have been structurally determined by single-crystal X-ray diffraction. The dimeric Cu-pydc coordination framework bridged by a bpo spacer in 1 is hydrogen-bonded to four others to result in a two-dimensional (2-D) sheet array. The neutral monomeric molecules in 2 have an ordered 3-D stacking stabilized via hydrogen bonds and significant π-π interactions in the lattice, possessing large porous channels with the inclusion of guest solvates. In coordination polymer 3, the Pb^II ion takes the unusual distorted capped trigonal prismatic geometry (PbNO₆) and each pydc dianion binds to four Pb^II centres to form a 2-D infinite network. The thermal stabilities of these complexes have also been investigated.     

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.     

One-dimensional helical coordination polymers of cobalt(II) and iron(II) ions with 2,2′-bipyridyl-3,3′-dicarboxylate (BPDC)

One-dimensional (1-D) helical coordination polymers, [M^II(H₂O)₃(BPDC)]_n · nH₂O (M = Co (1), Fe (2)), have been prepared by the self-assembly of cobalt(II) and iron(II) ions, respectively, with 2,2′-bipyridyl-3,3′-dicarboxylic acid (H₂BPDC) in an aqueous solution. X-ray crystal structures of compounds 1 and 2 show that each metal ion displays a distorted octahedral coordination geometry including three water oxygen atoms, one oxygen atom of the carboxylate of a BPDC²⁻ belonging to the adjacent metal ion and two nitrogen atoms from the BPDC²⁻ acting as a chelating ligand. In 1 and 2, one carboxylate oxygen atom of coordinated BPDC²⁻ binds to the neighboring metal ion, which give rise to 1-D helical coordination polymers. The helical chains of 1 and 2 are linked by the hydrogen bonding interactions between the carboxylate oxygen atom of the BPDC²⁻ ion belonging to a chain and the water molecule of the adjacent helical chain, which lead to 2-D networks extending along the ab plane. The supramolecules 1 and 2 show isomorphous structures regardless of the metal ions.     

Synthesis, characterization, and magnetic study of pyrazine bridged polymeric complexes of copper(II)

The synthesis, structural characterization and magnetic property of two new coordination polymers [Cu(pyz)(μ-CH₃CO₂)₄]_n (1) and [Cu(pyz)(μ-CCl₃CO₂)₄]_n (2) (pyz = pyrazine) are reported. Here, the carboxylato bridged two dinuclear copper(II) complexes are linked through pyrazine giving a 1-D alternating chain. The magnetic property of the complexes indicates a significant difference originated from the introduction of electron withdrawing substituent on the bridging dicarboxylate. Complex 1 exhibits strong antiferromagnetic interactions with J = −344.61 cm⁻¹, whereas 2 exhibits comparatively less strong antiferromagnetic coupling with J = −238.53 cm⁻¹.     

A 3D chiral supramolecular framework of Cu(II): Synthesis, structure and magneto-structural correlations

A metal-organic coordination chain of Cu(II), viz {[Cu(Hbtc)(NH₃)₄](H₂O)}_n (1) (btc = benzenetricarboxylate) has been synthesized and structurally characterized. The sky blue single crystals of 1 were grown by the dissolution of the as-synthesized insoluble product obtained from the reaction of Cu(II), H₃btc and 4,4′-bipy in aqueous NH₃ solution. Structural determination reveals that 1 crystallizes chiral P2₁2₁2₁ space group and 1D coordination chain of Cu(II) bridged by the Hbtc linker. 1D chains are H-bonded via the guest water molecules forming a 2D sheet like structure and 2D sheets through π-π and N-H···O H-bonding interactions produce a 3D supramolecular framework with 1D water filled channels along the a-axis. Temperature dependent magnetic measurement exhibits weak antiferromagnetic intrachain interaction between Cu(II) centers through the Hbtc linker with J = −0.17 cm⁻¹ and g = 2.01 and at low temperature interchain ferromagnetic interaction is predominates. The dominant antiferromagnetic interaction is supported by the DFT calculations.     

Structure and magnetic properties of a tetranuclear Cu(II) complex containing the 2-(pyridine-2-yliminomethyl)-phenol ligand

A tetranuclear Cu(II) complex [Cu₄L₄(H₂O)₄](ClO₄)₄ has been synthesized using the terdentate Schiff base 2-(pyridine-2-yliminomethyl)-phenol (HL) (the condensation product of salicylaldehyde and 2-aminopyridine) and copper perchlorate. Chemical characterizations such as IR and UV/Vis of the complex have been carried out. A single-crystal diffraction study shows that the complex contains a nearly planar tetranuclear core containing four copper atoms, which occupy four equivalent five-coordinate sites with a square pyramidal environment. Magnetic measurements have been carried out over the temperature range 2-300 K and with 100 Oe field strengths. Analysis of magnetic susceptibility data indicates a strong antiferromagnetic (J₁ = −638 cm⁻¹) exchange interaction between diphenoxo-bridged Cu(II) centers and a moderate antiferromagnetic (J₂ = −34 cm⁻¹) interaction between N-C-N bridged Cu(II) centers. Magnetic exchange interactions (J’s) are also discussed on the basis of a computational study using DFT methodology. The spin density distribution (singlet ground state) is calculated to visualize the effect of delocalization of spin density through bridging groups.     

3D supramolecular network assembly and thermal decomposition of new copper(II) complexes with pyrazine-2,6-dicarboxylic acid

Four new Cu(II) complexes [Cu(pzda)(2,2′-bpy)(H₂O)] · 2.5H₂O (1), [Cu(pzda)(phen)(H₂O)] · H₂O (2), [Cu(pzda)(4,4′-bpy)] · H₂O (3) and [Cu(pzda)(bpe)_0.5(H₂O)] (4) were synthesized by hydrothermal reactions of copper salt (acetate or sulphate) with pyrazine-2,6-dicarboxylic acid (H₂pzda), and 2,2′-bipyridine (2,2′-bpy), 1,10-phenanthroline (phen), 4,4′-bipyridine (4,4′-bpy) or 1,2-bis(4-pyridyl)-ethane (bpe), respectively. For 1 and 2, they are both monomeric entities which are further assembled into 3D supramolecular networks by hydrogen bonds and π-π stacking interactions. Complex 3 has a 2D metal-organic framework which is connected into 3D supramolecular network by hydrogen bonds. However, for 4, the bpe ligand bridges two Cu(II) ions into binuclear unit, and then the binuclear molecules are assembled into 3D supramolecular network by hydrogen bonds between the coordination water molecule and the carboxylate oxygen atoms. The thermal decomposition mechanism of complexes 1 and 2 cooperated with powder XRD at different temperatures is discussed. The results reveal that once liberation of water molecules takes place the supramolecular network of 1 and 2 collapses.     

Structure and magnetic properties of a tetranuclear Cu4O4 open-cubane in [Cu(L)]4·4H2O with L = (E)-N′-(2-oxy-3-methoxybenzylidene)benzohydrazide

The in-situ formed hydrazone Schiff base ligand (E)-N′-(2-oxy-3-methoxybenzylidene)benzohydrazide (L²⁻) reacts with copper(II) acetate to a tetranuclear open cubane [Cu(L)]₄ complex which crystallizes as two symmetry-independent (Z′ = 2) S₄-symmetrical molecules in different twofold special positions with a homodromic water tetramer. The two independent (A and B) open- or pseudo-cubanes with Cu₄O₄ cores of 4 + 2 class (Ruiz classification) each have three different magnetic exchange pathways leading to an overall antiferromagnetic coupling with J_1B = J_2B = −17.2 cm⁻¹, J_1A = −36.7 cm⁻¹, J_2A = −159 cm⁻¹, J_3A = J_3B = 33.5 cm⁻¹, g = 2.40 and ρ = 0.0687. The magnetic properties have been analysed using the H = −Σ_i,jJ_ij(S_iS_j) spin Hamiltonian.     

Crystal structure and magnetic behavior of a copper(II)-(pyrazine 2,3-dicarboxylate) coordination polymer: 3D architecture stabilized by H-bonding

Reaction of Cu(ClO₄)₂ · 6H₂O and pyrazine 2,3-dicarboxylate (pzdc) in aqueous ammonia medium results [Cu(pyrazine 2,3-dicarboxylate)(H₂O)₂] · H₂O (1). The X-ray single crystal structure reveals that the compound is a 1D polymeric sinusoidal infinite chain which through intra- and inter-molecular hydrogen bonding interactions, involving lattice and coordinated water molecules with dicarboxylate oxygens and pyrazine nitrogens, gives rise to a 3D architecture. The variable temperature magnetic measurements show weak antiferromagnetic interactions between the Cu(II) centers. The best fit parameters through the typical equation for a uniform copper (II) chain are: J=−0.25 cm⁻¹, g=2.17, R=1.3×10−6. The EPR spectrum does not alter with temperature (from r.t. to 4 K). The spectra are typical for square-pyramidal geometry of copper(II) ions, g_∥=2.24 and g_⊥=2.10 (average g=2.15, in good agreement to the value obtained by susceptibility fit).     

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.     

Dinuclear copper(II) chloro complex of the ligand 2,3,5,6-tetra(2-pyridyl)pyrazine

Crystallographic and magnetic studies have been performed on the complex, [{CuCl}₂(μ-tppz)][PF₆]₂, where tppz is 2,3,5,6-tetra-2-pyridinylpyrazine. The crystal structure revealed an infinite, ionic chain wherein Cu(II) ions are respectively above and below the plane of the pyrazine moiety of the bridging tppz ligand with the pyridine moieties moving out of the pyrazine plane in order to coordinate to Cu(II). Each chloride ligand bonds equatorially to Cu(II) in a [{CuCl}₂(μ-tppz)]²⁺ ion and axially to a neighboring [{CuCl}₂(μ-tppz)]²⁺ ion so as to form a one-dimensional chain in the solid state. The temperature-dependent magnetic susceptibilitity could be satisfactorily fitted by using a modified Bleaney-Bowers expression (for H = −JS_a · S_bJ = −5.6 cm⁻¹ and g = 2.16) where the exchange interaction is suggested to involve the orbitals of the tppz ligand.     

[Cu4(H2O)4(dmapox)2(btc)]n · 10nH2O: The first two-dimensional polymeric copper(II) complex with bridging μ-trans-oxamidate and μ4-1,2,4,5-benzentetracarboxylato ligands: Synthesis, crystal structure and DNA binding studies

A two-dimensional copper(II) polymer with formula of [Cu₄(H₂O)₄(dmapox)₂(btc)]_n · 10nH₂O, where dmapox is the dianion of N,N′-bis[3-(dimethylamino)propyl]oxamide and btc is the tetra-anion of 1,2,4,5-benzenetetracarboxylic acid, was synthesized and characterized by elemental analysis, conductivity measurement, IR and electronic spectral studies. The crystal structure of the complex has been determined by X-ray single-crystal diffraction. The structure consists of crystallized water molecules and neutral two-dimensional copper(II) coordination polymeric networks constructed both by the bis-tridentate μ-trans-dmapox and tetra-monodentate μ₄-btc bridging ligands. Each btc ligand links four trans-dmapox-bridged binuclear copper(II) building blocks [Cu₂(H₂O)₂(trans-dmapox)]²⁺ and each binuclear copper(II) building block attaches to two btc ligands forming an infinite 2D layer which consists of 4+4 grids with dimensions of 13.563(5) × 15.616(5) Å. The environment around the copper(II) atom can be described as a distorted square-pyramid and the Cu?Cu separations through μ-trans-dmapox and μ₄-btc bridging ligands are 5.225 Å (Cu1-Cu1ⁱ), 5.270 Å (Cu2-Cu2ⁱⁱ), 6.115 Å (Cu1-Cu2), 9.047 Å (Cu1-Cu2ⁱⁱⁱ) and 10.968 Å (Cu1-Cu1ⁱⁱⁱ), respectively. Abundant hydrogen bonds among the crystallized, the coordinated water molecules, and the uncoordinated carboxyl oxygen atoms cross-link the two-dimensional layers into an overall three-dimensional channel-like framework. The interaction of the copper(II) polymer with calf thymus DNA (CT-DNA) has been investigated by using absorption, emission spectral and electrochemical techniques. The results indicate that the copper(II) polymer interacts with DNA strongly (K_b = 4.8 × 10⁵ M⁻¹ and K_sv = 1.1 × 10⁴) and the interaction mode between the copper(II) polymer and DNA may be the groove binding. To the best of our knowledge, this is the first report about the crystal structure and DNA-binding studies of a two-dimensional copper(II) polymer bridged both by the trans-oxamidate and btc ligands.     

Synthesis, crystal structure and interaction with DNA and HSA of (N,N'-dibenzylethane-1,2-diamine) transition metal complexes

A new ligand, N,N′-dibenzylethane-1,2-diamine (L) and its four transition metal(II) complexes, ML₂(OAc)₂ · 2H₂O (M = Cu, Ni, Zn, Co), have been synthesized and characterized by elemental analysis, mass spectra, molar conductivity, NMR and IR. Moreover, the crystals structure of Cu(II) and Ni(II) complexes characterized by single crystal X-ray diffraction showed that the complexes have a similar molecular structure. Ni(II) has an regular octahedral coordination environment complexes, but typical Jahn Teller effect influenced Cu(II) in an elongated octahedral environment. The interaction between complexes and calf thymus DNA were studied by UV and fluorescence spectra measure, which showed that the binding mode of complexes with DNA is intercalation. Under physiological pH condition, the effects of Cu(OAc)₂L₂ · 2H₂O and Ni(OAc)₂L₂ · 2H₂O on human serum albumin were examined by fluorescence. The results of spectroscopic measurements suggested that the hydrophobic interaction is the predominant intermolecular force. The enthalpy change ΔH⁰ and the entropy change ΔS⁰ of Cu(OAc)₂L₂ · 2H₂O and Ni(OAc)₂L₂ · 2H₂O were calculated to be −11.533 kJ mol⁻¹ and 46.339 J mol⁻¹ K⁻¹, −11.026 kJ mol⁻¹ and 46.396 J mol⁻¹ K⁻¹, respectively, according to the Scatchard’s equation. The quenching mechanism and the number of binding site (n ≈ 1) were also obtained from fluorescence titration data.     

Synthesis, structure, sorption and magnetic properties of Ni(II) and Cu(II) complexes with thiosemicarbazone of 2-hydroxybenzaldehyde, bridged by 4,4′-bipyridine

(ML)₂(bipy) complexes (LH₂ = thiosemicarbazone of 2-hydroxybenzaldehyde, bipy = 4,4′-bipyridine, M = Ni(II), 1, or Cu(II), 2) were synthesized and characterized by X-ray crystallography. Compound 1 possessed porous structure due to peculiarities of crystal packing, whereas 2 formed infinite zig-zag chains with dense non-porous packing. It was shown that 1 absorbed 0.013 cm³/g of methanol vapor in two steps. Complex 1 was diamagnetic; for 2, the dependency of χ versus T could be interpreted by Bleaney-Bowers expression in 20-300 K temperature range (J = −6.8 cm⁻¹, g = 2.07).     

Structure and magnetic properties of polynuclear copper(II) compounds with syn-anti carboxylato- and bromo-bridges

Synthesis, spectroscopic and magnetic properties, and X-ray crystal structures of two copper(II) polymers Cu(2-qic)Br (2-qic = quinoline-2-carboxylate) (1) and Cu(2-pic)Br (2-pic = pyridine-2-carboxylate) (2) are described. These compounds are isostructural with Cu(2-qic)Cl and Cu(2-pic)Cl, respectively, the X-ray crystal structures of which were reported recently. Both complexes are polynuclear copper(II) compounds (1D and 2D, respectively) based on syn-anti carboxylate bridges and additionally on linear monobromo- (in 1) and dibromo-bridging (in 2) motifs. The magnetic properties were investigated in the temperature range 1.8-300 K. They reveal the occurrence of strong antiferromagnetic coupling (J₁ = −102.5 cm⁻¹) through the single bromo-bridge in 1, which is much stronger than that transmitted by the single chloro-bridge (J = −57.0 cm⁻¹). Very weak ferromagnetic interaction through the syn-anti carboxylate bridge J₂ is expected as it was observed in isomorphous Cu(2-qic)Cl (J = 0.37 cm⁻¹). For 2 a weak ferromagnetic couplings through the syn-anti carboxylate (zJ′ = 1.35 cm⁻¹) and dibromo-bridges (J = 8.31 cm⁻¹) were found. The experimental results indicate that the observed ferromagnetic exchange through dibromo-bridge is weaker than that in the chloride analog (J = 15.0 cm⁻¹). The magnitude of magnetic interactions is discussed on the basis of structural data of compounds 1 and 2 and their halide analogues.     

Binding of copper(II) to thyrotropin-releasing hormone (TRH) and its analogs

Spectroscopy (UV-Vis, ¹H NMR, ESR) and electrochemistry revealed details of the structure of the Cu(II)-TRH (pyroglutamyl-histidyl-prolyl amide) complex. The ¹H NMR spectrum of TRH has been assigned. NMR spectra of TRH in the presence of Cu(II) showed that Cu(II) initially binds TRH through the imidazole. TRH analogs, pGlu-His-Pro-OH, pGlu-(1-Me)His-Pro-amide, pGlu-His-(3,4-dehydro)Pro-amide, pGlu-His-OH, pGlu-Glu-Pro-amide, and pGlu-Phe-Pro-amide provided comparison data. The stoichiometry of the major Cu(II)-TRH complex at pH 7.45 and greater is 1:1. The conditional formation constant (in pH 9.84 borate with 12.0 mM tartrate) for the formation of the complex is above 10⁵ M⁻¹. The coordination starts from the 1-N of the histidyl imidazole, and then proceeds along the backbone involving the deprotonated pGlu-His amide and the lactam nitrogen of the pGlu residue. The fourth equatorial donor is an oxygen donor from water. Hydroxide begins to replace the water before the pH reaches 11. Minority species with stoichiometry of Cu-(TRH)_x (x = 2-4) probably exist at pH lower than 8.0. In non-buffered aqueous solutions, TRH acts as a monodentate ligand and forms a Cu(II)-(TRH)₄ complex through imidazole nitrogens. All the His-containing analogs behave like TRH in terms of the above properties.     

Synthesis, spectral and magnetical characterization of monomeric [Cu(2-NO2bz)2(nia)2(H2O)2] and structural analysis of similar [Cu(RCOO)2(L-N)2(H2O)2] complexes

A new complex of composition [Cu(2-NO₂bz)₂(nia)₂(H₂O)₂] (1) (nia = nicotinamide, 2-NO₂bz = 2-nitrobenzoate) has been prepared and its composition and stereochemistry as well as coordination mode have been determined by elemental analysis, electronic, infrared and EPR spectroscopy, magnetization measurements over the temperature range 1.8-300 K, and its structure has been solved, as well. The complex structure consists of the centrosymmetric molecules with Cu(II) atom monodentately coordinated by the pair of 2-nitrobenzoato anions and by the pair of nicotinamide molecules, forming nearly tetragonal basal plane, and by a pair of water molecules that complete tetragonal-bipyramidal coordination polyhedron about the copper atom. The complex 1 exhibits magnetic moment μ_eff = 1.86 B.M. at 300 K which decreases to μ_eff = 1.83 B.M. at 1.8 K. The magnetic susceptibility temperature dependence obeys Curie-Weiss law with Curie constant of 0.442 cm³ K mol⁻¹ and with Weiss constant of −1.0 K. EPR spectra at room temperature as well as at 77 K are of axial type with g_⊥ = 2.065 and g_∥ = 2.280 and exhibit clearly, but partially resolved parallel hyperfine splitting with A_II = 160 G, that is consistent with the determined molecular structure of 1. In order to analyze the factors influencing the degree of tetragonal distortion of coordination polyhedron, the dataset of 72 structures similar to that of 1 was extracted from CCD and analyzed. A significant correlation between the average Cu-O_ax bond length and tetragonality parameter τ which was found as a consequence of the Jahn-Teller effect.     

Ternary copper(II) complexes involving 2-(aminomethyl)-benzimidazole and some bio-relevant ligands. Equilibrium studies and kinetics of hydrolysis for glycine methyl ester under complex formation

Formation equilibria of copper(II) complexes of 2-(aminomethyl)-benzimidazole (AMBI) and the ternary complexes Cu(AMBI)L (L = amino acid, amide, dicarboxylic acid or DNA constituents) have been investigated. Ternary complexes of amino acids or amides are formed by a simultaneous mechanism. Amino acids form the complex Cu(AMBI)L, whereas amides form two complex species Cu(AMBI)L and Cu(AMBI)(LH₋₁). The ternary complexes of copper(II) with AMBI and dicarboxylic acids or DNA units are formed by a stepwise mechanism, whereby binding of copper(II) to AMBI is followed by ligation of the dicarboxylic acids or DNA components. The values of Δ log K indicate that the ternary complexes containing aromatic amino acids are significantly more stable than the complexes containing alkyl- and hydroxyalkyl-substituted amino acids. This may be taken as an evidence for a stacking interaction between the aromatic moiety of AMBI and the aromatic side chains of the bio-active ligands. The solid complexes Cu(AMBI)L where L = 1,1-cyclobutanedicarboxylic acid (CBDCA) and malonic acid were separated and identified by elemental analysis and infrared spectroscopy and magnetic moment. The decomposition course and steps for the isolated complexes were analyzed and the kinetic parameters of the non-isothermal decomposition were calculated. The hydrolysis of glycine methyl ester (MeGly) is catalyzed by the Cu(AMBI)²⁺ complex. The kinetic data is fitted assuming that the hydrolysis reaction proceeds in two steps. The first step, involving coordination of the amino acid ester by the amino and carbonyl groups, is followed by rate-determining attack by OH⁻ ion. The second step involves the equilibrium formation of the hydroxo-complex Cu(AMBI)(MeGly)(OH) followed by intramolecular OH⁻ attack.     

Supramolecular manganese(II) compounds influenced by conformational flexibility and rigidity of bis(4-pyridyl) containing bridging ligands

A covalent-bonded one-dimensional (1D) chain, [Mn(bpe)₂(SCN)₂]_n (1) [bpe=1,2-bis(4-pyridyl)ethane], and a hydrogen-bonded two-dimensional (2D) sheet, [Mn(tbp)₂(H₂O)₂(SCN)₂] (2) [tbp=trans-1,2-bis(4-pyridyl)ethylene], have been prepared. Complex 1 can be viewed as a purely coordinative-bonded 1D motif doubly bridged by the bpe ligand that is a gauche conformational isomer with a large dihedral angle of 73.9°. The two bridging bpe ligands feature a shape of square with a dimension of 10.064 Å × 9.776 Å. The compound 2 possesses non-covalent bonding forces of hydrogen bonds and π-π interactions responsible for the fabrication of the 2D architecture. Magnetic susceptibility data for 1 were fitted by employing the infinite chain model (H=−J∑S_i·S_i+1) to give parameters of J=−0.052 cm⁻¹ and g=2.00, indicating the presence of a weak anti-ferromagnetic coupling.     

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.