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.     

Visual Detection of Triethylamine and a Dual Input/Output Logic Gate Based on a Eu3+-Complex

A series of Ln³⁺-metal centered complexes, Ln(TTA)₃(DPPI) (Ln = La, 1; Ln = Eu, 2; Ln = Tb, 3; or Ln = Gd, 4) [(DPPI = N-(4-(1H-imidazo [4,5-f][1,10]phenanthrolin-2-yl)phenyl)-N-phenylbenzenamine) and (TTA = 2-Thenoyltrifluoroacetone)] have been synthesized and characterized. Among which, the Eu³⁺-complex shows efficient purity red luminescence in dimethylsulfoxide (DMSO) solution, with a Commission International De L’ Eclairage (CIE) coordinate at x = 0.638, y = 0.323 and Φ_Eu^L = 38.9%. Interestingly, increasing the amounts of triethylamine (TEA) in the solution regulates the energy transfer between the ligand and the Eu³⁺-metal center, which further leads to the luminescence color changing from red to white, and then bluish-green depending on the different excitation wavelengths. Based on this, we have designed the IMPLICATION logic gate for TEA recognition by applying the amounts of TEA and the excitation wavelengths as the dual input signal, which makes this Eu³⁺-complex a promising candidate for TEA-sensing optical sensors.     

Facile sonochemical synthesis and photoluminescent properties of lanthanide orthophosphate nanoparticles

Uniform lanthanide orthophosphate LnPO₄ (Ln=La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho) nanoparticles have been systematically synthesized via a facile, fast, efficient ultrasonic irradiation of inorganic salt aqueous solution under ambient conditions without any surfactant or template. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), photoluminescence (PL) spectra as well as kinetic decays were employed to characterize the samples. The SEM and the TEM images show that the hexagonal structured lanthanide orthophosphate LnPO₄ (Ln=La, Ce, Pr, Nd, Sm, Eu, Gd) products have nanorod bundles morphology, while the tetragonal LnPO₄ (Ln=Tb, Dy, Ho) samples prepared under the same experimental conditions are composed of nanoparticles. HRTEM micrographs and SAED results prove that these nanostructures are polycrystalline in nature. The possible formation mechanism for LnPO₄ (Ln=La-Gd) nanorod bundles is proposed. Eu³⁺-doped LaPO₄ and Tb³⁺-doped CePO₄ samples were also prepared by using the same synthetic process, which exhibit an orange-red (Eu³⁺:⁵D₀-⁷F_{1, 2, 3, 4}) and green (Tb³⁺, ⁵D₄-⁷F_{3, 4, 5, 6}) emission, respectively.     

Potentiometric Study of Lanthanide Salicylaldimine Schiff Base Complexes

Formation of complexes between the lanthanide ions and N,N′-bis(salicylidene)-4-methyl-1,3-phenylenediamine ligand was studied in solution by pH potentiometry. The potentiometric titration was performed at 25.00 °C in 0.1 mol·dm^?3 NaClO₄ ionic strength and in DMSO:water (30:70 v:v) solvent mixture. N,N′-bis(salicylidene)-4-methyl-1,3-phenylenediamine ligand (H₂L) occurs in three forms: fully or partially deprotonated and unionized. Computer analysis of potentiometric data indicated that in solution the lanthanide (Ln) complexes exist as LnL₂, Ln(HL)₂ and Ln(H₂L)₂ species. This observation appears to be in contrast to the solid-state behavior of these complexes prepared in a self-assembly process and structurally defined. Stability constants for La³⁺, Eu³⁺, Gd³⁺, Tb³⁺, Ho³⁺ and Lu³⁺ (Ln³⁺) complexes were determined. The order of stabilities of LnL₂ species in terms of metal ions is La³⁺ > Eu³⁺ ≈ Gd³⁺ = Tb³⁺ < Ho³⁺ < Lu³⁺ with a prominent “gadolinium break”.     

Les phases SrLnMnO4 (Ln = La,Nd, Sm,Gd), BaLnMnO4 (Ln = La,Nd) et M1+xLa1−xMnO4 (M = Sr,Ba)

The phases SrLnMnO₄ (Ln = La, Nd, Sm, Gd), BaLnMnO₄ (Ln = La, Nd) and the solid solutions M_1+xLa_1?xMnO₄ (M = Sr: 0 ? x ? 1; M = Ba: 0 ? x ? 0.50) have a K₂NiF₄-type structure. The $\text{c}\text{a}$ ratio of the unit cell is related to the electronic configuration of the Mn³⁺ ions.     

Intermolecular dynamics and paramagnetic properties of ethylenediaminetetraacetate complexes with the yttrium subgroup rare earth elements using nuclear magnetic resonance

¹H nuclear magnetic resonance (NMR) measurements are reported for the D₂O solutions of [Ln³⁺(EDTA^4?)]^? complexes, where EDTA^4? is ethylenediaminetetraacetate anion, Ln³⁺ = Tb³⁺ (I), Ho³⁺ (II), Tm³⁺ (III), Yb³⁺ (IV) and Lu³⁺ (V). Temperature dependencies of the ¹H NMR spectra of paramagnetic I–IV have been analyzed using the dynamic NMR methods. It is found that the activation free energies (ΔG^?₂₉₈ ) of the intermolecular EDTA ions exchange at [Ln³⁺(EDTA^4?)]^? complexes are 60±3 (I), 66±3 (II), 69±3 (III) and 74±3 (IV) kJ/mol (at pD = 7). A monotonic increase of the free energy of chemical exchange processes along the series of lanthanide [Ln³⁺ (EDTA^4?)]^? complexes is probably related to the lanthanide contraction. The obtained results indicate that coordination compounds I–IV may be considered as thermometric NMR sensors and lanthanide paramagnetic probes for in situ temperature control in solution. Copyright © 2012 John Wiley & Sons, Ltd.     

Multiband orange-red photoluminescence of Eu ions in new “114” LnBaZn3GaO7 and LnBaZn3AlO7 oxides

A new series of gallozincates LnBaZn₃GaO₇ (Ln=La, Nd, Sm, Eu, Gd, Dy, Y) and new aluminozincates LnBaZn₃AlO₇ (Ln=Y, Eu, Dy) have been synthesized. Their structure refinements show that these phases belong to the “114” series, with hexagonal P6₃mc space group previously described for SmBaZn₃AlO₇. The photoluminescence study of these oxides shows that the Eu³⁺ activated LnBaZn₃MO₇ oxides with Ln=Y, La, Gd; and M=Al, Ga exhibit strong magnetic and electric dipole transitions (multiband emission) which is of interest for white light production. These results also confirm that the site occupied by Eu³⁺ is not strictly centrosymmetric. The electric dipole transition intensity is the highest in GdBaZn₃MO₇ [M=Al, Ga]: 0.05Eu³⁺ as compared with other Eu³⁺ activated compositions. This is due to the layer distortion around GdO₆ octahedra when compared with YO₆ and LaO₆ octahedra.     

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⁺.     

Nanosized thermometric NMR sensors based on the paramagnetic complex ion pairs of lanthanides(III) for temperature determinations in low-polar nonaqueous solutions

For temperature determination in solutions it is suggested that the temperature dependence of the paramagnetic lanthanide-induced shifts (LIS) in the NMR spectra on the ligand nuclei be used for [Ln(PTA)₂(18-crown-6)]⁺[Ln(PTA)₄]^? complex ion pairs formed in CCl₄, CDCl₃, CD₂Cl₂, CD₃C₆D₅, and C₂D₃N type low-polar solvents (Ln = La, Ce, Pr, Nd, Eu; PTA is the pivalyltrifluoroacetonato anion). It was found experimentally that the [Ln(PTA)₂(18-crown-6)]⁺ complex cation molecules (Ln = Ce and Pr) proved most suitable for use as nanosized (≈1.1 nm) probes for temperature determinations in nonaqueous solutions. A linear dependence of the LIS on the ¹H nuclei of different groups and the difference between the LIS corresponding to the CH₂ groups of the 18-crown-6 molecules and the CH groups of the PTA anions on the reciprocal temperature (1/T) was found. The LIS of the individual signals of different groups in Ln paramagnetic complexes (relative to the signals of the diamagnetic analogs, e.g., La or Lu) may be used for temperature control in the sample, although the temperature measurement error is smaller (≤ 0.04 K) when the difference between the LIS of the CH₂ and CH groups is used. Due to the high thermodynamic and kinetic stability combined with small sizes of [Ln(PTA)₂(18-crown-6)]⁺[Ln(PTA)₄]^? molecules in nonaqueous solutions, these compounds may be used as thermometric NMR sensors directly in reaction media for in situ control over temperature.     

Intermolecular nuclear relaxation in paramagnetic solutions: from free radicals to rare earths

The principles of the intermolecular relaxation of a nuclear spin by its fluctuating magnetic dipolar interactions with the electronic spins of the paramagnetic surrounding species in solution are briefly recalled. It is shown that a very high dynamic nuclear polarization (DNP) of solvent protons is obtained by saturating allowed transitions of free radicals with a hyperfine structure, and that this effect can be used in efficient Earth field magnetometers. Recent work on trivalent lanthanide Ln³⁺ aqua complexes in heavy water solutions is discussed, including paramagnetic shift and relaxation rate measurements of the ¹H NMR lines of probe solutes. This allows a determination of the effective electronic magnetic moments of the various Ln³⁺ ions in these complexes, and an estimation of their longitudinal and transverse electronic relaxation times T_1e and T_2e. Particular attention is given to Gd(III) hydrated chelates which can serve as contrast agents in magnetic resonance imaging (MRI). The full experimental electronic paramagnetic resonance (EPR) spectra of these complexes can be interpreted within the Redfield relaxation theory. Monte-Carlo simulations are used to explore situations beyond the validity of the Redfield approximation. For each Gd(III) complex, the EPR study leads to an accurate prediction of T_1e, which can be also derived from an independent relaxation dispersion study of the protons of the probe solutes.     

Schiff base derivatives of lanthanons

Bifunctional tridentate Schiff bases such as, $$\begin{gathered} HOC_6 H_4 C(CH_3 ) : NCH_2 CH_2 OH, \hfill \\ HOC_6 H_4 C(CH_3 ) : NCH_2 CH_2 (OH)CH_3 , \hfill \\ HOC_6 H_4 C(H) : NCH_2 CH_2 OH \hfill \\ \end{gathered} $$ and HOC₆H₄C(H)∶NCH₂CH(OH)CH₃ react with La(III), Pr(III) and Nd(III) isopropoxides to 1∶1 and 2∶3 derivatives of the type,Ln(O?i-C₃H₇)(OC₆H₄C[R]∶NR′O) andLn ₂(OC₆H₄C[R]∶ NR′O)₃ [where,Ln=La(III), Pr(III) or Nd(III); R=CH₃ or H and R′=CH₂?CH₂ or CH₂CHCH₃] in dry benzene. The labile nature of the isopropoxy groups in the 1∶1 derivatives has been shown by exchange reactions with an excess oft-butyl alcohol leading to the formation ofLn(O?t-C₄H₉)(OC₆H₄C[R]∶NR′O); (where R=CH₃ and R′=CH₂CHCH₃) type derivatives in almost quantitative yield. The IR spectra of the resulting derivatives have been recorded in the range of 4000–400 cm^?1, ν C=N frequency bands appear at ≈ 1620 cm^?1 and almost no change has been noted in their positions on complexation. Some new peaks are, however, observed in the range of 700–600 cm^?1 and these may be ascribed to the ring deformation coupled with both theLn?O stretching and C?CH₃ stretching modes.     

Studies on magnetic susceptibility and specific heat for 6H-perovskite-type oxides Ba3LnIr2O9 (Ln=La, Nd, Sm-Yb)

Magnetic properties of the 6H-perovskite-type oxides Ba₃LnIr₂O₉ (Ln=La and Nd: monoclinic; Ln=Sm-Yb: hexagonal symmetry) were investigated. For all the title compounds, a specific heat anomaly was found at 5.3-17.4 K. At the corresponding temperatures, the magnetic susceptibilities show a slight variation in its gradient. These magnetic anomalies suggest the magnetic ordering of the magnetic moments (S=1/2) remaining in the Ir^4.5+₂O₉ face-shared bioctahedra. In addition, the Ln³⁺ ions show the onset of the antiferromagnetic ordering around these temperatures. The Ba₃NdIr₂O₉ only shows a ferromagnetic behavior below 17.4 K with a remnant magnetization of 1.25 μ_B. This behavior may be due to the ferromagnetic ordering of the Nd³⁺ moments.     

Decanuclear Ln10 Wheels and Vertex‐Shared Spirocyclic Ln5 Cores: Synthesis,Structure, SMM Behavior,and MCE Properties

The reaction of a Schiff base ligand (LH₃) with lanthanide salts, pivalic acid and triethylamine in 1:1:1:3 and 4:5:8:20 stoichiometric ratios results in the formation of decanuclear Ln₁₀ (Ln=Dy( 1 ), Tb( 2 ), and Gd ( 3 )) and pentanuclear Ln₅ complexes (Ln=Gd ( 4 ), Tb ( 5 ), and Dy ( 6 )), respectively. The formation of Ln₁₀ and Ln₅ complexes are fully governed by the stoichiometry of the reagents used. Detailed magnetic studies on these complexes ( 1 – 6 ) have been carried out. Complex 1 shows a SMM behavior with an effective energy barrier for the reversal of the magnetization (U_eff)=16.12(8) K and relaxation time (τ_o)=3.3×10^?5 s under 4000 Oe direct current (dc) field. Complex 6 shows the frequency dependent maxima in the out‐of‐phase signal under zero dc field, without achieving maxima above 2 K. Complexes 3 and 4 show a large magnetocaloric effect with the following characteristic values: ?ΔS_m=26.6 J kg^?1 K^?1 at T=2.2 K for 3 and ?ΔS_m=27.1 J kg^?1 K^?1 at T=2.4 K for 4 , both for an applied field change of 7 T.     

New Homoleptic Rare‐Earth Metal Complexes Comprising the Unsymmetrically Substituted Amidinate Ligand [MeC(NEt)(NtBu)]–

New homoleptic complexes of selected rare‐earth elements containing the unsymmetrically substituted amidinate ligand [MeC(NEt)(NtBu)]^– [= (L)^–] were synthesized and fully characterized. Treatment of in situ‐prepared Li(L) ( 1 ) with anhydrous lanthanide(III) chlorides, LnCl₃ (Ln = Sc, La, Ce, Ho), afforded three different types of amidinate complexes depending on the ionic radius of the central metal atom. The large La³⁺ formed the octa‐coordinate DME solvate La(L)₃(DME) ( 2 ). Using Ce³⁺, the octa‐coordinate “ate” complex Li(THF)[Ce(L)₄] ( 3 ) was formed. Depending on the crystallization conditions, compound 3 could be crystallized in two modifications differing in the coordination environment around Li. In the case of the smaller Sc³⁺ and Ho³⁺ ions, six‐coordinate homoleptic Sc(L)₃ ( 4 ) and Ho(L)₃ ( 5 ) were isolated. The title compounds were fully characterized by spectroscopic and analytical methods as well as single‐crystal X‐ray diffraction. With Ln = La and Ce, several by‐products incorporating lithium, chlorine and/or oxygen were also isolated and structurally characterized.     

NMR-spektroskopische Untersuchungen zur Solvatation von Tetraphenylimidodiphosphatokomplexen der Lanthanoiden

NMR-spectroscopic Investigations on Solvation of Lanthanoide Complexes of Tetraphenylimidodiphosphate The additional coordination of solvent molecules to chelate complexes LnA₃ of rare earth ions (Ln³⁺) and tetraphenylimidodiphosphate ions (A^?) has been studied by ¹H-NMR spectroscopy. The nature of the solvent has a great influence on the spectra observed especially in the case of paramagnetic Ln³⁺ ions. In acetone as solvent TmA₃ forms a disolvate preferably. The brutto stability constants for the additional coordination of acetone as ligands by TmA₃ are β₁ = (0.013 ± 0.003) mol^?1 · l and β₂ = (0.016 ± 0.001) mol^?1 · l².     

The crystal growth and magnetic properties of Ln2LiIrO6 (Ln=La, Pr, Nd, Sm, Eu)

Single crystals of a series of lanthanide lithium iridium oxides, Ln₂LiIrO₆ (Ln=La, Pr, Nd, Sm, Eu) with the double perovskite structure have been grown from molten LiOH/KOH fluxes. The compounds crystallize in a distorted 1:1 rock salt lattice of Li⁺ and Ir⁵⁺ cations in the monoclinic space group P2₁/n. The magnetic susceptibilities of Ln₂LiIrO₆ (Ln=Pr, Nd, Sm, Eu) are presented.     

Thermodynamic behavior and stability constants of lanthanides–Schiff base complexes in mixed aqueous solvents

The stability constant of complexes of Ln³⁺ ions and butanamide-3-[(2-hydroxyphenyl methylene)amino]ethylimino N-phenyl were determined potentiometrically in 75% (v/v) dioxane?Cwater, 0.1?M (KNO₃) at different temperatures applying the Irving and Rossotti techniques. The nonlinear variation of the thermodynamic parameters (??G, ??H, and ??S) as a function of ionic potential of lanthanide elements was discussed. This behavior was explained in terms of difference in the dehydration of lighter Ln³⁺ from that of heavier ones. In different organic solvents (75% solvent?Cwater media), the stability constant values follow the order: dioxane?>?methanol?>?DMF, depending upon both the dielectric constant and the hydrogen bonding structure of the medium. The thermodynamic parameters at all complexes have been analyzed in terms of their electrostatic (el) and non-electrostatic (non) parts.     

Synthesis,spectral, thermal,solid state d.c. electrical conductivity,fluorescence and biological studies of lanthanum(III) and thorium(IV) complexes of 24-membered macrocyclic triazoles

A series of La(III) and Th(IV) complexes have been synthesized by template condensation of 2,6-diformyl-4-methylphenol, bis-(4-amino-5-mercapto-1,2,4-triazol-3-yl)alkanes and La(NO₃)₃ ·?6H₂O/Th(NO₃)₄ ·?5H₂O in 2 : 2 : 1 molar ratio in ethanol. These complexes were characterized by elemental analyses, magnetic susceptibility, molar conductance, spectral (IR, UV–Vis, ¹H-NMR, FAB-mass), thermal, fluorescence and solid state d.c. electrical conductivity studies. The complexes are insoluble in water but soluble in DMF and DMSO. The observed molar conductance values indicate non electrolytes. Elemental analyses suggest 1 : 1 stoichiometry, [La(L^I–IV)(NO₃)(H₂O)₂] ·?3H₂O and [Th(L^I–IV)(NO₃)₂(H₂O)₂] ·?3H₂O. Spectroscopic studies indicate that coordination occurs through phenolic oxygen after deprotonation, nitrogen of azomethine group and bridging bidentate nitrates. The solid state d.c. electrical conductivity indicates semiconducting nature. All the Schiff bases and their La(III) and Th(IV) complexes were evaluated for biological properties; some compounds show promising results.     

Luminescence of NaGdFPO4:Ln after VUV excitation: A comparison with GdPO4:Ln (Ln=Ce, Tb)

The phosphors NaGdFPO₄:Ln³⁺ and GdPO₄:Ln³⁺ (for Ln³⁺=Ce³⁺ and Tb³⁺) were prepared by solid-state reaction technique, the VUV-vis spectroscopic properties of the phosphors were investigated, and we vividly compare the luminescence of Ce³⁺ and Tb³⁺ in the hosts. For phosphors GdPO₄:Ln³⁺, the band near 155 nm in VUV excitation spectrum is assumed to be the host-related absorption, and for NaGdFPO₄:Ln³⁺ the absorption is moved to longer wavelength, near 170 nm, showing the P-O bond covalency increased after fluoridation. The f-d transitions of Ce³⁺ and Tb³⁺ in the host lattices are assigned and corroborated, and it was found that the 5d states are with lower energy in NaGdFPO₄:Ln³⁺ than those in GdPO₄:Ln³⁺. For fluoridation of GdPO₄:Ln³⁺ to NaGdFPO₄:Ln³⁺, the energy change of Ln³⁺ (Ln=Ce, Tb) 5d states is consistent with that of host-related absorption.     

Ln2Cl 7 − ions (Ln = La and Lu): Structures and thermodynamic stability

The equilibrium geometrical parameters and frequencies of the normal vibrations of Ln₂Cl ₇ ^? ions (Ln = La and Lu) and the enthalpies of the dissociation reactions Ln₂Cl ₇ ^? → Ln₂Cl₆ + Cl^? and Ln₂Cl ₇ ^? → LnCl₃ + LnCl ₄ ^? were calculated at the MP2 and MP4 levels (with regard to single, double, triple, and quadruple perturbations). The basis set superposition errors were eliminated by using the counterpoise approach. The potential energy surface of the Ln₂Cl ₇ ^? ions was found to reach a minimum for a configuration with three bridging and four terminal Cl atoms (symmetry C ₂). The terminal fragments LnCl₂ show almost free inherent rotation. The lanthanide compression of the interatomic Ln-Cl distances differed for the bridging and terminal Ln-Cl bonds. The calculated enthalpies of dissociation of the Ln₂Cl ₇ ^? ions were compared with data from high-temperature mass spectrometry.