Synthesis,antimicrobial screening,and DNA-binding/cleavage of new pyrazole-based binuclear CoII,NiII, CuII,and ZnII complexes

Pyrazolato endogenous bridged binuclear Co^II, Ni^II, Cu^II, and Zn^II complexes were prepared and characterized by spectro-analytical methods. The hexadentate N₄S₂ donor was synthesized by condensation of 3,5-dichloroformyl-1H-pyrazole with thiosemicarbazide in dry ethanol. All the complexes were binuclear and octahedral in nature. The ligand and complexes are screened for antimicrobial and DNA-binding/cleavage activities. The binding/cleavage activities with Escherichia coli DNA are monitored with absorption, hydrodynamic, thermal denaturation, and electrophoresis studies. The ligand possesses significant activity against microbes which is further enhanced upon complexation. The DNA-binding study reveals classical intercalation. The Ni^II and Cu^II complexes exhibit higher binding ability.     

Synthesis and characterisation of CoII,NiII and CuII complexes of a tridentate N5 macrocyclic ligand

Summary A novel tridentate macrocyclic ligand was synthesised by the reaction of 2,6-dipicolinic acid hydrazide and 2,3-butanedione. Complexes with Co^II, Ni^II and Cu^II are five-coordinate trigonal bipyramidal on the basis of analyses, electrical conductance, magnetic, electronic and infrared spectral studies. I.r. studies reveal that the ligand coordinates through the pyridine nitrogen and the amido-nitrogen.     

Core modified meso-aryl corrole: first examples of CuII, NiII, CoII and RhI complexes

A variety of metal complexes of 5,10,15-triphenyl-21-monooxa-corrole 4 have been investigated. This monooxa corrole, where one of the pyrrole ring is replaced by a furan moiety, is synthesized by the alpha-alpha coupling reaction of 16-oxa tripyrrane and dipyrromethane. The single crystal X-ray structure of 4 indicates only small deviation of the inner-core heteroatoms from planarity and this macrocycle arrange themselves into a columnar structure. Insertion of metals further flattens the corrole framework. Specifically, oxacorrole 4 binds to Nil(II), Cu(II), and Co(II) with the participation of all heteroatoms in the coordination. However, Rh(I) ion binds to only one imino and one amino nitrogen of the macrocycle. The bond angles at the metal center in the Ni(II) and Rh(I) complexes reveal square planar geometry completed by two CO molecules for Rh(I). The EPR spectra of the paramagnetic that Cu(II) and Col(II) complexes display significant decreases in the metal hyperfine couplings compared with the corresponding porphyrin complexes. The presence of superhyperfine coupling in the Cu(II) complex suggests delocalization of unpaired electron density into the ligand orbitals. Electrochemical studies reveal easier oxidations and harder reductions relative to the corresponding porphyrin derivatives while, the metallated derivatives did not show their characteristic metal reductions due to the high energy of their LUMO.     

Metal complexes of antibiotic drugs. Studies on dicluxacillin complexes of FeII, FeIII, CoII NiII and CuII

The synthesis and characterization of dicluxacillin (DC) complexes with di- and tri-valent metal ions are described. The nature of bonding of the chelated DC and its metal complexes structures have been elucidated on the basis of their spectroscopic (infrared, solid reflectance, magnetic spectra, mass and thermal analysis) properties. In all the complexes studied, the DC acts as a chelate monoanionic ligand with coordination involving the carboxylate O atom and the endocyclic N of the thiazole ring. The DC ligand forms mono-ligand complexes of the general formula [M(DC)(H2O)x(A)]. yH2O where DC is the uninegatively charged bidentate ligand and A = OAc in case of CuII and Cl in case of FeIII, FeII, CoII and NiII ions. IR, solid reflectance spectra and magnetic moment measurement are used to infer the structure and to illustrate the coordinating capacity of the ligand. From the thermal decomposition curves, the water molecules of crystallization are removed in a single stage while the decomposition of the ligand and coordinated water molecules occur in the second and subsequent stages. Different thermodynamic kinetic parameters namely activation energy (E*), enthalpy of activation (AH*), entropy of activation (AS*) and free energy change of activation (AG*) are calculated using Coats and Redfern equation.     

DFT description of the electronic structure and spectromagnetic properties of strongly correlated electronic systems: NiII, CuII and ZnII o-dioxolene complexes

The spectroscopic and magnetic properties of dioxolene complexes of zinc, copper and nickel were studied by DFT calculations on model complexes of formulas [(NH(3))(4)M(II)(SQ)](+) (M=Zn, Ni; SQ=semiquinonato) and [(NH(3))(2)Cu(II)(SQ)](+). Standard approaches such as time-dependent DFT (TDDFT), the Slater transition state (STS), and broken symmetry (BS) were found to be unable to completely account for the physical properties of the systems, and complete active space-configuration interaction (CAS-CI) calculations based on the Kohn-Sham (KS) orbitals was applied. The CAS-CI energies, properly corrected with multireference perturbation theory (MR-PT), were found to be in good agreement with experimental data. We present here a calculation protocol that has a low CPU cost/accuracy ratio and seems to be very promising for interpreting the properties of strongly correlated electronic systems in complexes of real chemical size.     

The relationship between ligand structures and their CoII and NiII complexes: Synthesis and characterization of novel dimeric CoII/CoIII complexes of bis(thiosemicarbazone)

4,6-Diacetylresorcinol serves as a starting point for the generation of multidentate S/N/O or O/N/O symmetrical chelating agents by condensation with thiosemicarbazide or semicarbazide to yield the corresponding bis(thiosemicarbazone) H₄L¹ or bis(semicarbazone) H₄L², respectively. Reaction of H₄L¹ and H₄L² with M(NO₃)₂·6H₂O (M?=?Co or Ni) afforded dimeric complexes for H₄L¹ and binuclear complexes for H₄L², revealing the tendency of S to form bridges. The dimeric cobalt complexes of H₄L¹ are very interesting in that they contain Co^II/Co^III, side/side, low-spin octahedral coordinated Co^III-ions and high-spin square-planar coordinated Co^II-ions. These complexes have the general formula [(H₂L¹)₂Co₂(H₂O) (NO₃)]·nEtOH. Arguments supporting these anomalous Co^II/Co^III structures are based on a pronounced decrease in their magnetic moments, elemental and thermal analyses, visible and IR spectra, as well as their unreactivity towards organic bases such as 1,10-phenanthroline (phen), 2,2′-bipyridine (Bpy), N,N,N′,N′-tetramethylethylenediamine (Tmen) and 8-hydroxyquinoline (oxine, Ox). The dimeric octahedral Ni^II complex [(H₂L¹)₂Ni₂(H₂O)₄]·3H₂O showed higher reactivity towards phen and Bpy and formed adducts; [(HL¹)Ni₂(B)(H₂O)₅] NO₃ (B?=?phen or Bpy). In the presence of oxine, the dimeric brown paramagnetic octahedral complex [(H₂L¹)₂Ni₂(H₂O)₄]·3H₂O was transformed to the dimeric brick-red diamagnetic square-planar complex [(H₃L¹)₂Ni₂](NO₃)₂. The latter showed dramatic behavior in its ¹H NMR spectrum in DMSO-d ₆, which was explained on the basis of H⁺-transfer. By contrast, the binuclear Ni^II–H₄L² complex (11) showed higher reactivity towards phen, Bpy and oxine. These reactions afforded mixed dimeric complexes having the molar ratio 2?:?2?:?1 (Ni^II?:?H₄L²?:?base). The binuclear Co^II–H₄L² complex afforded an adduct with phen and trinuclear complexes with Bpy and oxine. All complexes were found to be unreactive towards Tmen. Structural characterization was achieved by elemental and thermal analyses, spectral data (electronic, IR, mass and ¹H NMR spectra) and conductivity and magnetic susceptibility measurements.     

Isolation of four new CoII/CoIII and NiII complexes with a pentadentate Schiff base ligand: syntheses, structural descriptions and magnetic studies

In this paper we report the temperature and pH dependent syntheses and systematic characterization of four new Co(II)/Co(III) and Ni(II) complexes with a pentadentate Schiff base ligand H(3)L obtained by condensing 1,3,-diaminopropan-2-ol with 2-hydroxyacetophenone in 1:2 molar ratio. The room temperature syntheses involving Co(II) and Ni(II) nitrates and the ligand H(3)L lead to the isolation of the dinuclear species [Co(2)L(2)(H(2)O)] (1), and the mononuclear complex [Ni(LH)] (3), respectively, whereas refluxing at basic pH leads to the tetranuclear complexes, [Co(II)(2)Co(III)(2)L(2)(μ(3)-OMe)(2)(NO(3))(H(2)O)(2)]NO(3)·2(H(2)O) (2), and [Ni(4)L(2)(μ(3)-OMe)(2)(H(2)O)(2)]·2H(2)O (4). 1 is found to be a simple mono alkoxo-bridged Co(III) dinuclear species, whereas 2 and 4 are both rhomb-like tetrameric complexes with double oxo bridges and μ(3)-methoxo bridges, derived from the methanol solvent, in an open dicubane arrangement. Moreover 2 shows six coordinate ordered Co(II) and Co(III) ions and 4 has both six- and five-coordinate Ni(II) centers. Compound 3 is assigned a tentative mononuclear structure based on IR, UV-Vis spectroscopic, (1)H-NMR and ESI mass study results and is supposed to have one Ni(II) center coordinated with a ligand fragment in square planar geometry. The variable temperature magnetic susceptibility study for 2 and 4 is performed which indicate for both 2 and 4 the presence of intracluster dominant ferromagnetic interactions.     

Bi- and tetranuclear ligational deeds of a polyaza macrocycle having four diazine (N2) bridging components headed for CoII, NiII, CuII and ZnII ions: An emphasis on electrochemistry of non-innocent ligand system

Novel bi- and tetranuclear Co^II, Ni^II, Cu^II and Zn^II complexes having diazine bridging units have been prepared and characterised on the basis of analytical and spectroscopic techniques. With the help of electronic spectra and magnetic moment measurements, it is predicted that the Co^II and Ni^II complexes have octahedral geometry while Cu^II and Zn^II complexes found to be square pyramidal. Present Zn^II and Cu^II complexes are binuclear in nature, where as Co^II and Ni^II complexes are tetranuclear with feeble antiferromagnetic exchange interactions. UV–visible spectral studies, in the range 275–425 nm, evidence the significant blue shift in π → π* transition which provide the ease of stabilization of bonding molecular orbitals in the complexes. All complexes are monomeric in nature. Ligand and all complexes were found to be electrochemically active compounds. One electron transfer process is observed in ligand similarly, there is no significant change in the cyclic voltammograms of Co^II and Zn^II complexes, while Cu^II and Ni^II complexes show one and two electron transfer redox behaviours, respectively in the present macrocyclic ligand field.     

Crystal structures and magnetic properties of complexes of M(NO3)2; M = MnII,CoII, NiII,and CuII,with pyridine ligands carrying an aminoxyl radical

Four complexes of M(NO₃)₂(4NOPy-OMe)₂, (4NOPy-OMe = 4-(N-tert-butyloxylamino)-2-(methoxymethylenyl)pyridine, and M = Mn^II, 1; Co^II, 2; Ni^II, 3; Cu^II, 4), were prepared and fully characterized. X-ray single crystal analysis reveals that four complexes are isostructural. The molecular structures are distorted octahedral in which the methoxy oxygen atoms coordinate to the metal ion by trans-configuration while the pyridyl nitrogen atoms and the nitrate oxygen atoms coordinate by cis-configuration. The magnetic properties of all complexes were investigated by SQUID magneto/susceptometry. Temperature dependence of the molar magnetic susceptibilities in the temperature range of 2–300 K indicated that the magnetic coupling between aminoxyl radicals and metal ion was antiferromagnetic in the complex 1 and were ferromagnetic in the complexes 2–4. The quantitative analysis based on the spin Hamiltonian, H = −2J(S₁S_M + S_MS₂) yielded the best fit as J/k_B = −13.4 ± 0.1 K, g = 1.94 ± 0.002, and θ = −0.78 ± 0.02 K for the complex 1, J/k_B = 48.7 ± 2.1 K, g = 2.07 ± 0.02, and θ = −2.83 ± 0.41 K for the complex 3 (the data in the temperature range 300–50 K were used), and J/k_B = 57.0 ± 1.2 K, g = 2.002 ± 0.004, and θ = −9.8 ± 0.1 K for the complex 4.     

N,S,O-Containing organic ligands based on salicylaldehyde and 2-thiosubstituted ethylamines and their complexes with CoII, NiII, and CuII

The reaction of 2,2′-di(2-hydroxybenzaliminoethyl) disulfide (H₂L¹) and 2-[(2-thioethyl)iminomethyl]phenol (H₂L²) with MCl₂·xH₂O (M = Co, Ni, Cu) afforded the [M₂(L¹)Cl₂] and [M(L²)]₂ complexes, respectively. Their structures were determined by the data of electronic and IR spectroscopy and PM3 quantum chemical calculations. The H₂L¹ ligand and the complexes were studied by electrochemistry (CV and using a rotating disk electrode). The primary electronic changes are localized on the ligand fragment upon the electrochemical oxidation and reduction of the complexes. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1325–1330, July, 2007.     

5-(Pyridylmethylidene)-substituted 2-thiohydantoins and their complexes with CuII, NiII, and CoII: Synthesis, electrochemical study, and adsorption on the cystamine-modified gold surface

A series of Cu^II, Ni^II, and Co^II complexes with 5-(pyridylmethylidene)-substituted 2-thiohydantoins (L) were synthesized by the reactions of the corresponding organic ligands with MCl₂·nH₂O. The resulting complexes have the composition LMCl₂ (M = Cu or Ni) or L₂MCl₂ (M = Co). The reactions with N(3)-unsubstituted thiohydantoins afford complexes containing four-membered metallacycles, in which the metal ion is coordinated by the S and N(3) atoms of the thiohydantoin ligand. The reactions of N(3)-substituted thiohydantoins give complexes in which the S and N(1) atoms are involved in coordination. Study by IR spectroscopy demonstrated that the pyridine nitrogen atom is not involved in coordination. Based on the results of electrochemical study of the ligands and complexes by cyclic voltammetry and calculation of their frontier orbitals by the PM3(tm) method, the mechanism of oxidation and reduction of these compounds was proposed. In the first reduction and oxidation steps, the metal atom in the copper and nickel complexes remains, apparently, intact, and these processes occur with the involvement of the ligand fragments, viz., the coordinated thiohydantoin ligand and chloride anion, respectively. In the cobalt complexes, the first reduction step occurs at the ligand; the first oxidation state, at the metal atom. Measurements of the contact angle of aqueous wetting and electrochemical study demonstrated that carboxy-containing 2-thiohydantoins and their complexes can be adsorbed on the cystamine-modified gold surface. The structures of the complexes on the surface differ from the structures of these complexes in solution. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 978–990, June, 2006.     

Synthesis,structure and fluorescent properties of CdII,ZnII and NiII complexes with 2-amino-6-methylbenzothiazole and 5-nitroisophthalate as ligands

Three new coordination polymers, [M(Ambt)₂(Nip)] _n (M = Cd for 1 and Zn for 2) and [Ni_0.5(Nip)(H₂O)₂] (HAmbt) (3) (H₂Nip = 5-nitroisophthalic acid, Ambt = 2-amino-6-methylbenzothiazole), have been synthesized by hydrothermal methods and are further characterized by X-ray diffraction, IR spectra, elemental analysis, TG-DTA and fluorescence spectra. The structural analyses suggest that 1 and 2 are 1-D chains bridged by Nip anions, in which Ambt is a monodentate ligand and the carboxylate groups of Nip are monodentate and chelating bidentate. Complex 3 consists of two individual fragments, six-coordinate mononuclear Ni^II and HAmbt cation, in which HAmbts are encapsulated into the concave of the 2-D layer formed by mononuclear units through classic N?H·· · O hydrogen bonds. Abundant hydrogen bond interactions drive the formation of packing structure of the complexes. The three solid complexes display strong emission peaks from intraligand charge transfer similar to free Ambt at room temperature.     

Synthesis and electrochemical characterization of complexes of 1,2-bis[2-(pyridylmethylideneamino)phenylthio]ethanes with transition metals (CoII, NiII, CuII)

Transition metal (Ni^II, Co^II, and Cu^II) complexes with 1,2-bis[2-(3-pyridylmethylideneamino)phenylthio]ethane (1) and 1,2-bis[2-(4-pyridylmethylideneamino)phenylthio]ethane (2) were synthesized for the first time by slow diffusion of solutions of compounds 1 or 2 in CH₂Cl₂ into solutions of MX₂ · nH₂O (M = Ni, Co, or Cu; X = Cl or NO₃; n = 2 or 6) in ethanol. The reactions with Co^II and Cu^II chlorides afford complexes of composition M(L)Cl₂ (L = 1 or 2). The reactions of compound 1 with Ni^II salts produce complexes with 1,2-bis(2-aminophenylthio)ethane. The molecular structure of dinitrato[1,2-bis(2-aminophenylthio)ethane]nickel(ii) was confirmed by X-ray diffraction. The ligands and the complexes were investigated by cyclic voltammetry and rotating disk electrode voltammetry. The initial reduction of the complexes proceeds at the metal atom. The oxidation of the chlorine-containing complexes proceeds at the coordinated chloride anion. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 350–355, February, 2008.     

Synthesis, crystal structures, luminescent and magnetic properties of homodinuclear lanthanide complexes with a flexible tripodal carboxylate ligand

Six new homodinuclear lanthanide(III) complexes with a flexible tripodal carboxylate ligand (H(3)L), of formulae [Ln(2)L(2)(DMF)(4)]·4DMF (Ln = La (1), Nd (2), Eu (3), Gd (4), Tb (5), Dy (6), DMF = N, N-Dimethylformamide) have been synthesized. Among them, 1, 2, 3, 4, 6 were characterized by single-crystal X-ray diffraction, which crystallized in the monoclinic space group P2(1)/n with a = 13.309(2) ?, b = 27.404(4) ?, c = 16.686(3) ?, β = 105.115(2) and V = 5875.2(17) ?(3) for 1, a = 13.3016(5) ?, b = 27.1952(12) ?, c = 16.6339(7) ?, β = 105.030(2) and V = 5811.3(4) ?(3) for 2, a = 13.2797(10) ?, b = 27.072(2) ?, c = 16.6564(13) ?, β = 104.9390(10) and V = 5785.7(8) ?(3) for 3, a = 13.2855(3) ?, b = 27.0074(6) ?, c = 16.6357(3) ?, β = 104.9790(10) and V = 5766.2(2) ?(3) for 4, a = 13.2837(5) ?, b = 26.9105(10) ?, c = 16.6066(6) ?, β = 104.917(2) and V = 5736.3(4) ?(3) for 6. The crystal structures reveal that these complexes are isostructural, and molecules are connected from 0D to 3D supramolecular structures by hydrogen bonds. All of them were characterized by elemental analysis, IR spectroscopy, XRD and TGA. Unusually, non-luminescent Tb(III) complex was obtained. The photophysical property of the Eu(III) complex and the magnetic property of Gd(III) complex are investigated and discussed in detail.     

Synthesis and luminescent properties of the lanthanide isothiocyanate complexes with an amide-type tripodal ligand

Solid complexes of lanthanide isothiocyanates with an amide-type tripodal ligand, 2,2',2'-nitrilotris-(N-phenylmethyl)-acetamide (L) have been synthesized and characterized by elemental analysis, infrared spectra and molar conductivity measurements. At the same time, the luminescent properties of the Sm(III), Eu(III), Tb(III), Dy(III) isothiocyanate complexes in solid state and the Tb(III) complex in solvents were also investigated.     

Ligational behavior of a bidentate coumarin derivative towards CoII,NiII, and CuII: synthesis,characterization, electrochemistry,and antimicrobial studies

A series of new Co(II), Ni(II), and Cu(II) complexes of Schiff base derived from coumarin have been prepared and characterized by analytical and spectral methods. The Schiff base is synthesized by the condensation of 2,6-diaminopyridine and 3-acetylcoumarin in 1 : 1 stoichiometric ratio. All complexes have 1 : 1 metal : ligand ratio except the nickel complex, where it was found to be 1 : 2. UV-Vis spectra and magnetic moment studies confirm the existence of tetrahedral and octahedral geometries around cobalt(II) and nickel(II) metal ions, respectively, but copper(II) chloride/nitrate/sulfate complexes have square-planar geometry and copper(II) acetate complex is distorted octahedral. ESR spectra of copper complexes at room temperature and liquid nitrogen temperature were tetragonal. All the complexes were found to be more active against bacteria except Ni(II) complex; only CuLSO₄ and CuL(CH₃COO)₂ have shown the enhanced activity against fungi.     

Cyano-bridged FeIII2CuII3 and FeIII4NiII4 complexes: syntheses, structures, and magnetic properties

Two tricyanometallate precursors, (Bu4N)[(Tp4Bo)Fe(CN)3].H2O.2MeCN (1) and (Bu4N)[(pzTp)Fe(CN)3] (2) [Bu4N+ = tetrabutylammonium cation; Tp4Bo = tris(indazolyl)hydroborate; pzTp = tetrakis(pyrazolyl)borate], with a low-spin FeIII center have been synthesized and characterized. The reactions of 1 or 2 with [Cu(Me3tacn)(H2O)2](ClO4)2 (Me3tacn = N,N',N' '-trimethyl-1,4,7-triazacyclononane) afford two pentanuclear cyano-bridged clusters, [(Tp4Bo)2(Me3tacn)3Cu3Fe2(CN)6](ClO4)4.5H2O (3) and [(pzTp)2(Me3tacn)3Cu3Fe2(CN)6](ClO4)4.4H2O (4), respectively. Assembly reactions between 2 and [Ni(phen)(CH3OH)4](ClO4)2 (phen = 1,10-phenanthroline) or Zn(OAc)2.2H2O afford a molecular box [(pzTp)4(phen)4Ni4Fe4(CH3OH)4(CN)12](ClO4)4.4H2O (5) and a rectangular cluster [(pzTp)2Zn2Fe2(OAc)2(H2O)2(CN)6] (6). Their molecular structures were determined by single-crystal X-ray diffraction. In complexes 1 and 2, the central FeIII ions are coordinated by three cyanide carbon atoms and three nitrogen atoms of Tp4Bo- or pzTp-. Both complexes 3 and 4 show a trigonal-bipyramidal geometry, in which [(L)Fe(CN)3]- units occupy the apical positions and are linked through cyanide to [Cu(Me3tacn)]2+ units situated in the equatorial plane. Complex 5 possesses a cubic arrangement of eight metal irons linked through edge-spanning cyanide bridges, while complex 6 shows Zn2Fe2(CN)4 rectangular structure, in which FeIII and ZnII ions are alternately bridged by the cyanide groups. Intramolecular ferromagnetic couplings are observed for complexes 3-5, and they have S = 5/2, 5/2, and 6 ground states and appreciable magnetic anisotropies with negative D values equal to -0.49, -2.39, and -0.39 cm-1, respectively.     

Interaction of divalent metal ions with uracil III. Complexes of MnII,FeII, CoII,NiII and CuII with uracil acting as bidentate ligand

Summary Some novel nonelectrolytic complexes of uracil in its anionic form with divalent metal ions were synthesised by heating to reflux a methanolic solution of uracil and a metal salt at pHca. 7.5. The isolated complexes are formulated as [ML₂(H₂O)₂] where M = Mn, Fe, Co, Ni, or Cu; L = C₄H₃N₂O₂ Electronic spectra indicate the hexacoordination of the metal ion in all the complexes and also the presence of a weak metal-oxygen interaction. The disappearance of the (NH) band and also the appreciable change both in intensity and position the characteristic bands of the 2-keto group of the uracil in the infrared spectra of all the complexes indicate the chelation of the uracil through C(2)=O and N(3).