Versatility in the coordination behavior of a hexatopic compartmental Schiff-base ligand in the architecture of binuclear transition metal(II) complexes

Condensation of 1H-pyrazole-3,5-dicarboxylic hydrazide with 1H-indole-2,3-dione (isatin) yield the compartmental ligand, which is capable of encapsulating two transition metal ions namely Co^II, Ni^II, Cu^II, and Zn^II. The ligand is a binuclear hexadentate chelate with N₄O₂ donating sites. The pyrazole core provides the diazine fragment, which serves as an endogenous bridge between the two metal centers. In Co^II and Ni^II complexes, the ligand is in the imidol form and the subsequent coordination through the imidol oxygen. In other complexes, the lactonic oxygen takes part in ligation. All the complexes are non-electrolytes and soluble in DMSO, DMF, and acetonitrile. Spectral and magnetic studies along with analytical data suggest octahedral geometry for the Co^II and Ni^II complexes, whereas the Cu^II and Zn^II complexes are assigned square pyramidal geometry. The Cu^II and Ni^II complexes show one electron redox behavior and the rest are electrochemically inactive.     

The synthesis,characterization and spectral studies of Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) complexes with N,N-bis(2-{[(2-methyl-2-phenyl-1,3-dioxolan-4-yl) methyl]amino}butyl) N′,N′-dihydroxyethanediimidamide

Co^II, Ni^II, Cu^II, Zn^II and Cd^II complexes of N,N-bis(2-{[(2-methyl-2-phenyl-1,3-dioxolan-4-yl)methyl]amino}butyl)N′,N′-dihydroxyethanediimidamide (LH₂) were synthesized and characterized by elemental analyses, IR, ¹H- and ¹³C-NMR spectra, electronic spectra, magnetic susceptibility measurements, conductivity measurements and thermogravimetric analyses (TGA). The Co^II, Ni^II and Cu^II complexes of LH₂ were synthesized with 1?:?2 metal ligand stoichiometry. Zn^II and Cd^II complexes with LH₂ have a metal ligand ratio of 1?:?1. The reaction of LH₂ with Co^II, Ni^II, Cu^II, Zn^II and Cd^II chloride give complexes Ni(LH)₂, Cu(LH)₂, Zn(LH₂)(Cl)₂, Cd(LH₂)(Cl)₂, respectively.     

Ligational and molecular modeling of 3-(N-phenylthiocarbamyl)pentan-2,4-dione

Pentan-2,4-dione reacts with phenylisothiocyanate to give 3-(N-phenylthiocarbamyl)pentan-2,4-dione (HPTPD) containing N, O and S donor atoms. HPTPD has been characterized by elemental analysis, i.r., ¹H-n.m.r. and electronic spectral studies and its structure is confirmed by molecular modeling using a molecular mechanics program. Co^II, Ni^II, Cu^II, Zn^II and Pd^II complexes have been prepared and characterized by spectroscopic techniques. The Cu^II complex has also been studied by e.s.r. spectroscopy. Upon formation of these complexes, except for Pd^II, loss of methine hydrogen occurs and HPTPD coordinates to the metal centers as a monoanionic bidentate ligand. Co^II acetate forms two types of complexes according to the ratio of reactants. The first is brown–green having the formula [Co(PTPD)₂] and is characterized as square-planar and the other is blue with [Co(PTPD)(OAc)] formula and has a tetrahedral geometry; their thermal decompositions have been studied by t.g analysis. The other metal(II) complexes have square-planar structures based on magnetic and electronic spectral data.     

Synthesis,spectral characterization,redox and antimicrobial activity of Schiff base transition metal(II) complexes derived from 4-aminoantipyrine and 3-salicylideneacetylacetone

A novel tetradentate N₂O₂ type Schiff base, synthesized from 1-phenyl-2,3-dimethyl-4-aminopyrazol-5-one(4-aminoantipyrine) and 3-salicylidene-acetylacetone, forms stable complexes with transition metal ions such as Cu ^II , Ni ^II , Co ^II and Zn ^II in ethanol. Microanalytical data, magnetic susceptibility, IR, UV-Vis.,¹H-NMR, ESR and Mass spectral techniques were used to confirm the structures. Electronic absorption spectra of the complexes suggest a square-planar geometry around the central metal ion. These complexes show higher conductance values, supporting their electrolytic nature. The monomeric nature of the complexes was confirmed from their magnetic susceptibility values. Cyclic voltammogram of the copper(II) and nickel(II) complexes in DMSO solution at 300 K were recorded and the results are discussed. The X-band ESR spectra of the copper complex were recorded and the molecular orbital coefficient values were calculated from the spectra. The in vitro antimicrobial activities of the investigated compounds were tested against bacteria such as Klebsiella pneumoniae, Staphylococcus aureus, Bacillus subtilis and Escherichia coli and fungi like Aspergillus niger and Rhizoctonia bataicola. Most of the metal chelates show higher antimicrobial activity for the above microorganisms than that of the free ligand.     

Synthesis, Characterization and Antibacterial Activity of Some Transition Metal cis-3,7-dimethyl-2,6-octadiensemicarbazone Complexes

The synthesis and characterization of some transition metal cis-3,7-dimethyl-2,6-octadiensemicarbazone (CDOSC) complexes are reported. The ligand CDOSC yields: [ML₂ Cl₂] and [ML₂ Cl₂] Cl type complexes, where M = Cr^III, Mn^II, Fe^III, Co^II, Ni^II, Cu^II, Zn^II, Cd^II and Hg^II, L = CDOSC. Structures of the complexes were determined using elemental analysis, molar conductivity, magnetic measurements, i.r. and electronic, as well as n.m.r spectra. CDOSC acts as a bidentate ligand in all the complexes. All the newly synthesized metal complexes, as well as the ligand, were screened for their antibacterial activity. All the complexes exhibit strong inhibitory action against Gram (+) bacteria Staphylococcus aureus and Gram (−) bacteria Escherichia coli. The antibacterial activities of the complexes are stronger than those of the ligand CDOSC itself.     

The synthesis,spectroscopic and thermal study of oxamic acid compounds of some metal(II) ions

Summary The preparation of oxamic acid complexes of general formula M(H₂NCOCOO)₂·xH₂O (M = Mn^II, Co^II, Ni^II, Cu^II or Zn^II; x = 1 for Cu^II, x = 2 for the other metals) is reported. The i.r. and Raman spectra are discussed considering a trans-octahedral structure, formed by five-membered chelate rings with the amide oxygen and one carboxylic oxygen as donor atoms. The apical positions are occupied by water molecules. The thermal degradation process is very similar for the different complexes, first losing H₂O in one or different steps, then the fragments of the organic ligand to give the metal oxide as residue. The thermal degradation of the Cu^II and Zn^II compounds results in the formation of a new polymeric compound by deprotonation of the primary amide function in an endothermic process, the polymer further decomposes to form the metal oxide.     

Synthesis,characterization and antimicrobial activity of macrocylic phenoxo-bridged di- and tetra-nuclear complexes from <Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-bis[2,6-diiminomethyl-4-methyl-1-hydroxyphenyl]succinoyl/sebacoyldicarboxamides

Macrocyclic ligands N,N-bis[2,6-diiminomethyl-4-methyl-1-hydroxyphenyl]succinoyl dicarboxamide (H₂L¹) and N,N-bis[2,6-diiminomethyl-4-methyl-1-hydroxyphenyl]sebacoyl dicarboxamide (H₂L²) were synthesized and characterized by various spectral techniques. Macrocyclic di- and tetra-homonuclear phenoxo bridged Cu^II, Co^II, Ni^II, Zn^II, Cd^II and Hg^II complexes have been synthesized through the template method by using the precursors 2,6-diformyl-4-methylphenol, succinoyldihydrazide/ sebacoyldihydrazide and respective metal chlorides in 2:2:2/2:2:4 ratio respectively. The synthesized complexes were characterized by i.r., n.m.r., u.v.-vis., FAB-mass, e.s.r., magnetic susceptibility and elemental analyses data. The elemental analyses and FAB-mass spectral data have justified the dinuclear and tetra nuclear structure for the complexes of the ligands H₂L¹ and H₂L² respectively. The observed low magnetic moment values revealed the existence of antiferromagnetic spin exchange interaction operating between the two metal centers. Electronic data suggested the octahedral geometry for Ni^II complexes and square pyramidal geometry for Cu^II, Co^II, Zn^II, Cd^II and Hg^II complexes of both the ligands. The Cu^II, Co^II and Zn^II complexes of both the ligands have shown good antifungal activity against Aspergillus niger and Fusarium oxysporum and medium to weak antibacterial activity against Escherichia coli and Staphylococcus aureus when compared to the standard drugs Grisefulvin and Ciprofloxacin respectively.     

Metal(II) Ion Complexes with 5‐(Pyrazin‐2‐yl)‐2,4‐dihydro‐3H‐1,2,4‐triazole‐3‐thione; Synthesis,Structural Characterization,Acid‐base,and Complexing Properties in Solution

The study reports the synthesis of complexes Co(HL)Cl₂ ( 1 ), Ni(HL)Cl₂ ( 2 ), Cu(HL)Cl₂ ( 3 ), and Zn(HL)₃Cl₂ ( 4 ) with the title ligand, 5‐(pyrazin‐2‐yl)‐1,2,4‐triazole‐5‐thione (HL), and their characterization by elemental analyses, ESI‐MS (m/z), FT‐IR and UV/Vis spectroscopy, as well as EPR in the case of the Cu^II complex. The comparative analysis of IR spectra of the metal ion complexes with HL and HL alone indicated that the metal ions in 1 , 2 , and 3 are chelated by two nitrogen atoms, N(4) of pyrazine and N(5) of triazole in the thiol tautomeric form, whereas the Zn^II ion in 4 is coordinated by the non‐protonated N(2) nitrogen atom of triazole in the thione form. pH potentiometry and UV/Vis spectroscopy were used to examine Co^II, Ni^II, and Zn^II complexes in 10/90 (v/v) DMSO/water solution, whereas the Cu^II complex was examined in 40/60 (v/v) DMSO/water solution. Monodeprotonation of the thione triazole in solution enables the formation of the L:M = 1:1 species with Co^II, Ni^II and Zn^II, the 2:1 species with Co^II and Zn^II, and the 3:1 species with Zn^II. A distorted tetrahedral arrangement of the Cu^II complex was suggested on the basis of EPR and Vis/NIR spectra.     

N-Phthaloylglycinate ternary complexes with cobalt(II), nickel(II), copper(II), zinc(II) and cadmium(II) metal ions and aromatic mono,bi and tridentate amines

Complexes of N-phthaloylglycinate (N-phthgly) and Co^II, Ni^II, Cu^II, Zn^II and Cd^II containing imidazole (imi), N-methylimidazole (mimi), 2,2-bipyridyl (bipy) and 1,10-phenanthroline (phen), and tridentate amines such as 2,2,2-terpyridine (terpy) and 2,4,6-(2-pyridyl)s-triazine (tptz), were prepared and characterized by conventional methods, i.r. spectra and by thermogravimetric analysis. For imi and mimi ternary complexes, the general formula [M(imi/mimi)₂(N-phthgly)₂]·nH₂O, where M = Co^II, Ni^II, Cu^II and Zn^II applies. For Cd^II ternary complexes with imi, [Cd(imi)₃(N-phthgly)₂]·2H₂O applies. For the bi and tridentate ligands, ternary complexes of the formula [M(L)(N-phthgly)₂]·nH₂O were obtained, where M = Co^II, Ni^II, Cu^II and Zn^II; L = bipy, phen, tptz and terpy. In all complexes, N-phthgly acts as a monodentate ligand, coordinating metal ions through the carboxylate oxygen, except for the ternary complexes of Co^II, Ni^II and Cu^II with mimi and Cu^II and Zn^II with imi, where the N-phthgly acts as a bidentate ligand, coordinating the metal ions through both carboxylate oxygen atoms.     

Structure,Characterization, and Metal‐Complexation Properties of a New Tetraazamacrocycle Containing Two Phenolic Pendant Arms

The new tetraazamacrocycle 2 (=2,2′‐[[7‐Methyl‐3,7,11,17‐tetraazabicyclo[11.3.1]heptadeca‐1(17),13,15‐triene‐3,11‐diyl]bis(methylene)]bis(4‐bromophenol)) was synthesized and used as a ligand for different metal‐ion complexes. The X‐ray crystal structures of the complexes of the general formula [M(H‐ 2 )]⁺NO ?MeOH (M=Ni²⁺, Zn²⁺), in which only one of the two pendant phenolic OH groups of 2 is deprotonated, were determined. In both complexes, the coordination environment is of the [5+1] type, the four N‐atoms of the macrocyclic framework defining a square‐planar arrangement around the metal center, with similar Ni? N and Zn? N distances of 1.961(9) to 2.157(9) Å and 2.021(9) to 2.284(8) Å, respectively. In contrast, the M? O distances are markedly different, 2.060(6) and 2.449(8) Å in the Ni^II complex, and 2.027(7) and 2.941(9) Å in the Zn^II complex. The UV/VIS spectra of the Ni^II and Cu^II complexes with ligand 2 , and the EPR spectra of the Cu^II system, suggest the same type of structure for the complexes in solution as in the solid state. Theoretical studies by means of density functional theory (DFT) confirmed the experimental structures of the Ni^II and Zn^II complexes, and led to a proposal of a similar structure for the corresponding Cu^II complex. The calculated EPR parameters for the latter and comparison with related data support this interpretation. The singly occupied molecular orbital (SOMO) in these systems is mainly made of a d orbital of Cu, with a strong antibonding (σ*) contribution of the axially bound phenolate residue.     

meso‐Thiaporphyrinoids Revisited: Missing of Sulfur by Small Metals

Facile synthesis of meso‐aryl‐substituted 5,15‐dithiaporphyrins and 10‐thiacorroles has been achieved by sulfidation of α,α′‐dichlorodipyrrin metal complexes with sodium sulfide in DMF. Thiacorrole metal complexes exhibit distinct aromaticity due to 18 π‐conjugation including the lone pair on sulfur, whereas dithiaporphyrins are nonaromatic judging from ¹H NMR spectra, X‐ray analysis, and absorption spectra. We have found that Ni^II and Al^III dithiaporphyrin complexes undergo smooth thermal sulfur extrusion reaction to give the corresponding thiacorrole complexes, whereas free base, Zn^II, Pd^II, and Pt^II dithiaporphyrin complexes did not exhibit the similar reactivity. The DFT calculations have elucidated a reaction pathway involving an episulfide intermediate, which can explain the markedly different reactivity among dithiaporphyrin metal complexes.     

Complex formation equilibria between mercury(II) complexes of pencillamine and glutathione and transition metal ions

Summary The interaction between Hg^II complexes of the thiols pencillamine and glutathione and some transition metal ions has been investigated potentiometrically. Mixedmetal complexes of the forms Hg(ps)₂M and Hg(gs)₂M (where M=Co or Ni), were detected. The complexes formed between glutathione disulphide with bivalent metal ions Zn^II, Ni^II, Co^II and Cd^II have also been studied. Zn^II and Ni^II form the complexes M(gssg)H and M(gssg), while Co^II and Cd^II form only the fully deprotonated complex M(gssg). The formation constants of the complexes were determined at 25°C and I=0.1 M (NaNO₃). The concentration distribution of various complex species as a function of pH was evaluated.     

Preparation,characterization and antifungal properties of transition metal ion complexes of quadridentate N3S ligands

Summary New metal complexes [M(NNNS)X] (M = Ni^II, Cu^II, Zn^II and Cd^II; NNNS^– = anion of the quadridentate ligands formed from S-methyl--N-(2-aminophenyl)-methylenedithiocarbazate and pyridine-2-aldehyde or 6-methylpyridine-2-aldehyde; X = Cl, NCS, NO₃ or I) and [Co(NNNS)Cl₂]·2H₂O have been prepared and characterized by elemental analysis and conductance measurements. Magnetic and spectroscopic evidence support a five-coordinate structure for [M(NNNS)X] (M = Ni^II, Cu^II, Zn^II and Cd^II; X = Cl, NCS) and a squareplanar structure for [Ni(NNNS)]X (X = NO₃ or I). The [Co(NNNS)Cl₃]·2H₂O complex is low-spin and octahedral. The Schiff bases and some of their metal complexes were tested against three pathogenic fungi, Alternaria alternata, Curvularia geniculata and Fusarium palidoroseum. The metal complexes are less fungitoxic than the free ligands.     

Sulfadrug complexes of zinc(II), cadmium(II) and mercury(II)

Summary Zn^II, Cd^II and Hg^II complexes of sulfadrugs,viz., sulfathiazole, sulfadiazine, sulfamerazine and sulfamethazine were prepared and characterized by analytical and spectroscopic data. The complexes are insoluble and melt with decomposition. The drugs act as bidentate ligands yielding polymeric complexes except for the Zn^II(sulfamethazine) complex in which the drug is monodentate.     

Synthesis,characterization and biological studies of Co<Superscript>II</Superscript>, Ni<Superscript>II</Superscript>, Cu<Superscript>II</Superscript> and Zn<Superscript>II</Superscript> complexes of Schiff bases derived from 4-substituted carbostyrils[quinolin2(1H)-ones]

Schiff bases derived from 4-aminomethylcarbostyril and their transition metal complexes with Co^II, Ni^II, Cu^II and Zn^II have been synthesized and characterized by elemental analysis, molar conductance, magnetic susceptibilities electronic, IR, PMR, ESR, FAB-Mass and thermal studies. From the above spectral studies it is concluded that the ligands of 4-substituted carbostyril Schiff bases, viz, salicylidene 4-aminomethylcarbostyril (SAMC); o-vanillinsalicylidene 4-aminomethylcarbostyril (VAMC) and 5′ chlorosalicylidene 4-aminomethylcarbostyril (CSAMC) act as bidenate molecules coordinating through azomethine nitrogen and phenolic oxygen. The ligands and their metal complexes have been screened in vitro for antibacterial, antifungal and antitumor activity. The results indicate that the biological activity increases on complexation. The Cu^II complexes of the above ligands show greater inhibitory action towards the P388/s tumor cells at lower concentrations.     

Synthesis,characterization and DNA-binding properties of zinc(II) and nickel(II) Schiff base complexes

A new ligand, 2-carboxybenzaldehyde-(4’-hydroxy)benzoylhydrazone(H₂L) and its Zn^II and Ni^II complexes have been synthesized and characterized on the basis of elemental analyses, molar conductivities, ¹H-NMR, IR spectra and thermal analyses. In addition, DNA-binding properties of these two metal complexes were investigated using spectrometric titrations, ethidium bromide displacement experiments, and viscosity measurements. The results show that the two complexes, especially the Ni^II complex, strongly bind with calf-thymus DNA, presumably via an intercalation mechanism. The intrinsic binding constants of the Zn^II and Ni^II complexes with DNA are 2.46 × 10⁵ and 7.94 × 10⁵ M ⁻¹, respectively.     

Synthesis,spectroscopic and electrochemical studies of bis(<Emphasis Type="Italic">N</Emphasis>-aryl-3,5-di-<Emphasis Type="Italic">t</Emphasis>-butyl-salicylaldiminato)cobalt(II) complexes

The synthesis and characterization (elemental analysis, i.r., u.v., magnetic measurements and cyclic voltammetry) of some new Co^II complexes with bidentate bulky salicylaldimines derived from 3,5-di-t-butylsalicylaldehyde and o- or p-substituted (X = Cl, Me, OMe, Bu^t) aniline derivatives are reported in this paper. The presented ligands show very low complexation ability in respect of Ni^II, VO^II, Mn^II, Zn^II and Cd^II metal ions. Electrochemical studies on the complexes, though revealing a dependence of the metal centered redox potentials on electronic and steric effects of the aniline substituents X, the potentials of the ligand-centered oxidation do not correlate with the electronic effects of X.     

Coordinating behaviour of a new pyridylhydrazone; tris-complexes of manganese(II), cobalt(II), nickel(II), copper(II) and zinc(II) with 2-pyridylcarbaldehyde-N,N-dimethylhydrazone

Summary The preparation and characterization oftris-complexes of Mn^II, Co^II, Ni^II, Cu^II and Zn^II with a new pyridylhydrazone, 2-pyridylcarbaldehyde-N,N-dimethylhydrazone (pch), are described. In all the complexes pch behaves as a bidentate ligand binding through the pyridine and azomethyne nitrogen atoms. The complexes appear to be monomeric, high spin six-coordinate, and a distorted octahedral stereochemistry around the metal is suggested. The e.p.r. results for both Cu^II compounds indicate a mainly d_x ²–y² ground state with a static Jahn-Teller distortion, whilst for the Mn^II complex the e.p.r. data indicates a very low symmetry for the MnN₆ polyhedron.     

Transition metal complexes of 5-chlorouracil

Summary Complexes of 5-chlorouracil (5-ClU) (1) with 3d metal ions were characterized by elemental analysis, various spectroscopic methods (i.r., u.v. spectroscopy) and magnetic susceptibility measurements. The spectral evidence suggest that 5-ClU behaves as bidentate ligand in Ni^II, Cu^II, Zn^II, and Cd^II compounds, coordinating through its one carbonyl oxygen and one nitrogen whereas with Mn^II and Co^II it coordinates through the carbonyl oxygen only. The insolubility of the new complexes in organic solvents suggests that these are polymeric except for the Co^II complex which is soluble in pyridine. There is probable OH bridging in the Mn^II and Cu^II complexes and the 5-ClU may bridge in the rest.     

Syntheses,Structures, and Bioactivities Evaluation of some Transition Metal Complexes with 4,4'-Diacetylcurcumin

Stoichiometric reactions of 4,4'-diacetylcurcumin ( HL ) with series of transition metal ions, namely Fe³⁺, Co²⁺, Ni²⁺ and Zn²⁺, in methanol result in the corresponding homoleptic metal complexes. All the obtained complexes were characterized by elemental analysis, high resolution mass spectrometry, IR spectroscopy, magnetic moment and single-crystal X-ray diffraction. Structural analyses are unprecedentedly performed for the Fe^III, Co^II, and Ni^II complexes and reveal octahedral mononuclear complexes with the compositions [Fe(L)₃] and [M(L)₂(MeOH)₂] (M = Co²⁺, Ni²⁺, Zn²⁺) for trivalent and divalent metal ions, respectively. In all complexes, the deprotonated ligands serve as monoanionic and bidentate ligands with (O,O)-chelating β-diketonate moieties. The free ligand HL exhibits considerable antiproliferative effects for the human MCF-7 breast and HepG2 liver cancer cells with IC₅₀ values of 20.91 ± 2.16 μg · mL^–1 and 12.85 ± 1.85 μg · mL^–1, respectively. The Co^II and Zn^II complexes with IC₅₀ values in the range of 14.53–20.80 μg · mL^–1 for MCF-7 breast and 8.48–10.68 μg · mL^–1 for HepG2 liver cancer cells show stronger antiproliferative effects than HL, the Fe^III and Ni^II complexes cause weaker reductions of the growth of the two tested cancer cell lines.