Complex Formation Equilibria Between Zinc(II), Nitrilo-tris(Methyl Phosphonic Acid) and Some Bio-relevant Ligands. The Kinetics and Mechanism for Zinc(II) Ion Promoted Hydrolysis of Glycine Methyl Ester

Binary and ternary complexes of zinc(II) involving nitrilo-tris(methyl phosphonic acid (H₆A) and amino acids, peptides (HL), or DNA constituents have been investigated. The stoichiometry and stability constants for the complexes formed are reported. The results show that ternary complexes are formed in a stepwise manner whereby nitrilo-tris(methylphosphonic acid) binds to zinc(II), which is then followed by coordination of an amino acid, peptide or DNA. Zinc(II) was found to form ZnA and ZnAH _n complex species where n=3, 2 or 1. The stabilities of the ternary complexes are compared with the stabilities of their corresponding binary complexes. The concentration distributions of the various complex species have been evaluated. The kinetics of the base hydrolysis of glycine methyl ester in the presence of Zn(II)-NTP complexes was studied in aqueous solution using a pH-stat technique. The pK _a for ionization of the coordinated water molecule is 9.14 as determined from the kinetic results, while direct potentiometric titration of the complex [Zn(NTP)(H₂O)] gave 9.98 (±0.02). The rate constant for the intramolecular attack of coordinated hydroxide on the ester is k=(2.65×10⁻⁴±0.003) dm³⋅mol⁻¹⋅s⁻¹.     

Crystal structure of palladium(II) complex with 2,2′-dipyridylamine and 4-toluenesulfonyl-L-serine

The [Pd(dpa)(tsser)] complex (1) is prepared from the reaction of PdCl₂ and 2,2′-dipyridylamine (dpa) with 4-toluenesulfonyl-L-serine (tsserH₂). This complex is characterized by spectral methods (IR, UV-Vis, ¹H NMR, and luminescence), elemental analysis, thermal analysis (TG, DTA), and single crystal X-ray diffraction. X-ray structure determinations show that in this complex, Pd^II atoms are four-coordinated in a distorted square-planar configuration by two N atoms from a bidentate 2,2′-dipyridylamine ligand and one N atom and one O atom from a bidentate tsser^2– ligand.     

Kinetics and Mechanism for Hydrolysis of α-Amino Acid Esters in Mixed Ligand Complexes with Zn(II)–Nitrilo-tris(methyl phosphonic Acid)

The kinetics of base hydrolysis of the alanine ethyl ester, in addition to glycine, histidine and methionine methyl esters in the presence of the Zn-NTP complex, were studied in aqueous solution by the pH-potentiometric technique, where NTP denotes the nitrilo-tris(methyl phosphonic acid) ligand. The kinetic data fits assumed that hydrolysis proceeds through formation of a M–OH complex, followed by an intramolecular OH⁻ attack. The effect of an organic solvent on the hydrolysis of coordinated esters was investigated by measuring the rate of hydrolysis in dioxane–water solutions of different compositions at t=25.0 °C and I=0.1 mol⋅dm⁻³. The kinetics of base hydrolysis of the glycine methyl ester was studied at different temperatures. Activation parameters for the base hydrolysis of the complexes were evaluated.     

Reactions of Tertiary Alcohols with Palladium(II) Tetraaqua Complex. Formation of Palladium π-Allyl Complexes

Transformations of 2-methyl-2-propanol, 2-methyl-2-butanol, 2-methyl-2-pentanol, 1-methyl-1-cyclohexanol, and 1-ethyl-1-cyclohexanol in the presence of tetraaquapalladium(II) ions in perchloric acid madium were studied. It was found that the reactions give rise to palladium(II) -allyl complexes. The reaction rate increases and the yield of the corresponding -allyl complex decreases with increasing hydrocarbon chain length. Addition of iron(III) ions to the systems essentially increases the yield of palladium -allyl complexes. The olefin formed from the corresponding tertiary alcohol participates in the formation of the palladium -allyl complex. Oxidation of 2-methyl-2-butanol with tetraaquapalladium(II) ions gives the isomeric palladium -allyl complexes [Pd(³-(CH₃)₂CCHCH₂)bpy]ClO₄ and [Pd(³-(CH₂C(CH₃)CHCH₃))bpy]ClO₄, which were isolated using 2,2'-bipyridyl and characterized by ¹H and ¹³C NMR spectroscopy.     

Kinetics and mechanism of the oxidation of DL-methionine bybis(2,2′-bipyridyl)copper(II) permanganate

Summary The oxidation ofDL-methionine (MT) bybis(2,2-bipyridyl)copper(II) permanganate (BBCP) to the corresponding sulphoxide is first order in BBCP. Michaelis-Menten-type kinetics were observed with respect to MT. The formation constant of the intermediate complex and the rate constant for its decomposition were evaluated. The thermodynamic and activation parameters were also evaluated. The reaction is catalysed by H⁺ but 2,2-bipyridine does not affect the reaction rate. A mechanism is proposed.     

Hydrothermal Synthesis, Crystal Structure and Photoluminescent Property of a Zinc（II） Complex with 2,2′-Diphenic Acid and 2,2′-Bipyridine Ligands

A new dinuclear complex [Zn(dpa)(bipy)(H2O)]2 (dpa = 2,2'-diphenic acid, bipy = 2,2'-bipyridine) 1 has been hydrothermally synthesized and structurally characterized by elemental analysis, IR, fluorescence spectrum and single-crystal X-ray diffraction. The complex crystallizes in monoclinic, space group P21/c with a = 10.960(2), b = 9.4841(18), c = 20.599(4), β = 104.452(3)o, V = 2073.4(7)3, C48H36N4O10Zn2, Mr = 959.55, Dc = 1.537 g/cm3, μ(MoKα) = 1.225 mm-1, F(000) = 984, Z = 2, the final R = 0.0364 and wR = 0.0843 for 2788 observed reflections (I > 2σ(I)). In the crystal structure, the zinc atom is five-coordinated with two carboxylate oxygen atoms from different dpas, one coordinated water molecule and two nitrogen atoms from bipy ligands, showing a slightly distorted triangular bipyramidal geometry. Furthermore, it exhibits a zero-dimensional network structure with a sixteen-membered ring and shows yellow photoluminescent property at room temperature.     

2,2′-dipyridylamine complexes of rhenium(V)

The reactivity of oxorhenium(V) precursors with the potentially N,N-donor ligand 2,2′-dipyridylamine (dpa) has been investigated. Reaction of a two-fold molar excess of dpa with trans-[ReO(OEt)Cl₂(PPh₃)₂] in ethanol led to the isolation of [ReOCl₂(OEt)(dpa)] (1). Spectroscopic measurements indicate that dpa is coordinated as a bidentate in the equatorial plane cis to the oxo group, with the ethoxide in the trans position. Treatment of trans-[ReOCl₃(PPh₃)₂] with a tenfold molar excess of dpa in ethanol at reflux yielded the trans-dioxo complex [ReO₂(dpa)₂]Cl (2), but with a twofold molar excess (μ-O)[{ReOCl₂(dpa)}₂] (3a) was isolated. The latter reaction with (n-Bu₄N)[ReOCl₄] as starting material in ethanol at room temperature led to a dark green product, also with the formulation (μ-O)[{ReOCl₂(dpa)}₂] (3b). These compounds were characterised by common spectroscopic techniques, and the crystal structures of 2·3H₂O, 3a and 3b·2DMSO were determined. The structure of 3b presents a nearly linear O=Re–O–Re=O group, with the two [ReOCl₂(dpa)] halves of the dimer rotated by 180.0° about the Re–O–Re fragment away from an eclipsed conformation. In 3a, the two halves are only rotated by 61.4°.     

Formation kinetics of heteroligand Ni(II) complex with alkyl-substituted 2,2′-dipyrrolylmethenes

The formation kinetics of heteroligand Ni(II) complexes with alkylated dipyrrolylmethenes of symmetric and asymmetric structure was studied. The kinetic and activation parameters of the reactions were determined. The spectral and kinetic data obtained, as well as available data on the solvation of Ni(II) acetate in electron-donor solvents, allowed us to propose an associatively activated concerted mechanism. The Ni(II) complex formation is mainly determined by the rate of substitution of the entering ligand for solvent molecules in the initial Ni(II) complex, that is, by creation of conditions for efficient donor-acceptor interaction.     

Coordination interactions of alkyl-substituted 2,2′-dipyrrolylmethene derivatives with copper(II) aminoacid complexes

Using the method of electron spectroscopy we showed that reaction of alkyl-substituted 2,2′-dipyrrolylmethene derivatives with copper(II) aminoacid complexes led to the formation of heteroligand complexes with two chelated metallocycles forming their coordination sphere. Formation constants of the heteroligand complexes were established and their interrelations with the structure of the aminoacid residue side group were elucidated. It was found that alongside the ability to the primary solvolytic dissociation of aminoacid complex, the main effect on the formation of combined coordination sphere of the chelate is defined by the steric factor depending on the structure of substituent in the aminoacid.     

Kinetics and mechanism of reactions of bis(biguanide)copper(II) ion with 2,2′-bipyridyl and 1,10-phenanthroline in aqueous solution

Summary In aqueous solution [Cu(bigH)₂]²⁺ (bigH=biguanide) reacts with 2,2-bipyridyl (bipy) and 1,10-phenanthroline (phen) through intermediate formation of ternary complexes [Cu(bigH)(L)]²⁺ and [Cu(bipy)(phen)]²⁺ and binary complexes [CuL₂]²⁺ (L=bipy, phen). The rates of the different steps have been followed in borax buffer (pH 8.0±0.1) by stopped-flow spectrophotometry. For each step k_obs=k₀+k_L[L] and the k_L path appears to be associative. H and S values for the k_L path conform to an isokinetic trend.     

Synthesis and Crystal Structure of Bis(2,2′-Bipyridine-N,N′)Dichloromanganese(II) Complex with Free 2,2′-Bipyridine

The title complex [Mn(bipy)₂Cl₂]·0.5bipy·2.5H₂O, where bipy = 2,2'-bipyridine, has been prepared and its crystal structure has been determined by X-ray diffraction methods. The complex crystallizes in the triclinic space group P-1, with a = 8.814(2), b = 11.335(2), c = 13.347(3) Å, α = 76.85(2), β = 89.55(2), γ = 86.52(2)°. Two chloride and two bipy ligands cis-coordinate to a Mn(II) atom with a distorted octahedral geometry. The crystal consists of Mn(II) complex, free bipy and crystalline water. The complex crystalline water link to each other by H-bonding to form supra-molecular chains, and free bipy molecules locate between parallel chains with a van der Waals contact distance of 3.58(1) Å. A π-π interaction is also observed between adjacent bipy rings. The chelating bipy and free bipy showed different IR absorptions.     

Hydrothermal Synthesis and Crystal Structure of a Manganese(II) Coordination Polymer with 1,1′-Biphenyl-2,2′,6,6′-tetracarboxyl Acid and 2,2′:6,2′′-Terpyridine Ligands

The title compound {[Mn(H2BPTC)(tpy)(H2O)]·(H2O)3}n (1, H4BPTC = 1,1′- biphenyl-2,2′,6,6′-tetracarboxylic acid, tby = 2,2′:6,2′′-terpyridine) has been synthesized by the hydrothermal reaction, and its structure was determined by X-ray diffraction and characterized by elemental analysis, IR spectrum and thermogravimetric analysis. The crystal is of monoclinic, space group P21/c with a = 10.971(2), b = 20.776(4), c = 14.332(3) , β = 109.25(3)o, MnC31H27N3O12, Mr = 688.50, V = 3084.1(10) 3, Dc = 1.483 g/cm3, F(000) = 1420, μ = 0.498 mm-1, S = 1.066 and Z = 4. The final refinement gave R = 0.0447 and wR = 0.1103 for 5107 observed reflections with I > 2σ(I). The title complex has a {[Mn(H2BPTC)(tpy)(H2O)]}n chain structure, and the hydrogen bonding interactions make it more stable. Each chain is further connected to the adjacent ones through π···π, C-H···π and rich hydrogen bonds to form a metal-organic coordination polymer.     

Mixed Ligand Complex Formation Reactions and Equilibrium Studies of Cu(II) with Bidentate Heterocyclic Alcohol (N,O) and Some Bio-Relevant Ligands

The formation equilibria of copper(II) complexes and the ternary complexes Cu(HMI)L (HMI=4-Hydroxymethyl-imidazole, L=amino acid, amides or DNA constituents) have been investigated. Ternary complexes are formed by a simultaneous mechanism. The results showed the formation of Cu(HMI)L and Cu(HMI,H₋₁)(L) complexes. The stability of ternary complexes was quantitatively compared with their corresponding binary complexes in terms of the parameters Δlog ₁₀ K and log ₁₀ X. The effect of the side chains of amino acid ligands (Δ_R) on complex formation was discussed. The concentration distributions of various species formed in solution were also evaluated as a function of pH. The thermodynamic parameters ΔH° and ΔS° calculated from the temperature dependence of the equilibrium constants are investigated. The effects of dioxane as a solvent, on the protonation constant of HMI and the formation constants of Cu^II–HMI complexes, were discussed.     

Hydrothermal Synthesis, Crystal Structure and Photoluminescent Property of a Zinc(Ⅱ)Complex with 2,2'-Diphenic Acid and 2,2'-Bipyridine Ligands

A new dinuclear complex[Zn(dpa)(bipy)(H2O)]2(dpa=2,2'-diphenic acid,bipy=2,2'-bipyridine)1 has been hydrothermally synthesized and structurally characterized by elemental analysis,IR,fluorescence spectrum and single-crystal X-ray diffraction.The complex crystallizes in monoclinic,space group P21/c with a=10.960(2),b=9.4841(18),c=20.599(4)(A),β=104.452(3)°,V=2073.4(7)(A)3,C48H36N4O10Zn2,Mr=959.55,Dc=1.537 g/cm3,μ(MoKa)=1.225 mm-1,F(000)=984,Z=2,the final R=0.0364 and wR=0.0843 for 2788 observed reflections(I>20(I)).In the crystal structure,the zinc atom is five-coordinated with two carboxylate oxygen atoms from different dpas,one coordinated water molecule and two nitrogen atoms from bipy ligands,showing a slightly distorted triangular bipyramidal geometry.Furthermore,it exhibits a zero-dimensional network structure with a sixteen-membered ring and shows yellow photoluminescent property at room temperature.     

Assembly of four copper(II)–2,2′-biimidazole complex-supported Strandberg-type phosphomolybdates

Four Strandberg-type phosphomolybdate-based Cu(II) complexes of 2,2′-biimidazole (C₆H₆N₄, H₂biim) and H₂O molecules, namely [Cu(H₂biim)₂(H₂O)][Cu(H₂biim)₂(HPO₄)₂(Mo₅O₁₅)]·2H₂O (1), [{Cu(H₂biim)(H₂O)}₂{μ-Cu(H₂biim)(H₂O)}(P₂Mo₅O₂₃)]₂·20H₂O (2), [Cu(H₂biim)₂][{Cu(H₂biim)(H₂O)₂}{Cu(H₂biim)₂}(HPO₄)(PO₄)(Mo₅ O₁₅)]₂·20H₂O (3), and [Cu(H₂biim)₂(H₂O)][Cu(H₂biim)₂(HPO₄)₂(Mo₅O₁₅)]·6H₂O (4) have been synthesized and characterized by physico-chemical and spectroscopic methods. Single-crystal X-ray diffraction analysis reveals that compound 1 consists of a mono-supporting heteropolyoxoanion [Cu(H₂biim)₂(H₂P₂Mo₅O₂₃)]²⁻and an isolated [Cu(H₂biim)₂(H₂O)]²⁺ cation. Compound 2 is composed of two tetra-supporting heteropolyoxoanions linked via two Cu(II) complex fragments. In compound 3, there exist two symmetrical bi-supported polyoxoanion clusters and an isolated [Cu(H₂biim)₂]²⁺ fragment lying in the center of the clusters. Compound 4 is also constructed from a [Cu(H₂biim)₂(H₂P₂Mo₅O₂₃)]²⁻ polyoxoanion and a [Cu(H₂biim)₂(H₂O)]²⁺ cation, but it has a different space group and packing interactions compared with compound 1.     

Interconversion of copper(II) to copper(I): synthesis,characterization of copper(II) and copper(I) 2,2′-biquinoline complexes and their microbiological activity

The complexes [Cu(biq)₂]Cl₂ and [Cu(biq)₂]BF₄·biq (biq?=?2,2′-biquinoline) have been prepared and characterized. The interconversion to copper(I) complex [Cu(biq)₂]BF₄·biq, from [Cu(biq)₂]Cl₂ has been established. The new complexes have been characterized by elemental analysis, conductivity and magnetic measurements, IR, UV-vis and ¹H- and ¹³C-NMR spectroscopy. The X-ray analysis of the complex [Cu(biq)₂]BF₄·biq supports the assumption of the interconversion of copper(II) to copper(I) in this case. The crystal structure shows that geometry around the metal is severely distorted from T_d, and displays many supramolecular motifs incorporating both hydrophobic (aryl···aryl) and hydrophilic (C–H···F) intermolecular interactions. The microbiological activity of the complexes against bacteria and fungi was found to be high against Candida albicans, and slight to moderate against bacteria. The antimicrobial activity of [Cu(biq)₂]BF₄·biq was slightly better than that observed for [Cu(biq)₂]Cl₂ against both bacteria and fungi.     

Structural characterization of copper (II) tetradecanoate with 2,2′-bipyridine and 4,4′-bipyridine to study magnetic properties

This paper presents synthesis, structural characterization and spintronic applications of copper (II) tetradecanoate derived magnetic complexes. The complexes were prepared by a chemical reaction between [Cu₂(CH₃(CH₂)₁₂COO)₄](EtOH)₂ and 2,2′-bipyridine-4,4′-bipyridine ligands respectively. The complexes were further reacted between the product of the first reaction and 4,4′-bipyridine-2,2′-bipyridine respectively. The structural characterization techniques included elemental analysis, Fourier transformed infrared spectroscopy (FTIR), Ultra-violet–Visible (UV–Vis) spectroscopy, polarized optical microscopy, magnetic moment and thermogravimetric analysis. The structural and characterization results suggested that the synthesized complexes were binuclear and mononuclear covalent complexes of copper(II) with structural formulas [Cu₂(η²-(OOCR)₄](4,4′-bpy)2H₂O] and [Cu(η¹-(OOCR)₂(2,2′-bpy) (4,4′-bpy)] respectively.     

Complexation of copper(II) with 2′,2′-dialkyl-para-tert-butylbenzohydrazides

The complexation of copper(II) with 2′,2′-dimethyl-, 2′,2′-dibutyl-, and 2′,2′-diisobutyl-para-tert-butylbenzohydrazide in water-ethanol media was studied. The reagents (HL) formed [Cu(HL)]²⁺ and [Cu(HL)₂]²⁺ cationic complexes in a weakly acidic medium and uncharged CuL₂ complexes in an alkaline medium. logK _st was calculated for these complexes. The effect of 2′,2′-alkyl radicals on the stability of the complexes was considered. The obtained results were compared with data on the complexation of copper(II) ions with 2′,2′-dialkylbenzohydrazides.