Search Results
Abstract
Isothermal decomposition kinetic of three lanthanide mixed complexes with the general formula of Ln(thd)3phen (where Ln=Nd3+, Sm3+ or Er3+, thd=2,2,6,6-tetramethyl-3,5-heptanodione and phen=1,10-phenanthroline) has been studied in this work. The powders were characterized by their melting point, elemental analysis, FTIR spectroscopy and thermogravimetry. The isothermal TG curves have been recorded under the same conditions at 265–285, 265–285 and 250–270°C for Nd(thd)3phen, Sm(thd)3phen and Er(thd)3phen, respectively. The kinetic parameters, i.e. activation energy, reaction order and frequency factor were obtained through the technique of lineal regression using the relation g(α)=kt+g 0. The analysis was done at decomposed fractions between 0.10–0.90. The values of activation energy were: 114.10, 114.24 and 115.04 kJ mol–1 for the Nd(thd)3phen, Sm(thd)3phen and Er(thd)3phen complexes, respectively. The kinetic models that best described the isothermal decomposition reaction the complexes were R1 and R2. The values of activation energy suggests the following decreasing order of stability: Nd(thd)3phen<Sm(thd)3phen<Er(thd)3phen.
The present work deals with the synthesis of eight mixed complex combinations of Pd(II) with different α-amino acids. In order to prove the coordination of the ligands to the Pd(II) ion and to establish the structure of the prepared compounds, chemical analyses and physicochemical studies (IR spectra and thermogravimetric analysis) were performed.
New mixed complex combinations of Ni(II) withγ andβ-picoline were synthesized and characterized by means of thermogravimetry under dynamic temperature conditions. The formation of these complex combinations was confirmed, the structure-thermostability dependence was established, and a mechanism for the thermal degradation was proposed.
The thermal decompositions of nine mixed ligand complexes of Mn(II) containing picrate and mono- or bidentate nitrogen ligands were studied by thermogravimetry. The kinetics of decomposition were examined by using the Coats-Redfern and Horowitz-Metzger equations; the decomposition was in all cases of the first order. The activation energies and other kinetic parameters were computed. The decomposition mechanisms exhibited a similar character for all the studied compounds. It was observed from the TG curves that the complexes decomposed to give six-coordinate intermediates, formed from substitution of the picrate into the inner coordination sphere. These intermediates decomposed to Mn(II) picrate and finally to Mn2O3.
Double-double effect and the coordination number
II. Mixed lanthanide(III) complexes of trans-1,2-diaminocyclohexanetetraacetic acid with iminodiacetate, glycine and hydroxide ions
Abstract
The partial stability constants of the mixed complexes, Ln(III)-DCTA-L (where DCTA is trans-1,2-diaminocyclohexanetetraacetic acid and L, consecutively, OH−, glycine and iminodiacetate) have been determined potentiometrically at 25°C and at the ionic strength of 1 (KCl). It has been concluded that in the 1∶1 chelates, [(H2O)xLn(DCTA)]−, the number of water molecules decreases from 3 in the La−Sm range to 2 in the Dy−Lu one. The coordination numbers of the mixed complexes studied are discussed on the basis of the theory of the double-double effect. An explanation for the extrastability of the Ln(DCTA) chelates is given.
31P-NMR study of the organophosphorous complexes of uranium(VI)
II. The system uranyl nitrate-tri- N -butylphosphate-tri- N -octylphosphine oxide
Abstract
The formation of the mixed complex UO2(TOPO)(TBP)(NO3)2 is reported by31P-NMR spectroscopy for the first time. The extraction of the uranyl nitrate by a TBP and TOPO mixture was simulated in a NMR vial and monitored in situ. The equilibrium constant values of the processes in which the mixed complex is involved, i.e.:K R , for the redistribution of TBP and TOPO ligands between their uranyl complexes,K M , for the formation from consititutive molecules,K s , for the substitution of the uranyl coordinated TBP by TOPO are determined. The redistribution constant,K r at 25°C (4.43±0.5) and the changes of the thermodynamic variables H (0.59±0.14 kcal/mol). S (5.04±0.51 cal/mol·degree) have values close to the statistical values, suggesting a random nature of this process. TheK S value (4.5·103) reveals the much greater affinity for uranium(VI) of TOPO relative to TBP.
Abstract
The extraction of radium and barium into a mixture of 1-phenyl-3-methyl-4-benzoylpyrazol-5-one (HPy) and trioctylphosphine oxide (TOPO) in n-hexane or cyclohexane was investigated as a function of pH and TOPO concentration. It was found that the synergistic enhancement of the extraction is caused by the formation of mixed complexes of type M(Py)2 (TOPO)3 and the overall extraction constants of both complexes were calculated.
Abstract
The application of K3W2Cl9 as reducing agent in preparation of99mTc-labelled compounds is described. Pertechnetate reduction was carried out in solutions of pH 2 and also of pH 5.5. DTPA, citrate, gluconate, HEDSPA and MDP were successfully labelled. Two types of labelled gluconate complexes were obtained. Complex I exhibited in rats an increased99mTc affinity to kidneys (21%). Complex II exhibited an increased99mTc affinity to bone (8.7%). Two types of labelled HEDSPA preparations were obtained: one yielded 29%99mTc activity in bone, the other type exhibited only 13.4%. The results indicated the absence of mixed complexes.
Abstract
The extraction of radium into a mixture of 2-thenoyltrifluoroacetone (HTTA) and tributyl phosphate (TBP) or trioctylphosphine oxide (TOPO) in n-hexane or cyclohexane has been investigated with regard to the dependence on pH, and TBP and TOPO concentrations. It has been found that the formation of mixed complexes of the type Ra(TTA)2 (TBP)2 and Ra(TTA)2(TOPO)2 occurs and the overall extraction constants of both complexes were calculated. With the systems described, very high distribution ratios of radium have been attained; these may advantageously be used for the separation and concentration of traces of radium.
Abstract
Synergistic effect with a strong donor, trioctyl phosphine oxide (TOPO), has been studied in the extraction of thenoyltrifluoroacetone (TTA) complexes of uranyl ion. The chemical form of the species extracted was found to be the 1∶1 adduct, UO2A2·S (S∶TOPO), and no evidence was found concerning other mixed complexes. Adduct formation constants determined in twelve inert solvents vary from lg KS=6.79 in chloroform to 9.58 in n-hexane, while their increasing order is almost the same as that for the adducts with other phosphine oxides and TBP.