Synthesis,structural characterization,and anti-ulcerogenic activity of schiff base ligands derived from tryptamine and 5-chloro, 5-nitro, 3,5-ditertiarybutyl salicylaldehyde and their nickel(II), copper(II), and zinc(II) complexes

Ni(II), Cu(II), and Zn(II) complexes with bidentate Schiff bases derived from the condensation reaction of 5-chlorosalicylaldehyde, 5-nitrosalicylaldehyde, and 3,5 ditertiarybutyl-2-hydroxy benzaldehyde with tryptamine, have been reported. The ligands and complexes were characterized by elemental analysis, IR, ¹H NMR and UV–Vis spectroscopy as well as single crystal X-ray structure analysis whenever possible. The complexes were found to have the general formula [M(L)₂]. Spectral studies reveal that these Schiff bases were acting as bidentate ligands and co-ordinating to the metal center through deprotonated phenolate oxygen and azomethine nitrogen atoms. The Zn(II) complexes establish a tetrahedral geometry in a 1:2 metal to ligand stoichiometry, whereas a square planar geometry was proposed for the nickel and copper complexes, slightly distorted in the case of the latter.The antiulcer activity of 5-chlorosalicylaldehyde derivative and its nickel and copper complexes were evaluated in ethanol-induced gastric mucosal injury in rats. This Schiff base and its complexes promote ulcer protection as ascertained by the comparative decrease in ulcer areas, and inhibition of edema and leucocyte infiltration of the submucosal layer.     

Transition metal complexes of the Schiff bases derived from S-alkyldithiocarbazate with 2-pyridinecarboxaldehyde N-oxide—I. Synthesis, properties and structure of four-coordinate copper(II) complexes

Two new Schiff bases (SMPDH and SBPDH) of S-methyl- and S-benzyl-dithiocarbazate with 2-pyridinecarboxaldehyde N-oxide were prepared and confirmed by elemental analyses and IR spectra. Four copper(II) complexes of the above two Schiff base ligands with imidazole and pyridine were obtained and characterized spectroscopically. The crystal structure of [Cu(SMPD)ImH]ClO₄ was determined by X-ray diffraction analysis. The geometry of the copper atoms in these complexes is square planar with an unsymmetrical environment.     

Novel supramolecular assembly of symmetrical mixed-metal-ligand complexes of dioxouranium(VI)

Some binary and ternary novel complexes of dioxouranium(VI) with 8-hydroxy-7-quinolinecarboxaldehyde (OXH) have been prepared and characterized by elemental analyses, magnetic susceptibility measurements and spectral studies. Coordination effects on the vibrational spectra of the ligands have been investigated. The amine exchange reactions of coordinated Schiff bases in these complexes have been also studied, which reveal symmetrical tetradentate Schiff base complexes. Metal exchange reaction of dioxouranium(VI) complexes was obtained when reacted with tetradentate Schiff base complexes of Cu(II) with ZrCl(4)/UO(2)(CH(3)COO)(2) giving heterobinuclear complexes. Magnetic, electronic and IR spectral data suggest the configurations of distorted square planar ligand field copper(II) complexes. The ligands behave as bi-(O,O) and tetradentate (N(2),O(2)) donors. El-Sonbati equation has been used to evaluate the symmetric stretching frequency from which the F(U-O) and F(UO,UO)(-) were calculated. The bond distances of these complexes were also investigated.     

Synthesis, crystal structure and antiradical effect of copper(II) Schiff base complexes containing five-, six- and unusual seven-membered rings

The synthesis and solid-state structure of mononuclear copper(II) complexes [Cu(SAIB)(H(2)O)(2)] (1), [Cu(SBAIB)(H(2)O)(2)]·H(2)O (2) and [Cu(SGABA)(H(2)O)(2)] (3) are described. Schiff base ligands H(2)SAIB, H(2)SBAIB and H(2)SGABA chelate the copper(II) ion in an O,N,O tridentate fashion. The square-pyramidal geometry of the final complexes is completed by two water ligands. The formation of an unusual seven-membered ring in the set of copper(II) N-salicylidene-aminoacidates is reported. Compounds 1-3 were evaluated by the antiradical activity assay.     

Dicopper(II) complexes of a new pyrazolate-containing Schiff-base macrocycle and related acyclic ligand

Dicopper(II) complexes of two new 3,5-disubstituted-pyrazole-based ligands, bis(quadridentate) macrocyclic ligand (L1)(2-) and bis(terdentate) acyclic ligand (L2)(-), were synthesised by Schiff base condensation of 3,5-diformylpyrazole and either one equivalent of 1,3-diaminopropane or two equivalents of 2-(2-aminoethyl)pyridine in the presence of one or two equivalents of copper(II) ions, respectively. Copper(II) acetate monohydrate was employed in the synthesis of [Cu(2)(L1)(OAc)(2)], [Cu(2)(L2)(H(2)O)(2)(OAc)(3)] and [Cu(II)(2)(L1)(NCS)(2)]; in the last of these one equivalent of NaNCS per copper(II) ion was also added. The fourth complex, [Cu(2)(L2)(NCS)(2)(DMF)]BF(4), was prepared using copper(II) tetrafluoroborate hexahydrate, along with two equivalents of NaOH and six of NaSCN. All four of these dimetallic complexes have been characterised by single crystal X-ray diffraction: the two macrocyclic complexes are the first such Schiff base complexes to be so characterised. A feature common to all four of the structures is bridging of the two copper(II) centres by the pyrazolate moiety/moieties. The structure determinations show that the coordination mode of the acetate groups in both [Cu(2)(L1)(OAc)(2)].2MeOH.H(2)O and [Cu(2)(L2)(H(2)O)(2)(OAc)(3)] is unidentate as had been tentatively predicted by analysis of the infrared spectra (DeltaOCO of 199 and 208 cm(-1), respectively). The magnetochemical studies of the macrocyclic complexes, over the temperature range 4-300 K, revealed strong antiferromagnetic coupling with J = -169 and -213 cm(-1) for [Cu(2)(L1)(OAc)(2)].2H(2)O and [Cu(II)(2)(L1)(NCS)(2)].DMF respectively. The J values have been discussed in relation to a published correlation involving the CuN(pyrazolate)N(pyrazolate) angles.     

Syntheses,crystal structures,and physical properties of dinuclear copper(I) and tetranuclear mixed-valence copper(I,II) complexes with hydroxylated bipyridyl-like ligands

Four copper complexes with hydroxylated bipyridyl-like ligands, namely [Cu(2)(ophen)(2)] (1), [Cu(4)(ophen)(4)(tp)] (2), [Cu(4)(obpy)(4)(tp)] (3), and [Cu(4)(obpy)(4)(dpdc)].2H(2)O (4), (Hophen=2-hydroxy-1,10-phenanthroline, Hobpy=6-hydroxy-2,2'-bipyridine, tp=terephthalate, dpdc=diphenyl-4,4'-dicarboxylate) have been synthesized hydrothermally. X-ray single-crystal structural analyses of these complexes reveal that 1,10-phenanthroline (phen) or 2,2'-bipyridine (bpy) ligands are hydroxylated into ophen or obpy during the reaction, which provides structural evidence for the long-time argued Gillard mechanism. The dinuclear copper(I) complex 1 has three supramolecular isomers in the solid state, in which short copper-copper distances (2.66-2.68 A) indicate weak metal-metal bonding interactions. Each of the mixed-valence copper(i,ii) complexes 2-4 consists of a pair of [Cu(2)(ophen)(2)](+) or [Cu(2)(obpy)(2)](+) fragments bridged by a dicarboxylate ligand into a neutral tetranuclear dumbbell structure. Dinuclear 1 is an intermediate in the formation of 2 and can be converted into 2 in the presence of additional copper(II) salt and tp ligands under hydrothermal conditions. In addition to the ophen-centered pi-->pi* excited-state emission, 1 shows strong emissions at ambient temperature, which may be tentatively assigned as an admixture of copper-centered d-->s,p and MLCT excited states.     

Bistable copper complexes of bis-thia-bis-quinoline ligands

The new ligands R,R-trans-S,S'-bis[methyl(2'-quinolyl)]-1,2-dithiacyclohexane, cis-S,S'-bis[methyl(2'-quinolyl)]-1,2-dithiacyclohexane, and 1,6-bis(2'-quinolyl)-2,5-dithiahexane have been synthesized and their complexes with Cu(I) and Cu(II) prepared. The ligand/metal systems are bistable, as the complexes with copper in both its oxidation states are stable under the same conditions as solids and in solution. The crystal and molecular structure of [Cu(I)(1,6-bis(2'-quinolyl)-2,5-dithiahexane)]ClO(4) has been determined by X-ray diffraction and reveals that the complex is monomeric, with the ligand folding around the Cu(+) cation, imparting to it a tetrahedral coordination. UV-vis, MS-ESI, and NMR data indicate that the same is found for the Cu(I) complexes of all three ligands. Also, the Cu(II) complexes are monomeric, but with a square arrangement of the ligands around Cu(2+). On changing the oxidation state, the change in the geometrical arrangement is fast and complete in less than 80 ms, as demonstrated by cyclic voltammetry experiments. In the CV profiles, the oxidation and reduction events take place at separated E(ox) and E(red) values, with no return wave even at the fastest scan rates. In the E(ox)-E(red) interval (which ranges from 450 to 650 mV, depending on the ligand), the ligand/copper system can thus exist in one of its two states, depending on its history, and thus display electrochemical hysteretical behavior. The electrochemical cycle leading from the tetrahedral [Cu(I)(ligand)](+) to the square [Cu(II)(ligand)](2+) complex (and vice versa) is reversible and repeatable without degradation, as checked by coupled UV-vis-controlled potential coulometry experiments.     

Tri- and tetracoordinate copper(I) complexes bearing bidentate soft/hard SN and SeN ligands based on 2-aminopyridine

The coordination properties of the EN ligands N-(2-pyridinyl)amino-diphenylphosphine sulfide, N-(2-pyridinyl)amino-diisopropylphosphine sulfide, N-(2-pyridinyl)amino-diphenylphosphine selenide, N-(2-pyridinyl)amino-diisopropylphosphine selenide towards copper(I) precursors CuX (X = Br, I), [Cu(IPr)Cl] (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene), and [Cu(CH(3)CN)(4)]PF(6) were studied. Treatment of CuX with EN ligands resulted in the formation of tricoordinate complexes of the type [Cu(κ(2)(E,N)-EN)X]. The reaction of [Cu(IPr)Cl] with EN ligands, followed by halide abstraction with AgSbF(6), afforded cationic tricoordinate complexes [Cu(κ(2)(S,N)-EN)(IPr)](+), while the reaction of [Cu(CH(3)CN)(4)](+) with two equivalents of EN ligands yielded tetrahedral complexes [Cu(κ(2)(E,N)-EN)(2)](+). Halide removal from [Cu(κ(2)(S,N)-SN)I] with silver salts in the presence of L = CH(3)CN and CNtBu afforded dinuclear complexes of the type [Cu(κ(2)(S,N),μ(S)-SN)(L)](2)(2+) containing bridging SN ligands. With the terminal alkynes HC≡CC(6)H(4)Me and HC≡CC(6)H(4)OMe, complexes of the formula [Cu(κ(2)(S,N)-SN-iPr)(η(2)-HC≡CC(6)H(4)Me)](+) and [Cu(κ(2)(S,N)-SN-iPr)(η(2)-HC≡CC(6)H(4)OMe)](+) were obtained. The mononuclear nature of these compounds was supported by DFT calculations. Most complexes were also characterized by X-ray crystallography.     

Synthesis,crystal structure,spectroscopic, and biological studies on Cu(II) complexes of N,O donor dimethyl isoxazole Schiff bases

Cu(II) complexes with Schiff bases DMIIMP, DMIIMBD, DMIIMBP, DMIIMCP, DMIIMMP, and DMIIMNP (see Introduction for definitions) are derived from condensation of 3,4-dimethyl 5-amino-isoxazole with salicylaldehyde and substituted salicylaldehydes. The newly synthesized ligands were characterized by IR, UV-Vis, ¹H NMR, ¹³C NMR, mass spectra, and elemental analysis. The Cu(II) complexes were characterized by IR, UV-Vis, ESR, elemental analysis, magnetic moments, thermogram, DTA, and single crystal analysis. The complexes have general formula [M(L)₂]. The Schiff bases are bidentate coordinating through the azomethine nitrogen and phenolic oxygen of salicylaldehydes. Based on the analytical and spectral data, four-coordinate geometry is assigned for all the complexes. ESR and single crystal analysis suggests square planar geometry for all complexes. [Cu(DMIIMP)₂] crystallizes in the orthorhombic system. Antimicrobial studies of Schiff bases and their metal complexes show significant activity with the metal complexes showing more activity than corresponding Schiff bases. Cytotoxicity of the copper complexes on human cervical carcinoma cells (HeLa) was measured using the Methyl Thiazole Tetrazolium assay.     

Optically active 4- and 5-coordinate transition metal complexes of bifurcated dipeptide Schiff bases

Symmetrical and unsymmetrical benzophenone Schiff bases of bifurcated dipeptides [e.g., Ar2C=N-CHR1- CONH-HNCO-CHR2-N=CAr2] have been synthesized using Boc methodology. These ligands may be regarded as chiral porphyrin mimics because of the alpha-carbons of the amino acids. The Schiff bases function as effective ligands for transition metals, particularly the late transition metals Ni(II), Cu(II), and Zn. Upon metal insertion, there is loss of the amide protons, resulting in N4 chelating ligands that retain the amino acid based chirality as well as newly generated metal-centered chirality, which for the Ni(II) complexes have been shown by X-ray analysis to be lambda (left-handed helix) if the amino acids are S. For Ni(II) and Cu(II), metal insertion results in highly colored complexes and is easily followed by UV-vis spectrophotometry. Several Ni(II) complexes were also characterized by 1H NMR. Co(II) and Mn(II) complexes were characterized by CW EPR. Two Cu(II) complexes, 7f.CuII and 7k.CuII, were characterized by EPR (ENDOR and ESEEM), which clearly showed the pentacoordinate nature of 7k.CuII.     

Synthesis, structural characterization and antibacterial activity of 2,6-diacetylpyridine bis(benzenesulfonohydrazide) Schiff bases and their copper(II) complexes

2,6-Diacetylpyridine bis(benzenesulfonohydrazide) Schiff bases (L¹, L² and L³) and their Cu(II) complexes of the general formula [CuL·H₂O] were synthesized and characterized by various spectroscopic techniques. The crystal structure of [CuL³·(py)]·py was investigated by single crystal X-ray structure analysis. The Cu(II) cation has near square pyramidal, penta-coordinate geometry. The binegatively charged tetradentate Schiff base is asymmetrically coordinated to the Cu(II) ion via the pyridine N atom, the azomethine N atom, the sulfonyl O atom and the deprotonated hydrazine N atom. There is a pyridine molecule apically coordinated to the Cu(II) ion. All the Schiff bases and their copper(II) complexes were screened by the disc diffusion method against multi-drug resistant (MDR) gram-negative and gram-positive bacteria. The minimum inhibitory concentration (MIC) values were also determined. These results show that the antibacterial activity of the Schiff bases against Methicillin-resistant Staphylococcus aureus (MRSA) is enhanced when they are chelated with the copper(II) ion.     

Identification of a copper(I) intermediate in the conversion of 1-aminocyclopropane carboxylic acid (ACC) into ethylene by Cu(II)-ACC complexes and hydrogen peroxide

Several Cu(II) complexes with ACC (=1-aminocyclopropane carboxylic acid) or AIB (=aminoisobutyric acid) were prepared using 2,2'-bipyridine, 1,10-phenanthroline, and 2-picolylamine ligands: [Cu(2,2'-bipyridine)(ACC)(H2O)](ClO4) (1a), [Cu(1,10-phenanthroline)(ACC)](ClO4) (2a), [Cu(2-picolylamine)(ACC)](ClO4) (3a), and [Cu(2,2'-bipyridine)(AIB)(H2O)](ClO4) (1b). All of the complexes were characterized by X-ray diffraction analysis. The Cu(II)-ACC complexes are able to convert the bound ACC moiety into ethylene in the presence of hydrogen peroxide, in an "ACC-oxidase-like" activity. A few equivalents of base are necessary to deprotonate H2O2 for optimum activity. The presence of dioxygen lowers the yield of ACC conversion into ethylene by the copper(II) complexes. During the course of the reaction of Cu(II)-ACC complexes with H2O2, brown species (EPR silent and lambda max approximately 435 nm) were detected and characterized as being the Cu(I)-ACC complexes that are obtained upon reduction of the corresponding Cu(II) complexes by the deprotonated form of hydrogen peroxide. The geometry of the Cu(I) species was optimized by DFT calculations that reveal a change from square-planar to tetrahedral geometry upon reduction of the copper ion, in accordance with the observed nonreversibility of the redox process. In situ prepared Cu(I)-ACC complexes were also reacted with hydrogen peroxide, and a high level of ethylene formation was obtained. We propose Cu(I)-OOH as a possible active species for the conversion of ACC into ethylene, the structure of which was examined by DFT calculation.     

Structural and luminescence studies of nickel(II) and copper(II) complexes with (1R,2R)-cyclohexanediamine derived unsymmetric Schiff base

Unsymmetrical Schiff base obtained by the condensation reaction of (1R,2R)(-)cyclohexanediamine with 2-hydroxybenzaldehyde and 2-hydroxynaphthaldehyde was used as a ligand for copper(II) and nickel(II). The ligand and complexes were characterized by circular dichroism (CD), UV-VIS, fluorescence, IR and (1)H (NOE diff), NOESY and (13)C NMR (ligand) spectra. The X-ray crystal structures solved for (1R,2R)(-)chxn(salH)(naftalH) and Cu(II)(1R,2R)(-)chxn(sal)(naftal) revealed tetrahedral distortion of coordination sphere in the solid phase. The [Cu(1R,2R)(-)chxn(sal)(naftal)]·0.5EtOH·1.25H(2)O complex crystallized in the monoclinic chiral C2 space group with two molecules in the asymmetric unit as well as disordered ethanol and water molecules. For both molecules Cu(II) ions were found in square-planar environments and adopts conformation described as "semi-open armed", because of distinctly oriented arms according to cyclohexane ring defined by three torsion angles. The thin layers of the ligands, copper(II) and nickel(II) complexes were deposited on Si(111) by a spin coating method and characterized with scanning electron microscopy SEM/EDS and fluorescence spectra. The ligand layers exhibit the most intensive fluorescence band at 498 nm, which can be assigned to emission transition π* → n of Schiff base ligand. For copper(II) layers the most intensive band from intraligand transition at 550 nm was observed. The highest intensity band was registered for the layer obtained when rotation speed was 1000 rpm and time 20 s. The nickel(II) complex layers fluorescence spectra exhibit an intensive band at 564 nm. The emission maxima of the copper(II) and nickel(II) complexes are shifted towards longer wavelength in comparison to the free ligand layers. CD spectra of the complexes in solution are characteristic for tetrahedral planar distortion of the chelate ring. The (1)H NMR NOE diff were measured and the position of the nearest hydrogen atoms in the cyclohexane and aromatic rings were discussed, suggesting the tetrahedral distortion of the central ion of the coordination sphere in solution.     

The first stereochemically nonrigid monomeric two-coordinate copper(I) complexes with homoleptic and heteroleptic "N2" donor set

A novel set of stereochemically nonrigid monomeric two-coordinate copper(I) complexes, [Cu(eta(1)-H(2)CPz'(2))(2)]ClO(4) 1, [Cu(HPz')(2)]ClO(4) 2, and [Cu(HPz')(eta(1)-H(2)CPz'(2))]ClO(4) 3, where Pz' = 3,5-di-tert-butylpyrazolyl, has been synthesized and characterized by X-ray diffraction and variable-temperature (1)H NMR spectroscopy. Based on the (1)H NMR line shape analysis of complexes 1 and 2, the intramolecular fluxional process was proposed for these two-coordinate copper(I) complexes. Also, the mixed ligand complex 3 shows that these two different dynamic binding modes of the coordinated HPz' and H(2)CPz'(2) ligands can proceed simultaneously on a single copper(I) ion.     

Three Schiff base complexes based on diethylenetriamine: synthesis,structure, DNA binding and cleavage,and in vitro cytotoxicity

Transition Metal Chemistry - Cu(II) and Zn(II) complexes with Schiff bases derived from diethylenetriamine, [Cu(C22H23N5)(H2O)(ClO4)2] (1), [Cu(C14H18N4)(ClO4)](ClO4) (2), and...     

Anomalous coordination behaviour of 6‐methyl‐2‐oxo‐1,2‐dihydroquinoline‐3‐carboxaldehyde‐4(N)‐substituted Schiff bases in Cu(II) complexes: Studies of structure,biomolecular interactions and cytotoxicity

A series of copper(II) complexes containing 6‐methyl‐2‐oxo‐1,2‐dihydroquinoline‐3‐carboxaldehyde‐derived Schiff bases have been synthesized and characterised using various analytical and spectroscopic techniques. X‐ray crystallographic analysis confirmed the true coordinating nature of ligands with copper ion. The ligands exhibited ONS tridentate neutral and monobasic coordination. The spectroscopic results evidenced the interaction of the ligands and their copper(II) complexes with nucleic acid/serum albumin. Further, the complexes showed significant activity against human skin cancer cell line (A431) and less toxicity against human keratinocyte cell line (HaCaT). Acridine orange/propidium iodide dual staining studies indicated that the major cause of A431 cell death was through necrosis. By comparing the biological activity of all the ligands, Cu(II) complexes and standard (cisplatin), complex [Cu(H‐6MOQtsc‐Ph)(H₂O)]?NO₃ ( 4 ) exhibited better activity than others, the activity being arranged as follows: 4  >  1  > cisplatin >  3  >  2 .     

Synthesis, spectral, thermal and magnetic studies of Mn(II), Ni(II) and Cu(II) complexes with some benzopyran-4-one Schiff bases

The Schiff bases of N(2)O(2) dibasic ligands, H(2)La and H(2)Lb are prepared by the condensation of ethylenediamine (a) and trimethylenediamine (b) with 6-formyl-7-hydroxy-5-methoxy-2-methylbenzopyran-4-one. Also tetra basic ligands, H(4)La and H(4)Lb are prepared by the condensation of aliphatic amines (a) and (b) with 6-formyl-5,7-dihydroxy-2-methylbenzopyran-4-one. New complexes of H(4)La and H(4)Lb with metal ions Mn(II), Ni(II) and Cu(II) are synthesized, in addition Mn(II) complexes with ligands H(2)La and H(2)Lb are also synthesized. Elemental and thermal analyses, infrared, ultraviolet-visible as well as conductivity and magnetic susceptibility measurements are used to elucidate the structure of the newly prepared metal complexes. The structures of copper(II) complexes are also assigned based upon ESR spectra study. All the complexes separated with the stoichiometric ratio (1:1) (M:L) except Mn-H(4)La and Mn-H(4)Lb with (2:1) (M:L) molar ratio. In metal chelates of the type 1:1 (M:L), the Schiff bases behave as a dinegative N(2)O(2) tetradentate ligands. Moreover in 2:1 (M:L) complexes, the Schiff base molecules act as mono negative bidentate ligand and binuclear complex is then formed. The Schiff bases were assayed by the disc diffusion method for antibacterial activity against Staphylococcus aureus and Escherichia coli. The antifungal activity of the Schiff bases was also evaluated against the fungi Aspergillus flavus and Candida albicans.     

Structural modulation of Cu(I) and Cu(II) complexes of sterically hindered tripyridine ligands by the bridgehead alkyl groups

Structures of Cu(I) and Cu(II) complexes of sterically hindered tripyridine ligands RL = tris(6-methyl-2-pyridyl)methane (HL), 1,1,1-tris(6-methyl-2-pyridyl)ethane (MeL), and 1,1,1-tris(6-methyl-2-pyridyl)propane (EtL), [Cu(RL)(MeCN)]PF(6) (1-3), [Cu(RL)(SO(4))] (4-6), and [Cu(RL)(NO(3))(2)] (7-9), have been explored in the solid state and in solution to gain some insights into modulation of the copper coordination structures by bridgehead alkyl groups (CH, CMe, and CEt). The crystal structures of 1-9 show that RL binds a copper ion in a tridentate facial-capping mode, except for 3, where EtL chelates in a bidentate mode with two pyridyl nitrogen atoms. To avoid the steric repulsion between the bridgehead alkyl group and the 3-H(py) atoms, the pyridine rings in Cu(I) and Cu(II) complexes of MeL and EtL shift toward the Cu side as compared to those in Cu(I) and Cu(II) complexes of HL, leading to the significant differences in the nonbonding interatomic distances, H.H (between the 3-H(py) atoms), N.N (between the N(py) atoms), and C.C (between the 6-Me carbon atoms), the Cu-N(py), Cu-N(MeCN), and Cu-O bond distances, and the tilt of the pyridine rings. The copper coordination geometries in 4-6, where a SO(4) ligand chelates in a bidentate mode, are varied from a square pyramid of 4 to distorted trigonal bipyramids of 5 and 6. Such structural differences are not observed for 7-9, where two NO(3) ligands coordinate in a monodentate mode. The structures of 1-9 in solution are investigated by means of the electronic, (1)H NMR, and ESR spectroscopy. The (1)H NMR spectra show that the structures of 1-3 in the solid state are kept in solution with rapid coordination exchange of the pyridine rings. The electronic and the ESR spectra reveal the structural changes of 5 and 6 in solution. The bridgehead alkyl groups and 6-Me groups in the sterically hindered tripyridine ligand play important roles in modulating the copper coordination structures.     

Synthesis,characterization and bioactivity of mixed-ligand Cu(II) complexes containing Schiff bases derived from S-benzyldithiocarbazate and saccharinate ligand and the X-ray crystal structure of the copper-saccharinate complex containing S-benzyl-β-N-(acetylpyrid-2-yl)methylenedithiocarbazate

Mixed-ligand complexes of general formula, [Cu(NNS)(sac)] (NNS′ = S-benzyl-β-N-(2-acetylpyrid-2-yl)methylenedithiocarbazate, NNS″ = S-benzyl-β-N-(2-benzoylpyrid-2-yl)methylenedithiocarbazate and NNS? = S-benzyl-β-N-(6-methylpyrid-2-yl)methylenedithio-carbazate, sac = the saccharinate anion) have been synthesized by reacting [Cu(sac)₂(H₂O)₄] · 2H₂O with the appropriate ligands in ethanol and characterized by various physico-chemical techniques. Magnetic and spectral evidence indicate that the complexes are four-coordinate in which the Schiff bases coordinate as NNS ligands and the sac- anion coordinates as a unidentate N-donor ligand. An X-ray crystallographic structural analysis of [Cu(NNS′)(sac)] shows that the complex has a distorted square-planar geometry with the Schiff base coordinated to the copper (II) ion as a uninegatively charged tridentate chelating agent via the pyridine nitrogen atom, the azomethine nitrogen atom and the thiolate sulphur atom while the fourth coordination position is occupied by the N-bonded saccharinate anion. The complexes have been evaluated for their biological activities against selected pathogens and cancer cell lines. They display weak activity against the pathogenic bacteria and fungi. The complexes were highly active against the leukemic cell line (HL-60) but only [Cu(NNS′)(sac)] was found to exhibit strong cytotoxicity against the ovarian cancer cell line (Caov-3). All complexes were inactive against the breast cancer cell line (MCF-7).     

Dioxygen activation of a trinuclear Cu(I)Cu(I)Cu(I) cluster capable of mediating facile oxidation of organic substrates: competition between O-atom transfer and abortive intercomplex reduction

The dioxygen activation of a series of Cu(I)Cu(I)Cu(I) complexes based on the ligands (L) 3,3'-(1,4-diazepane- 1,4-diyl)bis(1-{[2-(dimethylamino)ethyl](methyl)amino}propan-2-ol)(7-Me) or 3,3'-(1,4-diazepane-1,4-diyl)bis(1-{[2-(diethylamino)ethyl](ethyl)amino}propan-2-ol)(7-Et) forms an intermediate capable of mediating facile O-atom transfer to simple organic substrates at room temperature. To elucidate the dioxygen chemistry, we have examined the reactions of 7-Me, 7-Et, and 3,3'-(1,4-diazepane-1,4-diyl)bis[1-(4-methylpiperazin-1-yl)propan-2-ol] (7-N-Meppz) with dioxygen at -80, -55, and -35?°C in propionitrile (EtCN) by UV-visible, 77?K EPR, and X-ray absorption spectroscopy, and 7-N-Meppz and 7-Me with dioxygen at room temperature in acetonitrile (MeCN) by diode array spectrophotometry. At both -80 and -55?°C, the mixing of the starting [Cu(I)Cu(I)Cu(I)(L)](1+) complex (1) with O(2)-saturated propionitrile (EtCN) led to a bright green solution consisting of two paramagnetic species: the green dioxygen adduct [Cu(II)Cu(II)(μ-η(2):η(2)-peroxo)Cu(II)(L)](2+) (2) and the blue [Cu(II)Cu(II)(μ-O)Cu(II)(L)](2+) species (3). These observations are consistent with the initial formation of [Cu(II)Cu(II)(μ-O)(2)Cu(III)(L)](1+)(4), followed by rapid abortion of this highly reactive species by intercluster electron transfer from a second molecule of complex 1 to give the blue species 3 and subsequent oxygenation of the partially oxidized [Cu(II)Cu(I)Cu(I)(L)](2+)(5) to form the green dioxygen adduct 2. Assignment of 2 to [Cu(II)Cu(II)(μ-η(2):η(2)-peroxo)Cu(II)(L)](2+) is consistent with its reactivity with water to give H(2)O(2) and the blue species 3, as well as its propensity to be photoreduced in the X-ray beam during X-ray absorption experiments at room temperature. In light of these observations, the development of an oxidation catalyst based on the tricopper system requires consideration of the following design criteria: 1)?rapid dioxygen chemistry; 2)?facile O-atom transfer from the activated cluster to substrate; and 3)?a suitable reductant to rapidly regenerate complex 1 to accomplish efficient catalytic turnover.