Spectroelectrochemical studies of [Mo(dtc)_4][Eu(dtc)_4] and [Mo(dtc)_4][Er(dtc)_4]

Redox and spectroscopic properties of the eight-coordination complexes of molybdenum and the rare-earth elements Eu or Er with N,N-diethyldithiocarbamate (dtc) were characterised by cyclic voltamrnetry and UV-visible absorption spectra.The complex cation [Mo(dtc)4]+ is more stable than the complex anions [Eu(dtc)4]-and [Er(dtc)4]-in redox processes,and possesses good redox reversibility.The electron transfer number,formal standard electrode potential in the redox process for the complex cation and its diffusion coefficients were obtained by in aitu spectroelectro-chemistry.     

meso-四(4-磺苯基)卟啉对铕(Ⅲ)与羧酸络合物电还原的催化作用

水溶液中Eu³⁺与meso-四(4-磺苯基)卟啉(TPPS)不易形成卟啉络合物,但在乙酸、酒石酸、丙二酸等共存时,在循环伏安图上可得一对Eu³⁺还原-氧化的可逆或准可逆峰,此峰与Eu³⁺在NaClO₄底液中的还原峰相比,峰电位正移,峰电流增高。从6种Eu³⁺-羧酸络合物与TPPS共存时的实验中证明这些络合物并没有和TPPS形成三元络合物,而是吸附在汞电极上的TPPS产生电催化作用。     

Novel macrocyclic EuII complexes: fast water exchange related to an extreme M-O water distance

Eu(II) complexes are potential candidates for pO(2)-responsive contrast agents in magnetic resonance imaging. In this regard, we have characterized two novel macrocyclic Eu(II) chelates, [Eu(II)(DOTA)(H(2)O)](2-) and [Eu(II)(TETA)](2-) (H(4)DOTA=1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid, H(4)TETA=1,4,8,11-tetraazacyclotetradecane-1,4,8,11-tetraacetic acid) in terms of redox and thermodynamic complex stability, proton relaxivity, water exchange, rotation and electron spin relaxation. Additionally, solid-state structures were determined for the Sr(II) analogues. They revealed no inner-sphere water in the TETA and one inner-sphere water molecule in the DOTA complex. This hydration pattern is retained in solution, as the (17)O chemical shifts and (1)H relaxation rates proved for the corresponding Eu(II) compounds. The thermodynamic complex stability, determined from the formal redox potential and by pH potentiometry, of [Eu(II)(DOTA)(H(2)O)](2-) (lg K(Eu(II))=16.75) is the highest among all known Eu(II) complexes, whereas the redox stabilities of both [Eu(II)(DOTA)(H(2)O)](2-) and [Eu(II)(TETA)](2-) are inferior to that of 18-membered macrocyclic Eu(II) chelates. Variable-temperature (17)O NMR, NMRD and EPR studies yielded the rates of water exchange, rotation and electron spin relaxation. Water exchange on [Eu(II)(DOTA)(H(2)O)](2-) is remarkably fast (k298(ex)=2.5 x 10(9) s(-1)). The near zero activation volume (DeltaV++ =+0.1+/-1.0 cm(3) mol(-1)), determined by variable-pressure (17)O NMR spectroscopy, points to an interchange mechanism. The fast water exchange can be related to the low charge density on Eu(II), to an unexpectedly long M-O(water) distance (2.85 A) and to the consequent interchange mechanism. Electron spin relaxation is considerably slower on [Eu(II)(DOTA)(H(2)O)](2-) than on the linear [Eu(II)(DTPA)(H(2)O)](3-) (H(5)DTPA=diethylenetriaminepentaacetic acid), and this difference is responsible for its 25 percent higher proton relaxivity (r(1)=4.32 mM(-1) s(-1) for [Eu(II)(DOTA)(H(2)O)](2-) versus 3.49 mM(-1) s(-1) for [Eu(II)(DTPA)(H(2)O)](3-); 20 MHz, 298 K).     

Solution and solid-state characterization of Eu(II) chelates: a possible route towards redox responsive MRI contrast agents

We report the first solid state X-ray crystal structure for a Eu(II) chelate, [C(NH2)3]3[Eu(II)(DTPA)(H2O)].8H2O, in comparison with those for the corresponding Sr analogue, [C(NH2)3]3[Sr(DTPA)(H2O).8H2O and for [Sr(ODDA)].8H2O (DTPA5 = diethylenetriamine-N,N,N',N",N"-pentaacetate, ODDA2- =1,4,10,13-tetraoxa-7,16-diazacyclooctadecane-7,16-diacetate ). The two DTPA complexes are isostructural due to the similar ionic size and charge of Sr(2+) and Eu(2+). The redox stability of [Eu(II)(ODDA)(H2O)] and [Eu(II)(ODDM)]2- complexes has been investigated by cyclovoltammetry and UV/Vis spectrophotometry (ODDM4- =1,4,10,13-tetraoxa-7,16-diaza-cyclooctadecane-7,16-++ +dimalonate). The macrocyclic complexes are much more stable against oxidation than [Eu(II)(DTPA)(H2O)]3- (the redox potentials are E1/2 =-0.82 V, -0.92 V, and -1.35 V versus Ag/AgCl electrode for [Eu(III/II)(ODDA)(H2O)],[Eu(III/II)(ODDM)], and [Eu(III/II)(DTPA)(H2O)], respectively, compared with -0.63 V for Eu(III/II) aqua). The thermodynamic stability constants of [Eu(II)(ODDA)(H2O)], [Eu(II)(ODDM)]2-, [Sr(ODDA)(H2O)], and [Sr(ODDM)]2- were also determined by pH potentiometry. They are slightly higher for the EuII complexes than those for the corresponding Sr analogues (logK(ML)=9.85, 13.07, 8.66, and 11.34 for [Eu(II)(ODDA)(H2O)], [Eu(II)(ODDM)]2-, [Sr(ODDA)(H2O)], and [Sr(ODDM)]2-, respectively, 0.1M (CH3)4NCl). The increased thermodynamic and redox stability of the Eu(II) complex formed with ODDA as compared with the traditional ligand DTPA can be of importance when biomedical application is concerned. A variable-temperature 17O-NMR and 1H-nuclear magnetic relaxation dispersion (NMRD) study has been performed on [Eu(II)(ODDA)(H2O)] and [Eu(II)(ODDM)]2- in aqueous solution. [Eu(II)(ODDM)]2- has no inner-sphere water molecule which allowed us to use it as an outer-sphere model for [Eu(II)(ODDA)(H2O)]. The water exchange rate (k298(ex)= 0.43 x 10(9)s(-1)) is one third of that obtained for [Eu(II)(DTPA)(H2O)]3-. The variable pressure 17O-NMR study yielded a negative activation volume, deltaV (not=) = -3.9cm3mol(-1); this indicates associatively activated water exchange. This water exchange rate is in the optimal range to attain maximum proton relaxivities, which are, however, strongly limited by the fast rotation of the small molecular weight complex.     

Europium(III) reduction and speciation within a Wells-Dawson heteropolytungstate

The redox speciation of Eu(III) in the 1:1 stoichiometric complex with the alpha-1 isomer of the Wells-Dawson anion, [alpha-1-P 2W 17O 61] (10-), was studied by electrochemical techniques (cyclic voltammetry and bulk electrolysis), in situ XAFS (X-ray absorption fine structure) spectroelectrochemistry, NMR spectroscopy ( (31)P), and optical luminescence. Solutions of K 7[(H 2O) 4Eu(alpha-1-P 2W 17O 61)] in a 0.2 M Li 2SO 4 aqueous electrolyte (pH 3.0) show a pronounced concentration dependence to the voltammetric response. The fully oxidized anion and its reduced forms were probed by Eu L 3-edge XANES (X-ray absorption near edge structure) measurements in simultaneous combination with controlled potential electrolysis, demonstrating that Eu(III) in the original complex is reduced to Eu(II) in conjunction with the reduction of polyoxometalate (POM) ligand. After exhaustive reduction, the heteropoly blue species with Eu(II) is unstable with respect to cluster isomerization, fragmentation, and recombination to form three other Eu-POMs as well as the parent Wells-Dawson anion, alpha-[P 2W 18O 62] (6-). EXAFS data obtained for the reduced, metastable Eu(II)-POM before the onset of Eu(II) autoxidation provides an average Eu-O bond length of 2.55(4) A, which is 0.17 A longer than that for the oxidized anion, and consistent with the 0.184 A difference between the Eu(II) and Eu(III) ionic radii. The reduction of Eu(III) is unusual among POM complexes with Lindqvist and alpha-2 isomers of Wells-Dawson anions, that is, [Eu(W 5O 18) 2] (9-) and [Eu(alpha-2-As 2W 17O 61) 2] (17-), but not to the Preyssler complex anion, [EuP 5W 30O 110] (12-), and fundamental studies of materials based on coupling Eu and POM redox properties are still needed to address new avenues of research in europium hydrometallurgy, separations, and catalysis sciences.     

First example of low-valence ion substitution in Ln5O(OPri)13: mixed-valence europium oxoalkoxide [EuIII4EuIIO(OPri)12(HOPri)]HOPri

The novel mixed-valence alkoxide [Eu3+(4)Eu2+O(OPri)12(HOPri)]HOPri (1) has been prepared and structurally and spectroscopically characterized. The three synthesis routes (i) metathesis of 4EuCl3, EuI2, and 14KOPri combined with hydrolysis with 1H2O, (ii) oxidation of 5[Eu4(OPri)10(HOPri)3]2HOPri with 1.5O2, and (iii) reduction of Eu5O(OPri)13 with 0.8[Eu4(OPri)10(HOPri)3]2HOPri all yielded pure 1, whereas (iv) reduction of Eu5O(OPri)13 with 0.36-0.5 mol of europium metal produced impure 1. The compound, having the average Eu oxidation number +2.8, is very sensitive toward further oxidation to Eu5O(OPri)13 and is part of a redox series of europium 2-propoxides with average oxidation states +2.5, +2.8, and +3. The square pyramidal molecular structure, containing an oxo-oxygen atom in the basal plane, is similar to that of the well-known Ln5O(OPri)13; the main difference is the substitution of an Eu3+(-)OPri pair for an Eu2+(-)HOPri pair in the basal plane. Fourier transform infrared (FT-IR) and UV-visible spectroscopy showed that the solid-state structure was retained on dissolution in hexane and toluene-HOPri. The compound was further characterized by differential scanning calorimetry and solubility studies.     

Lanthanide compounds with fluorinated OC6F5 ligands: homo- and heterovalent complexes of Eu(II) and Eu(III)

The fluorinated phenoxide OC6F5 forms the stable Eu(II) and Eu(III) derivatives (DME)2Eu(mu-OC6F5)3Eu(mu-OC6F5)3Eu(DME)2 and (DME)2Eu(OC6F5)3, as well as the heterovalent product (DME)2Eu(mu-OC6F5)3Eu(DME)(OC6F5)2, in redox reactions of Eu with HOC6F5 or in proton-transfer reactions of HOC6F5 with Eu(SPh)2. The divalent complex crystallizes as a trimer with three bridging phenoxides bridging each pair of metals, with the terminal metals coordinating DME and the central metal ion encapsulated totally by O(C6F5) and dative fluoride interactions. The trivalent compound is monomeric with terminal phenoxide ligands and no Eu-F interactions. The heterovalent compound has clearly localized metal valence states and coordination features that mimic the homovalent species with the terminal OC6F5 bound to the Eu(III) ion, three bridging OR ligands spanning the Eu(II) and Eu(III) ions, and dative Eu(II)-F bonds. At elevated temperatures, these compounds decompose to give a mixture of solid-state fluoride phases.     

Crystal structures of extended europium cyanamide-carbodiimide compounds derived from different reaction conditions: temperature-controlled syntheses of In(0.08)Eu4(NCN)3I3, Eu8I9(CN)(NCN)3, and In(0.28)Eu12(NCN)5I(14.91)

A different thermal treatment of identical reactants (EuI2, NaCN, NaN3, and InI) leads to the formation of the three title compounds. In(0.08)Eu4(NCN)3I3 is isotypic with the reported LiEu4(NCN)3I3, Eu8I9(CN)(NCN)3 represents the first mixed cyanide-cyanamide rare-earth compound, and In(0.28)Eu12(NCN)5I(14.91) is characterized by a sandwich-like stacking motif involving Eu4-NCN double layers stuffed by a layer of vertex-sharing InI6 octahedra. The redox behavior of In is the main factor that leads to alternative product formation as a function of the temperature.     

Spectrophotometric method for the determination of europium with 2,2′-biquinoxalyl

A selective and sensitive method for the determination of europium was developed. Other lanthanides and oxidants do not require separation. The method is based on the redox reaction of Eu(III) with 2,2′-biquinoxalyl. It was checked for the range of 0.5 to 10 μg/Eu/mL. Sm(III) does not interfere in 1000-fold excess.     

Heterodinuclear cryptates [EuML(dmf)](ClO(4))(2)(M=Ca,Cd, Ni,Zn): tuning the luminescence of europium(III) through the selection of the second metal ion

Four heterodinuclear cryptates [EuML(dmf)](ClO(4))(2) (M=Ca, Cd, Ni, Zn) were synthesized by a two-step method (L denotes deprotonated anionic cryptand synthesized by condensation of tris(2-aminoethyl)amine with 2,6-diformyl-4-chlorophenol). The ES-MS spectra of the four cryptates and the crystal structure of [EuNiL(dmf)](ClO(4))(2) x MeCN confirm that a strict dinuclear Eu(III)-M(II) entity exits in the cryptates. The cyclic voltammetry and luminescence spectral investigations indicate that the introduction of second metal ions into the mononuclear Eu(III) cryptate result in a negative shift of the redox potential of Eu(III) and a change in luminescence intensity of Eu(III). The cryptate [EuML(dmf)](ClO(4))(2) was shown to quench the emission of Eu(III) when M=Ni and to enhance the emission of Eu(III) when M=Ca, Cd, and Zn in the sequence: mononuclear相似文献   

Europium(III) DOTA-tetraamide complexes as redox-active MRI sensors

PARACEST redox sensors containing the NAD(+)/NADH mimic N-methylquinolinium moiety as a redox-active functional group have been designed and synthesized. The Eu(3+) complex with two quinolinium moieties was nearly completely CEST-silent in the oxidized form but was "turned on" upon reduction with β-NADH. The CEST effect of the Eu(3+) complex containing only one quinolinium group was much less redox-responsive but showed an unexpected sensitivity to pH in the physiologically relevant pH range.     

Eu3+/Eu2+ redox energy in a new lithium intercalation compound LixEuTa7O19 (0 ≤ x ≤ 1)

Journal of Solid State Electrochemistry - Electrochemical lithium intercalation is observed in LixEuTa7O19 with 0 ≤ x ≤ 1; the voltage profiles show a 4f6/4f7 Eu3+/Eu2+ redox plateau at...     

硝酸铕和穴醚配合物的电化学研究

用循环伏安法在二氯甲烷、二氯乙烷、乙腈、丙酮,苯腈、吡啶、二甲基甲酰胺、二甲基亚砜等不同溶剂中,研究了稀土穴醚配合物Eu(NO₃)₃(2,2)和Eu₂(NO₃)₆(2,2,2)的电化学行为。测定了其氧化还原反应的半波电位及电子转移速度常数,讨论了E_1/2、k_s与溶剂及支持电解质的关系。     

铕离子在乙二醇低聚物中的配合作用与电化学行为

研究了乙二醇低聚物（ＰＥＧ）与Ｅｕ（２＋）及Ｅｕ（３＋）所形成配合物的结构，荧光性质和电化学行为．Ｅｕ（３＋）的配合物是由ＥｕＣｌ３溶于具有不同摩尔质量的ＰＥＧ而成的．它们在３９４ｎｍ和６１４ｎｍ处分别有很强的激发和发射光谱峰，并且这两峰的强度随着ＰＥＧ的摩尔质量的增大而加强．Ｅｕ（２＋）的配合物是通过用涂布有氧化铟及氧化锡的玻璃板作为工作电极，在氮气气氛下，加－２Ｖ（ｖｓＡｇ）电压还原ＥｕＣｌ３的ＰＥＧ溶液来制备的．它们的荧光性质和１８—Ｃ—６冠醚与Ｅｕ（２＋）所形成配合物的性质非常接近，从而表明ＰＥＧ的化学环境与大环聚醚配体的很相似．进一步的红外与荧光谱实验结果表明：铕离子不但与聚乙二醇的末端－ＯＨ基团结合，而且亦能与链中间的氧原子作用．随着聚合物分子量的增大，铕离子的点对称性不断下降．Ｅｕ（３＋）在聚合物中的氧化还原很不可逆．添加支持盐对其电化学行为有很大影响．     

Direct reaction of iodine-activated lanthanoid metals with 2,6-diisopropylphenol

Rare earth metals activated with ca. 2% iodine react directly with 2,6-diisopropylphenol (HOdip) in tetrahydrofuran (thf), 1,2-dimethoxyethane (dme), and dig-dme (dig = di(2-methoxyethyl) ether) to give solvated phenolate complexes [Ln(Odip)(3)(thf)(n)] (Ln = La, Nd, n = 3; Ln = Sm, Dy, Y, Yb, n = 2), [Eu(Odip)(μ-Odip)(thf)(2)](2), [Ln(Odip)(3)(dme)(2)] (Ln = La, Yb) and [La(Odip)(3)(dig)] in good yield for Ln = La, Nd, Eu but modest yield for smaller Ln metals under comparable conditions. However, increasing the excess of metal greatly increased the yield for Ln = Y. The synthetic method has general potential, at least for lanthanoid phenolates. Comparison redox transmetallation/protolysis (RTP) reactions between Ln metals, Hg(C(6)F(5))(2) and the phenol gave higher yields in shorter time and, for Eu, gave [Eu(Odip)(3)(thf)(3)] in contrast to an Eu(II) complex from Eu(I(2)). New [Ln(Odip)(3)(thf)(3)] complexes have fac-octahedral structures and [Ln(Odip)(3)(thf)(2)] monomeric five coordinate distorted trigonal bipyramidal structures with apical thf ligands. [Eu(Odip)(μ-Odip)(thf)(2)](2) is an unsymmetrical dimer with two bridging Odip ligands. One five coordinate Eu atom has distorted trigonal bipyramidal stereochemistry and the other is distorted square pyramidal. Whilst [La(Odip)(3)(dme)(2)] has irregular seven coordination with mer-Odip and chelating dme ligands, [Ln(Odip)(3)(dme)(2)] (Ln = Dy, Y (prepared by ligand exchange), Yb) are monomeric six coordinate with one chelating and one unidentate dme. A six coordinate fac-octahedral arrangement is observed in [La(Odip)(3)(dig)].     

Structure and emission spectra of dinuclear lanthanide(III) β-diketonate complexes with a bridging 2,2′-bipyrimidine ligand

The 2,2′-bipyrimidine (bpm) adducts of the β-diketonate complexes of Eu(III), Sm(III), or Yb(III) with 2,2′,6,6′-tetramethyl-2,4-heptanedione (tmhd) resulted in the formation of dinuclear species. The synthesis and X-ray structure of these three new dinuclear lanthanide complexes are found to be similar. Each lanthanide ion is eight coordinate, bound to six O-atoms from the β-diketonates and 2N atoms from the bridging bpm ligand. They exhibit Ln–Ln distances (Sm(III): 6.935 Å, Eu(III): 6.901 Å, Yb(III): 6.679 Å) and Ln–ligand distances that are consistent with the decrease in radii across the lanthanide series. Absorption spectra of the complexes are dominated by ligand absorptions. Both the solution and solid state emission spectra of the complexes resemble ordinary monomeric lanthanide species, indicating independent ions in the dinuclear species. Cyclic voltammetry of all the complexes appear almost identical with discernable ligand centered redox reactions. The complex with Eu(III) ions, having the lowest possible lanthanide redox potential, was not found to display a signal corresponding to metal reduction.     

Unsteady-state direct partial oxidation of methane to synthesis gas in a fixed-bed reactor using AFeO3 (A = La, Nd, Eu) perovskite-type oxides as oxygen storage

Direct partial oxidation of methane to synthesis gas on AFeO(3) (A = La, Nd, Eu) oxides by a novel sequential redox cyclic reaction in the absence of gaseous oxygen was investigated over a fixed-bed reactor. These oxides were prepared by the sol-gel method and characterized by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) techniques. XRD analysis showed that all AFeO(3) (A = La, Nd, Eu) oxides, calcined at 1173 K, are single-phase perovskites. The CH(4)-TPSR/MS and continuous reaction experiments indicated that the AFeO(3) (A = La, Nd, Eu) oxides provide mostly oxygen species, as the sole oxidant originated from lattice oxygen instead of gaseous oxygen, which can oxidize CH(4) to synthesis gas with high selectivity in the absence of gaseous oxygen. In terms of material economics and the amount of oxygen species for synthesis gas formation, the LaFeO(3) sample exhibits the best performance among these tested AFeO(3) oxides for synthesis gas production. The pulse experiments at different temperatures showed that the rate of oxygen migration during the CH(4) reaction with LaFeO(3) is strongly affected by the reaction temperature, and increases with rising temperature, which is favorable to much more CH(4) selective oxidation at high temperature. The two types of oxygen species are identified by experiments of continuous reactions and pulses, and confirmed by XPS. Methane can be converted selectively to synthesis gas by consumption of lattice oxygen, and general carbonaceous deposits on the catalyst surface do not occur under the appropriate reaction conditions by sequential redox cycles. The performance of selective oxidation of CH(4) to synthesis gas can be recovered by reoxidation using gaseous molecular oxygen; the LaFeO(3) oxide maintains relatively high catalytic activity and structural stability in redox atmospheres.     

含铕硅钼钨多金属氧酸盐水溶液的电化学性质

采用循环伏安法,研究双-Keggin型含铕硅钼钨多金属氧酸盐(Eu(SiMo4W7)213-)水溶液的电化学性质,结果表明,在0.7~-0.45V的电位区间内,Eu(SiMo4W7)213-呈现了两对准可逆的单电子氧化还原峰,峰电位随着溶液pH值的升高而线性负移,催化活性实验显示,在酸性溶液中该化合物对NaNO2和H2O2的还原反应具有良好的催化作用.     

La3＋或Eu3＋与微过氧化物酶-8相互作用强弱的研究

研究了La3＋或Eu3＋与微过氧化酶-8(MP-8)相互作用并比较了它们与MP-8相互作用的强弱. 紫外-可见(UV-Vis)吸收光谱和电化学的结果表明, 不论在不含NaCl或含NaCl的溶液中,一个La3＋或Eu3＋优先与MP-8分子中血红素上两个丙酸基中的羧基氧发生强的键合作用,而过量的La3＋或Eu3＋与肽链上的羰基氧发生弱的相互作用.实验结果还清楚地证明Eu3＋与MP-8的相互作用要强于La3＋与MP-8的相互作用.     

Sorption of Sr(II) and Eu(III) onto pyrite under different redox potential conditions

Understanding sorption processes is fundamental for the prediction of radionuclide migration in the surroundings of a deep geological disposal of high-level nuclear wastes. Pyrite (FeS2) is a mineral phase often present as inclusions in temperate soils. Moreover, it constitutes an indirect corrosion product of steel, a containment material that is candidate to confine radionuclides in deep geological disposals. The present study was thus initiated to determine the capacity of pyrite to immobilize Sr(II) and Eu(III). An air oxidized pyrite and a freshly acid-washed (non-oxidized) pyrite were used in background electrolytes of varying reducing-oxidizing ability (NaCl, NH3OHCl, and NaClO4) to study the sorption of both cationic species. The sorptive capacity of pyrite appeared directly correlated to the oxidation of the surface. Non-oxidized pyrite had nearly no affinity for the studied cations whereas Sr(II) and Eu(III) species were significantly retained by oxidized pyrite surface. Using the surface complexation theory, sorption mechanisms were modeled with the Fiteql v3.2 and the Jchess 2.0 codes. Sorption of both Sr and Eu was well fitted, assuming hydroxylated species as the major surface species. This study demonstrates that not only the components of a barrier but also the redox conditions and specifications should be well characterized to predict transport of contaminants in the surrounding of a nuclear wastes disposal.