Metal chelates of phosphonate-containing ligands-I Stability of some N,N,N',N'-ethylenediaminetetra(methylenephosphonic) acid metal chelates

A potentiometric investigation of the acid dissociation constants of the octabasic ENTMP [N,N,N',N'-ethylenediaminetetra(methylenephosphonic) acid] is reported. The stability constants of protonated MH(n)L (n = 1, 2, 3 and 4) and unprotonated ML metal chelates of Mg, Ca, Ba and Cd with ENTMP have been measured. The stabilities are in the order Mg < Ca < Ba < Cd.     

Metal chelates of phosphonate-containing ligands-IV (Stability of some 1,6-hexamethylenediamine-N,N,N',N'-tetra(methylenephosphonic) acid metal chelates)

The stability constants of the complexes formed between the anion of 1,6-hexamethylenediamine-N,N,N',N'-tetra(methylenephosphonic) acid and some transition and non-transition metal ions have been measured potentiometrically at a temperature of 25 degrees and an ionic strength of 0.1M (KNO(3)). The acid dissociation constants of the ligand and stability constants of the protonated complexes are also reported. Comparisons are made with the acid dissociation constants of the analogous compounds EDTA, ENTMP and HDTA, and possible structural formulae are given.     

Metal chelates of phosphonate-containing ligands-VI Complexes of ethylenediaminetetra(methylenephosphonic) acid with Cd, Mg, Ca and Ba

A correction is made to results previously obtained, as a result of further calculations.     

Metal chelates of phosphonate-containing ligands: VII. Analytical applications of 1-hydroxyethane-1,1-diphosphonic acid

The polarographic behavior of copper, lead, antimony, and zinc ions in the presence of the title ligand, HEDP, is discussed. In highly alkaline solutions, the reversible wave of copper splits into two components, reversible and irreversible, the first of which is attributed to the reduction of the free cupric ions and the second wave was assigned to the reduction of the copper phosphonate species. The polarograms of zinc and antimony showed the presence of a single irreversible wave. In the case of lead, a quasi-reversible wave is observed. Cobalt and nickel forms inactive phosphonate chelates as inferred from the suppression of the wave heights with increasing of both the concentration of the ligand and the pH of the medium. In the presence of sufficiently excess HEDP buffered to pH 11.8, mixtures of the six elements showed the presence of four reasonably separated waves at half-wave potential values ?0.51, ?0.83, ?1.17, and ?1.55 V vs SCE corresponding to the reductions of copper, lead, antimony, and zinc complexes, respectively. The possibility of the individual and simultaneous analysis of these elements in their ternary mixtures with cobalt and nickel is discussed.     

Metal chelates of phosphonate-containing ligands-II: stability constants of some beta-styrylphosphonic acid metal chelates

The synthesis and properties of beta-styrylphosphonic acid (SPA) are reported. The values of the protonation constants of the ligand were determined potentiometrically at different ionic strengths and in the temperature range 0-65 degrees. The enthalpy and entropy of protonation have been calculated by using the van't Hoff isochore. The protonation process is endothermic and is stabilized by a relatively large positive entropy change. The stability constants of the complexes formed between SPA and the bivalent Mg, Ca, Ba, Co, Ni and Pd ions at 25 degrees and ionic strength of 0.12M KNO(3) were also determined. All measurements were carried out in 18% dimethylformamide-water mixture.     

Liquid chromatography of lanthanide chelates of 1-(p-nitrophenyl)ethylenediamine-N,N,N',N' -tetra-acetic acid

Preparation of the chelating agent, 1-(p-nitrophenyl)ethylenediamine-N,N,N',N'-tetra-acetic acid (p-nitrophenylEDTA), is described in detail. Separation of p-nitrophenylEDTA chelates of ytterbium(III), erbium(III), dysprosium(III) and europium(III) has been achieved by reversed-phase ion-pair liquid chromatography. With spectrophotometric detection at 254 nm, linear responses over about four orders of magnitude were achieved with detection limits (S/N = 2) of about 0.5 pmole.     

Metal chelates of phosphonate-containing ligands-V Stability of some 1-hydroxyethane-1,1-diphosphonic acid metal chelates

A detailed study of the complexes formed between 1-hydroxyethane-1,1-diphosphonic acid and twelve metal ions, including the alkaline earth and transition non-transition metal ions, is reported. The formation constants of the protonated and unprotonated complexes are measured from potentiometric data and possible structural formulae are given. The results reveal that only mononuclear (1:1) di-, mono- and unprotonated metal chelates are formed and that the general order of stability for the unprotonated complexes is Zn > Mn > Ca > Cu > Cd > Pd > Ni > Co reverse similar Sr > Mg > Ag > Ba.     

Coordination ability of trans-cyclohexane-1,2-diamine-N,N,N',N'-tetrakis(methylenephosphonic acid) towards lanthanide(III) ions

The proton and metal complex equilibria of trans-cyclohexane-1,2-diamine-N,N,N',N'-tetrakis(methylenephosphonic acid) (CDTP) with lanthanide(iii) ions, where Ln(III) = La(III), Nd(III), Sm(III), Eu(III), Gd(III), Tb(III), Ho(III) and Lu(III) were studied. The stoichiometry, protonation and complex formation constants were determined by potentiometric titration at 25.0 degrees C and ionic strength of 0.1 mol dm(-3) (KCl). All metal ions form several species: [LnH4L]-, [LnH3L](2-), [LnH2L](3-), [LnHL](4-), [LnL](5-), [LnH(-1)L](6-) and [LnH(-2)L](7-) in the pH range between 2 and 11. The stability constants log beta(LnL) were found to be between 14.7 and 16.7. The studied complexes were also characterized by spectroscopic methods (31P NMR, UV-Vis absorption and emission spectroscopy). These studies allowed to reveal a distinct structural change of the Ln(III)-CDTP complex which occurs between protonated and hydroxy species in solutions at pH around 7.5. The major change is caused by the involvement of both nitrogen donors in the metal ion coordination occurring in ML species. The data obtained from UV-Vis spectroscopy allowed to draw conclusions about complex symmetry and to estimate a number of coordinated water molecules. The hydration number or more precisely the number of two OH oscillators was found to be approximately one in all species formed over the pH range between 5 and 10. The structure of the major hydroxy complex was supported by X-ray crystallographic data. The crystal structures of the Eu(III) and Tb(III) complexes clearly show that the CDTP ligand is coordinated to the Ln(III) ion by two nitrogen and four oxygen atoms in such a way that only one oxygen atom from each phosphonic group is placed in the lanthanide inner sphere. The monomeric complex anion is connected to a symmetry related ion through short hydrogen bonds formed by two hydroxy ions and one water molecule. In this way the two neighbouring anions form a quasi-dimer in which one of the Ln(III) ion is seven-coordinate (two N atoms, four O atoms and one hydroxy ion) and the other is eight-coordinate (two N atoms, four O atoms, one hydroxy ion and one water molecule).     

Ethylenediamine-N,N,N′,N′-tetrakis(methylenephosphonic) acid as complexing agent

Metal derivatives of ethylenediamine-N,N,N′,N′-tetrakis(methylenephosphonic) acid (EDTMP, H₈L) with some bivalent ions—Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Pb(II) have been isolated in various stoichiometric ratios from aqueous medium. Electronic spectra indicate them to be six-coordinated. EPR studies of Cu(II) complexes show that they are tetragonally elongated. Magnetic moments of M₄L derivatives are very low due to antiferromagnetic exchange interactions, but the moments go on increasing for M₃Na₂L and M₂Na₄L and are normal for MNa₆L derivatives, due to isolation of paramagnetic centres by diamagnetic sodium ions. IR spectra and thermal stability of the complexes have also been studied.     

The formation of 2-hydroxy-1,3-diaminopropane-N,N,N',N'-tetra-acetic acid silver and mercury(III) chelates

The stability constants of mononuclear (1:1) and binuclear (2:1) chelates of the Ag-HDPTA and Hg(II)-HDPTA systems (HDPTA = 2-hydroxy-1,3-diaminopropane-N,N,N',N'-tetra-acetic acid) were evaluated from pM and pH data, using a method proposed earlier by Ringbom and the author. The determinations yielded the following stability constants (concentration): The use of the reagent for the analytical determination of silver and mercury(II) ions is also discussed.     

Radiolysis of cobalt(III)-1,2 bis(beta-aminoethoxy)ethane N,N,N',N' sodium sulfonate triacetic acid chelate

Chelation studies of cobalt(III) with 1,2 bis(beta-aminoethoxy)ethane N,N,N',N' sodium sulfonate triacetic acid (ASTA) were performed. The results showed the effectiveness of ASTA as a chelating agent by using: molar ratio, continuous variation and slope ratio methods. Stable complex 1∶1 was formed at pH from 6.0 to 10.5. Solutions of Co-ASTA chelate of different molar ratios at pH 6.5 and 8.0 were irradiated by different gamma-radiation doses. The results showed a linear decrease of absorbance with gamma-radiation dose which can be utilized as a dosimeter for low dose rate measurement in the range studied. A proposed radiolytic mechanism is discussed. The degradation of the ASTA ligand has been related to hydroxyl radical attack.     

First principles study of the ignition mechanism for hypergolic bipropellants: N,N,N',N'-tetramethylethylenediamine (TMEDA) and N,N,N',N'-tetramethylmethylenediamine (TMMDA) with nitric acid

We report quantum mechanics calculations (B3LYP flavor of density functional theory) to determine the chemical reaction mechanism underlying the hypergolic reaction of pure HNO(3) with N,N,N',N'-tetramethylethylenediamine (TMEDA) and N,N,N',N'-tetramethylmethylenediamine (TMMDA). TMEDA and TMMDA are dimethyl amines linked by two CH(2) groups or one CH(2) group, respectively, but ignite very differently with HNO(3). We explain this dramatic difference in terms of the role that N lone-pair electrons play in activating adjacent chemical bonds. We identify two key atomistic level factors that affect the ignition delay: (1) The exothermicity for formation of the dinitrate salt from TMEDA or TMMDA. With only a single CH(2) group between basic amines, the diprotonation of TMMDA results in much stronger electrostatic repulsion, reducing the heat of dinitrate salt formation by 6.3 kcal/mol. (2) The reaction of NO(2) with TMEDA or TMMDA, which is the step that releases the heat and reactive species required to propagate the reaction. Two factors of TMEDA promote the kinetics by providing routes with low barriers to oxidize the C: (a) formation of a stable intermediate with a C-C double bond and (b) the lower bond energy for breaking the C-C single bond (by 18 kcal/mol comparing to alkane) between two amines. Both factors would decrease the ignition delay for TMEDA versus TMMDA. The same factors also explain the shorter ignition delay of 1,4-dimethylpiperazine (DMPipZ) versus 1,3,5-trimethylhexahydro-1,3,5-triazine (TMTZ). These results indicate that TMEDA and DMPipZ are excellent green replacements for hydrazines as the fuel in bipropellants.