Kinetic analysis of TG data XXXVI: Influence of procedural variables upon the apparent kinetic parameters of the thermal deamination

A number of 7 complexes of the [Co(DH)₂(amine)₂)]I type (DH₂ stands for dimethyloxime) have been studied by means of thermogravimetry and differential scanning calorimetry in nitrogen atmosphere, by using heating rates of 2.5, 5 and 10 K min^–1. In all cases an endothermal deamination reaction occurs leading to the relatively stable [Co(DH)₂I(amine)] intermediate. For this reaction apparent kinetic parameters have been derived. The influence of heating rate is discussed. The validity of a linear and a non-linear kinetic compensation law was verified.This revised version was published online in November 2005 with corrections to the Cover Date.     

Salting-out thin-layer chromatography of transition metal complexes. IV: Effect of sorbent on the behaviour of mixed aminocarboxylato cobalt (III) complexes

Summary From literature data for 14 mixed aminocarboxylato cobalt(III) complexes, the effect of the sorbent on R_M values, salting-out efficiency (m) and separation factors () of adjacent members of homologous series was investigated in salting-out, thin-layer chromatography on silica gel, polyacrylonitrile and cellulose sorbents, using ammonium sulphate solutions as developers. For complexes belonging to the same homologous series, linear dependence was found between R_M,m and log values, respectively, on two different sorbents. Polyacrylonitrile was shown to be the most suitable sorbent for the separation of the complexes since it gave the highest values for R_M,m and .     

Conductance behavior of some tris(ethylenediamine)cobalt(III) complexes and their ion association in aqueous solutions

The conductance behavior of some tris(ethylenediamine)cobalt(III) complexes was studied in dilute aqueous solutions at 25°C to investigate the ion-pair formation. The thermodynamic formation constants of the ion pairs [Co(en)₃]³⁺·X^– are 28 (chloride), 28 (bromide), 19 (nitrate), and 15 (perchlorate). These values were compared with theoretical values calculated by using Bjerrum's theory of ion association. The formation constant of [Co(en)₃]³⁺·Cl^– was larger than that obtained from the spectrophotometric measurement in solutions containing perchlorate ion. This difference in the formation constants was explained by considering the contribution of ion association of the complex cation with perchlorate ion.     

Effect of ligand nonplanarity and solvent nature on the kinetic stability of zinc porphyrin complexes

Planarity disturbance in metal porphyrin macrorings produces destabilization of complexes in dimethyl sulfoxide-acetic acid and benzene-acetic acid systems, except for cases where the coordination center is additionally stabilized by endocyclic substituents and/or extra ligands. The first dissociation stage of complexes with N-substituted analogs of porphyrins involves substitution of the acido ligand in the strongly shielded coordination sphere by an electron-donor solvent molecule. The revealed dependences of dissociation rate constants on acid concentration in DMSO, untypical of most metal porphyrins, are explained by a change in the type of the attacking species with changing solvent composition. The dissociation rate constants of complexes in an electron donor solvent can be lower by several orders of magnitude than in a weakly solvating medium.     

Separation and kinetic study of chromium(III) chloro complexes by capillary electrophoresis

Summary Three Cr(III) species (dichlorotetraaquachromium (III), [CrCl₂(H₂O)₄]⁺; monochloropentaaquachromium(III), [CrCl(H₂O)₅]²⁺; and hexaaquachromium(III), [Cr(H₂O)₆]³⁺) have been separated and determined by capillary electrophoresis. The first two complexes could be detected in direct mode in phosphate buffer, but because the absorption of complex [Cr(H₂O)₆]³⁺ is poor in the UV range, indirect UV detection had to be used. For indirect detection 5 mM imidazole was added to the buffer solution. The formation and decomposition of the different Cr(III) complexes were monitored in time after the preparation of solutions of CrCl₃.6H₂O. The slowest process was the decomposition of [CrCl(H₂O)₅]²⁺; 300 h after preparation of a solution of CrCl₃.6H₂O of pH 1 the solution contained only [Cr(H₂O)₆]³⁺. The effects of pH and the content of some matrix ions on the rates of conversion of the complexes were studied. The kinetic characteristics of this complex system could be investigated adequately by means of capillary electrophoresis. Presented at Balaton Symposium on High-Performance Separation Methods, Siófok, Hungary, September 1–3, 1999     

Resonance Raman spectra of tris(acetylacetonato)iron(III) and ruthenium(III) complexes and their solvent effect

The resonance Raman spectra of tris(acetylacetonatoiron(III)) and ruthenium(III) complexes in various solvents and in water-acetonitrile (W-AN) mixtures were measured. The resonance Raman spectra of both complexes indicated peaks near 460 and around 1580 cm^–1. Thev(C-O) peak (around 1580 cm^–1) is shifted to low frequency with an increase in the dielectric constant _T of the solvents, whereas thev(M-O) (M=Fe and Ru, near 460 cm^–1) are constant, independent of _T. It implies that the C-O bond in the acac^– ligand is lengthened by the polarizability effect of the solvents, while both the Fe-O and Ru-O bonds, which are located in the inside of the complexes, are not influenced by the solvents indicating that the interaction does not depend on the properties of individual solvent molecules but on those of the aggregate.     

Synthesis and characterization of norfloxacin-transition metal complexes (group 11, IB): spectroscopic, thermal, kinetic measurements and biological activity

The investigation of the new structures of Ag(I), Cu(II) and Au(III) complexes, [Ag(2)(Nor)(2)](NO(3))(2), [Cu(Nor)(2)(H(2)O)(2)]SO(4).5H(2)O and [Au(Nor)(2) (H(2)O)(2)]Cl(3) (where, Nor=norfloxacin) was done during the reaction of silver(I), copper(II) and gold(III) ions with norfloxacin drug ligand. Elemental analysis of CHN, infrared, electronic, (1)H NMR and mass spectra, as well as thermo gravimetric analysis (TG and DTG) and conductivity measurements have been used to characterize the isolated complexes. The powder XRD studies confirm the amorphous nature of the complexes. The norfloxacin ligand is coordinated to Ag(I) and Au(III) ions as a neutral monodentate chelating through the N atom of piperidyl ring, but the copper(II) complex is coordinated through the carbonyl oxygen atom (quinolone group) and the oxygen atom of the carboxylic group. The norfloxacin and their metal complexes have been biologically tested, which resulted in norfloxacin complexes showing moderate activity against the gram positive and gram negative bacteria as well as against fungi.     

Formation and reactivity of cobalt(III)-dioxygen complexes promoted by 2-methylpropanal: Oxidation of alkenes and alcohols

2-Methylpropanal promotes the formation of cobalt(III)-dioxygen species from catalysts1 or2 and dioxygen. The cobalt(III)-dioxygen complexes efficiently catalyse the oxidation of various alcohols to carbonyl compounds in the presence of dioxygen and 2-methylpropanal. Similarly substituted alkenes are smoothly transformed to the corresponding monoepoxides under these reaction conditions. EPR study of these reactions indicates that different activated dioxygen species are formed in the presence of catalysts1 and2.     

Influence of organic solvent on tristhioureazinc(II)sulphate crystals

It was observed that the addition of a very small quantity (5·10⁻³ M L⁻¹) of an organic solvent, benzene (C₆H₆) in the aqueous growth medium (pH ∼5.9) of tristhioureazinc(II)sulphate (ZTS) markedly influences the SHG efficiency. The measurements using Nd:YAG laser source reveal that second harmonic generation (SHG) conversion efficiency which is one of the most important nonlinear optical (NLO) properties is enhanced by benzene dopant by a factor of nearly 1.5 times. The crystalline perfection of the grown crystals was evaluated by high-resolution X-ray diffractometry (HRXRD). The full width at half maximum (FWHM) of the diffraction curve (which gives an estimate for the degree of crystalline perfection) for undoped and benzene doped specimen crystals are 26 and 15 arc sec, respectively. The reduction in FWHM due to the benzene solvent indicates the significant improvement in crystalline perfection. This very much suggests that the dissolution of trace impurities in the presence of benzene prevents the entry of impurities into the crystal lattice and at the same time enhances the growth promoting effect (GPE). Not much variation is observed in XRD, FTIR and TG-DTA of ZTS in the presence and absence of benzene in the aqueous growth medium.     

Electron transfer reactions of iron(III)-polypyridyl complexes with organic sulfoxides

The redox reactions of four iron(III)-polypyridyl complexes with six aryl methyl sulfoxides have been investigated by spectrophotometric technique. The reaction follows clean second order kinetics and proceeds through rate determining electron transfer (ET) from organic sulfoxides to iron(III). The Marcus cross-reaction relation has been applied to obtain the self exchange rate constant for the ArSOR/ArS⁺(O)R couple as 1.3×10⁷ M⁻¹ s⁻¹. The application of Marcus theory to this ET reaction shows that the contribution of inner sphere reorganization energy is 0.4 eV. The rate constant and reaction constant values observed with organic sulfoxides are small compared with organic sulfides towards the same oxidant Fe(NN)₃³⁺.     

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.     

Kinetic Analyis of TG Data XXXV. Spectroscopic and thermal studies of some cobalt(III) chelates with ethylenediamine

A number of 30 [Co(en)₃ ]Y₃ , [Co(en)₂ X₂ ]Y and [Co(en)₂ X(amine)]Y₂ type complexes (X =Cl, Br; Y =Cl, Br, I, NCO, NCS, NO₃ , ClO₄ , etc.; amine =aromatic and alkylamines) were obtained from trans-[Co(en)₂ Cl₂ ]Cl by double decomposition and by substitution reactions, respectively. The structure of the complexes was proved by means of far and middle FTIR spectra. The thermal decomposition was studied by TG, DTA and DSC measurements. Mass spectra were also recorded. In the case of [Co(en)₃ ]Y₃ complexes the nitrate, perchlorate and dimesoperiodates decompose suddenly, frequently explosion like. The halides and thiocyanates seem to substitute an ethylenediamine ligand, yielding a rather unstable intermediate. The pyrolysis of [Co(en)₂ X₂ ]Y type derivatives yields no relatively stable intermediates, but the decomposition temperatures may be correlated with the nature of Y and with the cis or trans configuration of the compound. With the [Co(en)₂ X(amine)]Y₂ type complexes one observes the formation of [Co(en)₂ XY]Y as intermediate product. From the TG curves kinetic parameters were derived for some dehydration and deamination processes, by using the nomogram method. The validity of a non-linear kinetic compensation law was observed. This revised version was published online in July 2006 with corrections to the Cover Date.     

A thermal decomposition study on cobalt(II) complexes of 1,2-bis(IMINO-4'-antipyrinyl)ethane

The phenomenological, kinetic and mechanistic aspects of thermal decomposition of perchlorate, nitrate, chloride, bromide and iodide complexes of cobalt(II) with the Schiff base 1,2-bis(imino-4'-antipyrinyl)ethane (GA) have been studied by TG and DTG analyses. The kinetic parameters like the activation energy, pre-exponential factor and entropy of activation were calculated. The decomposition reactions follow 'random nucleation with one nucleus on each particle - Mampel model'. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of electron donors on the radical polymerization of vinyl acetate mediated by [Co(acac)2]: degenerative transfer versus reversible homolytic cleavage of an organocobalt(III) complex

The molecular structure of bis(acetylacetonate)cobalt(II) ([Co(acac)2]) in solution and in the presence of the electron donors (ED) pyridine (py), NEt3, and vinyl acetate (VOAc) was investigated using 1H NMR spectroscopy in C6D6. The extent of formation of ligand adducts, [Co(acac)2(ED)x], varies in the order py>NEt3>VOAc (no interaction). Density functional theory (DFT) calculations on a model system agree with Co--ED bond strengths decreasing in the same order. The effect of electron donors on the [Co(acac)2]-mediated radical polymerization of VOAc was examined at 30 degrees C by the addition of excess py or NEt3 to the complex in the molar ratio [VOAc]0/[Co]0/[V-70]0/[py or NEt3]0=500:1:1:30 (V-70=2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile)). As previously reported by R. Jerome et al., the polymerization showed long induction periods in the absence of ED. However, a controlled polymerization without an induction period took place in the presence of ED, though the level of control was poorer. The effective polymerization rate decreased in the order py>NEt3. A similar behavior was found when these electron donors were added to an ongoing [Co(acac)2]-mediated radical polymerization of VOAc. On the basis of the NMR and DFT studies, it is proposed that the polymerization is controlled by the reversible homolytic cleavage of an organocobalt(III) dormant species in the presence of ED. Conversely, the faster polymerization after the induction period in the absence of ED is due to a degenerative transfer process with the radicals produced by the continuous decomposition of the excess initiator. Complementary experiments provide additional results in agreement with this interpretation.     

Cationic complexes of Eu(III) and Sr(II) with diphosphine dioxides in organic extracts

IR spectroscopy was used to study the structure and composition of Eu(III) and Sr(II) complexes formed by cation-exchange extraction of these metals from their aqueous nitrate solutions with dichlorethane solutions of mixtures of chlorinated cobalt(III) dicarbollide (CCD) as a superacid with diphenyldiphosphine dioxides containing a methyl (Me-DPDO), ethyl (Et-DPDO), or polyoxyethylene bridge between two phosphorus atoms of phosphine oxide groups. At molar ratios DPDO/CCD ≤ 1, [Eu(H₂O)_nL₄]³⁺ complexes are formed in organic phases, whereas with an excess of DPDO relative to CCD, Eu(NO₃)L ₄ ²⁺ complexes are formed, where L = Me-or Et-DPDO. Polyoxyethylenediphosphine dioxide forms anhydrous complexes of composition Eu:L = 1:1 and 1:2 with Eu(III) and outer-spheric complexes of composition Sr:L = 1:1 and 1:2 with Sr(II), where the organic ligand molecules envelop the hydrated Sr(H₂O) _n ²⁺ cation. The peculiarities of extraction of the complexes are explained based on data about their composition and structure.     

Structure and aggregation behavior of cobalt-di(2-ethylhexy1)-phosphoric acid complexes in solvent extraction systems

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Synthesis,characterization and biological evaluation of Ru(III) mercaptopyrimidine Schiff base complexes

A new series of mercaptopyrimidine Ru(III) complexes were synthesized and characterized using various spectral techniques like single‐crystal X‐ray diffraction, Fourier transform infrared and NMR spectroscopies, thermogravimetric analysis and energy‐dispersive X‐ray analysis. The complexes were evaluated for their pharmacological activities like in vitro antimicrobial, anticancer, antituberculosis and antioxidant activities. The DNA binding of the complexes was investigated by absorption and emission spectral measurements which indicated that the complexes bind to DNA via intercalation, with molecular docking studies validating the results. DNA cleavage studies of the complexes were carried out.     

Electron transfer reactions of organic sulfoxides with photochemically generated ruthenium(III)-polypyridyl complexes

The electron transfer (ET) reaction of aryl methyl sulfoxides with ruthenium(III)-polypyridine complexes is sensitive to the change of substituent in the aryl moiety of ArS(O)CH₃ and ligand of Ru(III) complex. The detection of sulfoxide radical cation as the transient by conventional flash photolysis confirms ET in the rate-controlling step. The successful application of Marcus cross relation of ET leads to the evaluation of self-exchange rate constant of ArS⁺(O)CH₃/ArS(O)CH₃ as 4.0×10⁵ M⁻¹ s⁻¹ similar to organic sulfides. Comparison with the reactivity of iron(III)-polypyridyl complexes points out that both reactivity and ρ values are higher with Ru(III) complexes.