Synthesis of lateral macrobicyclic compartmental ligands: structural,magnetic, electrochemical,and catalytic studies of mono- and binuclear copper(II) complexes

A series of putative mono- and binuclear copper(II) complexes, of general formulas [CuL](ClO(4)) and [Cu(2)L](ClO(4))(2), respectively, have been synthesized from lateral macrocyclic ligands that have different compartments, originated from their corresponding precursor compounds (PC-1, 3,4:9,10-dibenzo-1,12-[N,N'-bis[(3-formyl-2-hydroxy-5-methyl)benzyl]diaza]-5,8-dioxacyclotetradecane; and PC-2, 3,4:9,10-dibenzo-1,12-[N,N'-bis[(3-formyl-2-hydroxy-5-methyl)benzyl]diaza]-5,8-dioxacyclopentadecane). The precursor compound PC-1 crystallized in the triclinic system with space group P(-)1. The mononuclear copper(II) complex [CuL(1a)](ClO(4)) is crystallized in the monoclinic system with space group P2(1)/c. The binuclear copper(II) complex [Cu(2)L(2c)](ClO(4))(2) is crystallized in the triclinic system with space group P(-)1; the two Cu ions have two different geometries. Electrochemical studies evidenced that one quasi-reversible reduction wave (E(pc) = -0.78 to -0.87 V) for mononuclear complexes and two quasi-reversible one-electron-transfer reduction waves (E(1)(pc) = -0.83 to -0.92 V, E(2)(pc) = -1.07 to -1.38 V) for binuclear complexes are obtained in the cathodic region. Room-temperature magnetic-moment studies convey the presence of antiferromagnetic coupling in binuclear complexes [mu(eff) = (1.45-1.55)mu(B)], which is also suggested from the broad ESR spectra with g = 2.10-2.11, whereas mononuclear complexes show hyperfine splitting in ESR spectra and they have magnetic-moment values that are similar to the spin-only value [mu(eff) = (1.69-1.72)mu(B)]. Variable-temperature magnetic susceptibility study of the complex shows that the observed -2J value for the binuclear complex [Cu(2)L(1b)](ClO(4))(2) is 214 cm(-1). The observed initial rate-constant values of catechol oxidation, using complexes as catalysts, range from 4.89 x 10(-3) to 5.32 x 10(-2) min(-1) and the values are found to be higher for binuclear complexes than for the corresponding mononuclear complexes.     

Magnetic, electronic and electrochemical studies of mono and binuclear Cu(II) complexes using novel macrocyclic ligands

A series of new mono and binuclear copper (II) complexes [Cul]X(2)and [Cu(2)lX(2)] where 1 = L(1), L(2) and L(3) are the macrocyclic ligands. In mononuclear complexes the geometry of Cu(II) ion is distorted squareplanar and in binuclear complexes the geometry of Cu(II) is tetragonal. The synthesized complexes were characterized by spectroscopic (IR,UV-vis and ESR) techniques. Electrochemical studies of the complexes reveals that all the mononuclear Cu(II) complexes show a single quasireversible one-electron transfer reduction wave (E(pc) = -0.76 to -0.84V) and the binuclear complexes show two quasireversible one electron transfer reduction waves (E(pc)(1) = -0.86 to -1.01V, E(pc)(2) = -1.11 to -1.43V) in cathodic region. The ESR spectra of mononuclear complexes show four lines with nuclear hyperfine splittings with the observed g(11) values in the ranges 2.20-2.28, g( perpendicular) = 2.01-2.06 and A(11) = 125-273. The binuclear complexes show a broad ESR spectra with g = 2.10-2.11. The room temperature magnetic moment values for the mononuclear complexes are in the range [mu(eff) = 1.70-1.72BM] and for the binuclear complexes the range is [mu(eff) = 1.46-1.59BM].     

Synthesis, Characterization, Spectroscopic and Electro-chemical Properties of New Mono- and Binuclear Copper(I) Complexes with Substituted 2,2''''-Bipyridine

Introduction Copper(I) complexes have received much attention for their being less expensive and environmentally friendly, various coordination geometry, rich photo-chemical and photophysical properties.1-7 It is well known that copper complexes with diimine (2,2'-bipy- ridine, 1,10-phenanthroline and their substituted deriva-tives designated as diimine) generally exhibit low en-ergy metal-to-ligand charge-transfer (MLCT) states lo-cated in the regions of 350650 nm (e ≈ 103—104 dm3昺ol-1昪…     

Synthesis,spectral, magnetic,electrochemical and kinetic studies of copper(II), nickel(II) and zinc(II) complexes derived from a phenol-based unsymmetrical “end-off” ligand

A new unsymmetrical end-off, aminomethylated N-methylpiperazine and aminomethylated diethanolamine armed binucleating ligand, 2-[bis(2-hydroxyethyl)aminomethyl]-6-[(4-methylpiperazin-1-yl)methyl]-4-formylphenol (HL), was synthesized by following sequential aromatic Mannich reactions. Mononuclear and binuclear Cu(II), Ni(II) and Zn(II) complexes were synthesized and characterized by elemental and spectral analysis. The EPR spectrum of the mononuclear copper complex shows four hyperfine splittings and the binuclear complex shows a broad signal due to anti-ferromagnetic interaction. The room temperature magnetic moment of the mono and binuclear copper complexes are 1.72 and 2.68 BM, respectively. Variable temperature magnetic moment study of the binuclear copper(II) complex shows weak antiferromagnetic coupling (?2J value, 21 cm^?1). The mononuclear Ni(II) complex is square planar and diamagnetic. The six-coordinate binuclear Ni(II) complex shows a magnetic moment of 3.06 BM. Electrochemical studies of the complexes reveal that all mononuclear complexes show a single irreversible one-electron reduction wave and the binuclear complexes show two irreversible one-electron reduction waves in the cathodic region. Catecholase activity of copper(II) complexes using pyrocatechol as a model substrate and the hydrolysis of 4-nitrophenylphosphate using copper(II), nickel(II) and zinc(II) complexes as catalysts showed that binuclear complexes have higher rate constants than corresponding mononuclear complexes.     

Identification of Cu(II)/Cu(III) couples in binuclear copper(II) complexes

A new series of binuclear copper(II) complexes were synthesised and studied by magnetic, spectral, ESR and cyclic voltammetry methods. The μ_eff values per copper atom correspond to the values observed for mononuclear copper(II) complexes. ESR spectral data in solution indicate weak interactions resulting from the electron delocalisation through the ligand system. Two nearly reversible red-ox couples are identified at $\text{+}\text{?}$0.50 V and $\text{+}\text{?}$0.75 V vs SCE. They correspond to Cu(II)αCu(III) red-ox processes, successively occurring at the two copper sites in the binuclear complexes.     

Rigid NON- and NSN-ligand complexes of tetravalent and trivalent uranium: comparison of U-OAr2 and U-SAr2 bonding

A rigid NSN-donor proligand, 4,5-bis(2,6-diisopropylanilino)-2,7-di-tert-butyl-9,9-dimethylthioxanthene (H(2)[TXA(2)], 1) was prepared by palladium-catalyzed coupling of 2,6-diisopropylaniline with 4,5-dibromo-2,7-di-tert-butyl-9,9-dimethylthioxanthene. Deprotonation of 1 using (n)BuLi provided Li(2)(DME)(2)[TXA(2)] (2), and subsequent reaction with UCl(4) afforded [Li(DME)(3)][(TXA(2))UCl(3)] (4). The analogous NON-donor ligated complex [(XA(2))UCl(3)K(DME)(3)] [3; XA(2) = 4,5-bis(2,6-diisopropylanilino)-2,7-di-tert-butyl-9,9-dimethylxanthene] was prepared by the reaction of K(2)(DME)(x)[XA(2)] with UCl(4). A cyclic voltammogram (CV) of 3 in THF/[NBu(4)][B(C(6)F(5))(4)] at 200 mV s(-1) showed an irreversible reduction to uranium(III) at E(pc) = -2.46 V versus FeCp(2)(0/+1), followed by a product wave at E(1/2) = -1.83 V. Complex 4 also underwent irreversible reduction to uranium(iii) [E(pc) = -2.56 V], resulting in an irreversible product peak at E(pa) = -1.83 V. One-electron reduction of complexes 3 and 4 using K(naphthalenide) under an argon atmosphere in DME yielded 6-coordinate [(XA(2))UCl(DME)] (5) and the thermally unstable 7-coordinate [(TXA(2))U(DME)Cl(2)Li(DME)(2)] (6), respectively. The U-S distances in 4 and 6 are uncommonly short, the C-S-U angles are unusually acute, and the thioxanthene backbone of the TXA(2) ligand is significantly bent. By contrast, the xanthene backbone in XA(2) complexes 3 and 5 is planar. However, κ(3)-coordination and an approximately meridional arrangement of the ancillary ligand donor atoms is maintained in all complexes. DFT and Atoms in Molecules (AIM) calculations were carried out on 3, 4, 5, 6, [(XA(2))UCl(3)](-) (3B), [(TXA(2))UCl(2)(DME)](-) (6B) and [(TXA(2))UCl(DME)] (6C) to probe the extent of covalency in U-SAr(2) bonding relative to U-OAr(2) bonding.     

一种新型双核Cu配合物的电化学性质及其应用研究

本文研究了一种新型平面双核Cu配合物 (deCu)的电化学性质及其修饰电极在水溶液中对半胱氨酸和L_色氨酸的电催化作用 .悬汞电极循环伏安曲线示出 ,在 - 0 .5V和 - 0 .2 5V处显示的还原峰分别对应于配体和配合物中心金属离子的还原反应 .光谱电化学实验进一步表明 :电位价跃至 - 0 .75V时 ,在 4 40nm处出现Cu(Ⅱ )向低价铜的电子跃迁吸收峰 ,而紫外光谱在 2 70和 2 80nm两处出现的吸收峰红移 ,这可能是因为配合物分子氧桥联发生配位形成大偶合体系所致 .利用循环伏安法制备deCu/GC和deCu/石墨碳修饰电极 ,实验表明 ,该修饰电极修饰膜的氧 /还反应为 2电子 2质子过程 ,并对半胱氨酸和L_色氨酸等具有较好的电催化氧化效果     

Synthesis, characterization and biological activities of Cu(II), Co(II), Mn(II), Fe(II), and UO2(VI) complexes with a new Schiff Base hydrazone: O-hydroxyacetophenone-7-chloro-4-quinoline hydrazone

The Schiff base hydrazone ligand HL was prepared by the condensation reaction of 7-chloro-4-quinoline with o-hydroxyacetophenone. The ligand behaves either as monobasic bidentate or dibasic tridentate and contain ONN coordination sites. This was accounted for be the presence in the ligand of a phenolic azomethine and imine groups. It reacts with Cu(II), Ni(II), Co(II), Mn(II), UO(2) (VI) and Fe(II) to form either mono- or binuclear complexes. The ligand and its metal complexes were characterized by elemental analyses, IR, NMR, Mass, and UV-Visible spectra. The magnetic moments and electrical conductance of the complexes were also determined. The Co(II), Ni(II) and UO(2) (VI) complexes are mononuclear and coordinated to NO sites of two ligand molecules. The Cu(II) complex has a square-planar geometry distorted towards tetrahedral, the Ni(II) complex is octahedral while the UO(2) (VI) complex has its favoured heptacoordination. The Co(II), Mn(II) complexes and also other Ni(II) and Fe(III) complexes, which were obtained in the presence of Li(OH) as deprotonating agent, are binuclear and coordinated via the NNNO sites of two ligand molecules. All the binuclear complexes have octahedral geometries and their magnetic moments are quite low compared to the calculated value for two metal ions complexes and thus antiferromagnetic interactions between the two adjacent metal ions. The ligand HL and metal complexes were tested against a strain of Gram +ve bacteria (Staphylococcus aureus), Gram -ve bacteria (Escherichia coli), and fungi (Candida albicans). The tested compounds exhibited high antibacterial activities.     

Synthesis and complexes of an N4 Schiff-base macrocycle derived from 2,2'-iminobisbenzaldehyde

An N(4) tetradentate [1 + 1] Schiff base metal free macrocycle HL was prepared, by 1?:?1 condensation of 2,2'-iminobisbenzaldehyde (1) and diethylenetriamine, and characterised. Seven mononuclear complexes, [Zn(II)L(py)](BF(4)) (2), [Cu(II)L](BF(4))]·H(2)O (3), [Ni(II)L](BF(4))·H(2)O (4), [Co(II)L](BF(4))]·H(2)O (5), Fe(III)L(BF(4))(2)·2H(2)O·MeCN (6), [Co(III)L(NCS)(2)]·0.3py (7) and [Fe(III)L(NCS)(2)] (8), of L(-) are reported. The Cu(II) and Ni(II) complexes were prepared by a template approach whereas the others were accessed by metallation of pre-formed HL. The X-ray crystal structure determinations show that [Cu(II)L](BF(4)) and [Ni(II)L](BF(4)) feature square planar N(4) coordinated Cu(II) and Ni(II) centres, respectively, whereas [Fe(III)L(NCS)(2)]·NO(2)Me features an octahedral N(6) coordinated Fe(III) centre (two NCS anions bound axially) and the Zn(II) complex, which crystallised as 2{[Zn(II)L(py)](BF(4))}·py, features square pyramidal Zn(II) ions (a pyridine molecule bound axially). In all cases the N(4) macrocycle is bound equatorially to the metal ion. Cyclic voltammograms of the soluble BF(4) complexes, 2-5, were carried out in MeCN vs. 0.01 mol L(-1) AgNO(3)/Ag and revealed multiple, mostly irreversible or quasi-reversible, redox processes. The Zn(II) complex 2 exhibited two irreversible oxidation processes and one irreversible reduction process, all of which are ligand-centered. The Ni(II) complex 4 showed a process with a weak return wave at E(m) = +0.57 V (ΔE = 0.05 V). Interestingly, after controlled potential coulometry experiments on 2, 3 and 4 (at +0.48, +0.61 and +0.71 V which transferred 1.2, 1.0 and 1.6 e(-) equiv. per complex, respectively), a new reversible or quasi-reversible process was obtained, with a lower potential than beforehand (E(m) (ΔE)/V = +0.16 (0.08), +0.31 (0.13) and +0.45 (0.11) respectively).     

Synthesis, spectroscopy, and electrochemistry of copper(II) complexes with N,N'-bis(3,5-di-t-butylsalicylideneimine)polymethylenediamine ligands

Bulky salen CuL(x) derived from aliphatic polymethylene diamines, H(2)N-(CH(2))(x)-NH(2), where n = 2-6, and 3,5-di-t-butylsalicylaldehyde (H(2)L(x)) and some corresponding tetrahydrosalan complexes (CuL(x)') have been synthesized and characterized by their IR, UV-vis absorption and EPR spectra, by magnetic moments and by cyclic voltammetry in acetonitrile (for H(2)L(x)) and DMF (for CuL(x)). Complexes CuL(x) and CuL(x)' are magnetically normal (mu(exp) = 1.83-1.91 mu(B)). EPR spectra CuL(x) characterized by the axial g and A(Cu) tensors with g parallel > g perpendicular and without (14)N-shf resolution in CHCl(3)/toluene at 300 and 150K. The CV studies on acetonitrile solutions of H(2)L(x) revealed a well-defined quasi-reversible redox wave at E(1/2) = 0.95-1.15 V versus Ag/AgCl but CV of the CuL(x) complexes in DMF exhibit weak pronounced irreversible oxidation waves at E(pa)(1) = 0.51 - 098 V and E(pa)(2) = 1.16 - 1.33 V attributable to metal centered Cu(II/III) and ligand centered CuL(x)/CuL(x)*+ couples, respectively. A poorly defined wave was observed for the quasi-reversible reduction Cu(II)/Cu(I) at potentials less than -1.0 V.     

Synthesis, magnetic, spectral, and antimicrobial studies of Cu(II), Ni(II) Co(II), Fe(III), and UO2(II) complexes of a new Schiff base hydrazone derived from 7-chloro-4-hydrazinoquinoline

A new hydrazone ligand, HL, was prepared by the reaction of 7-chloro-4-hydrazinoquinoline with o-hydroxybenzaldehyde. The ligand behaves as monoprotic bidentate. This was accounted for as the ligand contains a phenolic group and its hydrogen atom is reluctant to be replaced by a metal ion. The ligand reacted with Cu(II), Ni(II), Co(II), Fe(III), and UO2(II) ions to yield mononuclear complexes. In the case of Fe(III) ion two complexes, mono- and binuclear complexes, were obtained in the absence and presence of LiOH, respectively. Also, mixed ligand complexes were obtained from the reaction of the metal cations Cu(II), Ni(II) and Fe(III) with the ligand (HL) and 8-hydroxyquinoline (8-OHqu) in the presence of LiOH, in the molar ratio 1:1:1:1. It is clear that 8-OHqu behaves as monoprotic bidentate ligand in such mixed ligand complexes. The ligand, HL, and its metal complexes were characterized by elemental analyses, IR, UV-vis, mass, and 1H NMR spectra, as well as magnetic moment, conductance measurements, and thermal analyses. All complexes have octahedral configurations except Cu(II) complex which has an extra square-planar geometry, while Ni(II) mixed complex has also formed a tetrahedral configuration and UO2(II) complex which formed a favorable pentagonal biprymidial geometry. Magnetic moment of the binuclear Fe(III) complex is quite low compared to calculated value for two iron ions complex and thus shows antiferromagnetic interactions between the two adjacent ferric ions. The HL and metal complexes were tested against one stain Gram positive bacteria (Staphylococcus aureus), Gram negative bacteria (Escherichia coli), and fungi (Candida albicans). The tested compounds exhibited higher antibacterial acivities.     

Synthesis, crystal structure, magnetic properties and theoretical studies on a one-dimensional polynuclear copper(II) complex [Cu2(mu1,3-SCN)2(mu'1,3-SCN)2(MPyO)2]n

A new one-dimensional polynuclear copper(II) complex [Cu(2)(mu(1,3)-SCN)(2)(mu'(1,3)-SCN)(2)(MPyO)(2)](n)(where MPyO = 4-methylpyridine N-oxide) has been synthesized and its crystal structure determined by X-ray crystallography. In the complex there exist two kinds of bridging coordination modes, namely, mu(1,3)-SCN(-) equatorial-equatorial (EE) bridging ligand and micro'(1,3)-SCN(-) equatorial-axial (EA) bridging ligand. Two micro(1,3)-SCN(-) EE bridging ligands coordinate two copper(II) ions in a binuclear unit, and the S atoms from the micro'(1,3)-SCN(-) EA bridging ligands as axial coordinated atoms link the binuclear units into one-dimensional chains. The ESR spectra have been investigated, and variable temperature (4-300 K) magnetic measurements were analyzed using a binuclear Cu(ii) magnetic interaction formula and indicate the existence of strong antiferromagnetic coupling with 2J=- 216.00 cm(-1) between bridged copper(II) ions. Density functional calculations have been carried out on this binuclear unit, yielding a similar singlet-triplet splitting. The mechanism of strong antiferromangetic interaction is revealed according to the calculations.     

Synthesis and characterization of some binuclear metal complexes with a pentadentate azodye ligand: An experimental and theoretical study

A novel series of binuclear complexes with Mn(II), Co(II), Ni(II), Cu(II), Zn(II), and Cd(II) ions derived from a pentadentate azo dye ligand (H₃L) was synthesized and structurally investigated by various physicochemical analyses, namely, scanning electron microscopy, transmission electron microscopy, NMR, UV–visible spectroscopy, and Electron-Spin Resonance (ESR) studies. The infrared spectral data revealed characteristic bands due to ν(N=N) and ν(C=O) at 1606 and 1631 cm⁻¹ in the free ligand. However, their positions shifted and appeared at ~1564 and ~1592 cm⁻¹ on coordination, suggesting the involvement of carbonyl oxygen and azo nitrogen in complex formation. The spectral data suggested octahedral geometry for the complexes. The kinetic parameters such as order and activation energy were determined from the thermal decomposition values. X-ray powder diffraction analysis showed the orthorhombic nature of the cadmium complex. Furthermore, Density functional theory (DFT) calculations were also recorded to describe the insight bonding. The synthesized compounds were tested for in vitro antibacterial activity against K. aerogenes, S. aureus, B. acidoterrestris, E. coli, and V. cholerae strains by the cup-plate method. In addition, the interactions that occurred in the protein–ligand complexes have been predicted by docking analysis.     

Synthesis, characterization and properties of some divalent metal(II) complexes: their electrochemical, catalytic, thermal and antimicrobial activity studies

In this study, we synthesized the amine compound 2-(2-aminoethyliminomethyl)phenol (H(3)A) as the starting material, and then we prepared the polydentate Schiff base ligands from the reactions of the amine compound (H(3)A) with phtaldialdehyde (H(2)L), 4-methyl-2,6-di-formlyphenol (H(3)L(1)) and 4-t-butyl-2,6-di-formylphenol (H(3)L(2)) in the ethanol solution. Moreover, the complexes Cd(II), Cu(II), Co(II), Ni(II), Zn(II) and Sn(II) of the ligands H(2)L, H(3)L(1) and H(3)L(2) have been prepared. All compounds have been characterized by the analytical and spectroscopic methods. In addition, the magnetic susceptibility and molar conductance measurements have been made. The catalytic properties of the mono- and binuclear Co(II) and Cu(II) complexes have been studied on the 3,5-di-tert-butylcatechol (3,5-DTBC) and ascorbic acid (aa) as a substrate. The oxidative C-C coupling properties of the Co(II) and Cu(II) complexes have been investigated on the sterically hindered 2,6-di-tert-butylphenol (dtbp). The antimicrobial activity properties of the ligands and their mono- and binuclear complexes have been studied against the bacteria and fungi. The results have been compared to the antibacterial and fungi drugs. The TGA curves show that the decomposition takes place in three steps for all complexes. Electrochemical properties of the complexes Cu(II) and Ni(II) have been investigated for the first time in acetonitrile by cyclic voltammetry.     

Studies on Binuclear Co(II) and Cu(II) Complexes of Tridentate N-(2-Carboxyphenyl)Salicylideneimine

Homo Cu(II) and Co(II) binuclear complexes H[MLClMCl₂] formed by using the donor properties of the cis two oxygen atoms of the tridentate N-(2-carboxyphenyl)-salicylaldimine Schiff base derived from salicylaldehyde and anthranilic acid have been synthesized. It was found that the Cu(II) “complexed ligand” readily reacts with CoCl₂ to form mononuclear Co(II) and binuclear oxygen bridged Co(II) complex [Co₂-L₂](H₂O)₂. The structure of the so prepared complexes was investigated using microchemical analysis, molar conductance measurements as well as electronic and vibrational spectral studies. It was concluded that in the Cu(II) binuclear complex, the Cu(II) ion inside the “complexed ligand” has a planar structure while the other Cu(II) ion is distorted away from planarity. In the Co(II) binuclear complex, the Co atom of the “complexed ligand” is distorted from tetrahedral structure when it coordinates to the second Co atom.     

Electronic Structure and Substitution and Redox Reactivity of Imidazolate-Bridged Complexes of Pentacyanoferrate and Pentaammineruthenium

The mixed-valence compound [(NC)(5)Fe(II)-Im-Ru(III)(NH(3))(5)](-),M(i), was prepared in solution and as a solid sodium salt from [Fe(CN)(5)H(2)O](3)(-) and [Ru(NH(3))(5)Im](2+). The binuclear complex shows two bands at 366 nm (epsilon = 3350 M(-)(1) cm(-)(1)) and 576 nm (epsilon = 1025 M(-)(1) cm(-)(1)), assigned as LMCT transitions, as well as a near-IR band at 979 nm (epsilon = 962 M(-)(1) cm(-)(1)) associated with an intervalence transition. By calculation of the Hush model parameters alpha(2) and H(ab) (delocalization and electronic coupling factors, respectively), the complex is defined as a valence-trapped Fe(II)-Ru(III) system; this is confirmed by the measured redox potentials at -0.20 V and 0.30 V, associated with redox processes at the ruthenium and iron center, respectively. The formation stability constant of the mixed-valence ion was obtained through independent measurements of k(f) and k(d), the formation and dissociation specific rate constants, respectively. The stabilization of M(i) with respect to disproportionation into the isovalent states, as well as toward the formation of the electronic isomer, Fe(III)-Im-Ru(II), was also estimated. The fully reduced (R(i)) and fully oxidized (O(i)) binuclear complexes were prepared in solution and characterized by UV-vis spectroscopy. The kinetics of the reactions of R(i) and M(i) with peroxydisulfate were measured and a mechanistic analysis was performed, showing the relevance of electronic isomerization in completing the full conversion to O(i), through the assistance of the Ru(II)(NH(3))(5)(2+) center in the oxidation of the neighboring Fe(II)(CN)(5)(3)(-) moiety. The latter results are compared with those obtained with related complexes comprising different X(5)M-L moieties bound to Ru(II)(NH(3))(5)(2+). A linear correlation is displayed by plotting ln k(et) against E degrees (Ru), associated with the intramolecular oxidation rate constant of Ru(II) in the ion pair (binuclear species + peroxydisulfate) and the reduction potential of the corresponding Ru(III,II) couple in the ion pair.     

Structure and properties of bivalent nickel and copper complexes with pyrazine-amide-thioether coordination: stabilization of trivalent nickel

Acyclic pyrazine-2-carboxamide and thioether containing hexadentate ligand 1,4-bis[o-(pyrazine-2-carboxamidophenyl)]-1,4-dithiobutane (H(2)bpzctb), in its deprotonated form, has afforded light brown [Ni(II)(bpzctb)](1)(S=1) and green [Cu(II)(bpzctb)](2)(S=1/2) complexes. The crystal structures of 1.CH(3)OH and 2.CH(2)Cl(2) revealed that in these complexes the ligand coordinates in a hexadentate mode, affording examples of distorted octahedral M(II)N(2)(pyrazine)N'(2)(amide)S(2)(thioether) coordination. Each complex exhibits in CH(2)Cl(2) a reversible to quasireversible cyclic voltammetric response, corresponding to the Ni(III)/Ni(II)(1) and Cu(II)/Cu(I)(2) redox process. The E(1/2) values reveal that the complexes of bpzctb(2-) are uniformly more anodic by approximately 0.2 V than those of the corresponding complexes with the analogous pyridine ligand, 1,4-bis[o-(pyridine-2-carboxamidophenyl)]-1,4-dithiobutane (H(2)bpctb), attesting that compared to pyridine, pyrazine is a better stabilizer of the Ni(ii) or Cu(i) state. Coulometric oxidation of the previously reported complex [Ni(II)(bpctb)] and 1 generates [Ni(III)(bpctb)](+) and [Ni(III)(bpzctb)](+) species, which exhibit a LMCT transition in the 470--480 nm region and axial EPR spectra corresponding to a tetragonally elongated octahedral geometry. Complex 2 exhibits EPR spectra characteristic of the d(z(2)) ground state.     

Homo-and heterodinuclear complexes of the tris(catecholamide) derivative of a tetraazamacrocycle with Fe3+, Cu2+ and Zn2+ metal ions

The new ditopic catecholamide 3,7,11-tris-{N-[3,4-(dihydroxybenzoyl)-aminopropyl]} derivative of a 14-membered tetraazamacrocycle containing pyridine (H(6)L(1)) has been synthesized. The protonation constants of (L(1))(6-) and the stability constants of its mono-, homo- and hetero-dinuclear complexes with Fe(3+), Cu(2+) and Zn(2+) metal ions were determined at 298.2 K and ionic strength 0.10 mol dm(-3) in KNO(3). The large overall basicity of the ligand was ascribed to the very high protonation constants of the catecholate groups, and its acid-base behaviour was correlated with the presence of tertiary nitrogen atoms and secondary amide functions. The UV-vis spectrum of the red solution of [FeL(1)](3-) complex exhibits the LMCT band of catecholate to iron(III), and its EPR spectrum revealed a typical isotropic signal of a rhombic distorted ferric centre in a high-spin state and E/D approximately 0.31, both characteristic of a tris-catecholate octahedral environment. The ligand forms with copper(II) and zinc(II) ions mono- and dinuclear protonated complexes and their stability constants were determined, except for the [ML(1)](4-) complexes as the last proton is released at very high pH. Electronic spectroscopic studies of the copper complexes revealed the involvement of catecholate groups in the coordination to the metal centre in the mono- and dinuclear copper(II) complexes. This information together with the determined stability constants indicated that the copper(II) ion can be involved in both types of coordination site of the ligand with comparable binding affinity. The EPR spectrum of [Cu(2)L(1)](2-) showed a well resolved seven-line hyperfine pattern of copper(II) dinuclear species typical of a paramagnetic triplet spin state with weak coupling between the two metal centres. Thermodynamically stable heterodinuclear complexes, [CuFeH(h)L(1)](h-1) (h = 0-3) and [CuZnH(h)L(1)](h-2) (h = 0-4), were formed as expected from a ditopic ligand having two dissimilar coordination sites. At physiological pH, the [CuFeL(1)](-) complex is formed at approximately 100%. The formation of the [CuFeH(h)L(1)](h-1) complexes in solution was supported by electronic spectroscopic measurements. The data indicated the specific coordination of each metal centre at the dissimilar sites of the ligand, the iron(III) bound to the oxygen donors of the catecholate arms and the copper(II) coordinated to the amine donors of the macrocyclic ring. The two metal centres are weakly coupled, due to the fairly large distance between them.     

Role of ruthenium oxidation states in ligand-to-ligand charge transfer processes

We describe in this paper the properties of [Ru(II/III)(bpy)(2)ClL](+1/+2) and [Ru(II/III)(bpy)(2)L(2)](+2/+3). L = ditolyl-3-pyridylamine (dt3pya) is a redox active ligand related to triarylamines, which is very similar to 3-aminopyridine except for the reversible redox behavior. The monosubstituted complex shows a metal-to-ligand charge-transfer (MLCT) at 502 nm, and reversible waves in acetonitrile at E(0)(Ru(III/II)) = 1.07 V, E(0)(L(+/0)) = 1.46 V (NHE). The disubstituted complex shows an MLCT at 461 nm, a photorelease of dt3pya with quantum yield of 0.11 at 473 nm, and two reversible one-electron overlapped waves at 1.39 V associated with one of the ligands (1.37 V) and Ru(III/II) (1.41 V). Further oxidation of the second ligand at 1.80 V forms a 2,2'-bipiridine derivative, in an irreversible reaction similar to dimerization of triphenylamine to yield tetraphenylbenzidine. In the dioxidized state, the spectroelectrochemistry of the disubstituted complex shows a ligand-to-ligand charge transfer at 1425 nm, with a transition moment of 1.25 ? and an effective two-state coupling of 1200 cm(-1). No charge transfer between ligands was observed when Ru was in a 2+ oxidation state. We propose that a superexchange process would be involved in ligand-metal-ligand charge transfer, when ligands and metals are engaged in complementary π interactions, as in metal-ligand-metal complexes. Best orbital matching occurs when metallic donor fragments are combined with acceptor ligands and vice versa. In our case, Ru(III) bridge (an acceptor) and two dt3pya (donors, one of them being oxidized) made the complex a Robin-Day Class II system, while the Ru(II) bridge (a donor, reduced) was not able to couple two dt3pya (also donors, one oxidized).     

Synthesis and characterization of 3-methyl-5-oxo-N,1-diphenyl-4,5-dihydro-1-H-pyrazole-4-carbothioamide and its metal complexes

The molecular parameters have been calculated to confirm the geometry of 3-methyl-5-oxo-N,1-diphenyl-4,5-dihydro-1-H-pyrazole-4-carbothioamide, HL. The compound is introduced as a new chelating agent for complexation with Cr(III), Fe(III), Co(II), Ni(II) and Cu(II) ions. The isolated chelates were characterized by partial elemental analyses, magnetic moments, spectra (IR, UV–vis, ESR; ¹H NMR) and thermal studies. The protonation constant of HL (5.04) and the stepwise stability constants of its Co(II), Cu(II), Cr(III) and Fe(III) complexes were calculated. The ligand coordinates as a monobasic bidentate through hydroxo and thiol groups in all complexes except Cr(III) which acts as a monobasic monodentate through the enolized carbonyl oxygen. Cr(III) and Fe(III) complexes measured normal magnetic moments; Cu(II) and Co(II) measured subnormal while Ni(II) complex is diamagnetic. The data confirm a high spin and low spin octahedral structures for the Fe(III) and Co(II) complexes. The ESR spectrum of the Cu(II) complex support the binuclear structure. The molecular parameters have also been calculated for the Cu(II) and Fe(III) complexes. The thermal decomposition stages of the complexes confirm the MS to be the residual part. Also, the thermodynamic and kinetic parameters were calculated for some decomposition steps.