Synthesis and spectroscopic studies of dimeric copper(II) complexes containing imidazoles and dipeptides

Six dimeric copper(II) complexes of the type Na[Cu₂(D)(L)], where D = glycylglycinate dianion, and HL = imidazole and 2-methylimidazole; D = glycyl-L-tyrosinate dianion, HL = imidazole and benzimidazole; D = glycyl-L-phenylalaninate dianion, and HL = imidazole; and D = glycyl-L-tryptophenate dianion, and HL = benzimidazole, have been prepared. They were characterized by IR, visible absorption, and EPR spectroscopy. The EPR data indicated their complete dimeric behaviour in basic solution with two Cu(II) ions in close proximity of <7Å with imidazolate, 2-methyl-imidazolate, and benzimidazolate bridges.     

Helical-chain copper(II) complexes and a cyclic tetranuclear copper(II) complex with single syn-anti carboxylate bridges and ferromagnetic exchange interactions

Tridentate Schiff-base carboxylate-containing ligands, derived from the condensation of 2-imidazolecarboxaldehyde with the amino acids beta-alanine (H2L1) and 2-aminobenzoic acid (H2L5) and the condensation of 2-pyridinecarboxaldehyde with beta-alanine (HL2), D,L-3-aminobutyric acid (HL3), and 4-aminobutyric acid (HL4), react with copper(II) perchlorate to give rise to the helical-chain complexes [[Cu(mu-HL1)(H2O)](ClO4)]n (1), [[Cu(mu-L2)(H2O)](ClO4).2H2O]n (2), and [[Cu(mu-L3)(H2O)](ClO4).2H2O]n (3), the tetranuclear complex [[Cu(mu-L4)(H2O)](ClO4)]4 (4), and the mononuclear complex [Cu(HL5)(H2O)](ClO4).1/2H2O (5). The reaction of copper(II) chloride with H2L1 leads not to a syn-anti carboxylate-bridged compound but to the chloride-bridged dinuclear complex [Cu(HL1)(mu-Cl)]2 (6). The structures of these complexes have been solved by X-ray crystallography. In complexes 1-4, roughly square-pyramidal copper(II) ions are sequentially bridged by syn-anti carboxylate groups. Copper(II) ions exhibit CuN2O3 coordination environments with the three donor atoms of the ligand and one oxygen atom belonging to the carboxylate group of an adjacent molecule occupying the basal positions and an oxygen atom (from a water molecule in the case of compounds 1-3 and from a perchlorate anion in 4) coordinated in the apical position. Therefore, carboxylate groups are mutually cis oriented and each syn-anti carboxylate group bridges two copper(II) ions in basal-basal positions with Cu...Cu distances ranging from 4.541 A for 4 to 5.186 A for 2. In complex 5, the water molecule occupies an equatorial position in the distorted octahedral environment of the copper(II) ion and the Cu-O carboxylate distances in axial positions are very large (>2.78 A). Therefore, this complex can be considered as mononuclear. Complex 6 exhibits a dinuclear parallel planar structure with Ci symmetry. Copper(II) ions display a square-pyramidal coordination geometry (tau = 0.06) for the N2OCl2 donor set, where the basal coordination sites are occupied by one of the bridging chlorine atoms and the three donor atoms of the tridentate ligand and the apical site is occupied by the remaining bridging chlorine atom. Magnetic susceptibility measurements indicate that complexes 1-4 exhibit weak ferromagnetic interactions whereas a weak antiferromagnetic coupling has been established for 6. The magnetic behavior can be satisfactorily explained on the basis of the structural data for these and related complexes.     

Structural, spectroscopic and thermal characterization of 2-tert-butylaminomethylpyridine-6-carboxylic acid methylester and its Fe(III), Co(II), Ni(II), Cu(II), Zn(II) and UO(2)(II) complexes

Fe(III), Co(II), Ni(II), Cu(II), Zn(II) and UO(2)(II) complexes with the ligand 2-tert-butylaminomethylpyridine-6-carboxylic acid methylester (HL(2)) have been prepared and characterized by elemental analyses, molar conductance, magnetic moment, thermal analysis and spectral data. 1:1 M:HL(2) complexes, with the general formula [M(HL(2))X(2)].nH(2)O (where M = Co(II) (X = Cl, n = 0), Ni(II) (X = Cl, n = 3), Cu(II) (grey colour, X = AcO, n = 1), Cu(II) (yellow colour, X = Cl, n = 0) and Zn(II) (X = Br, n = 0). In addition, the Fe(III) and UO(2)(II) complexes of the type 1:2 M:HL(2) and with the formulae [Fe(L(2))(2)]Cl and [UO(2)(HL(2))(2)](NO(3))(2) are prepared. From the IR data, it is seen that HL(2) ligand behaves as a terdentate ligand coordinated to the metal ions via the pyridyl N, carboxylate O and protonated NH group; except the Fe(III) complex, it coordinates via the deprotonated NH group. This is supported by the molar conductance data, which show that all the complexes are non-electrolytes, while the Fe(III) and UO(2)(II) complexes are 1:1 electrolytes. IR and H1-NMR spectral studies suggest a similar behaviour of the Zn(II) complex in solid and solution states. From the solid reflectance spectral data and magnetic moment measurements, the complexes have a trigonal bipyramidal (Co(II), Ni(II), Cu(II) and Zn(II) complexes) and octahedral (Fe(III), UO(2)(II) complexes) geometrical structures. The thermal behaviour of the complexes is studied and the different dynamic parameters are calculated applying Coats-Redfern equation.     

Synthesis, Characterization, and Single-Crystal EPR Studies of Three Dinuclear Copper(II) Complexes and One Mixed-Valence Tetranuclear Copper(I)-Copper(II) Cluster with an Asymmetric Imidazole-Containing Tripodal Ligand with Copper(II)-Copper(II) Distances between 3.35 and 3.63 Å

The synthesis and characterization of three dinuclear copper(II) complexes and one mixed-valence tetranuclear cluster with the asymmetric imidazole-containing ligand bis(1,1'-imidazole-2-yl)(4-imidazole-4(5)-yl)-2-azabutane (biib) are described. X-ray crystallographic parameters for the copper complexes are as follows. [Cu(2)(biib)(2)(BF(4))(2)](BF(4))(2)(H(2)O)(4): triclinic, space group P&onemacr;, a = 10.178(1) ?, b = 9.4881(9) ?, c = 11.037(1) ?, alpha = 95.130(10) degrees, beta = 112.20(1) degrees, gamma = 92.142(9) degrees, and Z = 1. [Cu(2)(biib)(2)(NO(3))(2)](NO(3))(2)(H(2)O)(4): monoclinic, space group &Pmacr;2(1)/n, a = 9.207(6) ?, b = 17.0516(6) ?, c = 12.6107(7) ?, beta = 109.82(1) degrees, and Z = 2. [Cu(2)(biib)(2)(CuBr(3))(2)]: monoclinic, space group P2(1)/c, a = 11.583(2) ?, b = 11.864(2) ?, c = 16.070(2) ?, beta = 112.459(12) degrees, and Z = 2. The two Cu(II) ions in all four complexes are coordinated in a square-pyramidal geometry by three imidazole nitrogens and one amine nitrogen donor in the equatorial plane, and each copper ion is weakly coordinated at the axial position by respectively a tetrafluoroborate, a perchlorate, a nitrate, or a tribromocuprate(I) anion. By comparison of the structural data of the four complexes a relationship has been established between the donor strength of the anion and some structural features, like the Cu(II)-Cu(II) distance, of the dinuclear Cu(II)-Cu(II) unit in the four complexes. Single-crystal EPR spectra of [Cu(2)(biib)(2)(BF(4))(2)](BF(4))(2)(H(2)O)(4) were recorded at room temperature at X-band frequencies. The triplet spectra have been fit with nonparallel g and D tensors, whose principle values are as follows: g(xx)() = 2.022(8), g(yy)() = 2.060(7), g(zz)() = 2.211(8), D(x)()(')(x)()(') = -0.0182(9) cm(-)(1), D(y)()(')(y)()(') = -0.081(6) cm(-)(1), D(z)()(')(z)()(') = 0.0264(7) cm(-)(1). The compounds were further characterized and studied by ligand field and by frozen-solution and polycrystalline powder EPR spectroscopy. EPR spectra recorded at 77 K of frozen solutions of the perchlorate complex show that upon dilution in methanol the dinuclear complex reacts to form a mononuclear species.     

From model compounds to protein binding: syntheses, characterizations and fluorescence studies of [RuII(bipy)(terpy)L]2+ complexes (bipy = 2,2'-bipyridine; terpy = 2,2':6',2''-terpyridine; L = imidazole, pyrazole and derivatives, cytochrome c)

Compounds [RuII(bipy)(terpy)L](PF6)2 with bipy = 2,2'-bipyridine, terpy = 2,2':6',2"-terpyridine, L = H2O, imidazole (imi), 4-methylimidazole, 2-methylimidazole, benzimidazole, 4,5-diphenylimidazole, indazole, pyrazole, 3-methylpyrazole have been synthesized and characterized by 1H NMR, ESI-MS and UV/Vis (in CH3CN and H2O). For L = H2O, imidazole, 4,5-diphenylimidazole and indazole the X-ray structures of the complexes have been determined with the crystal packing featuring only few intermolecular C-H...pi or pi-pi interactions due to the separating action of the PF6-anions. Complexes with L = imidazole and 4-methylimidazole exhibit a fluorescence emission with a maximum at 662 and 667 nm, respectively (lambdaexc= 475 nm, solvent CH3CN or H2O). The substitution of the aqua ligand in [Ru(bipy)(terpy)(H2O)]2+ in aqueous solution by imidazole to give [Ru(bipy)(terpy)(imi)]2+ is fastest at a pH of 8.5 (as followed by the increase in emission intensity). Coupling of the [Ru(bipy)(terpy)]2+ fragment to cytochrome c(Yeast iso-1) starting from the Ru-aqua complex was successful at 35 degrees C and pH 7.0 after 5 d under argon in the dark. The [Ru(bipy)(terpy)(cyt c)]-product was characterized by UV/Vis, emission and mass spectrometry. The location where the [Ru(bipy)(terpy)] complex was coupled to the protein was identified as His44 (corresponding to His39 in other numbering schemes) using digestion of the Ru-coupled protein by trypsin and analysis of the tryptic peptides by HPLC-high resolution MS.     

Characterization and biological activities of two copper(II) complexes with diethylenetriamine and 2,2'-bipyridine or 1,10-phenanthroline as ligands

Two new mixed ligand copper(II) complexes with diethylenetriamine, 2,2'-bipyridine and 1,10-phenanthroline have been synthesized. The crystal and molecular structures of [Cu(dien)(phen)](ClO(4))(2) and [Cu(dien)(bipy)](BF(4))(2) (dien=diethylenetriamine, phen=1,10-phenanthroline, bipy=2,2'-bipyridine) were determined by X-ray crystallography from single crystal data. These two complexes have similar structures. The EPR spectral data also suggest that these complexes have distorted square pyramidal geometry about copper(II). Anti-microbial and superoxide dismutase activities of these complexes have also been measured. They show the higher SOD activity than the corresponding simple Cu(II)-dien/Cu(II)-PMDT (PMDT=N,N,N',N',N'-pentamethyldiethylenetriamine) complexes because of a strong axial bond of one of the nitrogen atoms of the alpha-diimine. Both the complexes have been found to cleave plasmid DNA in the presence of co-reductants such as ascorbic acid and glutathione.     

EPR, IR and electronic spectral studies on Ni(II) and Cu(II) complexes with N-donor tetradentate [N4] macrocyclic ligand

Nickel(II) and copper(II) complexes are synthesized with a novel tetradentate macrocyclic ligand, i.e. 2,6,12,16,21,22-hexaaza;3,5,13,15-tetraphenyltricyclo[15,3,1,1(7-11)] docosa;1(21),2,5,7,9,11(22),12,15,17,19-decaene (L) and characterized by the elemental analysis, magnetic susceptibility measurements, mass, (1)H NMR, IR, electronic and EPR spectral studies. All the complexes are non-electrolytic in nature. Thus, these may be formulated as [M(L)X(2)] [M=Ni(II), Cu(II) and X=Cl(-), NO(3)(-) and (1/2)SO(4)(2-)]. Ni(II) and Cu(II) complexes show magnetic moments corresponding to two and one unpaired electron, respectively. On the basis of IR, electronic and EPR spectral studies an octahedral geometry has been assigned for Ni(II) and tetragonal geometry for Cu(II) complexes.     

Spectroscopic and biological approach of Ni(II) and Cu(II) complexes of 2-pyridinecarboxaldehyde thiosemicarbazone

Ni(II) and Cu(II) complexes having the general composition [M(L)(2)X(2)] [where L=2-pyridinecarboxaldehyde thiosemicarbazone, M=Ni(II) and Cu(II), X=Cl(-), NO(3)(-) and 1/2 SO(4)(2-)] have been synthesized. All the metal complexes were characterized by elemental analysis, molar conductance, magnetic moment, mass, IR, EPR and electronic spectral studies. The magnetic moment measurements of the complexes indicate that all the complexes are of high-spin type. On the basis of spectral studies an octahedral geometry has been assigned for Ni(II) complexes whereas tetragonal geometry for Cu(II) except [Cu(L)(2)SO(4)] which posseses five coordinated geometry. The ligand and its metal complexes were screened against phytopathogenic fungi and bacteria in vitro.     

A rational design for imidazolate-bridged linear trinuclear compounds from mononuclear copper(II) complexes with 2-[((imidazol-2-ylmethylidene)amino)ethyl]pyridine (HL): syntheses, structures, and magnetic properties of [Cu(L)(hfac)M(hfac)2Cu(hfac)(L)] (M = ZnII, CuII, MnII)

Two mononuclear copper(II) complexes with the unsymmetrical tridentate ligand 2-[((imidazol-2-ylmethylidene)amino)ethyl]pyridine (HL), [Cu(HL)(H2O)](ClO4)2.2H2O (1) and [Cu(HL)Cl2] (2), have been prepared and characterized. The X-ray analysis of 2 revealed that the copper(II) ion assumes a pentacoordinated square pyramidal geometry with an N3Cl2 donor set. When 1 and 2 are treated with an equimolecular amount of potassium hydroxide, the deprotonation of the imidazole moiety promotes a self-assembled process, by coordination of the imidazolate nitrogen atom to a Cu(II) center of an adjacent unit, leading to the polynuclear complexes [[Cu(L)(H2O)](ClO4)]n (3) and [[Cu(L)Cl].2H2O]n (4). Variable-temperature magnetic data are well reproduced for one-dimensional infinite regular chain systems with J = -60.3 cm(-1) and g = 2.02 for 3 and J = -69.5 cm(-1) and g = 2.06, for 4. When 1 is used as a "ligand complex" for [M(hfac)2] (M = Cu(II), Ni(II), Mn(II), Zn(II)) in a basic medium, only the imidazolate-bridged trinuclear complexes [Cu(L)(hfac)M(hfac)2Cu(hfac)(L)] (M = Zn(II), Cu(II)) (5, 6) can be isolated. Nevertheless, the analogous complex containing Mn(II) as the central metal (7) can be prepared from the precursor [Cu(HL)Cl2] (2). All the trinuclear complexes are isostructural. The structures of 5 and 6 have been solved by X-ray crystallographic methods and consist of well-isolated molecules with Ci symmetry, the center of symmetry being located at the central metal. Thus, the copper(II) fragments are in trans positions, leading to a linear conformation. The magnetic susceptibility data (2-300 K), which reveal the occurrence of antiferromagnetic interactions between copper(II) ions and the central metal, were quantitatively analyzed for symmetrical three-spin systems to give the coupling parameters JCuCu = -37.2 and JCuMn = -3.7 cm(-1) with D = +/-0.4 cm(-1) for 6 and 7, respectively. These magnetic behaviors are compared with those for analogous systems and discussed on the basis of a localized-orbital model of exchange interactions.     

Dicopper(II) complexes of H-BPMP-type ligands: pH-induced changes of redox, spectroscopic ((19)F NMR studies of fluorinated complexes), structural properties, and catecholase activities

Substitution of the methyl group from the H-BPMP (HL(CH)3) ligand (2,6-bis[(bis(2-pyridylmethyl)amino)methyl]-4-methylphenol) by electron withdrawing (F or CF(3)) or electron donating (OCH(3)) groups afforded a series of dinucleating ligand (HL(OCH)3, HL(F), HL(CF)3), allowing one to understand the changes in the properties of the corresponding dicopper complexes. Dinuclear Cu(II) complexes have been synthesized and characterized by spectroscopic (UV-vis, EPR, (1)H NMR) as well as electrochemical techniques and, in some cases, by single-crystal X-ray diffraction: [Cu(2)(L(OCH)3)(muOH)][(ClO(4))(2)].C(4)H(8)O, [Cu(2)(L(F))(muOH)][(ClO(4))(2)], [Cu(2)(L(F))(H(2)O)(2)][(ClO(4))(3)].C(3)D(6)O, and [Cu(2)(L(CF)3)(H(2)O)(2)][(ClO(4))(3)].4H(2)O. Significant differences are observed for the Cu-Cu distance in the two mu-hydroxo complexes (2.980 A (R = OCH(3)) and 2.967 A (R = F)) compared to the two bis aqua complexes (4.084 A (R = F) and 4.222 A (R = CF(3))). The mu-hydroxo and bis aqua complexes are reversibly interconverted upon acid/base titration. In basic medium, new species are reversibly formed and identified as the bis hydroxo complexes except for the complex from HL(CF)3 which is irreversibly transformed near pH = 10. pH-driven interconversions have been studied by UV-vis, EPR, and (1)H NMR, and the corresponding pK are determinated. In addition, with the fluorinated complexes, the changes in the coordination sphere around the copper centers and in their redox states are evidenced by the fluorine chemical shift changes ((19)F NMR). For all the complexes described here, investigations of the catechol oxidase activities (oxidation of 3,5-di-tert-butylcatechol to the corresponding quinone) are of interest in modeling the catecholase enzyme active site and in understanding aspects of structure/reactivity. These studies show the pH-dependence for the catalytic abilities of the complexes, related with changes in the coordination sphere of the metal centers: only the mu-hydroxo complexes from HL(CH)3, HL(F), and HL(OCH)3 exhibit a catecholase activity. Modification on R-substituent induces a drastic effect on the catecholase activity: the presence of an electron donating group on the ligand increases this activity; the reverse effect is observed with an electron withdrawing group.     

Copper(II) coordination chemistry of westiellamide and its imidazole, oxazole, and thiazole analogues

The copper(II) coordination chemistry of westiellamide (H(3)L(wa)), as well as of three synthetic analogues with an [18]azacrown-6 macrocyclic structure but with three imidazole (H(3)L(1)), oxazole (H(3)L(2)), and thiazole (H(3)L(3)) rings instead of oxazoline, is reported. As in the larger patellamide rings, the N(heterocycle)-N(peptide)-N(heterocycle) binding site is highly preorganized for copper(II) coordination. In contrast to earlier reports, the macrocyclic peptides have been found to form stable mono- and dinuclear copper(II) complexes. The coordination of copper(II) has been monitored by high-resolution electrospray mass spectrometry (ESI-MS), spectrophotometric and polarimetric titrations, and EPR and IR spectroscopies, and the structural assignments have been supported by time-dependent studies (UV/Vis/NIR, ESI-MS, and EPR) of the complexation reaction of copper(II) with H(3)L(1). Density functional theory (DFT) calculations have been used to model the structures of the copper(II) complexes on the basis of their spectroscopic data. The copper(II) ion has a distorted square-pyramidal geometry with one or two coordinated solvent molecules (CH(3)OH) in the mononuclear copper(II) cyclic peptide complexes, but the coordination sphere in [Cu(H(2)L(wa))(OHCH(3))](+) differs from those in the synthetic analogues, [Cu(H(2)L)(OHCH(3))(2)](+) (L = L(1), L(2), L(3)). Dinuclear copper(II) complexes ([Cu(II) (2)(HL)(mu-X)](+); X = OCH(3), OH; L = L(1), L(2), L(3), L(wa)) are observed in the mass spectra. While a dipole-dipole coupled EPR spectrum is observed for the dinuclear copper(II) complex of H(3)L(3), the corresponding complexes with H(3)L (L = L(1), L(2), L(wa)) are EPR-silent. This may be explained in terms of strong antiferromagnetic coupling (H(3)L(1)) and/or a low concentration of the dicopper(II) complexes (H(3)L(wa), H(3)L(2)), in agreement with the mass spectrometric observations.     

Characterization of imidazolate-bridged dinuclear and mononuclear hydroperoxo complexes

Dinucleating ligands having two metal-binding sites bridged by an imidazolate moiety, Hbdpi, HMe(2)bdpi, and HMe(4)bdpi (Hbdpi = 4,5-bis(di(2-pyridylmethyl)aminomethyl)imidazole, HMe(2)bdpi = 4,5-bis((6-methyl-2-pyridylmethyl)(2-pyridylmethyl)aminomethyl)imidazole, HMe(4)bdpi = 4,5-bis(di(6-methyl-2-pyridylmethyl)aminomethyl)imidazole), have been designed and synthesized as model ligands for copper-zinc superoxide dismutase (Cu,Zn-SOD). The corresponding mononucleating ligands, MeIm(Py)(2), MeIm(Me)(1), and MeIm(Me)(2) (MeIm(Py)(2) = (1-methyl-4-imidazolylmethyl)bis(2-pyridylmethyl)amine, MeIm(Me)(1) = (1-methyl-4-imidazolylmethyl)(6-methyl-2-pyridylmethyl)(2-pyridylmethyl)amine, MeIm(Me)(2) = (1-methyl-4-imidazolyl-methyl)bis(6-methyl-2-pyridylmethyl)amine), have also been synthesized for comparison. The imidazolate-bridged Cu(II)-Cu(II) homodinuclear complexes represented as [Cu(2)(bdpi)(CH(3)CN)(2)](ClO(4))(3).CH(3)CN.3H(2)O (1), [Cu(2)(Me(2)bdpi)(CH(3)CN)(2)](ClO(4))(3) (2), [Cu(2)(Me(4)bdpi)(H(2)O)(2)](ClO(4))(3).4H(2)O (3), a Cu(II)-Zn(II) heterodinuclear complex of the type of [CuZn(bdpi)(CH(3)CN)(2)](ClO(4))(3).2CH(3)CN (4), Cu(II) mononuclear complexes of [Cu(MeIm(Py)(2))(CH(3)CN)](ClO(4))(2).CH(3)CN (5), [Cu(MeIm(Me)(1))(CH(3)CN)](ClO(4))(2)( )()(6), and [Cu(MeIm(Me)(2))(CH(3)CN)](ClO(4))(2)( )()(7) have been synthesized and the structures of complexes 5-7 determined by X-ray crystallography. The complexes 1-7 have a pentacoordinate structure at each metal ion with the imidazolate or 1-methylimidazole nitrogen, two pyridine nitrogens, the tertiary amine nitrogen, and a solvent (CH(3)CN or H(2)O) which can be readily replaced by a substrate. The reactions between complexes 1-7 and hydrogen peroxide (H(2)O(2)) in the presence of a base at -80 degrees C yield green solutions which exhibit intense bands at 360-380 nm, consistent with the generation of hydroperoxo Cu(II) species in all cases. The resonance Raman spectra of all hydroperoxo intermediates at -80 degrees C exhibit a strong resonance-enhanced Raman band at 834-851 cm(-1), which shifts to 788-803 cm(-1) (Deltanu = 46 cm(-1)) when (18)O-labeled H(2)O(2) was used, which are assigned to the O-O stretching frequency of a hydroperoxo ion. The resonance Raman spectra of hydroperoxo adducts of complexes 2 and 6 show two Raman bands at 848 (802) and 834 (788), 851 (805), and 835 (789) cm(-1) (in the case of H(2)(18)O(2), Deltanu = 46 cm(-1)), respectively. The ESR spectra of all hydroperoxo complexes are quite close to those of the parent Cu(II) complexes except 6. The spectrum of 6 exhibits a mixture signal of trigonal-bipyramid and square-pyramid which is consistent with the results of resonance Raman spectrum.     

Pyrazolate-based copper(II) and nickel(II) [2 x 2] grid complexes: protonation-dependent self-assembly, structures and properties

The pyrazole-based diamide ligand N,N'-bis(2-pyridylmethyl)pyrazole-3,5-dicarboxamide (H(3)L) has been structurally characterised and successfully employed in the preparation of [2 x 2] grid-type complexes. Thus, the reaction of H(3)L with Cu(ClO(4))2.6H(2)O or Ni(ClO(4))2.6H(2)O in the presence of added base (NaOH) affords the tetranuclear complexes [M(4)(HL(4))].8H(2)O (1: M = Cu, 2: M = Ni). Employment of a mixture of the two metal salts under otherwise identical reaction conditions leads to the formation of the mixed-metal species [Cu(x)Ni(4-x)(HL)(4)].8H(2)O (x相似文献   

Synthesis, spectral and thermal studies of some transition metal mixed ligand complexes: modeling of equilibrium composition and biological activity

Several mixed ligand Ni(II), Cu(II) and Zn(II) complexes of 2-amino-3-hydroxypyridine (AHP) and imidazoles viz., imidazole (him), benzimidazole (bim), histamine (hist) and L-histidine (his) have been synthesized and characterized by elemental and spectral (vibrational, electronic, 1H NMR and EPR) data as well as by magnetic moment values. On the basis of elemental analysis and molar conductance values, all the complexes can be formulated as [MAB]Cl except histidine complexes as MAB. Thermogravimetric studies reveal the presence of coordinated water molecules in most of the complexes. From the magnetic measurements and electronic spectral data, octahedral structure was proposed for Ni(II) and Cu(II)-AHP-his, tetrahedral for Cu(II)-AHP-him/bim/hist, but square planar for the Cu(II)-AHP complex. The g∥/A∥ calculated supports tetrahedral environment around the Cu(II) in Cu(II)-AHP-him/bim/hist and distorted octahedral for Cu(II)-AHP-his complexes. The morphology of the reported metal complexes was investigated by scanning electron micrographs (SEM). The potentiometric study has been performed in aqueous solution at 37 °C and I=0.15 mol dm(-3) NaClO4. MABH, MAB and MAB2 species has been identified in the present systems. Proton dissociation constants of AHP and stability constants of metal complexes were determined using MINIQUAD-75. The most probable structure of the mixed ligand species is discussed based upon their stability constants. The in vitro biological activity of the complexes was tested against the Gram positive and Gram negative bacteria, fungus and yeast. The oxidative DNA cleavage studies of the complexes were performed using gel electrophoresis method. Cu(II) complexes have been found to promote DNA cleavage in presence of biological reductant such as ascorbate and oxidant like hydrogen peroxide.     

EPR, mass, IR, electronic, and magnetic studies on copper(II) complexes of semicarbazones and thiosemicarbazones

Copper(II) complexes having the general composition Cu(L)(2)X(2) [where L = isopropyl methyl ketone semicarbazone (LLA), isopropyl methyl ketone thiosemicarbazone (LLB), 4-aminoacetophenone semicarbazone (LLC), and 4-aminoacetophenone thiosemicarbazone (LLD) and X = Cl(-), 1/2SO(4)(2-)] have been synthesized. All the Cu(II) complexes reported here have been characterized by elemental analyses, molar conductance, magnetic moment susceptibility, EI mass, (1)H NMR, IR, EPR, and electronic spectral studies. All the complexes were found to have magnetic moments corresponding to one unpaired electrons. The possible geometries of the complexes were assigned on the basis of EPR, electronic, and infrared spectral studies.     

Trigonal planar copper(I) complex: synthesis, structure, and spectra of a redox pair of novel copper(II/I) complexes of tridentate bis(benzimidazol-2'-yl) ligand framework as models for electron-transfer copper proteins

The copper(II) and copper(I) complexes of the chelating ligands 2,6-bis(benzimidazol-2'-ylthiomethyl)pyridine (bbtmp) and N,N-bis(benzimidazol-2'-ylthioethyl)methylamine (bbtma) have been isolated and characterized by electronic and EPR spectra. The molecular structures of a redox pair of Cu(II/I) complexes, viz., [Cu(bbtmp)(NO(3))]NO(3), 1, and [Cu(bbtmp)]NO(3), 2, and of [Cu(bbtmp)Cl], 3, have been determined by single-crystal X-ray crystallography. The cation of the green complex [Cu(bbtmp)(NO(3))]NO(3) possesses an almost perfectly square planar coordination geometry in which the corners are occupied by the pyridine and two benzimidazole nitrogen atoms of the bbtmp ligand and an oxygen atom of the nitrate ion. The light-yellow complex [Cu(bbtmp)]NO(3) contains copper(I) with trigonal planar coordination geometry constituted by the pyridine and two benzimidazole nitrogen atoms of the bbtmp ligand. In the yellow chloride complex [Cu(bbtmp)Cl] the asymmetric unit consists of two complex molecules that are crystallographically independent. The coordination geometry of copper(I) in these molecules, in contrast to the nitrate, is tetrahedral, with pyridine and two benzimidazole nitrogen atoms of bbtmp ligand and the chloride ion occupying the apexes. The above coordination structures are unusual in that the thioether sulfurs are not engaged in coordination and the presence of two seven-membered chelate rings facilitates strong coordination of the benzimidazole nitrogens and discourage any distortion in Cu(II) coordination geometry. The solid-state coordination geometries are retained even in solution, as revealed by electronic, EPR, and (1)H NMR spectra. The electrochemical behavior of the present and other similar CuN(3) complexes has been examined, and the thermodynamic aspects of the electrode process are correlated to the stereochemical reorganizations accompanying the redox changes. The influence of coordinated pyridine and amine nitrogen atoms on the spectral and electrochemical properties has been discussed.     

Spectral studies on metal-ligand bonding in complexes of 1-acetyl-2-(coumariniminecarboxamide-3-yl)hydrazine

Several new transition metal complexes derived from 1-acetyl-2-(coumariniminecarboxamide-3-yl)hydrazine (HL) have been prepared and characterized by elemental analyses, 1H-NMR, magnetic susceptibility, IR, UV, EPR and thermal analyses. Stereochemistries are proposed for the complexes on the basis of the spectral and magnetic studies. The i.r. data indicate that the carbonyl oxygen of the carboxamide constituents chelating backbone in most complexes. The visible and EPR spectral studies indicated that the Cu(II) complexes have a tetragonal geometry. From the EPR spectrum of the Cu(II) complexes, various parameters were calculated.     

Oxovanadium(IV) and -(V) complexes of dithiocarbazate-based tridentate Schiff base ligands: syntheses,structure, and photochemical reactivity of compounds involving imidazole derivatives as coligands

The tridentate dithiocarbazate-based Schiff base ligands H(2)L (S-methyl-3-((5-R-2-hydroxyphenyl)methyl)dithiocarbazate, R = NO(2), L = L(2); R = Br, L = L(3)) react with [VO(acac)(2)] in the presence of imidazole derivatives as coligands to form oxovanadium(IV) and cis-dioxovanadium(V) complexes. With benzimidazole and N-methylimidazole, the products are oxovanadium(IV) complexes, viz. [VOL(3)(BzIm)].0.5CH(3)CN (1a) and [VOL(N-MeIm)(2)] (L = L(3), 1b; L = L(2), 1c), respectively. In both 1a,b, the O and S donor atoms of the tridentate ligand are cis to the terminal oxo group (in the "equatorial" plane) and mutually trans, but the N donor atom is respectively cis and trans to the oxo atom, as revealed from X-ray crystallography. When imidazole or 4-methylimidazole is used as the ancillary ligand, the products obtained are water-soluble cis-dioxovanadium(V) complexes [VO(2)L(R'-ImH)] (L = L(3) and L(2), R' = H and Me, 2a-d). These compounds have zigzag chain structures in the solid state as confirmed by X-ray crystallographic investigations of 2a,d, involving an alternating array of LVO(2)(-) species and the imidazolium counterions held together by Coulombic interactions and strong hydrogen bonding. Complexes 2a-d are stable in water or methanol. In aprotic solvents, viz. CH(3)CN, DMF, or DMSO, however, they undergo photochemical transformation when exposed to visible light. The putative product is a mixed-oxidation divanadium(IV/V) species obtained by photoinduced reduction as established by EPR, electronic spectroscopy, and dynamic (1)H NMR experiments.     

Spectroscopic evaluation of Co(II), Ni(II) and Cu(II) complexes derived from thiosemicarbazone and semicarbazone

Co(II), Ni(II) and Cu(II) complexes were synthesized with thiosemicarbazone (L(1)) and semicarbazone (L(2)) derived from 2-acetyl furan. These complexes were characterized by elemental analysis, molar conductance, magnetic moment, mass, IR, electronic and EPR spectral studies. The molar conductance measurement of the complexes in DMSO corresponds to non-electrolytic nature. All the complexes are of high-spin type. On the basis of different spectral studies six coordinated geometry may be assigned for all the complexes except Co(L)(2)(SO(4)) and Cu(L)(2)(SO(4)) [where L=L(1) and L(2)] which are of five coordinated square pyramidal geometry.     

Polynuclear and mixed-ligand mononuclear Cu(I) complexes with N-thiophosphorylated thioureas and 1,10-phenanthroline or PPh3

Deprotonation of the N-thiophosphorylated thioureas RC(S)NHP(S)(OiPr)(2) (R = Me(2)N, HL(I); iPrNH, HL(II); 2,6-Me(2)C(6)H(3)NH, HL(III), 2,4,6-Me(3)C(6)H(2)NH, HL(IV), aza-15-crown-5, HL(V)) and reaction with CuI or Cu(NO(3))(2) in aqueous EtOH leads to the polynuclear complexes [Cu(4)(L(I)-S,S')(4)], [Cu(8)(L(II)-S,S')(8)], and [Cu(3)(L(III-V)-S,S')(3)]. The structures of these compounds were investigated by IR, (1)H, (31)P{(1)H} NMR, UV-vis spectroscopy and elemental analyses. The crystal structures of [Cu(4)L(I)(4)], [Cu(8)L(II)(8)], [Cu(3)L(III,IV)(3)] were determined by single-crystal X-ray diffraction. Reaction of the deprotonated ligands (L(I-V))(-) with a mixture of CuI and 1,10-phenanthroline (phen) or PPh(3) leads to the mixed-ligand mononuclear complexes [Cu(phen)L(I-V)], [Cu(PPh(3))L(I-V)] or [Cu(PPh(3))(2)L(I-V)]. The same mixed-ligand complexes were obtained from the reaction of [Cu(4)L(I)(4)], [Cu(8)L(II)(8)], [Cu(3)L(III-V)(3)] with phen or PPh(3).