Complexation of Lanthanides with Nitrate at Variable Temperatures: Thermodynamics and Coordination Modes

Rao, Linfeng; Tian, Guoxin

doi:10.1021/ic801604f

Cited by 61 publications

(56 citation statements)

References 35 publications

(92 reference statements)

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“…Previous spectroscopic studies on EuÀBTC complexes have been restricted to conditions which prevent polymerization, i.e., low complex concentrations and ambient temperatures, 17 but studies of complex formation at variable temperatures are essential because the chemical speciation and metal mobility in soils strongly depend on varying environmental conditions. 4,18,19 Here, we extend previous TRLFS and calorimetric studies on the EuÀBTC complex 17,20 to elevated temperatures and concentrations. We identify the limits within which thermodynamic parameters derived from temperature-dependent TRLFS are consistent with the direct measurement of reaction heats by ITC.…”

Section: Articlesupporting

confidence: 53%

Eu³⁺-Mediated Polymerization of Benzenetetracarboxylic Acid Studied by Spectroscopy, Temperature-Dependent Calorimetry, and Density Functional Theory

et al. 2011

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Thermodynamic parameters for the complexation of Eu(3+) with pyromellitic acid (1,2,4,5-benzenetetracarboxylic acid, BTC) as a model system for polymerizable metal-complexing humic acids were determined using temperature-dependent time-resolved laser-induced fluorescence spectroscopy (TRLFS) and isothermal titration calorimetry (ITC). At low metal and ligand concentrations (<50 μM Eu(3+), <1 mM BTC), a 1:1 monomeric Eu-BTC complex was identified in the range of 25-60 °C. At elevated concentrations (>500 μM Eu(3+) and BTC) a temperature-dependent polymerization was observed, where BTC monomers are linked via coordinating shared Eu(3+) ions. The two methods lead to comparable thermodynamic data (ΔH = 18.5 ± 1.5/16.5 ± 0.1 kJ mol(-1); ΔS = 152 ± 5/130 ± 5 J mol(-1) K(-1); TRLFS/ITC) in the absence of polymerization. With the onset of polymerization, TRLFS reveals the water coordination number of the lanthanide, whereas calorimetry is superior in determining the thermodynamic data in this regime. Evaluating the heat uptake kinetics, the monomer and polymer formation steps could be separated by "time-resolved" ITC, revealing almost identical binding enthalpies for the sequential reactions. Structural features of the complexes were studied by Fourier-transform infrared (FTIR) spectroscopy in combination with density functional theory (DFT) calculations showing predominantly chelating coordination with two carboxylate groups in the monomeric complex and monodentate binding of a single carboxylate group in the polymeric complex of the polycarboxylate with Eu(3+). The data show that pyromellitic acid is a suitable model for the study of metal-mediated polymerization as a crucial factor in determining the effect of humic acids on the mobility of heavy metals in the environment.

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Section: Articlesupporting

confidence: 53%

Eu³⁺-Mediated Polymerization of Benzenetetracarboxylic Acid Studied by Spectroscopy, Temperature-Dependent Calorimetry, and Density Functional Theory

et al. 2011

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“…As a result, the stability constant of the Nd(III)/nitrate complex, Nd(NO 3 ) 2+ , must be known so that correction can be made to account for the complexation of Nd(III) with nitrate in the spectrophotometric titrations of Table 2. A value of ΔH for the Nd 3+ + NO 3 − → Nd(NO 3 ) 2+ reaction, determined in a previous study, 36 was used in the calculation for the complexation of Nd(III) with L I (TMOGA) to correct the contribution of the formation of Nd(NO 3 ) 2+ in the titrations. Table 2 show that the complexation of Nd(III) with the ligands becomes weaker upon moving from L III (two −COO − groups) to L II [one −COO − group and one −C(O)N(CH 3 ) 2 group] and L I [two −C(O)N(CH 3 ) 2 groups], which is consistent with the general observation that the negatively charged oxygen of the carboxylic group is a stronger donor to Nd(III) than the oxygen of the neutral amide group.…”

Section: Methodsmentioning

confidence: 99%

Structural and Thermodynamic Study of the Complexes of Nd(III) with N,N,N′,N′-Tetramethyl-3-oxa-glutaramide and the Acid Analogues

2014

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The thermodynamics of Nd(III) complexes with N,N,N',N'-tetramethyl-3-oxa-glutaramide (TMOGA, L(I)), N,N-dimethyl-3-oxa-glutaramic acid (DMOGA, HL(II)), and oxydiacetic acid (ODA, H2L(III)) in aqueous solutions was studied. Stability constants, enthalpies, and entropies of complexation were determined by spectrophotometry, potentiometry, and calorimetry. The stability constants of corresponding Nd(III) complexes decrease in the following order: Nd(III)/L(III) > Nd(III)/L(II) > Nd(III)/L(I). For all complexes, the enthalpies of complexation are negative and the entropies of complexation are positive, indicating that the complexation is driven by both enthalpy and entropy. Furthermore, from L(III) to L(II), and to L(I), the enthalpy of complexation becomes more exothermic and the entropy of complexation less positive, suggesting that the substitution of a carboxylate group with an amide group on the ligands enhances the enthalpy-driven force but weakens the entropy-driven force of the complexation with Nd(III). Crystal structures of three 1:3 Nd(III) complexes, Nd(L(I))3(ClO4)3 (I), Nd(L(I))3(NO3)3(H2O)2 (II), and Nd(L(II))3(H2O)7.5 (III), were determined by single-crystal X-ray diffraction and compared with the structure of a 1:3 Nd(III)/L(III) complex in the literature, Na3NdL(III)3(NaClO4)2(H2O)6 (IV). In all four structures, the ligands are tridentate and Nd(III) is nine-coordinated with similar distorted tricapped trigonal prism geometry by three ether oxygen atoms capped on the three faces of the prism, and six oxygen atoms from the ketone group or carboxyl group at the corners. The absorption spectra of Nd(III) in solutions showed very similar patterns as Nd(III) formed successive 1:1, 1:2, and 1:3 complexes with L(I), L(II), and L(III), respectively, implying that the Nd(III) complexes with the three ligands have similar coordination geometries in aqueous solutions, as observed in the solids.

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“…They determined thermodynamic parameters and isotope effects for the quenching of the excited state of Ln(III) in H 2 O and D 2 O. Additionally, no effect of pressure on the emission spectra was observed. Kimura et al [10] also employed the same cell to study the complexation of U(VI) with OH − , SO 4 2− and F − in the temperature range from 25 to 150 • C. In a very recent paper Rao and Tian [11] studied the nitrate complexation of Eu 3+ by laser fluorescence spectroscopy at 25 • C and of Nd 3+ by absorption spectroscopy in the temperature range from 25 to 70 • C in 1 M NaClO 4 -NaNO 3 solutions. The slight increase of the formation constant of Nd(NO 3 ) 2+ was additionally confirmed by the reaction enthalpy determined by microcalorimetry.…”

Section: Introductionmentioning

confidence: 99%

TRLFS study on the complexation of Cm(III) with nitrate in the temperature range from 5 to 200 °C

Skerencak¹,

Panak

Haüser

et al. 2009

Radiochimica Acta

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The formation of aqueous Cm(III) nitrate complexes is studied in the temperature range from 5 to 200 • C by time resolved laser fluorescence spectroscopy (TRLFS). The experiments are performed in a custom build high pressure and high temperature fluorescence cell. The complex formation is measured at nitrate concentrations ranging from 0.10 to 4.61 mol/kg H 2 O. The mono-and dinitrate complexes are quantified by peak deconvolution of the fluorescence spectra and the complexation constants are determined as a function of the temperature. The conditional equilibrium constants are extrapolated to zero ionic strength using the specific ion interaction theory (SIT) and the thermodynamic standard state data (Δ r H • m , Δ r S • m , Δ r G • m , Δ r C • p,m ) are determined from the temperature dependence of the equilibrium constants at I = 0. The equilibrium constants up to 75 • C are well described by the Van't Hoff equation (Δ r H • m independent of T and Δ r C • p,m = 0). Modelling of the data at higher temperatures requires an extended equation including a term for the heat capacity changes (Δ r C • p,m ).

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Complexation of Lanthanides with Nitrate at Variable Temperatures: Thermodynamics and Coordination Modes

Cited by 61 publications

References 35 publications

Eu³⁺-Mediated Polymerization of Benzenetetracarboxylic Acid Studied by Spectroscopy, Temperature-Dependent Calorimetry, and Density Functional Theory

Eu³⁺-Mediated Polymerization of Benzenetetracarboxylic Acid Studied by Spectroscopy, Temperature-Dependent Calorimetry, and Density Functional Theory

Structural and Thermodynamic Study of the Complexes of Nd(III) with N,N,N′,N′-Tetramethyl-3-oxa-glutaramide and the Acid Analogues

TRLFS study on the complexation of Cm(III) with nitrate in the temperature range from 5 to 200 °C

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Complexation of Lanthanides with Nitrate at Variable Temperatures: Thermodynamics and Coordination Modes

Cited by 61 publications

References 35 publications

Eu3+-Mediated Polymerization of Benzenetetracarboxylic Acid Studied by Spectroscopy, Temperature-Dependent Calorimetry, and Density Functional Theory

Eu3+-Mediated Polymerization of Benzenetetracarboxylic Acid Studied by Spectroscopy, Temperature-Dependent Calorimetry, and Density Functional Theory

Structural and Thermodynamic Study of the Complexes of Nd(III) with N,N,N′,N′-Tetramethyl-3-oxa-glutaramide and the Acid Analogues

TRLFS study on the complexation of Cm(III) with nitrate in the temperature range from 5 to 200 °C

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Eu³⁺-Mediated Polymerization of Benzenetetracarboxylic Acid Studied by Spectroscopy, Temperature-Dependent Calorimetry, and Density Functional Theory

Eu³⁺-Mediated Polymerization of Benzenetetracarboxylic Acid Studied by Spectroscopy, Temperature-Dependent Calorimetry, and Density Functional Theory