Showing papers in "Transition Metal Chemistry in 2003"

Redox and antimicrobial studies of transition metal(II) tetradentate Schiff base complexes

Abstract: Neutral tetradentate chelate complexes of CuII, NiII, CoII, MnII, ZnII and VOII have been prepared in EtOH using Schiff bases derived from acetoacetanilido-4-aminoantipyrine and 2-aminophenol/2-aminothiophenol. Microanalytical data, magnetic susceptibility, i.r., u.v.–vis., 1H-n.m.r. and e.s.r. spectral techniques were used to confirm the structures of the chelates. Electronic absorption and i.r. spectra of the complexes suggest a square-planar geometry around the central metal ion, except for VOII and MnII complexes which have square-pyramidal and octahedral geometry respectively. The cyclic voltammetric data for the CuII complexes in MeCN show two waves for copper(II) → copper(III) and copper(II) → copper(I) couples, whereas the VOII complexes in MeCN show two waves for vanadium(IV) → vanadium(V) and vanadium(IV) → vanadium(III) couples. The e.s.r. spectra of the CuII, VOII and MnII complexes were recorded in DMSO solution and their salient features reported. The in vitro antimicrobial activity of the investigated compounds was tested against the microorganisms such as Salmonella typhi, Staphylococcus aureus, Klebsiella pneumoniae, Bacillus subtilis, Shigella flexneri, Pseudomonas aeruginosa, Aspergillus niger and Rhizoctonia bataicola. Most of the metal chelates have higher antimicrobial activity than the free ligands.

Synthesis and characterization of copper(II), nickel(II) and cobalt(II) complexes with novel thiourea derivatives

Abstract: A novel series of thiourea derivatives, namely, N,N-diphenyl-N′-(4-phenyl-benzoyl)thiourea (HL1), N,N-diphenyl-N′-(4-chloro-benzoyl)thiourea (HL2) and N,N-di-n-propyl-N′-(4-chloro-benzoyl)thiourea (HL3), and its metal complexes has been prepared and characterised by elemental analysis, i.r. spectroscopy, 1H-n.m.r. spectroscopy, mass spectrometry and single crystal X-ray diffraction. The ligand coordinates to NiII, CuII and CoII in a bidentate manner yielding essentially neutral complexes of the type cis-[ML2]. N.m.r. spectra and single crystal X-ray diffraction analysis revealed the presence of a distorted tetrahedral coordination ML2 complex.

Synthesis and characterisation of four novel NxOy-Schiff-base macrocyclic ligands and their metal complexes

Abstract: Macrocyclic Schiff-bases, L1 and L2, and bis-macrocyclic ligands, L3 and L4, have been prepared by [1 + 1] and [2 + 1] cyclocondensation of 1,7-bis(2′-formylphenyl)-1,4,7-trioxaheptane or 2,6-bis(2-formylphenoxymethyl)pyridine with 2,6-bis(o-aminophenoxymethyl)pyridine or 1,2,4,5-tetraaminebenzene · 4HCl, respectively. The related YIII, MII (M=Co, Ni, Zn, Cd or Pb) and LnIII nitrate or perchlorate complexes have been synthesised following a template procedure, demonstrating the effectiveness of these metal ions to promote the assembly of these four symmetric Schiff-base macrocycles. The complexes were characterised by elemental analyses, molar conductivity, mass spectrometry, i.r., u.v.–vis, and 1H-n.m.r spectroscopy.

Synthesis, DNA-binding and cleavage studies of macrocyclic copper(II) complexes

Abstract: Two macrocyclic copper(II) complexes, [CuL1](ClO4)2 (L1 = 2,6,9,13-tetraparacyclophane, a Schiff base) and [CuL2]Cl2 [L2 = 3,10-bis(2-benzyl)-1,3,5,8,10,13-hexaazacyclotetradecane] have been prepared and characterized by elemental analysis, u.v.–vis., i.r. and mass spectra. Absorption, fluorescence, circular dichroic spectra and viscosity experiments have been carried out on the interaction of the two complexes with calf thymus CT DNA. The results suggest that both complexes can bind to CT DNA by intercalation via the aromatic moiety ring in the macrocycle into the base pairs of DNA. [CuL1](ClO4)2 binds to CT DNA more strongly than [CuL2]Cl2. The position of the aromatic ring in the macrocycle plays an important role in deciding the extent of binding of the complexes to DNA. Significantly, the complexes have been found to be single-strand DNA cleavers in the presence of H2O2 or/and 2-mercaptoethanol.

Spectroscopic and voltammetric studies of the cobalt (II) complex of Morin bound to calf thymus DNA

Abstract: Absorption and emission spectra, viscometric and electrochemical studies have been carried out on the interaction of Morin (2′, 3, 4′, 5, 7-pentahydroxyflavone) and its Co complex, CoL2·3H2O[L = Morin (2′-OH group deprotonated)], with calf thymus DNA. In the presence of DNA, the complex exhibits a hypochromism in the u.v.–vis. spectra and a large enhancement in emission spectra suggests that the complex binds to DNA via a weak partial intercalation, revealed by competitive experiments, viscosity and by electrochemical studies. The binding constant is ca. 2 × 103 M−1 at 20 °C. Both ZnL2·3H2O and CoL2·3H2O complexes have the same molecular structure, ZnL2·3H2O shows the spectral characteristics and electrochemical behaviour which agrees with observations for other intercalators in the presence and absence of DNA, whereas the CoL2·3H2O complex shows different spectral characteristics and electrochemical behaviour to that of ZnL2·3H2O, which suggests that the mode and affinity of the complex CoL2·3H2O binding to DNA are different from that of ZnL2·3H2O. Both ZnL2·3H2O and CoL2·3H2O complexes exhibited different antitumour activity. So the binding mode and affinity of complexes to DNA may play an important role in determining the antitumour activity.

The reactivity of nitrosyl ruthenium complexes containing polypyridyl ligands

Abstract: A series of cis nitrosyl complexes containing polypyridyl ligands were prepared and characterized as cis-[RuL(bpy)2(NO)](PF6)3 (L = pyridine, 4-picoline, or 4-acetylpyridine), by elemental analysis, u.v.–vis. and i.r. spectroscopy, and by electrochemical techniques such as cyclic voltammetry, differential pulse voltammetry, spectroelectrochemistry, and coulometry. The complexes exhibit stretching frequencies ν(NO) at ca. 1950 cm−1 indicating that nitrosyl group has a sufficiently high degree of nitrosonium ion (NO+) character. In non-aqueous solution, the reduction of these complexes induce nitrosyl to nitro conversion. In aqueous solution the reduction product is cis-[RuL(bpy)2(NH3)]2+ formed by a six electron mechanism. The nitrosyl compounds are susceptible to nucleophilic attack by hydroxide ion. The equilibrium constants were determined.

DNA-binding and cleavage studies of a novel porphyrin ruthenium mixed complex [MPyTPP-Ru(pip)2Cl]+

Abstract: A novel porphyrin ruthenium mixed complex, [MPyTPP—Ru(pip)2Cl]+, has been prepared and characterized by elemental analyses, ES-MS, uv–vis and electrochemistry The DNA binding properties of this complex have been investigated by absorption spectroscopy, fluorescence spectroscopy and by viscosity measurements The results indicate that the complex may bind with DNA in a groove-binding mode Upon irradiation with uv light, this complex has been found to promote cleavage of plasmid pBR 322 DNA from the supercoiled form I to the open circular form II

Synthesis, characterization and antimicrobial activity of the Schiff bases derived from 2,4-disubstituted thiazoles and 3-methoxysalicylaldehyde, and their cobalt(II), copper(II), nickel(II) and zinc(II) complexes

Abstract: Two new Schiff base ligands containing 2,4–disubstituted thiazoles and cyclobutane rings, 4-(1-methyl-1-phenylcyclobutane-3-yl)-2-(2-hydroxy-3-methoxybenzylidenehydrazino)thiazole (L1H), 4-(1-methyl-1-p-xylylcyclobutane-3-yl)-2-(2-hydroxy-3-methoxybenzylidenehydrazino)thiazole (L2H) and their mononuclear complexes with a 1:2 metal–ligand ratio have been prepared from acetate salts of CoII, CuII, NiII and ZnII in EtOH. The authenticity of the ligands and their complexes have been established by microanalyses, i.r., 13C- and 1H-n.m.r. spectra, and by magnetic susceptibility and conductivity measurements. The complexes are mononuclear. Thermal properties of the ligands and complexes have been studied by t.g.a. and d.s.c. techniques. Antimicrobial activities of the ligands and their complexes have been tested against six different microorganisms; three are yeast and three are bacteria. One of the ligands and many of the complexes were found to be active against some of the microorganisms studied.

Ruthenium(III)- and osmium(VIII)-catalyzed oxidation of 2-thiouracil by bromamine-B in acid and alkaline media: A kinetic and mechanistic study

Abstract: The kinetics of oxidation of 2-thiouracil (TU) by sodium N-bromobenzenesulphonamide or bromamine-B (BAB) have been studied in an HCl medium, catalyzed by RuCl3, and in a NaOH media with OsO4 as catalyst, at 313 K. The stoichiometry and oxidation products are the same in both cases, but their kinetic patterns were found to be different. In acid medium the rate shows a first order dependence in each of [BAB] and [TU], and is dependent on [RuIII]. The reaction rate is inversely dependent on [H+]. In alkaline medium, the rate is first order in [BAB] and in [OsVIII] and zero order in [TU]. The reaction rate is dependent on [NaOH]. Activation parameters have been evaluated, solvent isotope effects have been studied in D2O medium, and equilibrium constants were calculated. The activation parameters and rate constants indicate that the catalytic efficiency is: OsVIII > RuIII. The proposed mechanisms and the derived rate laws are consistent with the observed kinetics.

Synthesis, characterization and antibacterial activities of manganese(II), cobalt(II), nickel(II), copper(II) and zinc(II) complexes with soluble Vitamin K3 thiosemicarbazone

Abstract: A thiosemicarbazone derivative of the Vitamin K3 has been synthesized. Five transition metal complexes of the thiosemicarbazone have been prepared and characterized by i.r., u.v.–vis., molar conductance and thermal analyses. All of the complexes possess strong inhibitory action against G(+) Staphylococcus aureus, G(−) Hay bacillus, and G(−) Eschericha coli. The antibacterial activities of the complexes are stronger than those of the thiosemicarbazone itself.

Simple fast preparation of neutral palladium(II) complexes with SnCl− 3 and Cl− ligands

Abstract: A new method for preparing neutral trichlorostannate complexes of PdII, based on the interaction between solid [PdCl2(MeCN)2] and SnCl2 suspension and a solution of an appropriate ligand in CH2Cl2, has been developed. The analogous method can be used to prepare complexes without tin, as well as compounds containing mixed anionic ligands. A number of complexes (including several new compounds) with amines, phosphines and diene ligands have been obtained by these methods. The procedures are simple and fast – the total preparation time (without recrystallisation) is ca. 30 min.

Synthesis, potentiometric and antimicrobial activity studies on 2-pyridinilidene-DL-amino acids and their complexes

Abstract: To investigate the relationship between antimicrobial activities and the formation constants of CuII, NiII and CoII complexes with three Schiff bases, which were obtained by the condensation of 2-pyridinecarboxyaldehyde with DL-alanine, DL-valine and DL-phenylalanine, have been synthesized. Schiff bases and the complexes have been characterized on the basis of elemental analyses, magnetic moments (at ca. 25 °C), molar conductivity, thermal analyses and spectral (i.r., u.v., n.m.r.) studies. The i.r. spectra show that the ligands act in a monovalent bidentate fashion, depending on the metal salt used and the reaction pH = 9, 8 and 7 medium, for CuII, NiII and CoII, respectively. Square-planar, tetrahedral and octahedral structures are proposed for CuII, NiII and CoII, respectively. The protonation constants of the Schiff bases and stability constants of their ML-type complexes have been calculated potentiometrically in aqueous solution at 25 ± 0.1 °C and at 0.1 M KCl ionic strength. Antimicrobial activities of the Schiff bases and the complexes were evaluated for three bacteria (Bacillus subtillis, Staphylococcus aureus, and Escherichia coli) and a yeast (Candida albicans). The structure–activity correlation in Schiff bases and their metal(II) complexes are discussed, based on the effect of their stability contants.

Reactions of a carbene stabilised indium trihydride complex, [InH3{CN(Mes)C2H2N(Mes)}] Mes = mesityl, with transition metal complexes

Abstract: The reactivity of the carbene stabilised indium trihydride complex, [InH3(IMes)] IMes = 1,3-dimesitylimidazol-2-ylidene, toward a variety of transition metal complexes has been investigated. The study has shown that the InH3 complex can act as a carbene and/or hydride transfer reagent to transition metal centres but does not yield heterobimetallic materials. Two new complexes, [Cp2Ti(μ-Cl)2Zn(IMes)Cl] and [CpNi(H)(IMes)], have resulted from this work, both of which have been spectroscopically and structurally characterised.

Spectral and structural studies of cobalt(II,III), nickel(II), and copper(II) complexes of dehydroacetic acid N4-dialkyl- and 3-azacyclothiosemicarbazones

Abstract: CoII,III, NiII, and CuII complexes of new dehydroacetic acid N4-substituted thiosemicarbazones have been studied. The substituted thiosemicarbazones, N4-dimethyl-(DA4DM), N4-diethyl-(DA4DE), 3-piperidyl-(DApip) and 3-hexamethyleneiminyl-(DAhexim), when reacted with the metal chlorides, produced two CoII complexes, [Co(DA4DE)Cl2] and [Co(DAhexim)2Cl2]; two CoIII complexes, [Co(DA4DM-H)2Cl] and [Co(DApip-H)(DApip-2H)]; a paramagnetic NiII complex, [Ni(DAhexim)(DAhexim-H)Cl]; three diamagnetic NiII complexes, [Ni(DA4DM-H)Cl], [Ni(DA4DE-H)Cl] and [Ni(DApip-H)Cl]; and four CuII complexes with the analogous stoichiometry of the latter three NiII complexes. These new thiosemicarbazones have been characterized by their melting points, as well as i.r., electronic and 1H-n.m.r. spectra. The metal complexes have been characterized by i.r. and electronic spectra, and when possible, n.m.r. and e.s.r. spectra, as well as elemental analyses, molar conductivities, and magnetic susceptibilities. The crystal and molecular structure of the four-coordinate CuII complex, [Cu(DAhexim-H)Cl] has been determined by single crystal X-ray diffraction and the anionic ligand coordinates via an oxygen of the dehydroacetic acid and the thiosemicarbazone moiety's imine nitrogen and thione sulfur.

Kinetics and mechanism of exchange of cyanide in hexacyanoferrate(II) by N -methylpyrazinium ion in the presence of mercury(II) as a catalyst

Abstract: The kinetics of the mercury(II) catalysed ligand exchange of the hexacyanoferrate(II) complex with the N-methylpyrazinium ion (Mpz+) in a potassium hydrogen phthalate buffer medium has been investigated at 25.0 ± 0.1 °C, pH = 5.0 ± 0.02 and ionic strength, I = 0.1 M (KNO3). The reaction was followed spectrophotometrically in the aqueous medium by measuring the increase in absorbance of the intense blue complex [Fe(CN)5Mpz]2− at its λmax 655 nm. The effect of pH, and the concentrations of [Fe(CN)6 4−] and Mpz+ on the reaction rate have been studied and analysed. The varying catalytic activity of mercury(II) as a function of concentration has also been explained. The kinetic data suggest that substitution follows an interchange dissociative (I d) mechanism and occurs via formation of a solvent-bound intermediate. The effects of the dielectric constant of the medium on the reaction rates have been used to visualize the formation of a polar activated complex and an interchange dissociative mechanism for the reaction. A mechanism has been proposed in order to interpret the kinetic data. Kinetic evidence is reported for the displacement of CN− by Mpz+ in [Fe(CN)6 4−]. Activation parameters for the catalysed and uncatalysed reaction have been evaluated, and lend further support to the proposed mechanism.

Cobalt(II), nickel(II) and copper(II) complexes of 5-(2-carboxyphenylazo)-2-thiohydantoin

Abstract: A new series of hexacoordinate cobalt(II), nickel(II) and copper(II) complexes of 5-(2-carboxyphenylazo)-2-thiohydantoin HL having formulae [LM(OAc)(H2O)2] · nH2O (M = CoII, CuII and NiII), [LM′Cl(H2O)2] · nH2O (M′ = CoII and NiII), [LCuCl(H2O)]2 · 2H2O, [LCu(H2O)3](ClO4) and [LCu(HSO4)(H2O)2] were isolated and characterized by elemental analyses, molar conductivities and magnetic susceptibilities, and by i.r., electronic and e.s.r. spectral measurements, as well as by thermal (t.g. and d.t.g.) analyses. The i.r. spectra indicate that the ligand HL behaves as a monobasic tridentate towards the three divalent metal ions via an azo-N, carboxylate-O and thiohydantoin-O atom. The magnetic moments and electronic spectral data suggest an octahedral geometry for CoII complexes, distorted octahedral geometry for both NiII and CuII complexes with a dimeric structure for [LCuCl(H2O)]2 · 2H2O through bridged chloro ligands. The X-band e.s.r. spectra reveal an axial symmetry for the copper(II) complexes with unsymmetrical ΔMs = ± 1 signal and G-parameter less than four for the dimeric [LCuCl(H2O)]2 · 2H2O. The thermogravimetry (t.g. and d.t.g.) of some complexes were studied; the order and kinetic parameters of their thermal degradation were determined by applying Coats–Redfern method and discussed.

A mechanistic study of the ethylenediaminetetraacetic acid-, 2,2′-bipyridyl-, and manganese(II)-assisted one-step two- and three-electron oxidation of lactic acid by chromium(VI)

Abstract: The kinetic results of the oxidation of lactic acid by CrVI in the absence and presence of ethylenediaminetetraacetic acid (EDTA), 2,2′-bipyridyl (bpy), MnII and CeIV are presented. EDTA, bpy and MnII catalyse the reaction, whereas CeIV acts as an inhibitor. Irrespective of the conditions, the order with respect to [lactic acid] was found to lie between one and two, and one in [CrVI]. In the EDTA, bpy and MnII-catalysed paths, CrVI–EDTA, CrVI–bpy and lactic acid–MnII complexes have respectively been suggested as the active oxidant and reductant. The kinetic and cerium(IV) effect studies are consistent with a one-step two-electron transfer mechanism in the absence/presence of EDTA and bpy where a chromate–ester mechanism experiences a redox decomposition (C—H cleavage) in the rate-determining step. On the other hand, the catalytic effect of MnII is described as a one-step three-electron redox decomposition (C—C cleavage) mechanism. Mechanisms in accordance with the experimental data have been proposed for the reactions. Activation parameters have also been evaluated and discussed.

N-Heterocyclic carbene complexes of palladium(II) and rhodium(I) with pendant ferrocenylmethyl groups: synthesis and electrochemistry

Abstract: 1-Ferrocenylmethyl-3-benzylimidazolidinium iodide and 1-ferrocenylmethyl-3-(2,4,6-trimethylbenzyl)imi-dazolidinium iodide were prepared in good yields by boiling, under reflux, a solution of (ferrocenylmethyl)- trimethylammonium iodide and the appropriate N-alkyl-2-imidazoline in MeCN. From the 1-ferrocenylmethyl-3-ben- zylimidazolidinium iodide salt, N-heterocylic carbene complexes of PdII and RhI were synthesized by in situ deprotonation and subsequent trapping. The new compounds were characterized by C, H, N analyses, 1H-n.m.r., 13C-n.m.r. and by cyclic voltammetry. The n.m.r. properties of the complexes are compared with those of non-ferrocenylated carbene derivatives. The c.v.'s of these compounds show a number of resolved redox processes, indicating that CH2Fc substituents are electronically isolated from the remaining molecular framework.

Substitution of [Pt(terpy)H2O]2+ and [Pt(bpma)H2O]2+ with thiols in acidic aqueous solution. terpy = 2,2' :6'2 -terpyridine; bpma = bis(2-pyridylmethyl)amine

Abstract: The substitution behaviour of [Pt(terpy)H2O]2+ and [Pt(bpma)H2O]2+, where terpy is 2,2′:6′2″-terpyridine and bpma is bis(2-pyridylmethyl)amine, was studied as a function of entering thiol concentration and temperature. The reactions between the Pt-complexes and DL-penicillamine, L-cysteine and glutathione were carried out in a 0.10 mol dm−3 aqueous HClO4 medium using stopped-flow and conventional u.v.–vis spectrophotometry. The observed pseudo-first-order rate constants for the substitutions are given by k obs = k 2[thiol] + k −2. The k −2 term represents the reverse solvolysis. This was found to be zero for PtII(terpy) which was the most reactive complex. The second-order rate constants, k 2, for the three thiols varied between 0.107 ± 0.001 and 0.517 ± 0.025 M−1 s−1 for PtII(bpma) and 10.7 ± 0.7–711.9 ± 18.3 M−1 S−1 for PtII(terpy), whereas glutathione was found to be the strongest nucleophile. An analysis of the activation parameters, ΔH ‡ and ΔS ‡, clearly shows that the substitution process is associative in nature.

Palladium(II) and platinum(II) complexes of Schiff bases derived from 2,6-diacetylpyridine and S-methyldithiocarbazate and the X-ray crystal structure of the [Pd(mdapsme)Cl]* complex

Abstract: Condensation of 2,6-diacetylpyridine (dap) with S-methyldithiocarbazate (smdtc) in a 1:2 molar ratio yields a bicondensed pentadentate Schiff base (H2dapsme) which reacts with K2MCl4 (M = PdII, PtII) giving stable complexes of empirical formula, [M(dapsme)] · 0.5Me2CO. These complexes have been characterized by a variety of physico-chemical techniques. Condensation of dap with smdtc in a 1:1 molar ratio also yields the bicondensed Schiff base (H2dapsme) as the major product, but a mono-condensed one-armed Schiff base (Hmdapsme) is also obtained as a minor product. The latter reacts with K2PdCl4 in an EtOH–H2O mixture yielding a crystalline complex of empirical formula, [Pd(mdapsme)Cl], the crystal structure of which has been determined by X-ray diffraction. The complex has a distorted square-planar structure in which the ligand is coordinated to the palladium(II) ion as a uninegatively charged tridentate chelating agent via the pyridine nitrogen atom, the azomethine nitrogen atom and the thiolate sulfur atom; the oxygen atom of the acetyl group does not participate in coordination.

New bis -macrocyclic complexes with transition metal ions

Abstract: Template condensation of benzidine, formaldehyde, ethylenediamine or 1,3-diaminopropane, metal salt and 1-phenyl-1,3-butanedione or 2,3-butanedione in a 1:4:2:2 molar ratio results in the formation of two new series of binuclear pentaaza macrocyclic complexes: dichloro[1,1′-phenylbis(7-methyl-9-phenyl-1,3,6,10,13-pentaazacyclotetradeca-6,9-diene) metal(II)], [M2LCl4] (M = CoII, CuII, FeIII and ZnII) and dichloro[1,1′-phenylbis(8,9-dimethyl-1,3,7,10,14-pentaazacyclopentadeca-7,9-diene) metal(II)], [M2L′Cl4] (M = NiII, CoII, CuII and CdII). Both series were characterized by i.r., 1H-n.m.r., u.v.–vis. spectral studies, conductivity and magnetic susceptibility measurements.

Crystal structure of the first SH-containing tetrahedral cobalt(II) complex, Co(quinoline)2(SH)2]. Superoxide dismutase activity

Abstract: The preparation, spectroscopic properties and crystal structure of the bis-quinoline–bis-mercaptocobalt(II) complex [Co(quinoline)2(SH)2] are reported. The complex is tetrahedral with nitrogen donor atoms from two quinoline ligands and sulphur donor atoms from two mercapto groups. The superoxide dismutase mimetic activity of the complex was investigated using the indirect xanthine–xanthine oxidase–nitroblue tetrazolium method and compared to that of the native enzyme.

Mild template synthesis of a copper(II)-containing macrocyclic compound with 4,4,6-trimethyl-2,3,7,8-tetraazanonen-6-dithiohydrazide-1,9 in a gelatin-immobilized matrix

Abstract: The complexing processes in the triple copper(II)–thiocarbohydrazide–propanone system taking place in a copper(II) hexacyanoferrate(II) gelatin-immobilized matrix in contact with aqueous-alkaline solutions (pH∼12), containing thiocarbohydrazide and propanone, have been studied. Template synthesis leading to a macrocyclic coordination compound with the tetradentate N,N,S,S-donor ligand, (4,4,6-trimethyl-2,3,7,8-tetraazanonen-6-dithiohydrazide-1,9), occurs under these specific conditions when thiocarbohydrazide and propanone are the ligand synthons.

Comparative kinetics of carboxylic esters hydrolysis catalyzed by the zinc(II) complex of a macrocyclic Schiff base ligand

Abstract: The comparative kinetic investigation of the hydrolysis of p-nitrophenyl picolinate (PNPP) and p-nitrophenyl acetate (PNPA) catalyzed by the tetracoordinate macrocyclic Schiff base complex of zinc(II) (1) at 30 °C is reported. The results indicate that the (1) catalyzed hydrolyses of PNPP and PNPA are acid-base catalytic processes and that the active species is the metal bound hydroxide ion, namely, ZnL—OH−. (1) promoted hydrolysis of PNPP proceeds much faster than that of PNPA. At pH 7.51, the apparent second-order rate constants kc for hydrolysis of PNPP and PNPA are 0.254 and 7.28 × 10−3 mol−1 dm3 s−1, respectively. The difference in hydrolytic rates may be attributed to the difference of hydrolytic mechanisms by which the PNPP and PNPA operate. The reasons are discussed in detail.

Deamination and decarboxylation in the chromium(III)-catalysed oxidation of L-valine by alkaline permanganate and analysis of chromium(III) in microscopic amounts by a kinetic method

Abstract: The kinetics of CrIII-catalysed oxidation of L-valine by permanganate in alkaline medium at a constant ionic strength has been studied spectrophotometrically. The reaction between permanganate and L-valine in alkaline medium exhibits 2:1 stoichiometry (KMnO4:l-valine). The reaction shows first order dependence on [permanganate] and [chromium(III)], and less than unit order dependence each in [L-valine] and alkali concentrations under the experimental conditions. However the order in [L-valine] and [alkali] changes from first order to zero order as the concentrations change from lower to higher respectively. The results suggest the formation of a complex between L-valine and the hydroxylated species of CrIII. The complex reacts further with 1 mol of alkaline permanganate species in a rate-determining step, resulting in the formation of a free radical, which again reacts with 1 mol of alkaline permanganate species in a subsequent fast step to yield the products. The reaction constants involved in the mechanism were evaluated. The activation parameters with respect to the slow step of the mechanism were obtained and discussed. The title reaction has been utilised to analyse chromium(III) in the 26.0 ng cm−3–1.0 μg cm−3 range.

Synthetic studies and structural aspects of novel metallacyclic compoundsof titanium(IV) incorporating nitrogen, oxygen and sulphur: 1. Reactions of cis-dialkoxy-bis(acetylacetonato)titanium(IV) with alkoxyalkanols and the crystal structure of a new modification: di-μ-oxo-bis[diacetylacetonatotitanium(IV)]

Abstract: Reactions of cis-dialkoxy-bis(acetylacetonato)titanium(IV), [(acac)2Ti(OR)2] (R = Et, Pr i ) with alkoxyalkanols (R′OCH2CH2OH) (R′ = Me, Et, n-Bu) in 1:1 and 1:2 molar ratios in refluxing benzene under anhydrous conditions yield [(acac)2Ti(OR)2−n(OCH2CH2OR′) n ] (n = 1 or 2) complexes, which were purified by distillation under reduced pressure. On the basis of i.r. and n.m.r. (1H- and 13C-) spectral studies, a cis-octahedral environment around TiIV is proposed. On keeping the distilled dark brown-red viscous liquid [(acac)2Ti(OEt)(OCH2CH2OBu)] for 2 weeks, orange yellow crystals of [(acac)2TiO]2 were obtained. A single crystal X-ray diffraction study suggests the product is a new modification of [(acac)2TiO]2.

Antimycobacterial activity of mixed-ligand copper quinolone complexes

Abstract: New mixed-ligand CuII, complexes: [Cu(cf)(phen)Cl)](BF4) · 4H2O (3), [Cu(cf)(bipy)(Cl)](BF4) · 2H2O (4) and [Cu(cf)(dafone)(Cl)](BF4) · 2H2O (5) (cf = ciprofloxacin, phen = 1,10-phenanthroline, bipy = 2,2′-bipyridine and dafone = 4,5-diazafluoren-9-one) have been isolated and characterized by elemental analyses, i.r., u.v.–vis. spectra, magnetic susceptibility and cyclic voltammetry. Complex (4) crystallizes in the monoclinic space group P21/n with a = 13.8919(13) A, b = 14.5718(13) A, c = 14.0725(13) A, β = 95.150(2)°, V=2837.2(5) A3. All complexes possess square-pyramidal geometry. The antimycobacterial activity of ciprofloxacin and complexes (3–5) has been evaluated against Mycobacterium smegmatis, which shows clear enhancement in the antitubercular activity upon copper complexation with N—N donors.

Oxidation of cyclohexane with molecular oxygen using a Schiff base cobalt complex bonded to carbamate-modified silica gel

Abstract: The Schiff base [1,2-bis(salicylidene amino)phenylene]cobalt(II) complex, chemically bonded to a carbamate-modified silica gel catalyst, has been prepared by a four step procedure. The oxidation of cyclohexane was studied in the presence of this catalyst under relatively mild conditions (150–200 °C, 15–20 atm) using molecular oxygen. The catalyst was found to be very selective for the production of cyclohexanol, with cyclohexanone formed in only a small amount (45:1). This is in contrast to the commercially available processes in which cyclohexanol and cyclohexanone are both formed in appreciable amounts. The t.g.a. analysis shows the catalyst to be stable up to 211 °C and atomic absorption spectroscopy indicated negligible metal loss during 50 h use of the catalyst up to 180 °C.

Potentiometric determination of the formation constants for complexes of 3,2¢,2¢¢-triaminopropyldiethylamine with cobalt(II), nickel(II), copper(II), zinc(II) and cadmium(II)

Abstract: The tripodal tetraamine ligand N{(CH2)3NH2}{(CH2)2NH2}2 (pee), has been investigated as an asymmetrical tetraamine chelating agent for CoII, NiII, CuII, ZnII and CdII. The protonation constants for this ligand and the formation constants for its complexes have been determined potentiometrically in 0.1 M KCl at 25 °C. The successive protonation constants (log Kn) are: 10.22, 9.51, 8.78 and 1.60 (n = 1–4). One complex with formula M(pee)2+ (M = Co, Ni, Cu, Zn and Cd) is common to all five metal ions and the formation constant (log βML) is: 12.15, 14.17, 16.55, 13.35 or 9.74, respectively. In addition to the simple complexes, CoII, CuII and ZnII also give hydroxo complexes, and CuII and NiII give complexes with monoprotonated pee. [Zn(pee)](ClO4)2 and [Cd(pee)Cl](ClO4) complexes were isolated and are believed to have tetrahedral and trigonal-bipyramidal structures, respectively.

Mixed ligand palladium(II) complexes of oxalate and malonate with vitamin-B6 molecules: synthesis, crystal structure and kinetics

Abstract: The synthesis of six mononuclear palladium complexes of general formula [Pd(ox)/(mal)L2] and [Pd(ox)/(mal)L′] (ox = oxalate, mal = malonate, both L and L′ are vitamin-B6 molecules (I), L = pyridoxine, pyridoxal and L′ = pyridoxamine) has been achieved. The structures of these compounds were established by elemental analysis, i.r. and 13C-n.m.r. [Pd(oxalate)(pyridoxine)2] was analyzed by single crystal X-ray diffraction. It exhibits square planar coordination with bond lengths 2.015 (2) A for Pd—N and 2.010 (2) A for Pd—O. The interaction of [Pd(ox)2]2− and [Pd(mal)2]2− with L has been followed kinetically in order to look into the nature of products and the mechanism of formation under the conditions [PdII-chelate] ≫ [L] and [L′].