Redox reactions in molten electrolytes containing chlorides of rare-earth metals

Solutions of rare-earth metals (REM, Ln) in molten chlorides, including mixtures MCl + LnCl₃, where M stands for an alkali metal, are studied by methods of potentiometry, voltammetry, and conductimetry in broad intervals of concentration and temperature. The results that had been obtained give sufficiently comprehensive and reliable enough information concerning the valence state of rare-earth metals, as well as the structure and composition of complex ions that make a substantial impact on the properties of electrolytes. It is demonstrated that the co-existence of ions of rare-earth metals in different oxidation states, which form as a result of possible redox reactions 2Ln³⁺ + Ln ? 3Ln²⁺, Ln²⁺ + Ln ? 2Ln⁺, and nM⁺ + Ln ? nM + Lnⁿ⁺, clearly manifests itself in the thermodynamic and transport properties of molten systems Ln-LnCl₃ and Ln-LnCl₃-MCl.     

Syntheses,characterization and thermal properties of lanthanide complexes with 2-mercaptonicotinic acid

Fourteen new complexes with the general formula of Ln(Hmna)₃·nH₂O (n=2 for Ln=La-Ho and n=1 for Er-Lu, H₂mna=2-mercaptonicotinic acid) were synthesized and characterized by elemental analyses, IR spectra and thermogravimetric analyses. In addition, molar specific heat capacities were determined by a microcalorimeter at 298.15 K. The IR spectra of the prepared complexes revealed that carboxyl groups of the ligands coordinated with Ln(III) ions in bidentate chelating mode. Hydrated complexes lost water molecules during heating in one step and then the anhydrous complexes decomposed directly to oxides Ln₂O₃, CeO₂, Pr₆O₁₁ and Tb₄O₇. The values of molar specific heat capacities for fourteen solid complexes were plotted against the atomic numbers of lanthanide, which presented as ‘tripartite effect’. It suggested a certain amount of covalent character existed in the bond of Ln³⁺ and ligands, according with nephelauxetic effect of 4f electrons of rare earth ions.     

Self-Assembly of Isopolyanion Clusters and Lanthanide-Organic Units into 2D Layers: (NH4)2{[Ln2(C7H4NO4)2(H2O)9][(H2W12O40)]}·nH2O (Ln?=?Gd, Tb, Ho)

Three novel 1:2 composite compounds prepared with the isopolyanions and lanthanide-organic units, (NH₄)₂{[Ln₂(HL)₂(H₂O)₉][(H₂W₁₂O₄₀)]}·nH₂O (Ln = Gd³⁺ (1), Tb³⁺ (2), n = 15; Ho³⁺ (3), n = 10; L = pyridine-3,5-dicarboxylate) were synthesized at room temperature and characterized by routine methods. X-ray structural analysis reveals that these structures are isomorphic: two crystallographically independent Ln³⁺ ions (Ln1 and Ln2) locate in different coordination environments; two ligands plays dissimilar coordination mode; the isopolyanion cluster acts as a tridentate ligand and connects three Ln³⁺ ions (Ln1, Ln1′ and Ln2) forming an unusual 2D undee-layer. The room temperature luminescent of 2 has been studied and exhibits a Tb³⁺ characteristic emission in the range of 450–650 nm.     

Synthesis and Characteristics of Self-Assembled Multifunctional Ln3+-DNA Hybrid Coordination Polymers

Owing to the unique catalytic, optical and magnetic properties, lanthanides (Ln) as multicomponent biomarkers, are widely used in the field of optical sensing, mass spectrometry and magnetic resonance imaging. As ligands, DNA molecules have good biocompatibility, high stability, cost efficiency, programmability and biodegradability. Based on the coordination-driven self-assembly between Ln ions (Ln³⁺) and DNA molecules, a multifunctional Ln³⁺-DNA hybrid coordination polymers (CPs) were synthesized. Not only a series of different Ln³⁺ (single Ln³⁺) and DNA hybrid CPs were synthesized, but one hybrid CP contains two kinds of Ln³⁺ was obtained. Besides, the synthetic CPs in cell fluorescence imaging and miRNA sensing also exhibited high performance. This work provides a novel idea for the synthesis of DNA based nanomaterials, which is promising for biologically-related applications.     

Rare-earth cobalticyanides LnCo(CN)6·nH2O

Crystalline cobalticyanides LnCo^III(CN)₆·nH₂O with Ln = La,…, Lu, Y have been synthesized by a double-infusion technique. In analogy to the Cr and Fe compounds, the large rare-earth ions form a hexagonal modification while the smaller ions lead to the orthorhombic structure with 4H₂O. Experiments show that no magnetic ordering occurs down to 1°K. The Stark splitting of the J ground state due to the crystalline field is analyzed for the Ce and Sm compounds.     

Syntheses,characterization and thermal properties of the lanthanide complexes with 2-mercaptonicotinic acid and 1,10-phenanthroline

Fourteen new complexes with the general formula of Ln(Hmna)₃(phen) (H₂mna = 2-mercaptonicotinic acid and phen = 1,10-phenanthroline) were synthesized and characterized by elemental analyses, IR spectra and thermogravimetric analyses. In addition, molar specific heat capacities were determined by a microcalorimeter at 298.15 K. The IR spectra of the complexes showed that the Ln³⁺ coordinated with the oxygen atoms of H₂mna and the nitrogen atoms of phen. The complexes decomposed directly to oxides Ln₂O₃, CeO₂, Pr₆O₁₁, and Tb₄O₇ in one step. The values of molar specific heat capacities for fourteen solid complexes were plotted against the atomic numbers of lanthanide, which presented as “tripartite effect”. It suggested a certain amount of covalent character existed in the bond of Ln³⁺ and ligands, according with nephelauxetic effect of 4f electrons of rare earth ions. The article is published in the original.     

Synthesis and luminescence properties of the Pr(III), Sm(III), Eu(III), Nd(III), and Yb(III) complexes with propane-1,3-dione derivatives

The luminescence method, mass spectrometry, and elemental analysis are used to reveal that under optimal conditions (pH 5–8) Ln³⁺ ions (Ln = Pr, Sm, Eu, Nd, and Yb) with 1-(2-hydroxy-4-methylphenyl)-3-(5-methyl-1-phenyl-¹ H-1,2,3-triazol-4-yl)propane-1,3-dione form complexes with the mole ratio Ln: ligand = 2: 3. According to the IR spectral data, Ln³⁺ ions coordinate three oxygen atoms of two carbonyl groups and one hydroxyl group. In the IR spectra of the complexes, an intense band at 628.7 cm^?1 is assigned to the Ln-O bond vibrations. The X-ray diffraction patterns of the complexes contain no lines corresponding to the ligand. The luminescence intensity of the complexes in the visible spectral range changes in the series Eu(III) > Sm(III) > Pr(III), whereas in the IR region the order is Yb(III) > Nd(III). In all cases, luminescence of the solid complexes is considerably more intense than that of their solutions.     

Rare-Earth Chloromethanephosphonates

Addition of KOH to aqueous solutions containing in a 3 : 1 molar ratio chloromethanephos-phonic acid (H₂L), rare-earth ions (Ln^{3 +}) results in crystallization of LnHL₂ (Ln = La-Er, Y) andKLn₃H₆L₈ (Ln = Yb, Lu). According to powder diffraction patterns, all the compounds within the LnHL₂ andKLn₃H₆L₈ groups are isostructural. Thulium forms a mixture of these two compounds. The solubility, IR spectra, and thermal stability of the products were studied.     

Application of rotate-bomb calorimeter for determining the standard molar enthalpy of formation of Ln(Pdc)3(Phen)

Thirteen solid ternary complexes Ln(Pdc)₃(Phen) (Ln = La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu;) have been synthesized in absolute ethanol by rare-earth element chloride low hydrate reacting with the mixed ligands of ammonium pyrrolidinedithiocarbamate (APdc) and 1,10-phenanthroline · H₂O (o-Phen · H₂O) in the ordinary laboratory atmosphere without any cautions against moisture or air sensitivity. IR spectra of the complexes showed that the Ln³⁺ ion was coordinated with six sulfur atoms of three Pdc⁻ and two nitrogen atoms of o-Phen · H₂O. It was assumed that the coordination number of Ln³⁺ is eight. The constant-volume combustion energies of the complexes, Δ_c U, were determined by a precise rotate-bomb calorimeter at 298.15 K. Their standard molar enthalpies of combustion, Δ_c H _m ^o , and standard molar enthalpies of formation, Δ_f H _m ^o were calculated. The text was submitted by the authors in English.     

New solid electrolytes of the pyrochlore family

The class of oxygen-ion-conducting rare-earth pyrochlores has been considerably extended. New solid electrolytes, Ln₂Ti₂O₇ (Ln = Dy-Lu) and Ln₂Hf₂O₇ (Ln = Eu, Gd) pyrochlores, are intrinsic ionic conductors at elevated temperatures, as are the well known Ln₂Zr₂O₇ (Ln = Sm-Gd) zirconates, which suggests that oxygen ion conduction in the rare-earth pyrochlore family has a general character. The thermodynamic order-disorder transitions that yield a PII cation- and anion-disordered pyrochlore phase possessing high oxygen ion conductivity occur throughout the rare-earth pyrochlore family: Ln₂M₂O₇ (Ln = Sm-Lu; M = Ti, Zr, Hf). The composition-structure-oxygen-ionic conductivity relationship is analyzed for Ln₂(M_{2 − x} Ln _x )O_{7 − δ} (Ln = Sm-Lu; M = Ti, Zr, Hf) with x from 0 to 0.81.     

Three organic–inorganic hybrid B-Anderson polyoxoanions as building blocks: syntheses,structures, and characterization of [(C6H5NO2)2Ln(H2O)6](CrMo6O24H6)·2C6H5NO2·6H2O (Ln = Sm,Dy, Er)

Three new B-Anderson type polyoxometalates, [(C₆H₅NO₂)₂Ln(H₂O)₆](CrMo₆O₂₄H₆)·2C₆H₅NO₂·6H₂O (Ln?=?Sm 1, Dy 2 and Er 3), have been synthesized in aqueous solution and structurally characterized by single-crystal X-ray diffraction, IR spectra, UV spectroscopy, and fluorescence spectroscopy. Crystal structure analysis reveals that these three compounds have the same composition and are isostructural, assembled by B-Anderson type polyoxoanion [CrMo₆O₂₄H₆]^3?, rare-earth ions, and ligands. UV spectroscopy shows that 1 is stable when pH is 4.50–5.83. The fluorescence spectra of 2 indicate that both rare-earth ions Dy³⁺ and pyridine-4-carboxylic acid ligands function in the charge transition of the compound.     

Mono and trinuclear lanthanide complexes of 13-membered tetraaza macrocycle: Synthesis and characterization

The reaction of 1,8-diamino-3,6-diazaoctane and diethyl malonate in dry methanol yielded a 13-membered macrocycle. Complexes of the type [Ln(tatd)Cl₂ (H₂O)₃]Cl [Ln^III=La, Pr, Nd, Sm, Eu, Gd, Tb, Dy; tatd=1, 5, 8, 11-tetra-azacyclotridecane-2,4-dione] have been synthesized by template condensation. The complex [La(tatd)Cl₂ (H₂O)₃]Cl in methanol was reacted with lanthanide chlorides to yield the trinuclear complexes of type [2{La(tatd)Cl₂(H₂O)₃}LnCl₃]Cl₂ [Ln^III=La, Pr, Nd, Sm, Eu, Gd, Tb, Dy]. The chemical compositions of mono and trinuclear complexes have been established on the basis of analytical, molar conductance, electrospray (ES) and fast atom bombardment (FAB) mass data. In mononuclear complexes the Ln³⁺ ion is encapsulated by four ring nitrogens and in trimetallic complexes the exo-carbonyl oxygens of two mononuclear units coordinate to the Ln³⁺ ions resulting in a polyhedron around the lanthanide ions. Thus the macrocycle is bonded in a tetradentate fashion in the former complexes and hexadentate in the latter. The coordination number nine around the encapsulated Ln³⁺ and seven around the exo-oxygen bonded Ln³⁺ ions are established. The symmetry of the ligand field around the metal ions is indicated from the emission spectra.     

Quenching of electronically excited Ln3+* ions by C60 fullerene

Quenching of electronically excited states of Ln^3+* ions generated upon photoexcitation of toluene solutions of Ln(acac)₃·H₂O (Ln = Tb, Eu) complexes by C₆₀ fullerene at 293 K was detected and investigated. The dependences of quenching efficiency on C₆₀ concentration obtained from data on the decrease in the photoluminescence intensity and Ln^3+* lifetimes obey the Stern-Volmer law. Quenching is due to inductive-resonant energy transfer from Ln^3+* to C₆₀ fullerene. The bimolecular rate constants for quenching, the overlap integrals of the Ln^3+* photoluminescence spectra with the C₆₀ absorption spectra, and the critical energy transfer distances were determined. No sensitized luminescence of C₆₀ in the system studied was detected. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 921–925, June, 2006.     

Target-responsive DNAzyme hydrogel for portable colorimetric detection of lanthanide(III) ions

Lanthanide elements (Ln) play an important role in industry and agriculture. As a result of the increasing consumption of lanthanides, environmental emission of Ln has become detrimental to the health of flora and fauna. Current methods for trace lanthanides detection mainly rely on sophisticated instruments. In this article, a Ln³⁺ dependent DNAzyme was incorporated into a hydrogel to generate Ln³⁺ sensitive DNAzyme hydrogel for portable colorimetric detection. The enzyme strand and its substrate strand act as crosslinker and functional unit of the hydrogel with polyacrylamide chains as the scaffold and gold nanoparticles (AuNPs) as the indicator of hydrogel stability. Any ions in the Ln³⁺ series can trigger the cleavage of substrate strand by activating the enzyme strand, thereby decreasing the crosslink ratio and leading to collapse of the hydrogel. The release of the encapsulated AuNPs turns the supernatant wine red. Using this colorimetric method, Ln³⁺ can be detected with high sensitivity, with a limit of detection (LOD) of 20 nM for Ce³⁺. The hydrogel responds specifically to any Ln³⁺ ion and works well with the spiked lake sample without the need of instruments and skilled operators. Our results suggest that the lanthanide responsive hydrogel can be used for portable and sensitive detection of Ln³⁺ contamination in the field.     

Analysis of pair heterovalent substitutions in scheelite-type molybdates and tungstates

An analysis of the formation of solid solutions in MAO₄-(Me_0.5Ln_0.5)AO₄ systems, where Me = Li, Na, K; M = Ca, Sr, Ba, Pb, Cd; Ln = La-Gd, Y, Bi; A = Mo, W, is performed in the approximation of regular solutions. Equations that make it possible to determine the temperature of the transition of limited solid solutions to unlimited ones at heterovalent substitutions M²⁺ ↔ (Me_0.5⁺Ln_0.5³⁺) are obtained.     

Synthesis,structure and luminescence properties of two novel lanthanide complexes with 2-fluorobenzoic acid and 1,10-phenanthroline

Two lanthanide complexes with 2-fluorobenzoate (2-FBA) and 1,10-phenanthroline (phen) were synthesized and characterized by X-ray diffraction. The structure of each complex contains two non-equivalent binuclear molecules, [Ln(2-FBA)₃?·?phen?·?CH₃CH₂OH]₂ and [Ln(2-FBA)₃?·?phen]₂ (Ln?=?Eu (1) and Sm (2)). In [Ln(2-FBA)₃?·?phen?·?CH₃CH₂OH]₂, the Ln³⁺ is surrounded by eight atoms, five O atoms from five 2-FBA groups, one O atom from ethanol and two N atoms from phen ligand; 2-FBA groups coordinate Ln³⁺ with monodentate and bridging coordination modes. The polyhedron around Ln³⁺ is a distorted square-antiprism. In [Ln(2-FBA)₃?·?phen]₂, the Ln³⁺ is coordinated by nine atoms, seven O atoms from five 2-FBA groups and two N atoms of phen ligand; 2-FBA groups coordinate Ln³⁺ ion with chelating, bridging and chelating-bridging three coordination modes. The polyhedron around Ln³⁺ ion is a distorted, monocapped square-antiprism. The europium complex exhibits strong red fluorescence from ⁵D₀?→?⁷F _j ( j?=?1–4) transition emission of Eu³⁺.     

Four‐Shell Polyoxometalates Featuring High‐Nuclearity Ln26 Clusters: Structural Transformations of Nanoclusters into Frameworks Triggered by Transition‐Metal Ions

A series of polyoxometalates (POMs) that incorporate the highest‐nuclearity Ln clusters that have been observed in such structures to date (Ln₂₆ , Ln=La and Ce) are described, which exhibit giant multishell configurations (Ln⊂W₆⊂Ln₂₆⊂W₁₀₀). Their structures are remarkably different from known giant POMs that feature multiple Ln ions. In particular, the incorporated Ln–O clusters with a nuclearity of 26 are significantly larger than known high‐nuclearity (≤10) Ln–O clusters in POM chemistry. Furthermore, they also contain the largest number of La and Ce centers for any POM reported to date and represent a new kind of rare giant POMs with more than 100 W atoms. Interestingly, the La₂₆‐containing POM can undergo a single‐crystal to single‐crystal structural transformation in the presence of various transition‐metal ions, such as Cu²⁺, Co²⁺, and Ni²⁺, from an inorganic molecular nanocluster into an inorganic–organic hybrid extended framework that is built from POM building blocks with even higher‐nuclearity La₂₈ clusters bridged by transition‐metal complexes.     

Magnetic properties of the semiconducting lanthanide cuprates Ln2CuO4 and their interpretation: Evidence for a new series of planar copper antiferromagnets

The magnetic susceptibility of the semiconducting lanthanide cuprates Nd₂CuO₄, Pr₂CuO₄, Eu₂CuO₄, and Sm₂CuO₄ has been measured in the range 4–300 K. Below 300 K, the Cu²⁺ ions are ordered antiferromagnetically in the CuO₂ planes of these compounds, and the exchange interactions involving the Ln³⁺ ions are relatively weak. The suceptibility of the Ln³⁺ ions obeys the Curie-Weiss law at elevated temperatures, but deviations from this law occur at lower temperatures. An attempt is made to account for these deviations by fitting theoretical expressions for the susceptibility of isolated Ln³⁺ ions under the influence of a cubic crystal field to the experimental data. Excellent agreement is obtained for Nd³⁺ and Eu³⁺ over the entire temperature range and for Pr³⁺ and Sm³⁺ at elevated temperatures. Deviations at lower temperatures for the latter two ions may be due to structural changes, exchange interactions involving the Ln³⁺ ions, or possibly oxygen nonstoichiometry. The susceptibility parameters derived by fitting the theoretical expressions to the experimental data are also discussed. It is concluded that these compounds form an interesting new series of planar Cu²⁺-ion antiferromagnets.     

Synthesis of New LnxBi2–xSe3 (Ln: Sm3+, Eu3+, Gd3+, Tb3+) Nanomaterials and Investigation of Their Optical Properties

New Ln_xBi_2–xSe₃ (Ln: Sm³⁺, Eu³⁺, Gd³⁺, Tb³⁺) based nanomaterials were synthesized by a co‐reduction method. Powder XRD patterns indicate that the Ln_xBi_2–xSe₃ crystals (Ln = Sm³⁺, Eu³⁺, x = 0.00–0.44 and Ln = Gd³⁺, Tb³⁺, x = 0.00–0.50) are isostructural with Bi₂Se₃. The cell parameter c decreases for Ln = Eu³⁺, Gd³⁺, Tb³⁺ upon increasing the dopant content (x), while a slightly increases. Changes in lattice parameters could be related to the radii of cations. SEM images show that doping of the lanthanide ions in the lattice of Bi₂Se₃ generally results in nanoflowers. For the terbium compound two kinds of morphologies (nanoflowers and nanobelts) were observed. UV/Vis absorption and emission spectroscopy reveals mainly electronic transitions of the Ln³⁺ ions. Emission spectra show intense transitions from the excited to the ground state of Ln³⁺ and energy transfer from the Bi₂Se₃ lattice. Emission spectra of europium‐doped materials, in addition to the characteristic red emission peaks of Eu³⁺, show an intense blue emission band centered at 432 nm, originating from the 4f⁶5d¹ to 4f⁷ configuration in Eu²⁺. EPR measurements confirm the existence of Eu²⁺ in the materials. Interestingly, for all samples starting at low Ln³⁺ concentration, the emission intensity rises to a maximum at a Ln³⁺ concentration of x = 0.2 and falls again steadily to a minimum at x = 0.45.     

Magnetic specific heat and spin-glass-like ordering in the pyrochlores: RE2Mo2O7 (RE=Y,Sm, Gd,Ho)

The pyrochlores RE₂Mo₂O₇ (RE=Y, Sm, Gd, Ho) display, with the exception of Ho₂Mo₂O₇, magnetic transitions at 18 K, 68 K, 55 K, respectively. No long-range order occurs. The rare-earth atoms remain in the paramagnetic state down to 1.5 K. The magnetic specific heat behaviour is explained by spin-glass-like ordering of Mo⁴⁺ ions, imposing a molecular field of random character on the rare-earth ions, and by crystalline field-splitting effects.