Synthesis and structure of metal complexes containing zwitterionic N-hydroxyimidazole ligands

Cu(II) and Zn(II) complexes of N-hydroxyimidazoles were synthesised by reacting simple metal perchlorate salts with the imidazole ligand in alcohol and formulated with a metal:ligand ratio of 1:2. The X-ray crystal structures of five complexes (four Cu(II) and one Zn(II)) were obtained and each showed the two trans, N-hydroxyimidazole ligands forming six-membered, chelate rings with the metal. Both of the NO chelating, neutral N-hydroxyimidazole ligands are in the zwitterion form, with the uncoordinated imidazole imine N atom being protonated and the oxime O atom deprotonated. In the solid state the complexes form hydrogen-bonded supramolecular structures.     

Synthesis, linear, and quadratic-nonlinear optical properties of octupolar D3 and D2d bipyridyl metal complexes

A series of D3 (Fe(II), Ru(II), Zn(II), Hg(II)) and D2d (Cu(I), Ag(I), Zn(II)) octupolar metal complexes featuring different functionalized bipyridyl ligands has been synthesized, and their thermal, linear (absorption and emission), and nonlinear optical (NLO) properties were determined. Their quadratic NLO susceptibilities were determined by harmonic light scattering at 1.91 microm, and the molecular hyperpolarizability (beta0) values are in the range of 200-657 x 10(-30) esu for octahedral complexes and 70-157 x 10(-30) esu for tetrahedral complexes. The octahedral zinc(II) complex 1 e, which contains a 4,4'-oligophenylenevinylene-functionalized 2,2'-bipyridine, exhibits the highest quadratic hyperpolarizability ever reported for an octupolar derivative (lambdamax=482 nm, beta1.91(1 e)=870 x 10(-30) esu, beta0(1 e)=657 x 10(-30) esu). Herein, we demonstrate that the optical and nonlinear optical (NLO) properties are strongly influenced by the symmetry of the complexes, the nature of the ligands (donor endgroups and pi linkers), and the nature of the metallic centers. For example, the length of the pi-conjugated backbone, the Lewis acidity of the metal ion, and the increase of ligand-to-metal ratio result in a substantial enhancement of beta. The contribution of the metal-to-ligand (MLCT) transition to the molecular hyperpolarizability is also discussed with respect to octahedral d6 complexes (M=Fe, Ru).     

Heteroligand α-Diimine-Zn(II) Complexes with O,N,O′- and O,N,S-Donor Redox-Active Schiff Bases: Synthesis,Structure and Electrochemical Properties

A number of novel heteroligand Zn(II) complexes (1–8) of the general type (Lⁿ)Zn(NN) containing O,N,O′-, O,N,S-donor redox-active Schiff bases and neutral N,N′-chelating ligands (NN) were synthesized. The target Schiff bases LⁿH₂ were obtained as a result of the condensation of 3,5-di-tert-butyl-2-hydroxybenzaldehyde with substituted o-aminophenols or o-aminothiophenol. These ligands with combination with 2,2′-bipyridine, 1,10-phenanthroline, and neocuproine are able to form stable complexes upon coordination with zinc(II) ion. The molecular structures of complexes 4∙H₂O, 6, and 8 in crystal state were determined by means of single-crystal X-ray analysis. In the prepared complexes, the redox-active Schiff bases are in the form of doubly deprotonated dianions and act as chelating tridentate ligands. Complexes 6 and 8 possess a strongly distorted pentacoordinate geometry while 4∙H₂O is hexacoordinate and contains water molecule coordinated to the central zinc atom. The electrochemical properties of zinc(II) complexes were studied by the cyclic voltammetry. For the studied complexes, O,N,O′- or O,N,S-donor Schiff base ligands are predominantly involved in electrochemical transformations in the anodic region, while the N,N′-coordinated neutral nitrogen donor ligands demonstrate the electrochemical activity in the cathode potential range. A feature of complexes 5 and 8 with sterically hindered tert-butyl groups is the possibility of the formation of relatively stable monocation and monoanion forms under electrochemical conditions. The values of the energy gap between the boundary redox orbitals were determined by electrochemical and spectral methods. The parameters obtained in the first case vary from 1.97 to 2.42 eV, while the optical bang gap reaches 2.87 eV.     

Facile, divergent route to bis-Zn(II)dipicolylamine type chemosensors for pyrophosphate

A new, two-step synthesis has been developed for a series of bis-DPA-type ligands whose dinuclear Zn(II) complexes function as fluorescent anion sensors. The Zn(II) complexes exhibit good selectivity for PP_i over other anions in aqueous medium (pH 7.5) and may be used to monitor the extent of enzyme-catalysed reactions, in which PP_i is produced or consumed.     

Equilibrium Studies of Binary and Mixed-Ligand Complexes of Zinc(II) Involving 2-(Aminomethyl)-Benzimidazole and Some Bio-Relevant Ligands

Binary and mixed-ligand complexes of zinc(II) involving 2-(aminomethyl)-benzimidazole (AMBI) and amino acids, peptides (HL) or DNA constituents have been investigated. Ternary complexes of amino acids or peptides are formed simultaneously. Amino acids form the complex Zn(AMBI)L, whereas amides form two complex species Zn(AMBI)L and Zn(AMBI)(LH_?1). The ternary complexes of zinc(II) with AMBI and DNA are formed in a stepwise process, whereby binding of zinc(II) to AMBI is followed by ligation of the DNA constituents. The stability of ternary complexes is quantitatively compared with their corresponding binary complexes in terms of the parameters ??log₁₀ K, log₁₀ ??_stat and log₁₀ X. The effect of the side chains of amino acid ligands (??_R) on complex formation is discussed. The values of ??log₁₀ K indicated 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 evidence for a stacking interaction between the aromatic moiety of AMBI and the aromatic side chains of the bio-active ligands. The concentration distributions of various species formed in solution were also evaluated as a function of the pH.     

Potentiometric study of the protonation and binary complexation equilibria between the hydrogen ion,copper(II) ion and zinc(II) ion and the picolinate ion in dioxane-water mixtures

Protonation constants of picolinic acid and stability constants of Cu(II) and Zn(II) picolinate complexes were determined potentiometrically in 50% (v/v) dioxane-water solution at 25°C and 0.2 M KNO₃. The values obtained for the constants were: protonation constants for picolinate ion: logβ₁ = 5.36±0.01 and logβ₂ = 6.80±0.04; stability constants for copper(II) complexes: logβ_1.1 = 7.766±0.001 and logβ_1.2 = 16.826±0.007; stability constants for the Zn(II) complexes: logβ_1.1 = 6.10±0.05, logβ_1.2 = 11.47±0.03 and logβ_1.3 = 15.77±0.08. No protonated nor hydroxo-complex was detected in the metal ion-picolinate systems.     

Nickel(II) and copper(II) complexes based on N-(2-carboxyethyl)alkanolamines: Influence of the amino alcohol structure on the coordination sphere of the metal center

New nickel(II) complexes based on N-(3-hydroxypropyl)-β-alanine, N-(bis(hydroxymethyl)methyl)-β-alanine, and N-(tris(hydroxymethyl)methyl)-β-alanine are synthesized, and their structures are studied by X-ray diffraction analysis. The coordination spheres of the nickel and copper metal centers in the condensed phase are compared for a series of N-substituted β-alaninate ligands with the regularly changed dentate mode. In the case of the copper(II) complexes, an increase in the size of the alkanolamine chelate ring or the number of hydroxymethyl groups provides the formation of achiral coordination structures, whereas the structures of the nickel(II) complexes are independent of the size of the alkanolamine chelate ring or the number of hydroxymethyl groups, thus providing the formation of the complexes as racemic modifications.     

Synthesis of star-shaped metallo-polymeric chromophores by atom transfer radical polymerization

The synthesis of bromoester-functionalized dialkylaminostyryl-2,2′-bipyridyl ligands and of the corresponding tris[dialkylaminostyryl-2,2′-bipyridine] metal(II) complexes are reported (M = Fe, Ru, Zn). These complexes are used as multifunctional metallo-initiators for the atom transfer radical polymerization (ATRP) of methyl methacrylate. The resulting new star-shaped polymers combine the optical (UV–visible and luminescence) properties of the monomers with good processability, which allow to build high optical quality thin films by the spin-coating technique. To cite this article: L. Viau et al., C. R. Chimie 8 (2005).     

Synthesis and characterization of novel Cd(II), Zn(II) and Ni(II) complexes with 2-quinolinecarboxaldehyde selenosemicarbazone. Crystal structure of bis(2-quinolinecarboxaldehyde selenosemicarbazonato)nickel(II)

New complexes of Cd(II), Zn(II) and Ni(II) with 2-quinolinecarboxaldehyde selenosemicarbazone (Hqasesc) were synthesized and structurally characterized. The structure of the ligand, Cd(II) and Zn(II) complexes was determined by NMR and IR spectroscopy, elemental microanalysis and molar conductivity measurements. Both complexes occur in solution in two forms, the major tetrahedral and minor octahedral. In the major Cd(II) complex one qasesc⁻ ligand is coordinated as a tridentate, the fourth coordination site being occupied by acetate, while in the major Zn(II) complex two qasesc⁻ ligands are coordinated as bidentates. In both minor complexes two qasesc⁻ ligands are coordinated as tridentates forming the octahedral geometry around the central metal ion. The only paramagnetic complex in the series is Ni(II) complex for which X-ray structure analysis was performed. The complex has the angularly distorted octahedral geometry with two qasesc⁻ ligands coordinated as tridentates, in a similar way as in the minor complexes of Cd(II) and Zn(II).     

Synthesis and characterization of Cu,Ni and Zn binding capability of some amino- and imidazole hydroxamic acids: Effects of substitution of side chain amino-N for imidazole-N or hydroxamic-N-H for -N-CH3 on metal complexation

Solution equilibrium studies on Cu(II)-, Ni(II)- and Zn(II)-N-Me-β-Alaninehydroxamic acid (N-Me-β-Alaha), -N-Me-α-alaninehydroxamic acid (N-Me-α-Alaha), -Imidazole-4-carbohydroxamic acid (Im-4-Cha), -N-Me-imidazole-4-carbohydroxamic acid (N-Me-Im-4-Cha) and -Imidazole-4-acetohydroxamic acid (Im-4-Aha) systems have been performed by pH-potentiometry, UV–Vis spectrophotometry, EPR, CD, ESI-MS and ¹H NMR methods. According to the results: (i) the amino-N atoms are more basic in N-Me-α-Alaha and N-Me-β-Alaha than the hydroxamate function, but the trend is just the opposite between the imidazole-N(3) and hydroxamate. (ii) The metal ion anchor is always the hydroxamate part in the amino acid derivatives, while it is always the imidazole-N(3) in the studied imidazolehydroxamic acids. (iii) The three studied N-Me derivatives do not form metallacrowns. Only hydroxamate type chelate is formed with N-Me-β-Alaha, but with N-Me-α-Alaha a new type of coordination mode (via amino-N and hydroxamate-O) also exists. N-Me-Im-4-Cha also forms a dinuclear complex, [M₂L₃], with Cu(II) and Ni(II) (but not with Zn(II)). In this complex, one of the three ligands might bridge the two metal ions (five-membered hydroxamate-(O,O) plus five-membered (N_im, O_carb) bridging bis-chelating mode), while each of the additional two ligands binds to one metal. (iv) The two studied N–H derivatives, having dissociable proton on the hydroxamic-N, are able to form metallacrown species. A pentanuclear complex, [M₅L₄H₋₄], is exclusively formed above pH 4 between Cu(II) and Im-4-Aha. Interestingly, this 12-metallacrown-4 type complex, although together with various mononuclear binding isomers, appears also with Ni(II) and Zn(II). Unfortunately, the complexes of Im-4-Cha are not soluble in water at physiological pH at all.     

Synthesis,spectroscopic properties,density functional theory calculations and nonlinear optical properties of novel complexes of 5‐hydroxy‐4,7‐dimethyl‐6‐(phenylazo)coumarin with Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) metal ions

5‐Hydroxy‐4,7‐dimethyl‐6‐(phenylazo)coumarin (L) has been synthesized and its novel complexes with Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) metal ions have also been prepared and identified using various analytical tools. The complexes are octahedral binding via one/two oxygen, nitrogen atoms for 1:1 and 1:2 complexes and two/three coordinated water molecules. All the prepared solid complexes behave as neutral in dimethylformamide. The optimized structures of the studied complexes were theoretically investigated at the B3LYP/6‐311G** level. Molecular stability and bond strengths were investigated by applying natural bond orbital analysis. The geometries of the studied complexes are non‐planar as indicated from the values of dihedral angles. The global properties of hardness, global softness and electronegativity were computed. The calculated small energy gap between highest occupied and lowest unoccupied molecular orbital energies shows that charge transfer occurs within the complexes. The obtained total static dipole moment, mean polarizability, anisotropy of polarizability and mean first‐order hyperpolarizability (<β>) were compared with those of urea as a reference material. The results for <β> showed that the complexes are excellent candidates as nonlinear optical materials. The three‐dimensional plots of the molecular electrostatic potential for some selected complexes were investigated.     

Syntheses and X-ray structures of Cu(II) and Zn(II) complexes of N,N′-dibenzyl-(R,R)-1,2-diaminocyclohexane and application to nitroaldol reaction

Chiral Cu(II) and Zn(II) complexes with N,N′-dibenzyl-(R,R)-1,2-diaminocyclohexane ligands were synthesized and characterized. X-ray crystal structures of these complexes reveal that Cu complex has the distorted square-planar geometry and the Zn one has the nearly tetrahedral pattern. The coordination of metals to the chiral diamine ligand leads to a 5-membered metallaheterocycle of (S,S)-configuration of nitrogen atoms. Their asymmetric catalytic activities to nitroaldol reaction of benzaldehyde and nitromethane were examined. The difference of the geometry around metals leads to the opposite preferential configuration of alcohol products using these chiral complexes as asymmetric catalysts in the presence of triethylamine or diisopropylethylamine.     

Spectroscopic studies,Density Functional Theory calculations,and non-linear optical properties of binuclear Fe(III), Co(II), Ni(II), Cu(II), and Zn(II) complexes of OONN Schiff base ligand

The binuclear complexes of Fe(III), Co(II), Ni(II), Cu(II), and Zn(II) with 2-[3-(benzylideneamino)-2-(benzylidenehydrazono)-4-oxothiazolidin-5-yl] acetic acid ligand (HL) were prepared and their stoichiometry was determined by elemental analysis. The stereochemistry of the studied binuclear metal complexes was confirmed by analyzing their infrared spectra, ¹H NMR, and magnetic moment. Thermal decomposition studies of the binuclear complexes have been performed to demonstrate the status of water molecules present in these binuclear complexes and their general decomposition pattern. The equilibrium geometry of the ligand and its studied complexes were calculated using density function theory (DFT) calculations at the B3LYP/GENECP level of the theory. The results show that the ligand and its complexes are nonplanar structures as indicated from the values of the dihedral angles. Extent of distortion from regular geometry has been performed and discussed in terms of the values of the angles between the central metals and the coordinated sites. The E_HOMO and E_LUMO energies of the studied ligand and its complexes are used to calculate the global properties. The nonlinear optical parameters (NLO), anisotropy of the polarizibility (Δα), and the mean first-order hyperpolarizability (<β>) were calculated. The (<β>) values were compared with Urea as a reference molecule and the results of (<β>) values showed that the ligand and the studied complexes have good NLO behaviors.     

Synthesis of novel ferrocene containing vic-dioxime ligands and their Ni(II), Cu(II) and Co(II) complexes: Spectral, electrochemical and biological activity studies

Two new vic-dioxime ligands bearing an important redox-active substituent, anti-β-ferrocenylethylaminoglyoxime (1a) and anti-β-ferrocenylethylaminophenylglyoxime (1b), have been synthesized, and their Ni(II), Cu(II) and Co(II) (2a-4a, 2b-4b) complexes were obtained. The composition and structure of the products were determined by elemental analysis, Fourier transform infrared (FT-IR), ultraviolet-visible (UV-vis), mass spectrometry (MS), one-dimensional (1D) ¹H, ¹³C NMR, and two-dimensional (2D) heteronuclear multiple bond correlation (HMBC) techniques. The redox behaviors of the ligands and their complexes were investigated by cyclic voltammetry (CV), which revealed that all the ferrocenyl redox centers are electrochemically independent and undergo a quasi-reversible oxidation at similar potentials. Also, antibacterial activity was studied against Staphylococcus aureus ATCC 29213, Streptococcus mutans RSHM 676, Enterococcus faecalis ATCC 29212, Escherichia coli ATCC 25922 and Pseudomonas aeruginosa ATCC 27853. The antimicrobial test results indicated that all the compounds have mild levels of antibacterial activity against both gram negative and gram-positive bacterial species.     

Syntheses, crystal structures, and magnetic and fluorescence properties of three metal complexes coordinated by mixed flexible (2-pyridylmethyl,3-pyridylmethyl)amine and rigid 5-sulfoisophthalate ligands

Three new complexes, {[Cu₃(2,3-pyma)₂(sip)₂(H₂O)₅]·5H₂O} _n , {[Zn(H-2,3-pyma)(sip)(H₂O)]·H₂O} _n , and {[Cd(H-2,3-pyma)(sip)(H₂O)]·H₂O} _n (2,3-pyma = (2-pyridylmethyl,3-pyridylmethyl)amine and H₃sip = 5-sulfoisophthalic acid) were synthesized and structurally characterized by single-crystal X-ray diffraction. The Cu(II) complex crystallizes in neutral two-dimensional layers in which the Cu(II) centers are bridged by both the flexible 2,3-pyma and the rigid sip ligands. The Zn(II) and Cd(II) complexes contain neutral one-dimensional chains linked by the rigid sip anions, whereas the flexible H-2,3-pyma ions only act as terminal ligands. The Cu(II) complex shows weak antiferromagnetic interactions, while the Zn(II) and Cd(II) complexes exhibit fluorescent emissions in the solid state.     

Coordination compounds of biological interest: Thermal properties of some compounds of saccharin (o-benzoic sulphimide) with nickel(II) and zinc(II)

The thermal properties of nickel(II) and zinc(II) complexes of saccharin (sacc) (o-benzoic sulphimide) have been studied and compared both with those of cobalt(II) and copper(II) previously studied and with those of ternary complexes of nickel(II) and zinc(II) having both saccharin and pyridine as ligands. The thermal behaviour is discussed in terms of the interaction between metal and ligands, interaction studied by IR spectroscopy, and by reflectance spectroscopy.The classical thermal stability scale Co(II) > Ni(II) > Cu(II) > Zn(II) is always obtained.     

Synthesis and characterization of binuclear Zn(II)–cyclen complexes bridged by α,ω-bis(4-methylphenoxy) alkanes

A series of novel α,ω-bis(4-methylphenoxy) alkane functionalized cyclen ligands were synthesized by the nucleophilic substitution reaction of 1,4,7-tris(tert-butyloxycarbonyl)-1,4,7,10-tetraazacyclododecane and α,ω-bis(4-bromomethylphenoxy) alkanes. The corresponding dimeric Zn(II)–cyclen complexes were obtained by reaction of these ligands with Zn(ClO₄)₂·6H₂O. Ligands and complexes were characterized by FT-IR, ¹H NMR, and elemental analysis.     

Metal chelates of ampicillin versus amoxicillin: synthesis,structural investigation,and biological studies

Solid chelates derived from some alkaline earth and transition metal complexes with ampicillin (Hamp, a) and amoxicillin (Hamox, b) were synthesized and characterized using elemental analysis, molar conductivity, IR, magnetic susceptibility, and thermogravimetric studies. Both drugs behave as tetradentate ligands coordinating to metal through amino, imino, and carboxylate as well as through β-lactamic carbonyl. All chelates have octahedral geometry except Cu(II) complexes which have square planar structure and uranium has pentagonal bipyramidal coordination. ¹H- and ¹³C-NMR of the Zn(II) and UO₂(VI) chelates are compared with the free ligands. The antimicrobial activity of the prepared chelates was determined.     

Tetranuclear Zn(II) and Mononuclear Nickel(II) Complexes Based on Asymmetric Salamo-Type Ligands: Syntheses,Crystal Structures,and Fluorescent Properties

Two new complexes [{Zn(L¹)(μ-OAc)Zn(CH₃CHOHCH₃)}₂] and [Ni(L₂)(H₂O)(CH₃OH)] with asymmetric Salamo-type ligands (H₃L¹ and H₂L²) are synthesized and structurally characterized. In the Zn(II) and Ni(II) complexes, the terminal and central Zn(II) atoms are found to have slightly distorted square pyramidal and trigonal bipyramidal symmetries respectively, while the Ni(II) atom is hexa-coordinated and has a slightly distorted octahedral symmetry. Interestingly, a self-assembling continual zigzag 1D chain is formed by intermolecular hydrogen bonds in the Ni(II) complex. Furthermore, the Zn(II) and Ni(II) complexes in the ethanol solution show intense photoluminescence.     

Synthesis,crystal structures,and third-order nonlinear optical properties of a series of ferrocenyl organometallics

Three novel ferrocenyl complexes [Zn(4-PFA)(2)(NO(3))(2)](H(2)O) (1), [Hg(2)(OAc)(4)(4-BPFA)(2)](CH(3)OH) (2), and [Cd(2)(OAc)(4)(4-BPFA)(2)] (3) (4-PFA = [(4-pyridylamino)carbonyl]ferrocene, 4-BPFA = 1,1'-bis[(4-pyridylamino)carbonyl]ferrocene) were prepared, and complexes 1 and 2 were structurally characterized by means of X-ray single-crystal diffraction. In complex 1, the zinc(II) atom is coordinated at a distorted tetrahedral environment by two nitrogen atoms from two 4-PFA moieties and two oxygen atoms from two nitrate anions; [Zn(4-PFA)(2)(NO(3))(2)] units are linked by hydrogen bonds N-H.O and O-H.O forming one-dimensional chains. Complex 2 is a tetranuclear macrocycle compound consisting of two 4-BPFA moieties and two Hg atoms; [Hg(2)(OAc)(4)(4-BPFA)(2)] units form 1-D chains by hydrogen bonds N-H.O as complex 1. Some complexes with 1,1'-bisubstituted pyridine-containing ferrocene ligands have been described, but their crystal data are limited. Compound 2 is the first example of a macrocyclic pyridine-containing ferrocenyl complex. The third-order nonlinear optical (NLO) properties of 4-PFA, 4-BPFA, and complexes 1-3 were determined by Z-scan techniques. The results indicate that all the compounds exhibit strong self-focusing effect. The hyperpolarizability gamma values are calculated to be in the range 1.51 x 10(-)(28) to 3.12 x 10(-)(28) esu. The gamma values are nearly twice as large for complexes 1-3 as for their individual ligands, showing that the optical nonlinearity of the complexes is dominated by the ligands.