Potentiometric investigations of some catechol derivatives of scandium

The equilibrium reactions of scandium(III) with some triprotic catechol derivatives (H₃L) were studied. The selected ligands that are 2,3-dihydroxybenzoic acid (2,3-DHBA), 3,4-dihydroxybenzoic acid (3,4-DHBA), 3.4-dihydroxyhydrocinnamic acid (3,4-DHHCA), and 3,4-dihydroxyphenylacetic acid (3,4-DHPA) were investigated in aqueous solution by means of potentiometry in 0.1 M ionic medium at 25°C. The stability constants are reported for the ScL and ScL(H₂L)^– mononuclear complexes. 2,3-DHBA can bind to Sc³⁺ ion strongly and the salicylate mode (COO^–, O^–) is effective over the acidic pH range. But in higher pH range, 3,4-DHBA, 3,4-DHHCA, and 3,4-DHPA act more efficiently through catecholate groups (O^–, O^–).Translated from Koordinatsionnaya Khimiya, Vol. 31, No. 3, 2005, pp. 229–233.Original Russian Text Copyright © 2005 by Türkel, Özer.This revised version was published online in April 2005 with a corrected cover date.This revised version was published online in April 2005 with a corrected cover date.     

IR spectra and crystal structure of hydrochlorides and complex salts of 2,3-polymethylene-3,4-dihydroquinazolines and-4-quinazolones

IR spectra are reconsidered on the basis of the results of x-ray structural analysis of the crystal structures of hydrochlorides and complex salts of 2,3-polymethylene-3,4-dihydroquinazolines and-4-quinazolones. It has been established that two absorption bands (Nl⁺–H) in the complex salts characterize different energies of formation of an H-bond, which is weaker than in the corresponding hydrochlorides. The nature of an absorption band in the 3400–3500 cm^–1 region has been established from the XSA results.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Republic of Uzbekistan, Tashkent, fax (371) 120 64 75. Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 364–367, May–June, 1999.     

Crystal and Molecular Structure of 2,3-Tetramethylen-3,4-dihydroquinazoline

The crystal and molecular structure of the alkaolid 2,3-tetramethylen-3,4-dihydroquinazoline hydrochloride was solved by X-ray structure analysis. It was demonstrated that the crystal contains an aqua system similar to those in the isostructural 2,3-trimethylen-3,4-dihydroquinazoline (deoxypeganine), and 2,3-pentamethylen-3,4-dihydroquinazoline hydrochlorides.     

Synthesis and structure of 6-bromo-4-hydroxy-2,3-tetramethylene-3,4-dihydroquinazoline and its mixed crystal with 4-hydroxy-2,3-tetramethylene-3,4-dihydroquinazoline

Bromination of the alkaloid 2,3-tetramethylene-3,4-dihydroquinazoline by N-bromosuccinimide was studied. It was shown that either 4-hydroxy-2,3-tetramethylene-3,4-dihydroquinazoline or 6-bromo-4-hydroxy-2,3tetramethylene-3,4-dihydroquinazoline was formed depending on the ratio of reagents. Oxidation of 2,3tetramethylene-3,4-dihydroquinazoline by KMnO₄ produced 4-hydroxy-2,3-tetramethylene-3,4dihydroquinazoline. The crystal structures of 6-bromo-4-hydroxy-2,3-tetramethylene-3,4-dihydroquinazoline and its mixed crystal with 4-hydroxy-2,3-tetramethylene-3,4-dihydroquinazoline were studied by x-ray structure analysis. The enantiomeric molecules in all crystal structures formed associates owing to two opposing OH...N1 H-bonds.     

Synthetic analogues of Peganum alkaloids. III. Pentamethylenequinazolones

Monosubstituted 5-, 6-, and 8-methoxy-3,4-dihydro-2,3-pentamethylenequinazolones (1–3) have been syntehsized by the condensation of monosubstituted methoxyanthranilic acids with caprolactam. Demethylation with hydrobromic acid gave the corresponding hydroxy compounds [4–6]. When the 6- and 8-methoxy- and 6- and 8-hydroxy-3,4-dihydro-2,3-pentamethylenequinazolones (2, 3, 5, and 6) were reduced with zinc in hydrochloric acid, the corresponding quinazoline derivatives (7–10) were obtained. The melting points of the basis and their hydrochlorides are given. Some features of their UV, mass, and PMR spectra are reported.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 465–469, July–August, 1986.     

Studies of thermal decomposition of palladium(II) complexes with olefin ligands

Thermal decomposition kinetics of ML₂ (M = Ni(II) and Co(II); L = 5-(2-(1,5-dimethyl-3-oxo-2-phenyl-2,3-dihydro-1H-pyrazol-4-yl)hydrazono)-1,3-dimethylpyrimidine-2,4,6(1H,3H,5H)-trione) complexes were investigated by thermogravimetric analysis (TGA). The first decomposition process of the NiL₂ and CoL₂ complexes occurs in the temperature range of 320–350 °C. Kinetics parameters corresponding to this step, such as activation energy, E_α, and apparent pre-exponential factor, ln A_aap, were calculated from the thermogravimetric data at the heating rates of 5, 10, 15 and 20 K min⁻¹ by differential (Friedman's equation) and integral (Flynn–Wall–Ozawa's equation) methods. The results show that the activation energy evidently depends on the extent of conversion. As far as their activation energy is concerned, NiL₂ complex shows a higher thermal stability than the CoL₂ complex.     

Synthesis,characterization and electrochemical behavior of mononuclear,binuclear nickel(II) and heterobinuclear zinc(II)nickel(II) complexes derived from novel macrobicyclic tricompartmental ligands: kinetics of the catalytic hydrolysis of 4-nitrophenyl phosphate by the complexes

Mononuclear, binuclear Ni^II and heterobinuclear Zn^IINi^II complexes have been derived from lateral macrobicyclic tricompartmental ligands embracing three different donor sets: (i) O₂N₂-donor set, derived from ether oxygens and tertiary amine nitrogens; (ii) N₂O₂-donor set, derived from tertiary amine nitrogens and phenolic oxygens; (iii) O₂N₂-donor set, derived from phenolic oxygens and azomethine nitrogens. Cyclic voltammograms of the mononuclear Ni^II complexes showed irreversible one-electron reduction processes in the –1.2 to –1.3 V region and an irreversible oxidation process in the range +0.8 V potential region. The binuclear complexes showed quasireversible two-step single electron reduction processes around the –1.3 and –1.7 V potential regions. The anodic potential region showed an irreversible oxidation process at +1.0 V. The heterobinuclear Zn^IINi^II complex showed an irreversible reduction of the Ni^II species at –1.55 V. The catalytic hydrolysis towards 4-nitrophenyl phosphate by the mononuclear, binuclear Ni^II complexes and the heterobinuclear complex were found to be appreciable. The pseudo-first order rate constant for the catalytic hydrolysis catalyzed by the binuclear and heterobinuclear complexes were found to be higher (9.8 × 10^–4 s^–1) than that of the corresponding mononuclear complexes (1.3 × 10^–5 s^–1), which ascertain the requirement of two metal ions in close proximity for the binding of the nucleophilic OH and the phosphate group.     

Transformations of the chiral diphosphine rhodium catalyst [(1,5-COD)Rh(—)R,R-DIOP]+CF3SO3– under conditions of hydrogenation

Transformation products of the cationic rhodium complex [(1,5-COD)Rh(—)R,R-DIOP]⁺CF₃SO₃ ^– (1) (COD is cycloocta-1,5-diene and DIOP is (±)-2,3-O-isopropylidene-2,3-dihydroxy-1,4-bis(diphenylphosphino)butane), which were obtained in its reactions with molecular hydrogen, base (NEt₃), and solvents in the absence of a substrate, were investigated by ¹H and ³¹P NMR spectroscopy. The solvate complexes [(Solv)₂Rh(—)R,R-DIOP]⁺CF₃SO₃ ^–, which were generated from complex 1 in its reaction with molecular hydrogen, underwent destruction of the diphosphine ligand with elimination of benzene and were subjected to oxidation by traces of moisture and oxygen to form the DIOP dioxide complex with Rh^I. In the absence of hydrogen, complex 1 in solutions produced the diphosphine dioxide rhodium(i) complex and mono- and binuclear rhodium(i) solvate complexes. The scheme of deactivation of the complex in the absence of the substrate was proposed. The catalytic activity of the solvate complexes [(ArH)Rh(—)R,R-DIOP]⁺CF₃SO₃ ^–, which contain benzene, p-xylene, and mesitylene in the coordination sphere, was studied in hydrogenation of Z--acetamidocinnamic acid.     

Mixed benzohydroxamato-acetylacetonato metal complexes: spectral,thermal and photochemical behaviour

Summary Bis(acetylacetonato)VO^II,–Co^II,–Ni^II,–Cu^II,–Zn^II, –UO ₂ ^II and tris(acetylacetonato)Fe^III react with benzohydroxamic acid to yield the corresponding mixed ligand complexes as a result of displacement of one acetylacetone molecule. Intermolecular association may be the reason for six-coordination geometry around the metal ions. A t.g.a. study of the complexes shows, in most cases, initial loss of alcohol and water molecules associated with the complexes; subsequent decomposition steps are characterised by very sharp weight loss. The photochemical stability of the complexes has been studied. Intraligand excitation causes a decomposition in the case of Fe^III and VO^II-complexes but no detectable effect for Co^II, Ni^II, Cu^II, Zn^II, or UO ₂ ^II -complexes.     

Coordination complexes of iron(III) with 3-hydroxy-2(1H)-pyridinone, 2,3-dihydroxybenzoic acid and 3,4-dihydroxybenzoic acid: preparation and characterization in the solid state

Summary The synthesis and study of a number of new iron(III) complexes of the ligands 3-hydroxy-2(1H)-pyridinone (3,2-opoH), 2,3-dihydroxybenzoic acid (2,3-dhbH₃) and 3,4-dihydroxybenzoic acid (3,4-dhbH₃) are described. These complexes have the formulae [Fe(3,2-opo)₂Cl]·PrⁿOH, K[Fe(2,3-dhbH)₂(H₂O)₂], [Fe(2,3-dhb)(H₂O)₂], K[Fe-(3,4-dhbH)₂(H₂O)₂], [Fe(3,4-dhb)(H₂O)₂] and K₆[Fe(3,4-dhb)₃]·3H₂O. The complexes were characterized by elemental analyses. X-ray powder patterns, t.g.a./d.t.g. techniques, magnetic susceptibilities and spectroscopic (u.v.-vis., i.r. and variable-temperature ⁵⁷Fe-M?ssbauer) studies. Monomeric octahedral structures are assigned for the 1∶2 2,3-dhbH²⁻ complex and the 1:3 3,4-dhb³⁻ compound. Dinuclear and/or oligonuclear structures are tentatively proposed for the remaining complexes in the solid state. In [FeL(H₂O)₂] (L³⁻ = 2,3-dhb³⁻ or 3,4-dhb³⁻), iron(III) appears to be 5-coordinate. Both oxygens of 3,2-opo⁻ participate in coordination, while the dihydroxybenzoato ligands exhibit various coordination modes, depending mainly on the positions of the hydroxy groups, their anionic charge and the ligand∶metal molar ratio used.     

Electrochemical analysis of the coordination sphere of ruthenium(ii) as electron transfer mediator in glucose oxidase catalysis in aqueous solutions

The redox potentials of the cis-[Ru(LL)₂XY]ⁿ⁺ complexes (LL = 2,2"-bipyridyl (bpy), 1,10-phenanthroline (phen), and 4,4"-dimethyl-2,2"-bipyridyl (Me₂bpy); X, Y = Cl^–, Br^–, CO₃ ^2–, NO₂ ^–, SCN^–, N₃ ^–, H₂O, and DMSO) in aqueous buffer solutions were measured and analyzed in the framework of the Lever theory on the additivity of contributions of ligands (E _L) to the apparent redox potential of the complex (E ^o"). The complexes manifest the properties of reversible or quasireversible redox systems, whose formal redox potentials lie in the 0.2—0.5 V range. The complexes are efficient electron transfer mediators between the active center of glucose oxidase (GO) from Aspergillus niger and an electrode.     

Cobalt(II) porphyrazine catalysed reduction of nitrite

Studies on the catalytic reduction of nitrite on carbon electrodes modified with Co(II) tetra-2,3-pyridinoporphyrazine (CoTppa, 1), N,N′,N′′,N′′′-tetramethyltetra-2,3-pyridinoporphyrazine ([CoTm-2,3-tppa]⁴⁺, 2) and Co(II) N,N′,N′′,N′′′-tetramethyltetra-3,4-pyridinoporphyrazine ([CoTm-3,4-tppa]⁴⁺, 3) are reported. There is a close correspondence between the proximity of the methyl groups to the porphyrazine ring and the catalytic activity of the porphyrazine complexes. Bulk electrolysis gave ammonia and hydroxylamine as some of the products. The catalytic activity of the cationic complex, 3, towards the detection of low concentrations of nitrite (<10⁻⁹ M) in water containing sodium sulfate, was compared with the activities of the anionic cobalt(II) tetrasulfophthalocyanine ([CoTSPc]⁴⁻, 4) and the mixed [Co^IITm-3,4-tppa]⁴⁺·[CoTSPc]⁴⁻ (5) complexes. Complex 5 showed the best catalytic activity of the three in that large currents were obtained for very low concentrations of nitrite.     

New pentafluorothiophenoxo derivatives of tin,lead, antimony,bismuth, gold and platinum

Summary Salts of the anions [SnX₅]^–, [SnX₄Cl, [SnX₃Cl₂]^–, [SnX₃]^–, [PbX₃]^–, [SbX₄]^–, [SbX₃Cl]^–, [SbX₂Cl₂]^–, [BiX₄]^–, [AuCl₂]^–, [AuX₂]^–, [AuXCl]^–, [AuX₄]^–, [Au₂X₆]^2– and [PtX₄]^2–, where X^– = C₆F₅S^–, have been isolated and characterised. The neutral SbX₃ and BiX₃ species, have also been isolated and shown to be pyramidal monomers (¹⁹F.n.m.r., i.r., and Raman spectral evidence). Various physical properties of the complexes prepared, as well as their stereochemistries (where these could be ascertained), are similar to those of the known corresponding halogeno compounds of these elements. These results further demonstrate the pseudo-halide nature of the pentafluorothiophenoxide ion.Author to whom all correspondence should be directed at: Laboratoire de Chimie de Coordination, Uniyersité Louis Pasteur, 67008 Strasbourg, France.     

Coordination chemistry of poly(1-pyrazolyl)alkanes Part V: Preparation and characterization of cobalt(II) complexes with bis(1-pyrazolyl)methane and bis(3-methylpyrazolyl)propane

Summary Bis(1-pyrazolyl)methane, H₂Cbpz, and bis(3-methylpyrazolyl)propane, Me₂Cbmpz, react with cobalt(II) salts to give the solid complexes: [Co(H₂Cbpz)₂X₂] ·2H₂O (X=Cl^–, Br^–, I^–, NO ₃ ^– or ClO ₄ ^– ) and [Co(Me₂-Cbmpz)X₂] (X=Cl^–, Br^–, or I^–), which were isolated and characterised by elemental analysis, i.r. and electronic spectra and conductance measurements. From spectral data, octahedral and tetrahedral structures have been proposed for the H₂Cbpz and Me₂Cbmpz complexes respectively. The molar conductance of the complexes indicates that they are non-ionic.     

Synthesis of new piperazine derived Cu(II)/Zn(II) metal complexes, their DNA binding studies, electrochemistry and anti-microbial activity: Validation for specific recognition of Zn(II) complex to DNA helix by interaction with thymine base

New 3,4:9,10-dibenzo-2,11-dihydroxy-1,12-bispiperazine-5,8-dioxododecane complexes [C₂₄H₃₆N₄O₆Cu] (1), [C₂₄H₃₂N₄O₄Zn] (2) have been synthesized and characterized by elemental analysis, IR, NMR, Mass, EPR, UV–vis spectroscopy and molar conductance measurements. The complexes are non-ionic in nature and possess octahedral geometry around Cu²⁺, Zn²⁺ central metal ions. The binding studies of 1 and 2 with calf thymus DNA (CT-DNA) were investigated by UV–vis, fluorescence, cyclic voltammetery and viscosity measurements. The calculated binding constant K_b for 1 and 2 obtained from UV–vis absorption studies was 7.6 × 10³ M⁻¹, 80.8 × 10⁴ M⁻¹, respectively. The intrinsic binding constants were also estimated to be 7.0 × 10⁴ M⁻¹ and 7.53 × 10⁵ M⁻¹ for 1 and 2, respectively by using emission titrations. These experimental results suggest that complexes are groove binders and interact to CT-DNA with different affinities. Both the complexes in presence and absence of CT-DNA show quasireversible wave corresponding to Cu^II/Cu^I and Zn^II/Zn^I redox couple. The changes in E_1/2, ΔE, I_pa/I_pc ascertain the interaction of 1 and 2 with CT-DNA. Further, decrease in viscosity of CT-DNA with increasing concentration of complexes was observed. In vitro, antimicrobial activity against fungi A. brassicicola, A. niger and bacteria E. coli, P. aeruginosa of complexes were carried out, which indicate that complex 2 is more active against both fungal and bacterial strains as shown by % inhibition data.     

Catalyzed Peptide Bond Formation in the Gas Phase. Role of Bivalent Cations and Water in Formation of 2-Aminoacetamide from Ammonia and Glycine and in Dimerization of Glycine

The formation of 2-aminoacetamide from ammonia and glycine and N-glycylglycine from two glycine molecules with and without Mg²⁺, Cu²⁺, and Zn²⁺ cations as catalysts have been studied as model reactions for peptide bond formation using the B3LYP functional with 6–311+G(d,p) and 6–31G(d) basis sets. The B3LYP method was also used to characterize the nine gas–phase complexes of neutral glycine, its amide (2-aminoacetamide), and N-glycylglycine with Lewis acids Mg²⁺, Cu²⁺, and Zn²⁺, respectively. Further, the gas-phase hydration of metal-coordinated complexes of glycine, 2-aminoacetamide, and N-glycylglycine was also investigated. Finally, the effect of water on the structure and reactivity of the metal coordinated complexes was determined. Enthalpies and Gibbs energies for the stationary points of each reaction have been calculated to determine the thermodynamics of the reactions investigated. A substantial decrease in reaction enthalpies and Gibbs energies was found for glycine–ammonia and glycine–glycine reactions coordinated by Mg²⁺, Cu²⁺, and Zn²⁺ ions compared to those of the uncoordinated 2-aminoacetamide bond formation. The formation of a dipeptide is a more exothermic process than the creation of simple 2-aminoacetamide from glycine. The energetic effect of the transition metal ions Cu²⁺ and Zn²⁺ is of similar strength and more pronounced than that of the Mg²⁺ cation. The basicity order of the amides investigated shows the order: NH₂CH₂CO₂H < NH₂CH₂CONH₂ < NH₂CH₂CONHCH₂CO₂H. Interaction enthalpies and Gibbs energies of metal ion–amide complexes increase as Mg²⁺2+2+. In both reactant (glycine) and reaction products (2-aminoacetamide, N-glycylglycine) dihydration caused considerable reduction (about 200–500 kJ-mol^–1) of the strength of the bifurcated metal–amide bonds. Solvent effects also reduce the reaction enthalpy and Gibbs energy of reactions under study.     

Complexes of Some 3d-Metal Salts with N,N-Dimethylhydrazide of 4-Nitrobenzoic Acid

The [M(HL)₂(H₂O)₂]X₂ complexes were synthesized (M = Mn(II), Co(II), Ni(II), Cu(II), Zn; X = CH₃COO^–, Cl^–, BF₄ ^–) that incorporate bidentately coordinated molecules of N,N-dimethylhydrazide of 4-nitrobenzoic acid (HL). The latter molecules chelate the metal atom through the carbonyl O atom and the N atom of dimethylamino group. The square-planar complexes of Cu and Ni with deprotonated form of a ligand with composition ML₂ were also isolated. The synthesized complexes were studied by IR, electronic and EPR spectroscopies, and by cyclic voltammetry.     

Metal complexes of 6-chloropurine

Summary Five Cu(II), Pd(II), Cd(II), Pt(IV), and Au(III) complexes of 6-chloropurine have been obtained. The complexes were characterized by elemental analysis, IR,¹H-NMR and¹³C-NMR spectroscopy. On the basis of these data the structure of the complexes and the coordination of the ligand have been proposed. Thus, the physical and chemical methods supported evidence that in acidic medium, with exception of the Cu(II) complex, 6-chloropurine acts in the monoprotonated form neutralizing the charge of [PdCl₄]^2–, [CdCl₄]^2–, [AuCl₄]^– and [PtCl₆]^2– anions. The thermal behaviour of the complexes has also been studied.

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Metallkomplexe von 6-Chlorpurin

Zusammenfassung Es wurden fünf Komplexe von 6-Chlorpurin mit Cu(II), Pd(II), Cd(II), Pt(IV) und Au(III) erhalten. Die Komplexe wurden mittels Elementaranalysen, IR,¹H-NMR und¹³C-NMR charakterisiert. Auf der Basis dieser Daten wurde eine Komplexstruktur und eine bestimmte Koordination der Liganden vorgeschlagen. Physikalische und chemische Methoden beweisen, daß im sauren Bereich [mit der Ausnahme von Cu(II)] das 6-Chlorpurin in der monoprotonierten Form koordiniert, wobei die Ladung von [PdCl₄]^2–, [CdCl₄]^2–, [AuCl₄]^– und [PtCl₆]^2– jeweils neutralisiert wird. Das thermische Verhalten der Komplexe wurde ebenfalls untersucht.

     

Copper(II) complexes of isobutyl methyl ketone semicarbazone

Summary Copper(II) complexes of isobutyl methyl ketone semicarbazone have been prepared and characterised by magnetic moments, i.r., electronic and e.s.r. spectral studies. The complexes were found to have CuL₂X₂ and CuL₂X₂ · 2H₂O compositions. The electronic and e.s.r. spectra suggest a five-coordinated trigonal bipyramidal geometry, for the CuL₂X₂ complexes, (X=Cl^–, Br^–, NO ₃ ^– , and 1/2 SO ₄ ^2– ) and six-coordinate octahedral geometry has been suggested for CuL₂X₂ · 2H₂O (X=Cl^–, Br^–, NO ₃ ^– , SO ₄ ^2– ).     

Preparation and properties of [PtII(SS)(NN)]-type complexes and their iodine-doped analogues

Summary Complexes of the general formula [Pt(SS) (NN)], where SS is dddt (5,6-dihydro-1,4-dithiin-2,3-dithiolate) or pddt (6,7-dihydro-5H-1,4-dithiepin-2,3-dithiolate) and NN is bipy (2,2-bipyridine) or phen (1,10-phenanthroline), were prepared by the reaction of [PtCl₂(NN)] with dithiolate ligands. The¹H-n.m.r. spectra shows upfield shifts in the bipy or phen signals upon substitution of the chlorides in [PtCl₂(bipy)] or [PtCl₂(phen)] by dddt or pddt. The u.v.-vis. spectra exhibits intense intramolecular ligand-to-ligand charge transfer bands ca. 600 nm. Cyclic voltammograms show a reversible oxidation step, assigned to [Pt(SS) (NN)]⁰/[Pt(SS)(NN)]⁺. When the complexes were partially oxidized by I₂, two broad e.s.r. signals atg = 1.91,g = 2.02 appeared. Raman spectra show the presence of I ₃ ^– and I^5/– in the iodine-doped complexes. The electrical conductivities of the neutral mixed ligand complexes (10^–9-10^–10S cm^–1) are raised to 10^–7–10^–8S cm^–1 by I₂ doping.