Synthesis and antibacterial activity of cephalexin metal complexes

The interactions of cephalexin (Hcepha) with transition and d¹⁰ metal ions have been investigated. The complexes [M(cepha)Cl]nH₂O [M?=?Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II), Hg(II)] were characterized by physicochemical and spectroscopic methods. The IR and ¹H NMR spectra of the complexes suggest that cephalexin behaves as a monoanionic tridentate ligand. In vitro antibacterial activities of Hcepha and the complexes were tested.     

Synthesis and characterization of violurate-based Mn(II) and Cu(II) complexes nano-crystallites as DNA-binders and therapeutics agents against SARS-CoV-2 virus

Synthesis and structural characterization of nano crystallites of bis-violurate-based manganese(II) and copper(II) chelates is the subject of the present study. Analytical data and mass spectra as well as thermal analysis determined the molecular formulas of the present metal chelates. Spectroscopic and magnetic measurements assigned the structural formula of the present violurate metal complexes. The spectroscopic and magnetic investigations along with structural analysis results indicated the square planar geometry of both the Mn(II) and Cu(II) complexes. The structural analysis of the synthesized metal complexes was achieved by processing the PXRD data using specialized software Expo 2014. Spectrophotometeric and viscosity measurements showed that violuric acid and its Mn(II) and Cu(II) complexes successfully bind to DNA with intrinsic binding constants K_b from 38.2 × 10⁵ to 26.4 × 10⁶ M^?1. The antiviral activity study displayed that the inhibitory concentrations (IC₅₀) of SARS-CoV-2 by violuric acid and its Mn(II) and Cu(II) complexes are 84.01, 39.58 and 44.86 μM respectively. Molecular docking calculations were performed on the SARS-CoV-2 virus protein and the computed binding energy values are ?0.8, ?3.860 ?5.187 and ?4.790, kcal/mol for the native ligand, violuric acid and its Mn(II) and Cu(II) complexes respectively. Insights into the relationship between structures of the current compounds and their degree of reactivity are discussed.     

Metal complexes of omeprazole. Preparation,spectroscopic and thermal characterization and biological activity

Metal complexes of omeprazole (OPZ) are prepared and characterized based on elemental analyses, IR, diffuse reflectance, magnetic moment, molar conductance and thermal analyses (TGA and DTA) techniques. From the elemental analyses, the complexes have the general formula [M(L)₂]X _n [where M = Cr(III) (X = Cl, n = 3), Ni(II) (X = ClO₄, n = 2) and Zn(II) (X = Cl, n = 2)], and [M(L)₂(H₂O)₂]X _n · yH₂O (where M = Fe(III) (X = Cl, n = 3, y = 0), Co(II) (X = Cl or ClO₄, n = 2, y = 0–4) and Ni(II) (X = Cl, n = 2, y = 4) and [Cu(L)₂]Cl₂ · H₂O. The molar conductance data reveal that all the metal chelates are 3 : 1 electrolytes (for Cr(III) and Fe(III) complexes) and 2 : 1 (for the remaining complexes). IR spectra show that OPZ coordinates to the metal ions as neutral bidentate with ON donor sites of the pyridine–N and sulphone-O. The magnetic and solid reflectance spectra indicate octahedral (FeCl₃, CoCl₂, CoClO₄ and NiCl₂), square planar [Cu(II)] and tetrahedral [Mn(II), Cr(III), NiClO₄ and Zn(II)] structures. The thermal behavior of these chelates using thermogravimetric and differential thermal analyses (TGA and DTA) techniques indicate the hydrated complexes lose water of hydration followed immediately by decomposition of the anions and ligand molecules in the successive overlapping OPZ and its metal complexes are screened for antibacterial activity against Escherichia coli, Staphylococcus aureus, Aspergillus flavus and fungi (Candida albicans). The activity data show the metal complexes to be more potent/antibacterial than the parent OPZ ligand against one or more bacterial species.     

Strukturaufklärung gemischter Komplexe von Eisen(II), Kobalt(II) und Nickel

Iron(II), cobalt(II) and nickel form complexes of the formula [Me(TTA)₂B¹] with 1-(2′-thenoyl)-3,3,3-trifluoroacetone (HTTA) and 2-pyridinalphenylimines (B¹) or bis-(2-pyridinal-R-diimines) (B²) and — in dependence of the -R group in the B² compounds — complexes of the formula [Me₂(TTA)₄B₂] and [Me₂(TTA)₂B²]. The octahedral geometry of the complexes can be unequivocally proven by means of electron spectra, IR spectra and from magnetic measurements. The labelling of solid [Ni(TTA)₂B¹] complexes with the nickel isotopes⁵⁸Ni or⁶²Ni permits an allocation of the Me-O- and Me-N-valency oscillations in the FIR.     

Metal complexes of fenoterol drug

Metal complexes of fenoterol (FEN) drug are prepared and characterized based on elemental analyses, IR, ¹H NMR, magnetic moment, molar conductance, and thermal analyses (TG and DTA) techniques. From the elemental analyses data, the complexes are formed in 1:2 [Metal]:[FEN] ratio and they are proposed to have the general formula [Cu(FEN)₂]·2H₂O; [M(FEN)₂(H₂O)₂]·yH₂O (where M = Mn(II) (y = 2), Co(II) (y = 4), Ni(II) (y = 4), and Zn(II) (y = 0) and [Cr(FEN)₂(H₂O)₂]Cl·H₂O. The molar conductance data reveal that all the metal chelates are non-electrolytes except Cr(III) complex, having 1:1 electrolyte. IR spectra show that FEN is coordinated to the metal ions in a uninegative bidentate manner with ON donor sites of the aliphatic –OH and secondary amine –NH. From the magnetic moment measurements, it is found that the geometrical structures of these complexes are octahedral (Cr(III), Mn(II), Co(II), Ni(II), and Zn(II)) and square planar (Cu(II)). The thermal behavior of these chelates is studied using thermogravimetric and differential thermal analyses (TG and DTA) techniques. The results obtained show that the hydrated complexes lose water molecules of hydration followed immediately by decomposition of the coordinated water and ligand molecules in the successive unseparate steps. The FEN drug, in comparison to its metal complexes is also screened for their antibacterial activity against bacterial species (Bacillus subtilis, Staphylococcus aureus, Escherichia coli, and Salmonella typhi), Yeasts (Candida albicans and Saccharomyces cervisiae), and Fungi (Aspergillus niger and Aspergillus flavus). The activity data show that the metal complexes have antibacterial activity like that of the parent FEN drug against one or more species.     

Preparation,characterization and biological activity of novel metal-NNNN donor Schiff base complexes

Novel Schiff base (H₂L) ligand is prepared via condensation of benzil and triethylenetetraamine. The ligand is characterized based on elemental analysis, mass, IR and ¹H NMR spectra. Metal complexes are reported and characterized based on elemental analyses, IR, ¹H NMR, solid reflectance, magnetic moment, molar conductance, and thermal analyses (TG, DTG and DTA). 1:1 [M]:[H₂L] complexes are found from the elemental analyses data having the formulae [M(H₂L)Cl₂]·yH₂O (M = Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II)), [Fe(H₂L)Cl₂]Cl·H₂O, [Th(H₂L)Cl₂]Cl₂·3H₂O and [UO₂(H₂L)](CH₃COO)₂·2H₂O. The metal chelates are found to be non-electrolytes except Fe(III), Th(IV) and UO₂(II) complexes are electrolytes. IR spectra show that H₂L is coordinated to the metal ions in a neutral tetradentate manner with 4Ns donor sites of the two azomethine N and two NH groups. The geometrical structures of these complexes are found to be octahedral. The thermal behaviour of these chelates is studied where the hydrated complexes lose water molecules of hydration in the first step followed immediately by decomposition of the anions and ligand molecules in the subsequent steps. The activation thermodynamic parameters are calculated using Coats–Redfern method. The ligand (H₂L), in comparison to its metal complexes, is screened for its antibacterial activity. The activity data show that the metal complexes have antibacterial activity more than the parent Schiff base ligand and cefepime standard against one or more bacterial species.     

Metal complexes of azo coumarin derivative: synthesis,spectroscopic, thermal,and antimicrobial studies

Cu(II), Co(II), Ni(II), Cd(II), and Zn(II) complexes of 6-(2-phenyldiazenyl)-7-hydroxy-4-methyl coumarin (PAHC) are characterized based on elemental analyses, infrared, ¹H NMR, magnetic moment, molar conductance, mass spectra, UV-Vis analysis, thermogravimetric analysis (TGA), and X-ray powder diffraction. From the elemental analyses, it is found that the complexes have formulae [M(L)₂(H₂O) _n ] ? xH₂O (where M = Cu(II), Co(II), Ni(II), Cd(II), and Zn(II), n = 0–2, x = 1–4). The molar conductance data reveal that all the metal chelates are non-electrolytes. From the magnetic and solid reflectance spectra, it is found that the structures of these complexes are octahedral or tetrahedral. The synthesized ligand and metal complexes were screened for antibacterial activity against some Gram-positive and Gram-negative bacteria.     

Studies on mononuclear transition metal chelates derived from a novel ( E,E )-dioxime: synthesis,characterization and biological activity

A novel vic-dioxime ligand with a thiourea moiety, (4E,5E)-1,3-bis{4-[(4-bromophenylamino)methylene]phenyl}-2-thiooxaimidazoline-4,5-dione dioxime (4) (bmdH₂) has been synthesized from N,N′-bis{4-[(4-bromophenylamino)methylene]phenyl}thiourea and (E,E)-dichloroglyoxime. The bmdH₂ ligand (4) forms transition metal complexes [M(bmdH)₂] with a metal?:?ligand ratio of 1?:?2 with M?=?Ni(II), Co(II), and Cu(II). The mononuclear Ni(II), Co(II) and Cu(II) complexes, [Ni(bmdH)₂] (5), [Co(bmdH)₂] (6) and [Cu(bmdH)₂] (7) have the metal ions coordinated through the two N,N atoms, as do most vic-dioximes. Elemental analyses, molar conductivity, magnetic susceptibility, IR, ¹H NMR spectra, and UV-Visible spectroscopy were used to elucidate the structures of the ligand and its complexes. Conductivity measurements have shown that the mononuclear complexes are non-electrolytes. In addition, the ligands and metal complexes were screened for antibacterial and antifungal activities by agar well diffusion techniques using DMF as solvent.     

Mononuclear and binuclear manganese(II) complexes with tridentate bis-benzimidazolyl ligands

Summary Manganese(II) complexes of bis(2-benzimidazolylmethyl) ether (DGB), bis(2-benzimidazolylmethyl) sulphide (TGB) and the n-butyl derivative of DGB (BDGB) were prepared and characterised. The solution e.p.r. spectrum of [Mn(TGB)Cl₂] in DMF at 143 K is commensurate with an axially distorted monomeric manganese(II) complex, room temperature magnetic moment (6.04 B.M.) per manganese(II) atom being in the range found for other d⁵ monomeric manganese(II) complexes. The solution e.p.r. spectrum of [Mn(BDGB)Cl₂]-2H₂O in DMF at 143 K indicates the presence of two equivalent manganese(II) ions coupled by an exchange interaction, fostered by bridging chlorides. Evidence for this is provided by a nearly isotropic 11 line hyperfine structure of ⁵⁵Mn, with a coupling constant 45 ± 5G. Contact-shifted ¹H n.m.r. data also supports an exchange coupled dimeric manganese complex. The room temperature magnetic moment, 5.64 B.M., per manganese(II) indicates quenching of the magnetic moment below that of monomeric manganese(II) ion. The [Mn(DGB)Cl₂]·H₂O complex exhibits a magnetic moment of 6.02 B.M. per manganese, indicating a monomeric manganese complex. E.p.r. data of the complex diluted in an analogous Zn-DGB complex (1∶20) correlates well for D = 0.22cm⁻¹ and λ ∼- 0.267. The [Mn(DGB)-(C1O₄)₂] and [Mn(BDGB)(ClO₄)₂] complexes, diluted in analogous Zn-DGB and Zn-BDGB complexes (1∶20), show a strong single e.p.r. line at g _eff ∼- 2. The complexes have low magnetic moments; 4.44 B.M./Mn and 4.39 B.M./Mn, at room temperature.     

Transition metal complexes of 2-Carbethoxypyridine (Ethyl picolinate)

Summary A variety of metal(II) complexes of 2-carbethoxypyridine (L) have been prepared and characterised. With metal(II) chlorides the bis complexes can be formulated [ML₂Cl₂]^o (M=Cu^II, Ni^II, Co^II, Fe^II or Mn^II). The complexes are six-coordinate with 2-carbethoxypyridine acting as a bidentate ligandvia the pyridine nitrogen and the carbonyl group of the ester. The chloro complexes are nonelectrolytes in nitroethane; magnetic susceptibility measurements, i.r. and d-d electronic spectra are reported. With metal(II) perchlorate salts the complexes can be formulated as six-coordinate [ML₂ (OH₂)₂] [ClO₄]₂ species containing ionic perchlorate. The ester exchanges of some of these complexes with a variety of primary alcohols have been investigated.     

Synthesis,characterization and biological activity of triaminoxime and its metal complexes

Mn(II), Fe(III), Co(II), Ni(II), Cu(II) and Zn(II) complexes of multifunctional triaminoxime have been synthesized and characterized by elemental analyses, IR, UV–Vis spectra, magnetic moments, ¹H- and ¹³C-NMR spectra for ligand and its Ni(II) complex, mass spectra, molar conductances, thermal analyses (DTA, DTG and TG) and ESR measurements. The IR spectral data show that the ligand is bi-basic or tri-basic tetradentate towards the metals. Molar conductances in DMF indicate that the complexes are non-electrolytes. The ESR spectra of solid copper(II) complexes [(HL)(Cu)₂(Cl)₂] · 2H₂O (2) and [(L)(Cu)₃(OH)₃(H₂O)₆] · 7H₂O (6) show axial symmetry of a d _{x²???y ²} ground state; however, [(HL)(Co)] (4) shows an axial type with d _Z ² ground state and manganese(II) complex [(L)(Mn)₃(OH)₃(H₂O)6] · 4H₂O (10) shows an isotropic type. The biological activity of the ligand and its metal complexes are discussed.     

A mass spectrometry and DFT study of pyrithione complexes with transition metals in the gas phase

2‐Mercaptopyridine N ‐oxide (pyrithione, PTOH) along with several transition metal ions forms coordination compounds displaying notable biological activities. Gas‐phase complexes formed between pyrithione and manganese (II), cobalt (II), nickel (II), copper (II), and zinc (II) were investigated by infusion in the electrospray source of a quadrupole‐time of flight mass spectrometer. Remarkably, positive ion mode spectra displayed the singly charged metal adduct ion [C₁₀H₈MN₂O₂S₂]²⁺ ([M(PTO)₂]^+• or [M(DPTO)]^+•), where DPTO is dipyrithione, 2,2′‐dithiobis(pyridine N ‐oxide), among the most abundant peaks, implying a change in the oxidation state of whether the metal ion or the ligands. In addition, doubly charged ions were recognized as metal adduct ions containing DPTO ligands, [M(DPTO)_n]²⁺. Generation of [M(PTO)₂]^+• / [M(DPTO)]^+• could be traced by CID of [M(DPTO)₂]²⁺, by observation of the sequential losses of a charged (PTO⁺) and a radical (PTO^•) deprotonated pyrithione ligand. The fragmentation pathways of [M(PTO)₂]^+• / [M(DPTO)]^+• were compared among the different metal ions, and some common features were noticed. Density functional theory (DFT) calculations were employed to study the structures of the observed adduct ions, and especially, to decide in the adduct ion [M(PTO)₂]^+• / [M(DPTO)]^+• whether the ligands are 2 deprotonated pyrithiones or a single dipyrithione as well as the oxidation state of the metal ion in the complex. Characterization of gas‐phase pyrithione metal ion complexes becomes important, especially taking into account the presence of a redox‐active ligand in the complexes, because redox state changes that produce new species can have a marked effect on the overall toxicological/biological response elicited by the metal system.     

Spectroscopic investigations and physico-chemical characterization of newly synthesized mixed-ligand complexes of 2-methylbenzimidazole with metal ions

Some mixed ligand complexes containing 2-methylbenzimidazole and thiocyanate ion were synthesized. Free ligands and their metal complexes were characterized using elemental analysis, determination of metal, magnetic susceptibility, molar conductivity, infrared, UV-VIS, and (¹H, ¹³C) NMR spectra, and X-ray structure analysis. The results suggest that the Ag(I) complex has linear geometry, Fe(II), Co(II), Ni(II), Cu(II), Zn(II), and Cd(II) have tetrahedral geometry, Pd(II) complex has square planar geometry, VO(IV) square pyramidal geometry, Pb(II) irregular tetrahedral geometry, and that the Cr(III) and Mn(II) complexes have octahedral geometry. The following general formulae were proposed for the prepared complexes: [AgBX], [CrB₃X₃], (HB)₂[MnB₂X₄] · 2B and [MB₂X₂], where B = 2-methylbenzimidazole, HB = 2-methylbenzimidazolium, X = thiocyanate ion, and M = VO(IV), Fe(II), Co(II), Ni(II), Cu(II), Zn(II), Pd(II), Cd(II), and Pb(II). Molar conductance of a 10⁻³ M solution in N,N-dimethyl formamide (DMF) indicates that all the complexes are non-electrolytes except the Mn(II) complex which is an electrolyte because the molar conductivity of its solution in DMF is high.     

Spectroscopic study of molecular structures of novel Schiff base derived from o-phthaldehyde and 2-aminophenol and its coordination compounds together with their biological activity

New Schiff base (H₂L) ligand is prepared via condensation of o-phthaldehyde and 2-aminophenol. The metal complexes of Cr(III), Mn(II), Fe(II), Fe(III), Co(II), Ni(II), Cu(II) and Zn(II) with the ligand are prepared in good yield from the reaction of the ligand with the corresponding metal salts. They are characterized based on elemental analyses, IR, solid reflectance, magnetic moment, electron spin resonance (ESR), molar conductance, ¹H NMR and thermal analysis (TGA). From the elemental analyses data, the complexes are proposed to have the general formulae [M(L)(H₂O)n]·yH₂O (where M = Mn(II) (n = 0, y = 1), Fe(II) (n = y = 0), Co(II) (n = 2, y = 0), Ni(II) (n = y = 2), Cu(II) (n = 0, y = 2) and Zn(II) (n = y = 0), and [MCl(L)(H₂O)]·yH₂O (where M = Cr(III) and Fe(III), y = 1–2). The molar conductance data reveal that all the metal chelates are non-electrolytes. IR spectra show that H₂L is coordinated to the metal ions in a bi-negatively tetradentate manner with ONNO donor sites of the azomethine N and deprotonated phenolic-OH. This is supported by the ¹H NMR and ESR data. From the magnetic and solid reflectance spectra, it is found that the geometrical structures of these complexes are octahedral (Cr(III), Fe(III), Co(II) and Ni(II) complexes), tetrahedral (Mn(II), Fe(II) and Zn(II) complexes) and square planar (Cu(II) complex). The thermal behaviour of these chelates is studied and the activation thermodynamic parameters, such as, E*, ΔH*, ΔS* and ΔG* are calculated from the DrTGA curves using Coats-Redfern method. The parent Schiff base and its eight metal complexes are assayed against two fungal and two bacterial species. With respect to antifungal activity, the parent Schiff base and four metal complexes inhibited the growth of the tested fungi at different rates. Ni(II) complex is the most inhibitory metal complex, followed by Cr(III) complex, parent Schiff base then Co(II) complex. With regard to bacteria, only two of the tested metal complexes (Mn(II) and Fe(II)) weakly inhibit the growth of the two tested bacteria.     

Synthesis,structural studies and bio-activity of Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) complexes with p -amino acetophenone salicyloyl hydrazone

Complexes of the type [M(pash)Cl] and [M(Hpash)(H₂O)SO₄] (M=Mn(II), Co(II), Ni(II), Cu(II) and Zn(II); Hpash = p-amino acetophenone salicyloyl hydrazone) have been synthesized and characterized by elemental analyses, molar electrical conductance, magnetic moments, electronic, ESR and IR spectra, thermal studies and X-ray powder diffraction. All the complexes are insoluble in common organic solvents and are non-electrolytes. The magnetic moment values and electronic spectra indicate a square-planar geometry for Co(II), Ni(II) and Cu(II) chloride complexes and spin-free octahedral geometry for the sulfato complexes. The ligand coordinates through >C=N–,–NH₂ and a deprotonated enolate group in all the chloro complexes, and through >C=N–, >C=O and–NH₂ in the sulfato complexes. Thermal analyses (TGA and DTA) of [Cu(pash)Cl] show a multi-step exothermic decomposition pattern. ESR spectral parameters of Cu(II) complexes in solid state at room temperature suggest the presence of the unpaired electron in d _{x ² ? y ²} . X-ray powder diffraction parameters for [Cu(pash)Cl] and [Ni(Hpash)(H₂O)SO₄] correspond to tetragonal and orthorhombic crystal lattices, respectively. The complexes show a fair degree of antifungal activity against Aspergillus sp., Stemphylium sp. and Trichoderma sp. and moderate antibacterial activity against E. coli and Clostridium sp.     

Cover Picture: Coordination Algorithms Control Molecular Architecture: [CuI4(L2)4]4+ Grid Complex Versus [MII2(L2)2X4]y+ Side‐By‐Side Complexes (M=Mn,Co, Ni,Zn; X=Solvent or Anion) and [FeII(L2)3][Cl3FeIIIOFeIIICl3] (Chem. Eur. J. 16/2003)

The cover picture shows how differing coordination algorithms control the molecular architecture of complexes of the pyridazine‐containing, two‐armed, acyclic Schiff base ligand L2 (left, prepared from one equivalent of 3,6‐diformylpyridazine and two equivalents of d‐anisidine). Two very different complexes of L2 self‐assemble from tetrahedral copper(I ) versus octahedral zinc(II ), nickel(II ), and cobalt(II ) controlled 1 : 1 reactions with L2. In both cases the metal ions are bridged by the pyridazine moieties in L2, but in the case of the tetrahedral copper(II ) the result is a tetrametallic [2×2] grid complex ([Cu^I₄(L2)⁴]⁴⁺: top right), whilst in the case of the octahedral metal(II ) ions dimetallic side‐by‐side complexes, [M^II₂(L2)²(X)₄]^y+ (M = Mn, Co, Ni, Zn; X = solvent or anion), are formed (bottom right). The cover image was kindly generated by M. Crawford (University of Otago) with Strata Studio Pro (Strata). More details are given by S. Brooker and co‐workers on p. 3772 ff.     

New homoleptic metal complexes of Schiff bases derived from 2,4-di-p-tolyl-3-azabicyclo[3.3.1]nonan-9-one

New bidentate Schiff-base ligands 2-(2,4-di-p-tolyl-3-azabicyclo[3.3.1]nonan-9-ylidene)hydrazinecarbothioamide HL¹ and 2-(2,4-di-p-tolyl-3-azabicyclo[3.3.1]nonan-9-ylidene)hydrazinecarboxamide HL² were synthesized from the condensation of 2,4-di-p-tolyl-3-azabicyclo[3.3.1]nonan-9-one with thiosemicarbazide and semicarbazide, respectively. Homoleptic complexes of these ligands, of general formula K[Cr(L ⁿ )₂Cl₂], K₂[Mn(L ⁿ )₂Cl₂], K₂[Fe(L¹)₂Cl₂] and [M(L ⁿ )₂] (where M = Co(II), Ni(II) Cu(II), Zn(II), Cd(II), and Hg(II) ions; n = 1 or 2) are reported. The mode of bonding and overall geometry of the complexes were determined through IR, UV-Vis, NMR and mass spectral studies, magnetic moment measurements, elemental analysis, metal content, and conductance. These studies revealed octahedral geometry for Cr(III), Mn(II), and Fe(II) complexes, square planar for Cu(II), Co(II), and Ni(II) complexes and tetrahedral for Zn(II), Cd(II), and Hg(II) complexes.     

Synthesis,spectral, DFT,and antimicrobial studies of tin(II) and lead(II) complexes with semicarbazone and thiosemicarbazones derived from (2-hydroxyphenyl)(pyrrolidin-1-yl)methanone

A new series of metal complexes [M(L)₂] (where M = Sn(II), Pb(II), and HL = semicarbazone, thiosemicarbazone or phenylthiosemicarbazone) have been prepared and characterized by elemental analysis, conductance measurements, molecular weight determinations, UV–visible, infrared, and nuclear magnetic resonance (¹H-, ¹³C-, and ¹¹⁹Sn-NMR) spectral studies. Elemental analysis of the metal complexes suggested 1 : 2 (metal–ligand) stoichiometry. Infrared spectra of the complexes agree with coordination to the metal through the nitrogen of the azomethine (>C=N?) and the oxygen/sulfur of the ketonic/thiolic group. Electronic spectra suggest a distorted tetrahedral geometry for all Schiff base complexes. The bond lengths, bond angles, highest occupied molecular orbital, lowest unoccupied molecular orbital, Mulliken atomic charges, and the lowest energy model structure of the complexes have been determined with DFT calculations. Representative Schiff base and its metal chelates have been screened for their in vitro antibacterial activity against four bacteria, Gram-positive (Bacillus cereus, Staphylococcus aureus) and Gram-negative (Escherichia coli, Klebsiella pneumoniae) and four strains of fungus (Penicillium chrysogenum, Aspergillus niger, Rhizopus nigricans, and Alternaria alternata). The metal chelates possess higher antimicrobial activity than the free ligands.     

Spectral,thermal and magnetic investigations of Mn(II), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) 4-methylphthalates

Conditions for the preparation of Mn(II), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) 4-methylphthalates were investigated and their composition, solubility in water at 295 K and magnetic moments were determined. IR spectra and powder diffraction patterns of the complexes prepared with molar ratio of metal to organic ligand of 1.0:1.0 and general formula: M [ CH₃C₆H₃(CO₂)₂]·nH₂o (n=1-3) were recorded and their decomposition in air were studied. During heating the hydrated complexes are dehydrated in one (Mn, Co, Ni, Zn, Cd) or two steps (Cu) and next the anhydrous complexes decompose to oxides directly (Cu, Zn), with intermediate formation of carbonates (Mn, Cd), oxocarbonates (Ni) or carbonate and free metal (Co). The carboxylate groups in the complexes studied are mono- and bidentate (Co, Ni), bidentate chelating and bridging (Zn) or bidentate chelating (Mn, Cu, Cd). The magnetic moments for paramagnetic complexes of Mn(II), Co(II), Ni(II) and Cu(II) attain values 5.92, 5.05, 3.36 and 1.96 M.B., respectively. This revised version was published online in July 2006 with corrections to the Cover Date.     

Magnetic Coupling in Enantiomerically Pure Trinuclear Helicate‐Type Complexes Formed by Hierarchical Self‐Assembly

Based on chiral, enantiomerically pure 7‐[(S)‐phenylethylurea]‐8‐hydroxyquinoline ( 1 ‐H), trinuclear helicate‐type complexes 2 – 5 are formed with divalent transition‐metal cations. X‐ray structural analyses reveal the connection of two monomeric complex units [M( 1 )₃]^? (M=Zn, Mn, Co, Ni) by a central metal ion to form a “dimer”. Due to the enantiopurity of the ligand, the complexes are obtained as pure enantiomers, resulting in pronounced circular dichroism (CD) spectra. Single‐ion effects and intra‐ and intermolecular coupling are observed with dominating ferromagnetic coupling in the case of the cobalt(II) and nickel(II) and dominating antiferromagnetic coupling in the case of the manganese(II) complex.