Stability Constants Of Lanthanide Complexes Research Articles

Effect of the stability of 1,3-bis(diphenylphosphoryl)-2-oxapropane complexes on the separation of lanthanide ions and their detection.

Phosphoryl podands of neutral type with a flexible ethylene glycol chain and diphenylphosphorylmethyl end groups are known for their complexation properties towards various cations. In this work, the complexation process between 1,3-bis(diphenylphosphoryl)-2-oxapropane (L) and lanthanide ions was studied. Namely, the stability constants of lanthanide complexes with L in acetonitrile were estimated by the method of spectrophotometric titration. It was found that the stability constants of Ln3+ complexes with L increase in the lanthanide series, which is consistent with the extraction and ion-selective properties of L. The extraction ability of L and this ligand in the presence of ionic liquids (ILs) such as methyltrioctylammonium nitrate (MTOAN) and bis[(trifluoromethyl)sulfonyl]imide 1-butyl-3-methylimidazolium (C4mimTf2N) was studied. It was found that in the presence of ILs, L extracts the elements of the yttrium subgroup of lanthanides much better than those of the cerium subgroup: SFLu/Ce(L-MTOAN) = 2.29; SFLu/Ce(L-C4mimTf2N) = 110.38. The use of the L-C4mimTf2N mixture in the processes of lanthanide separation into subgroups is much more efficient than the use of L without the addition of ILs or the use of the L-MTOAN mixture. The ion-selective properties of L towards Ln3+ ions were studied. Podand L exhibits potentiometric selectivity to Lu3+ ions.

Rigidified Derivative of the Non-macrocyclic Ligand H4OCTAPA for Stable Lanthanide(III) Complexation.

The stability constants of lanthanide complexes with the potentially octadentate ligand CHXOCTAPA4–, which contains a rigid 1,2-diaminocyclohexane scaffold functionalized with two acetate and two picolinate pendant arms, reveal the formation of stable complexes [log KLaL = 17.82(1) and log KYbL = 19.65(1)]. Luminescence studies on the Eu3+ and Tb3+ analogues evidenced rather high emission quantum yields of 3.4 and 11%, respectively. The emission lifetimes recorded in H2O and D2O solutions indicate the presence of a water molecule coordinated to the metal ion. 1H nuclear magnetic relaxation dispersion profiles and 17O NMR chemical shift and relaxation measurements point to a rather low water exchange rate of the coordinated water molecule (kex298 = 1.58 × 106 s–1) and relatively high relaxivities of 5.6 and 4.5 mM–1 s–1 at 20 MHz and 25 and 37 °C, respectively. Density functional theory calculations and analysis of the paramagnetic shifts induced by Yb3+ indicate that the complexes adopt an unprecedented cis geometry with the two picolinate groups situated on the same side of the coordination sphere. Dissociation kinetics experiments were conducted by investigating the exchange reactions of LuL occurring with Cu2+. The results confirmed the beneficial effect of the rigid cyclohexyl group on the inertness of the Lu3+ complex. Complex dissociation occurs following proton- and metal-assisted pathways. The latter is relatively efficient at neutral pH, thanks to the formation of a heterodinuclear hydroxo complex.

Determination of the stability constants of lanthanide complexes with oxyacids using capillary electrophoresis

Different algorithms for calculating the stability constants of lanthanide complexes with hydroxycarbonic acids on the basis of experimental data obtained by capillary electrophoresis are compared. It is shown that the optimal approach is based on the consideration of the electrophoretic mobilities of all complex forms present in the solution, taking into account their fractions. The most satisfactory approximation of the experimental data by the calculated ones is achieved on the assumption that the electrophoretic mobilities of the complex species depend on their charge only, regardless of the particle size. The obtained stability constants of lanthanide complexes with lactic and 2-hydroxy-2-methylpropanoic acids agree with the literature data. The stability constants of lanthanide complexes with tartaric and citric acids were significantly corrected, while the constants for complexes with mandelic, 2-hydroxy-2-methylbutanoic, 2-hydroxy-2-propy-lpentanoic, and malic acid were determined for the first time.

Potentiometry of the Dioxa–Triaza Macrocyclic Complexes as Receptors for First-Row Transition and Lanthanide Metals

The protonation constants and the complex stability constants of 1,7-dioxa-4,10,13-triazacyclopentadecane-4,10,13-tripropionic acid ( N-pr 3[15]ane N 3O 2) with some first-row transition metals (Co 2+, Ni 2+, Cu 2+, and Zn 2+) and lanthanide metals (Ce 3+, Eu 3+, Gd 3+, and Yb 3+) have been determined at 25°C in aqueous 0.1 MNaClO 4solution by a potentiometric method. The results obtained are compared to those obtained for a similar ligand, 1,7-dioxa-4,10,13-triazacyclopentadecane-4,10,13-triacetic acid ( N-ac 3[15]ane N 3O 2), which has been previously reported. The stability constants of lanthanide complexes of N-pr 3[15]ane N 3O 2) increase with the decreasing ionic radii of Ln 3+. The order of metal binding strengths with N-pr 3[15]ane N 3O 2for the first-row transition metals was Ni 2+> Zn 2+> Co 2+> Cu 2+, which is obviously reversed from that with N-ac 3[15]ane N 3O 2, Cu 2+> Co 2+= Zn 2+> Ni 2+. The tendency to the reversal of this trend is rationalized and discussed in terms of the matching of the ligand properties with metal ion characteristics by the use of molecular mechanic calculations. These facts suggest that the structure of a polyoxa-polyaza macrocyclic compound can be preorganized by modifying the pendant arms to achieve unique selectivity for a particular metal cation.

Equilibrium and kinetic studies of lanthanide complexes of macrocyclic polyamino carboxylates

The stability constants (log K[sub LnL]) of lanthanide complexes of macrocyclic polyamino carboxylates, LnL (where Ln is Ce[sup 3+], Gd[sup 3+], and Lu[sup 3+] and L is DO3A = 1,4,7,10-tetraazacyclododecane-1,3,7-triacetic acid and HP-DO3A = 10-(hydroxypropyl)-1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid), have been determined at 25.0 [plus minus] 0.1[degree]C and [mu] = 0.1 ((CH[sub 3])[sub 4]NCl). The stability constants of lanthanide complexes of DO3A increase with the decreasing ionic radii or increasing charge density of Ln[sup 3+]. For L = HP-DO3A, the stability constant of GdL is greater than that of CeL; however the stability constants of GdL and LuL are similar. The protonation constants, K[sub H] (M[sup [minus]1]), of the LnL complexes have been determined at 25.0 [plus minus] 0.1[degree]C and [mu] = 1.0 (NaCl), and the values are 18 [plus minus] 3 for Ce(DO3A), 115 [plus minus] 8 for Gd(DO3A), 11 [plus minus] 1 for Ce(HP-DO3A), and 240 [plus minus] 25 for Gd(HP-DO3A). The rates of acid-assisted dissociation of the protonated complexes, ML(H), have been measured at 25.0 [plus minus] 0.1[degree]C and [mu] = 1.0 (NaCl). Direct, k[sub d] (s[sup [minus]1]), and acid-assisted, k[sub 1] (M[sup [minus]1] s[sup [minus]1]), dissociation rate constants are k[sub d] = (1.8 [plus minus] 0.8) [times] 10[sup [minus]3]more » and k[sub 1] = (1.12 [plus minus] 0.04) [times] 10[sup [minus]1] for Ce(DO3A) and k[sub d] = (1.4 [plus minus] 0.2) [times] 10[sup [minus]4] and k[sub 1] = (2.00 [plus minus] 0.04) [times] 10[sup [minus]3] for Ce(HP-DO3A). The rates of dissociation of the other complexes are first order in acid at low [H[sup +]], but the rates saturate at high [H[sup +]]. 40 refs., 5 figs., 3 tabs.« less

Lanthanide complex formation with a hexaaza macrocyclic ligand, 1,4,7,10,13,16-hexaazacyclooctadecane (A 618-Crown-6)

Stability constants of lanthanide complexes with 1,4,7,10,13,16-hexaazacyclooctadecane (A 618C6) in aqueous 0.1 M NaC1 medium have been determined at 20 °C by an out-of-cell potentiometric titration method. Lanthanide complexes with A 618C6 are more stable than those of the macrocyclic polyethers and bicyclic cryptands. No appreciable metal ion specificity is observed, but with increasing atomic number of the lanthanides, the stability increases similarly to that observed for diazapolyoxa-macrocycles. The unusually high stability of the lanthanide A 618C6 complexes is discussed in terms of the formation of partial bonds between the lanthanide ion and nitrogen donors and the inertness of the Ln-hexaaza-18-membered system.

Stability constants of lanthanide complexes with salicylhydroxamic acid

The stability constants of La, Pr, Nd, Sm, Eu, Gd, Dy, Er, Yb and Y complexes of salicylhydroxamic acid have been determined potentiometrically in 3:1 v v acetone-water medium at 25 ± 0·5° and at an ionic strength of 0·1 with respect to sodium perchlorate. The stability constants are comparable with those of other lanthanide complexes with oxygen-donating ligands such as benzoylacetone and benzoylphenylhydroxylamine.