Showing papers in "Transition Metal Chemistry in 2001"

Ruthenium(II) complexes containing bidentate Schiff bases and their antifungal activity

Abstract: The reactions of ruthenium(II) complexes, [RuHCl(CO)(PPh3)2(B)] [B = PPh3, pyridine (py) or piperidine (pip)], with bidentate Schiff base ligands derived by condensing salicylaldehyde with aniline, o-, m- or p-toluidine have been carried out. The products were characterised by analytical, i.r., electronic, 1H-n.m.r. and 31P-n.m.r. spectral studies and are formulated as [RuCl(CO)(L)(PPh3)(B)] (L = Schiff base anion; B = PPh3, py or pip). An octahedral structure has been tentatively proposed for the new complexes. The Schiff bases and the new complexes were tested in vitro to evaluate their activity against the fungus Aspergillus flavus.

Antitumour activity of transition metal complexes with the thiosemicarbazone derived from 3-acetylumbelliferone

Abstract: Metal complexes of a new thiosemicarbazone derived from 3-acetylumbelliferone (HL) have been prepared and characterized. The complexes have the general formula ML2 · nH2O where MII = Co, Ni, Cu and Zn; n = 0 and 2. The ligand and its complexes have been studied for their possible antitumour activity against HL-60 human leukemia in vitro.

Synthesis, spectral, redox and antimicrobial activities of Schiff base complexes derived from 1-phenyl-2,3-dimethyl-4-aminopyrazol-5-one and acetoacetanilide

Abstract: Novel terdentate neutral complexes of CuII, NiII, CoII, MnII, ZnII, CdII, HgII, VOII, ZrOII and UO2 II have been prepared using a Schiff base derived from 1-phenyl-2,3-dimethyl-4-aminopyrazol-5-one (4-aminoantipyrine) and acetoacetanilide The structural features of the chelates have been confirmed by microanalytical data, ir, uv–vis, 1H-nmr, esr and mass spectral techniques Electronic absorption and ir spectra of the complexes indicate an octahedral geometry around the central metal ion, except for the VOII and ZrOII complexes which show square pyramidal geometry The monomeric and neutral nature of the complexes are confirmed from their magnetic susceptibility and low conductance values The cyclic voltammogram of the copper complex in MeCN at 300 K shows a quasi-reversible peak for the couple CuII/CuIII at Epc = 047 and Epa = 061 V versus Ag/AgCl and two irreversible peaks for CuII → CuI and CuI → Cu0 reduction at Epc = −063 and − 089 V respectively The esr spectra of copper and vanadyl complexes in DMSO solution at 300 K and 77 K were recorded and their salient features are reported The molecular orbital coefficients (α2, β2) were calculated for complexes The antimicrobial activity of the ligand and its complexes have been extensively studied on microorganisms such as Staphylococcus aureus, Klebsiela pneumoniae, Bacillus subtillis, Escherichia coli, Citrobacter ferundii and Salmonella typhi Most of the complexes have higher activities than that of the free ligand

Metal complexes of the flavonoid quercetin: antibacterial properties

Abstract: Two types of complexes were obtained when quercetin (L) was reacted with metal ions in EtOH. The compounds [M(L)Cl2(H2O)2] (M = MnII or CoII) and the semi-oxidized complexes [M(L)2CL2] · 2H2O (M = CdII or HgII) were characterized by elemental analysis., conductivity and magnetic susceptibility measurements, i.r., u.v.–vis. and e.p.r. spectroscopy. The ν(C=O) stretching mode located on the C ring of the ligand and the complexes remains in the same range, showing that this oxygen atom does not participate in coordination to the metal ions. Magnetic susceptibilities and e.p.r. spectra of powdered samples indicated that the monomeric form of the complexes in the solid state, and the paramagnetic nature of the CdII and HgII complexes is attributable to the semiquinone character of the ligand. The antibacterial activity of the metal complexes were tested against five bacterial strains and compared with penicillin activity.

Antioxidative and anti-tumour activities of solid quercetin metal(II) complexes

Abstract: Six metal(II) complexes with quercetin ML2 · nH2O [L = quercetin (3-OH group deprotonated); M = Mn, Co, Ni, Cu, Zn, and Pb; n = 2 or 3] have been prepared and characterized by elemental analysis, complexometric titration, thermal analysis, conductivity, i.r., u.v., 1H-n.m.r. and fluorescence spectral techniques as well as by cyclic voltammetry. The antioxidative and anti-tumour activities of quercetin · 2H2O and the complexes were tested by both the MTT and SRB methods. The results show that the suppression ratios of the complexes against the tested tumour cells are superior to quercetin · 2H2O. The effect of ZnL2 · 3H2O reacting with calf thymus DNA was studied by fluorescence methods. The Zn-complex binding to DNA has been determined by fluorescence titration in 0.05 M Tris-HCl, 0.5 M NaCl buffer (pHb = 7.0). The results indicate that the interaction of the complex with DNA is very evident.

Synthesis and antibacterial activity of metal complexes of ciprofloxacin

Abstract: The interactions of ciprofloxacin (HCipro) with transition metals have been investigated. Two types of complexes, [M(Cipro)(OAc)(H2O)2] · 3H2O (M = MnII, CoII, CuII or CdII) and [M(Cipro)(OAc)] · 6H2O (M = NiII or ZnII), were obtained and characterized by physicochemical and spectroscopic methods. The i.r. spectra of the complexes suggest that the ciprofloxacin behaves as a monoanionic bidentate ligand. In vitro antibacterial activities of the HCipro and the complexes were tested.

Synthesis, spectral and redox properties of metal complexes of macrocyclic tetraaza chiral Schiff bases

Abstract: New transition metal(II) coordination compounds of tetraaza macrocyclic chiral Schiff bases, derived from 2-hydroxybenzylideneacetylacetone or 4-hydroxybenzylideneacetylacetone and (1R, 2R)-(−)-1,2-diaminocyclohexane, have been prepared and characterised spectroscopically and electrochemically. E.p.r. spectral data for the CuII complexes reveal a strong metal-to-ligand π-interaction in their square-planar configuration and the broadening of the g ⊥ component is due to the strain created by 1R and 2R groups in the cyclohexane rings. The cyclic voltammetric (c.v.) data of the copper complexes show an unusual oxidation state of CuIII, while CoII complexes show a reversible CoII/CoIII redox peak along with an additional peak in the negative potential region characteristic of reversibly bound oxygen. The c.v. results reveal that both CuII and CoII complexes bind axially with added bases. The spectroscopic results reveal that copper, cobalt and nickel complexes are in square-planar geometry, whereas manganese is in octahedral geometry.

Reactions of 2,2′-bipyridine (bpy) and 1,10-phenanthroline (phen) with yttrium(III) nitrate: preparation, X-ray crystal structures and spectroscopic characterization of the bis-bpy and bis-phen complexes

Abstract: Y(NO3)3 · 5H2O reacts with 2,2′-bipyridine (bpy) and 1,10-phenanthroline (phen) to yield similar complexes of 1:2 yttrium:ligand stoichiometry. The crystal structures of the two complexes, namely, [Y(NO3)3(bpy)2] (1) and [Y(NO3)3(phen)2] (2), are reported. The three nitrate groups are O,O′-bidentate and the organic ligands are also bidentate. In both structures the metal ion lies on a crystallographic two-fold axis. The stereochemistry about YIII can be viewed as a sphenocorona. The new complexes were characterized by elemental analyses and spectroscopic (i.r., 1H-n.m.r. and 13C-n.m.r.) techniques. The data are discussed in terms of the nature of bonding and known solid state structures.

Mixed ligand complexes of ruthenium(II) containing α,β-unsaturated-β-ketoaminesand their antibacterial activity

Abstract: Hexacoordinated RuII complexes of the [RuX(CO)(PPh3)(B)(LL′)] type [X = Cl; B = PPh3, pyridine (py), piperidine (pip) or morpholine (morph); LL′ = α,β-unsaturated-β-ketoaminate] have been synthesised by reacting [RuHCl(CO)(PPh3)(B)] (B = PPh3, py, pip or morph) with the appropriate β-ketoamine in a 1:1 molar ratio. The replacement of hydride ion and the triphenylphosphine group by a bidentate chelating ligand from the starting compounds occurs. The complexes were characterised by elemental analyses and spectral (i.r., electronic, 1H- and 31P-n.m.r.) data. Antibacterial activity were also tested for in these new complexes.

Synthesis, characterization and antimicrobial activity of cobalt(II), nickel(II)and copper(II) complexes with new asymmetrical Schiff base ligands derived from 7-formyanil-substituted diamine-sulphoxine and acetylacetone

Abstract: Asymmetric 7-formyanil-substituted-imino-4-(4-methyl-2-butanone)-8-hydroxyquinoline-5-sulphonic acid (Schiff bases), react with CoII, NiII and CuII ions to give 1:2, 1:1 and 2:1 complexes as established by conductometric titrations in 1:1 DMF:H2O. The complexes were investigated by elemental analyses, molecular weight determinations, molar conductance, magnetic moments, thermal analysis, i.r., u.v.–vis. and e.s.r. spectra. The complexes have an octahedral crystal structure and general formula [ML·(OH2)2], where MII = Co, Ni and Cu, and L = Na[7—X—HL], (—X— = (CH2)2, (CH2)3, p-C6H4, o-C6H4). Antimicrobial activity of these new ligands and their transition metal complexes has been screened in vitro on common fungi and bacteria.

Synthesis, characterization and interaction of mixed polypyridyl ruthenium(II) complexes with calf thymus DNA

Abstract: New mixed polypyridyl {HPIP = 2-(2-hydroxyphenyl)imidazo[4,5-f][1,10]phenanthroline, phen = 1,10-phenanthroline, dmp = 2,9-dimethyl-1,10-phenanthroline, dmb = 4,4′-dimethyl-2,2′-bipyridine} ruthenium(II) complexes [Ru(phen)2(HPIP)]2+, [Ru(dmp)2(HPIP)]2+ and [Ru(dmb)2(HPIP)]2+ were synthesized and characterized by elemental analyses 1H-n.m.r., u.v.–vis. spectroscopy and cyclic voltammetry. Their DNA-binding properties were demonstrated by absorption, luminescence titrations, steady-state emission quenching and viscosity measurements. The results suggested that all the examined complexes bind with CT-DNA intercalatively. Methyl groups substituted at the 4,4′-positions of bpy has no obvious effect on its DNA binding, whereas substituents at the 2- and 9-positions of phen have an impressive effect on its DNA-binding, as revealed by the decreased binding affinity.

Complexes of 1-isonicotinoyl-4-benzoyl-3-thiosemicarbazide with manganese(II), iron(III), chromium(III), cobalt(II), nickel(II), copper(II) and zinc(II)

Abstract: 1-Isonicotinoyl-4-benzoyl-3-thiosemicarbazide (IBtsc) and its CrIII, MnII, FeIII, CoII, NiII, CuII and ZnII complexes have been prepared and characterized by elemental analyses, magnetic susceptibility measurements, u.v.–vis., i.r., n.m.r. and FAB mass spectral data. The room temperature e.s.r. spectra of the CrIII, FeIII and CuII complexes yield values, characteristic of octahedral, tetrahedral and square-planar complexes, respectively. The Mossbauer spectra of [Fe(IBtsc-H)Cl2] at room temperature and at 78 K suggest the presence of high-spin FeIII. The NiII, CrIII and CuII complexes show semiconducting behaviour in the solid state, but the ZnII complex is an insulator at room temperature. IBtsc and its soluble complexes have been screened against several bacteria, fungi and tumour cell lines.

Coordination chemistry and biological activity of nickel(II) and copper(II) ion complexes with nitrogen–sulphur donor ligands derived from S-benzyldithiocarbazate (SBDTC)

Abstract: A bidentate and a quadridentate Schiff base having NS and NNSS donor sequences were prepared by condensing S-benzyldithiocarbazate (NH2NHCSSCH2Ph) with 2,3-butanedione (1:1 and 1:2 mole ratio). NiII and CuII complexes of these ligands were studied and characterised by elemental analyses and various physico-chemical techniques. The nickel complexes, [Ni(NS)2] and [Ni(SNNS)], were diamagnetic with square-planar and five-coordinate structures, respectively. The copper complex was, however, pentacoordinated. The ligands and the complexes were screened for anticancer activity against T-lymphoblastic leukemic cells (CEM-SS) and colon cancer cells (HT-29). The NS Schiff base was strongly active against leukemic cells with a CD50 value of 2.05 μg cm−3. The nickel and copper complexes were found to be stronger antioxidants than Vitamin E.

Structural and spectral studies of di-2-pyridyl ketone N(4)-methyl- and N(4)-dimethylthiosemicarbazone and their metal complexes

Abstract: Cobalt(II), nickel(II) and copper(II) complexes of di-2-pyridyl ketone N(4)-methyl- and N(4)-dimethylthiosemicarbazone have been prepared and characterized by physical and spectral methods. Use of different ligand-to-metal chloride molar ratios in the preparation of the complexes has produced both mononuclear and polynuclear species for the three metal ions. Crystal structures of the uncomplexed di-2-pyridyl ketone N(4)-methylthiosemicarbazone and a nickel(II) complex, di-2-pyridyl ketone N(4)-dimethylthiosemicarbazone, have been determined and aid the assignments of the i.r., n.m.r., u.v.–vis.–n.i.r. and e.s.r. spectra.

Octakis(ferrocene)-substituted porphyrazines

Abstract: Metal-free porphyrazine and metal porphyrazinates (M = Mg, Cu, Co or Zn) substituted with eight ferrocene moieties on the periphery through flexible alkylthio-bridges have been synthesised in a multi-step reaction sequence. The new compounds have been characterised by elemental analyses, i.r., 1H- and 13C-n.m.r., u.v.–vis. and mass spectra. The electrochemical investigation of porphyrazines indicates that all the ferrocene moieties are oxidised at the same potential, confirming the lack of any interaction among ferrocene groups or between ferrocenes and the porphyrazine core.

Mixed ligand complexes of diaquo (2,2¢-bipyridine)palladium(II) with cyclobutane-1,1-dicarboxylic acid and DNA constituents

Abstract: Complex formation equilibria involving [Pd(bpy)(H2O)2]2+ (bpy = 2,2′-bipyridine) and the cyclobutanedicarboxylate ligand (cbdca), ethylenediamine and DNA have been investigated. Mixed ligand complexes of [Pd(bpy)(cbdca)] with inosine, inosine-5′-monophosphate (5′-IMP), uracil, uridine and adenine have been studied. The results show ring opening of the cbdca and monodentate chelation of the DNA components. Stoichiometries and stability constants for the complexes were determined at 25 °C and at constant 0.1 M ionic strength (adjusted using NaNO3). The coordination sites were found to be pH-dependent. The [Pd(bpy)Cl2], [Pd(bpy)(cbdca)] and [Pd(bpy)(inosine)](NO3) complexes were isolated.

Tridentate Schiff base complexes of ruthenium(III) containing ONS/ONO donor atoms and their biocidal activities

Abstract: New ruthenium(III) complexes of the [RuY(LL′)(E)2] type (Y = Cl or Br; LL′ = tridentate Schiff bases; E = PPh3 or AsPh3) have been synthesised by reacting [RuX3(EPh3)3] (X = Cl, E = P; X = Cl or Br, E = As) or [RuBr3(EPh3)2(MeOH)] with Schiff bases having the donor groups (O, N, X) viz., salicylaldehydethiosemicarbazone (X = S), salicylaldehydesemicarbazone (X = O), o-hydroxyacetophenonethiosemicarbazone (X = S) and o-hydroxyacetophenonesemicarbazone (X = O). The new complexes were characterised by elemental analysis, spectral (i.r., electronic spectra, e.p.r.), magnetic moment and cyclic voltammetry data. Biocidal activity studies were also carried out for the new complexes.

E.p.r. studies on dichloromono(1-phenylamidino-o-alkylurea)copper(II) complexes. Evidence for field induced partial ordering in the solid state and some unusual features in solution

Abstract: E.p.r. and optical absorption studies have been conducted on dichloromono(1-phenylamidino-o-alkylurea)copper(II) complexes (Alkyl = Me, Et, Pr, Bu or Pe). The e.p.r. spectra of solids, recorded at 300 K, confirmed the square-planar geometry with the unpaired electron in the dx2−y2 orbital of copper. Magnetic field-induced partial molecular alignment has been observed in some of the polycrystalline samples when cooled in a magnetic field of 1 T at 77 K. E.p.r. spectra at 77 K in pyridine and DMF has shown axial ligation of solvent molecules (pyridine and DMF), whereas in MeOH and DMSO at least three structurally different CuII species have been identified. These features are consistent with differences in electronic absorption spectra in the powder and in solution.

Hydrolysis of [Pt(dien)H2O]2+ and [Pd(dien)H2O]2+ complexes in water

Abstract: The hydrolysis of the [Pt(dien)H2O]2+ and [Pd(dien)H2O]2+ complexes has been investigated by potentiometry at 298 K, in 0.1 mol dm−3 aqueous NaClO4. Least-squares treatment of the data obtained indicates the formation of mononuclear and μ-hydroxo-bridged dinuclear complexes with stability constants: log β11 = −6.94 for [Pt(dien)OH]+, log β11 = −7.16 for [Pd(dien)OH]+, and also log β22 = −9.37 for [Pt2(dien)2(OH)2]2+ and log β22 = −10.56 for [Pd2(dien)2(OH)2]2+. At pH values > 5.5, formation of the dimer becomes significant for the PtII complex, and at pH > 6.5 for the PdII complex. These results have been analyzed in relation to the antitumor activity of PtII complexes.

Oxidation of cobalt(II) with air oxygen in aqueous ethylenediamine solutions

Abstract: Oxidation of aqueous Co(NO3)2–ethylenediamine (En) solutions with air oxygen was investigated at 20 °C and pH 5.2–7.0, with and without mechanical stirring, by measuring the CoII concentration, pH and redox potential on an Au electrode. In most cases, the oxidation rate was proportional to the concentration of CoEn2+n (n = 2, 3) complexes, and the influence of the solution pH on the rate of reaction was accounted for by the pH dependence of the CoII complex distribution. It was found that sulphate inhibits and bromide accelerates the oxidation process. Possible oxidation routes are discussed. The oxidation process is limited to some extent by O2 transport from the air to the bulk solution.

Coordination of RuCl3(NO)(H2O)2 by imidazole, histidine and iminodiacetate ligands: a study of complexation of 'Caged NO' by simple bio-cellular donors

Abstract: The 'caged NO' reagent, RuCl3NO(H2O)2, has been studied by n.m.r. and i.r. methods with imidazole, histidine, histamine, and N-methyliminodiacetate as complexing ligands. These ligands are representative of cellular donors that would be encountered as RuCl3NO(H2O)2 migrates through biological cells. [RuCl3NO(imH)(H2O)], [RuCl3(NO)(imH)2] and [RuCl2(NO)(imH)3]+ complexes (imH = imidazole) have been detected by 1H-n.m.r. and i.r. and electrospray mass spectrometry (e.s.i.–m.s.) methods. Based upon the effect of cis ligand addition on the ν(NO) frequency causing a decrease in frequency, the 1:1 and 1:2 complexes have the imidazole donors in the plane cis to the NO+ moiety, whereas the 1:3 species has the third imidazole trans to the NO+. The trans imidazole donor causes 'trans-strengthening' of the N–O bond of the {RuNO}6 chromophore. 1H-n.m.r. shows that the monodentate imidazole donor(s) is (are) in rapid exchange with free imidazole in solution for each of the n = 1–3 species. Histidine and histamine make kinetically more stable 1:1 complexes with the major isomer having an axially-coordinated histidine imidazole donor, but in-plane donation for histamine. The carboxylate of coordinated histidine remains pendant according to i.r. and 13C-n.m.r. data. From syntheses carried out at pH ca. 5, the amino donor is H-bonded to an in-plane H2O in the major species (ca. 75%) and coordinated with displacement of the in-plane H2O in the lesser isomer (25%). By contrast, the histamine ligand binds with an in-plane bound imidazole and a pendant protonated amino group (94%). The remaining 6% has an in-plane chelated histamine, analogous to the bis imidazole species and the known fac, cis-[RuCl3NO(en)] complex. N-Methyliminodiacetate is observed to form one main [RuCl(NO)(mida)(H2O)] complex (85%) with two chelated glycinato donor groups with RuCl3NO(H2O)2, one glycinato group chelated 'in-plane' with the central amine donor and one axial coordinated glycinato donor. A second [RuCl(NO)(mida)(H2O)] complex (the remaining 15%) has the amine donor trans to NO+ and chelated glycinato groups which coordinate in the RuClO2(OH2) plane, either cis or trans to each other, in a 60:40 split (ca. 9% and 6%). The presence of one Cl− and one H2O in the [RuCl(NO)(mida)(H2O)] complexes was established by e.s.i.–m.s. These results show that RuCl3NO(H2O)2 is likely to be freely mobile within a cellular environment, forming stable complexes via bidentate chelation with 'two-point' nitrogen donors (en, his, etc).

New asymmetric N2S2 macrocycles, their metal chelates and the photokinetics of DNA-complex interaction

Abstract: New asymmetric ligands have been synthesized by condensing o-phenylene diamine with CS2 and PhCHO/MeCHO, and their complexes with MnII, CoII, NiII, CuII and ZnII were prepared and characterized by elemental analyses, conductivity measurements, i.r., u.v.–vis., e.p.r. and n.m.r. spectra. The transition metals in the complexes show square planar geometry and are ionic. Photokinetic studies of the DNA-metal complexes [C10H10S4N2Cu](NO3)2 and [C10H10S4N2Ni](NO3)2 were carried out and the rate constants k′(DNA-complex) were calculated. The results indicate that DNA reacts with the metal complex in two steps. DNA first undergoes structural degradation and is then completely hydrolysed as indicated by spectral changes consistent with earlier results. The asymmetric N2S2 macrocyclic metal complexes show a strong propensity for DNA inhibition and can be used as an intercalating binding model.

Mono- and binuclear Schiff base complexes derived from glycine, 3-acetylpyridine and transition metal ions

Abstract: Binuclear Schiff base complexes derived from glycine (Gly) and 3-acetylpyridine (3-APy) in the presence of M(OAc)2 [M = CoII, NiII, CuII, ZnII and CdII] have been synthesized The role of pH in promoting the condensation of glycine and 3-acetylpyridine, as well as the substitution of acetates by hydroxide ion, has been discussed Also, the reaction of glycine with 3-acetylpyridine in the presence of MCl2 [M = CoII and NiII] and MCl3 [M = FeIII and CrIII] yields mono- and/or binuclear complexes containing both of glycine and 3-acetylpyridine without condensation Both types of complex were isolated and characterized by chemical analysis, conductance, spectral (uv–vis, ir, and 1H-nmr), magnetic and thermal measurements

Copper(II)–manganese(II) complexes of 3,3′-(1,3-propanediyldiimine)bis-(3-methyl-2-butanone)dioxime with superoxide dismutase-like activity

Abstract: Novel mononuclear [Cu(HPnAO)H2O]ClO4(2), homodinuclear [Cu(PnAO)Cu(phen)(H2O)2](ClO4)2(3), homotrinuclear [Cu3(PnAO)2(H2O)2](ClO4)2(4) and heterodinuclear [Cu(PnAO)Mn(phen)2(H2O)](ClO4)2(5) complexes have been prepared from 3,3′-(1,3-propanediyldiimine)bis-(3-methyl-2-butanone)dioxime (H2PnAO) and characterized by elemental analyses, magnetic moments, i.r., u.v.–vis., and by mass spectral studies. The geometry of the metal chelates is discussed with the help of magnetic and spectroscopic measurements. I.r. spectra show that the ligand acts in a tetradentate manner and coordinates through the (C=N) and (N—H) groups. The elemental analyses, stoichiometry and the spectroscopic data of the complexes indicate that the copper(II) ions are coordinated by the ligand dianion. The heterodinuclear complex (5) displays in vitro ability to scavenge superoxide radicals produced by the xanthine–xanthine oxidase (XXO) system, using nitroblue tetrazolium as an indicator. The complex also supports aerobic growth of Escherichia coli (sodA−sodB−) in vivo in minimal media, indicating that complex (5) is a speculative potent SOD-mimic.

Kinetics and mechanism of the picolinic acid catalysed chromium(VI) oxidation of ethane-1,2-diol in the presence and absence of surfactants

Abstract: The kinetics and mechanism of the CrVI oxidation of ethane-1,2-diol in the presence and absence of picolinic acid (PA) in aqueous acid media have been carried out under the conditions: [ethane-1,2-diol]T ≫ [CrVI]T and [PA]T ≫ [CrVI]T at different temperatures. The micellar effect on the title reactions has been studied in order to substantiate the suggested mechanism. Under the experimental conditions, ethane-1,2-diol is predominantly oxidised to hydroxyethanal and the kinetic contribution from the glycol splitting path is negligible. In the absence of PA, the simple alcohol oxidation mechanism, involving one —OH group, operates. In the PA-catalysed path, a CrVI–PA cyclic complex has been proposed as the active oxidant. In the PA-catalysed path, the CrVI–PA complex is the subject of nucleophilic attack by the substrate to form a ternary complex which subsequently experiences a redox decomposition (through 2e transfer) leading to hydroxyethanal and the CrIV–PA complex. The CrIV–PA complex then participates further in the oxidation of organic substrate and ultimately is converted into the inert CrIII–PA complex. It is striking to note that the uncatalysed path shows a second-order dependence on [H+], while the PA-catalysed path shows a zeroth-order dependence on [H+]. Both the uncatalysed and PA-catalysed paths show first-order dependence on [ethane-1,2-diol]T and on [CrVI]T. The PA-catalysed path is first-order in [PA]T. All these observations (i.e. dependence patterns on the reactants) remain unaltered in the presence of externally added surfactants. The effect of the cationic surfactant (i.e. cetylpyridinium chloride, CPC) and anionic surfactant (i.e. sodium dodecyl sulfate, SDS) has been studied both in the presence and absence of PA. CPC acts as an inhibitor and restricts the reaction to aqueous phase, while SDS acts as a catalyst and the reactions proceed simultaneously in both aqueous and micellar phase, with an enhanced rate in the micellar phase. The observed micellar effects have been explained by considering the preferential partitioning of the reactants between the micellar and aqueous phase. The applicability of different kinetic models, e.g. the Menger–Portnoy model, Piszkiewicz cooperative model, pseudo-phase ion exchange (PIE) model, has been tested to explain the observed micellar effects.

Synthesis, crystal structure and magnetic properties of A[Ni(mnt)2] complexes [A = 1-(4-nitrobenzyl)quinolinium or 1-benzylpyridinium; mnt2− = maleonitriledithiolate]

Abstract: Two new ion-pair complexes A[Ni(mnt)2], [A = 1-(4-nitrobenzyl)quinolinium (1), and 1-benzylpyridinium (2)] have been prepared and characterized. The crystal structure of (1) has been determined by X-ray diffraction analysis. In the solid state, anions and cations of (1) form completely segregated stacking columns, with the Ni···Ni distances alternating between 3.890(4) and 4.965(5) A in the [Ni(mnt)2]− stacking column. The variable temperature magnetic susceptibilities of (1) and (2) have been measured over the 77–300 K range and the results reveal that (1) is diamagnetic and that (2) shows a weak antiferromagnetic spin exchange interaction between the metal ions. The e.p.r. spectra of (1) and (2) in MeCN at room temperature were similar, the g-values being almost identical.

New vic-dioxime transition metal complexes

Abstract: New vic-dioxime ligands and their CuII, CoIII, NiII and VOIV complexes have been prepared and characterized by elemental analyses, i.r. and u.v. spectra, magnetic moments and molar conductance data. The CoIII complexes are diamagnetic. The 1H- and 13C-n.m.r. and g.c./m.s. spectra of the vic-dioxime ligands and their CoIII complexes were recorded. The compounds are all non-electrolytes.

Synthesis, crystal structures and physical properties of two terephthalate-bridged copper(II) and nickel(II) complexes

Abstract: Two μ2-terephthalate (tp) bridged complexes, [Cu2(tp)(pren)4](ClO4)2 (pren = 1,3-diaminopropane) (1) and [Ni2(tp)(pren)4(Him)2](ClO4)2 (Him = imidazole) (2), have been synthesized and characterized by X-ray single-crystal structural analysis. In the discrete dinuclear [Cu2(tp)(pren)4]2+ cation of complex (1), each CuII atom has a square-pyramidal geometry, being coordinated by four nitrogen atoms (avg. 2.031 A) from two pren ligands at the basal plane and one oxygen atom [2.259(3) A] from a bis-monodentate tp group at the axial position. In the discrete dinuclear [Ni2(tp)(pren)4(Him)2]2+ cation of complex (2), each NiII center is coordinated by five nitrogen atoms [Ni—N 2.069(3)–2.109(2) A] from one Him group and two pren groups, and completed by one oxygen atom [Ni—O 2.138(3) A] from a bis-monodentate tp group to furnish a distorted octahedron. Magnetic susceptibility studies show that the pair of metal atoms, although being separated by >11.5 A, exhibit weak intramolecular antiferromagnetic interactions in complexes (1) (g = 2.07 and J = −3.4 cm−1) and (2) (g = 2.10 and J = −0.7 cm−1). The electrochemical behaviors of the complexes have also been studied by cyclic voltammogram processes.

Mono-, di- and trinuclear copper(II) dioxime complexes; 3-{2-[2-(2-hydroxyimino-1-methylpropylideneamino)ethylamino]ethylimino}butan-2-one oxime

Abstract: A new ligand incorporating a dioxime moiety, 3-{2-[2-(2-hydroxyimino-1-methylpropylideneamino)ethylamino]ethylimino}butan-2-one oxime, (H2mdo), has been synthesized and its mono-, di- and trinuclear copper(II), and hetero-dinuclear copper(II)–manganese(II) complexes have been prepared and characterized by elemental analyses, magnetic moments, 1H- and 13C-n.m.r., i.r. and mass spectral studies. A mononuclear copper(II) complex of H2mdo was found to have a 1:1 metal:ligand ratio. Elemental analyses, stoichiometric and spectroscopic data of the metal complexes indicated that the metal ions are coordinated to the oxime and imine nitrogen atoms (C=N); the data support the proposed structure of H2mdo and its complexes.

Metal-phosphine chalcogenide interactions. Crystal and molecular structures of [di-μ-iodo-bis{(methyl cyanide-N)(triphenylthiophosphorane-S)copper(I)}] and [di-μ-chloro-bis{μ-1,2-ethylenebis(diphenylphosphine selenide-Se,Se)} dicopper(I)]

Abstract: Complexes of CuI with tertiary phosphine chalcogenides are described. CuI reacts with Ph3PS in MeCN/CH2Cl2 to form {CuI(Ph3PS)(MeCN)} and CuCl reacts with 1,2-ethylene-bis(tertiary phosphine selenide) {dpeSe2} in MeCN to yield {CuCl(dpeSe2)}. Both compounds exist as halogen-bridged centrosymmetric dimers: [Cu2(μ-I)2-(Ph3PS)2(MeCN)2] (1) and [Cu2(μ-Cl)2(dpeSe2)2] (2) respectively. Compound (1) has almost symmetric Cu—I bonds, d(Cu—I) = 2.6503(8) A and d(Cu—I′) = 2.7196(9) A, and each Cu is further bonded to a S atom [d(Cu—S) = 2.3444(13) A] from Ph3PS and to a N atom [d(Cu—N) = 2.030(5) A] from MeCN. Compound (2) has unequal Cu—Cl bonds, 2.6390(19) and 2.2806(18) A and nearly equal Cu—Se bonds [2.4042(11) and 2.4060(11) A]. The geometry about each Cu center in both cases is distorted tetrahedral. The Cu—Cu bond distance in (2) is 3.249(2) A as compared with 3.4141(16) A in (1). MeCN is bonded strongly to CuI as the excess of Ph3PS failed to remove it from the coordination sphere. Compound (2) represents the first structurally characterised example of copper(I) with a bis(tertiary phosphine selenide) (dpeSe2) acting as a bridging ligand.