Synthesis and magnetism of μ-isophthalato dinuclear lanthanide(Ⅲ) complexes

Seven new μ-isophthalato dinuclear lanthanide(Ⅲ) complexes, namely [Ln2(IPHTA)(Me2-phen)4-(ClO4)2](ClO4)2 (Ln = La, Nd, Sm, Eu, Gd, Ho, Er), where Me2-phen denotes 2,9-dimethyl-1, 10-phenanthroline (Me2-phen) , IPHTA represents isophthalate dianion, have been synthesized and characterized by elemental analyses, molar conductance measurements, IR, ESR and electronic spectra. The variable-temperature magnetic susceptibilities of [Gd2( IPHTA) (Mez-phen)4 (ClO4)2] (ClO4)2 complex were measured in the temperature range of 4-300 K and the observed data were successfully simulated by the equation based on the spin Hamiltonian operator, H = - 2JS1 · S2, giving the exchange parameter J =- 0.19 cm-1 . This result is commensurate with a weak antiferromagnetic spin-exchange interaction between Gd(Ⅲ)-Gd(Ⅲ) ions within the complex.     

Enantiospecific Synthesis of (–)-Cuspareine and (–)-Galipinine

An enantiospecific route to the synthesis of tetrahydroquinoline alkaloids (–)-cuspareine and (–)-galipinine is reported. Coupling of an iodide derivative of D-serine with aromatic dithianes and Pd-catalyzed intramolecular C–N coupling are the key steps in the synthesis.     

Multinuclear NMR study of lanthanide(Ⅲ)complexes of 1,2-PDTA in aqueous solution

The complexation oflanthanide(Ⅲ) cations with 1,2-propanediaminetetraacetate (1,2-PDTA)in aqueous solution has been investigated by ~(23)Na,~(35)Cl,~2H and ~(17)O NMR shift measurements.It hasbeen shown that the contact shifts are dominant for ~(17)O,~(35)Cl and ~2H (only for the heavier lanthanideseries) and the pseudocontact shifts are dominant for ~(23)Na.It is suggested that the 1,2-PDTA ligandis bound pentadentately via the two nitrogens and the three carboxylates for the lighter lanthanidecomplexes,hexdentately via the two nitrogens and the four carboxylates for the heavier ones.Thenumbers of the water coordinated were determined.The small amount of chloride anion in innercoordination sphere was observed.     

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 Ln~(3+)dependent DNAzyme was incorporated into a hydrogel to generate Ln~(3+)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 Ln~(3+)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,Ln~(3+)can be detected with high sensitivity,with a limit of detection(LOD)of 20 nM for Ce~(3+).The hydrogel responds specifically to any Ln~(3+)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 Ln~(3+)contamination in the field.     

Tunable white-light emission of lanthanide(Ⅲ) hybrid material based on hectorite

In this work, we present novel trivalent lanthanide ions(Ln~(3+))-based luminescent hybrid materials, in which the organic ligands are covalently grafted on the hectorite templates and the Ln~(3+) ions can be well immobilized by the ligands through coordination bond. The hybrid materials exhibit tunable emission colors by varying the molar ratio of Eu~(3+) to Tb~(3+), and the one with Eu~(3+):Tb~(3+)=1:1 exhibits excellent coordinate of(0.327, 0.328) located in the "white region" of the CIE 1931 chromaticity diagram(under300 nm UV illumination). These properties make the hybrid composites suitable for fabricating optoelectronic devices such as full-color displays and white LED.     

A variety of new tri- and tetranuclear Mn–Ln and Fe–Ln (Ln = lanthanide) complexes

The use of carboxylates in the synthesis of 3d/4f clusters, with or without a second organic ligand, has afforded a series of tetranuclear M₂Gd₂ complexes (M = Fe or Mn), and two new trinuclear M₂Gd (M = Fe or Mn) molecular compounds. Only one of these, [Mn₂Gd₂O₂(O₂CBu^t)₈(HO₂CBu^t)₄] (1), does not contain a multidentate chelate ligand. Two other similar tetranuclear clusters were synthesized from the use of triethanolamine (teaH₃) and 1,1,1-tris(hydroxymethyl)ethane (thmeH₃). [Mn₂Gd₂(OH)₂(O₂CPh)₄(NO₃)₂(teaH)₂] (2) has very similar structure with 1, bearing a defective incomplete double-cubane core bridged by μ₃-O atoms, whereas in the core of [NHEt₃]₂[Fe₂Gd₂(O₂CPh)₄(thme)₂(NO₃)₄] (3) the thme³⁻ ligand caps the two incomplete cubane units, providing the triply-bridging alkoxides needed for bridging. Two new oxide-centered triangular clusters were synthesized bearing the Schiff-based chelate 2-{[2-(dimethylamino)ethyl]methylamino}ethanol (dmemH), namely [Fe₂GdO(O₂CBu^t)₂(dmem)₂(NO₃)₃] (4), and [Mn₂GdO(O₂CBu^t)₂(dmem)₂(NO₃)₃] (5). Magnetic susceptibility measurements and/or reduced magnetization studies established that complexes 1 and 3 have an S = 5 ground state, complex 2 has S = 4, and complexes 4 and 5 are S = 7/2 in their ground states. These complexes portray the feasibility of obtaining products bearing metal cores commonly found in homometallic clusters, even when these include metals with completely different coordination chemistry and electronic structure, such as lanthanides.     

Determination of the stability constants of Pb–(DIPSO)x–(OH)y and Pb–(AMPSO)x–(OH)y systems

In this work, complexation between lead ion and the ligands 3-[N,N-bis(2-hydroxyethyl)amino]-2-hydroxypropanesulfonic acid (DIPSO) and N-(1,1-dimethyl-2-hydroxyethyl)-3-amino-2-hydroxypropanesulfonic acid (AMPSO), which are commercial pH buffers, is presented. Both ligands form complexes with lead in their pH buffer range (between pH 6.5 and 8.5 for DIPSO and between pH 8.0 and 9.0 for AMPSO). The final models and the overall stability constants, which are reported here, were determined by direct current polarography and glass electrode potentiometry [only for the Pb–(DIPSO)_x–(OH)_y system] at 25.0 °C and 0.1 M KNO₃ ionic strength. For the Pb–(DIPSO)_x–(OH)_y system, the proposed final model contains PbL, PbL₂, PbL₂(OH), and PbL₂(OH)₂ with stability constants, as log β, of 3.4 ± 0.1, 6.35 ± 0.15, 12.8 ± 0.2, and 18.0 ± 0.3, respectively. For the Pb–(AMPSO)_x–(OH)_y system, the species observed are PbL, PbL(OH), and PbL(OH)₂ with stability constants, as log β, of 2.9 ± 0.5, 9.4 ± 0.1, and 14.5 ± 0.2, respectively. For AMPSO, the possible adsorption of the ligand at the mercury electrode surface was evaluated by alternating current polarography through calculation of the capacitance of the double layer.     

Solvent-dependent structures of lanthanide–TCNQ coordination networks and their magnetic properties

Abstract

Lanthanide complexes were prepared with 2,6-diacetylpyridinebis(benzoylhydrazone) (DAPBH₂) and 7,7,8,8-tetracyano-p-quinodimethanide (TCNQ^??). The complexes adopted one of two structure types depending on the reaction solvent. The complexes were categorized as Type I (i.e. bis{[2,6-diacetylpyridinebis(benzoylhydrazone)] methanollanthanide(III)}bis(µ₂- 7,7,8,8-tetracyanoquinodimethanide(1?))bis(7,7,8,8-tetracyanoquinodimethanide(1?))bis(7,7,8,8-tetracyanoquinodimethanide(1?)) methanol disolvate, [Ln₂(DAPBH₂)₂ (µ₂-TCNQ^??)₂(TCNQ^??)₂(MeOH)₂](TCNQ^??)₂·2MeOH (Ln?=?Gd, Tb, or Dy) or Type-II (i.e. [Ln₂(DAPBH₂)₂(µ₂-TCNQ^??)₂(TCNQ^??)₂(EtOH)₂] (TCNQ^??)₂·solvent (Ln?=?Tb and Dy, solvent =4EtOH for the Tb and 2EtOH·2CH₂Cl₂ for the Dy complexes). These two complexes exhibit dramatically different molecular structures and packings. In all complexes, the strong intra- and intermolecular stacking interactions of the TCNQ^?? radicals lead to the formation of 1D TCNQ chains. Magnetic susceptibility measurements for Type I and Type II complexes reveal that they exhibit paramagnetic behavior and that their magnetic properties originate from the lanthanide ions alone, owing to the diamagnetic nature of the TCNQ^?? stacks.     

Relationship between the analytical properties of lanthanide(III) βdiketonates and the nature of ligands

The effect of the nature of β-diketones on the spectrochemical-luminescence properties of lanthanide complexes used as analytical forms for the highly sensitive determination of some rare-earth elements was examined. NMR spectroscopy, molecular mechanics, calculations, and an experimental evaluation of the hydrophobicity of the test β-diketones indicated that an increase in the intensity, quantum yield, and lifetime of luminescence of lanthanide (Ln) β-diketonates depends on the charge distribution in the chelate ring, on the spatial structure, and on the hydrophobicity of the coordinated ligand. These factors determine the efficiency of energy transfer from the β-diketone to the Ln⁺³ ion and the decrease in energy losses caused by the quenching action of water molecules.     

Asymmetric glyoxylate-ene reaction catalyzed by C2-symmetric chiral bis(oxazoline)–lanthanide complexes

Efficient C₂-symmetric chiral bis(oxazoline)-lanthanide catalysts are developed for the glyoxylate-ene reaction to afford the α-hydroxy esters in 85% yield and up to 54% ee. An enhanced level of diastereoselectivity (81% de) was obtained in the reaction between menthyl glyoxylate and alkenes catalyzed by bis(oxazoline)–Ln(OTf)₃ complex.     

Electronic characteristics of sandwich-type lanthanide octaethylporphyrins

The electronic behavior of sandwich-type rare earth octaethylporphyrinates Ln(oep)2 and Ln2(oep)3 (Ln=Ce, Pr and Eu) was characterized by measurements of the UV-vis or near infrared spectra and D.C. conductivity. However, the conductivity values measured at room temperature were distributed in an order of 10-7 to 10-8 S.cm-1 even after the partial oxidation of complex with the complexes with iodine and no remarkable change was observed among the complexes such as LnIV(Por2-)2 (Ln=Ce) and LnIV(Por2-)(Por.-) (Ln=Ce) or Ln2III(Por2-)3 and LnIII2(Por2-)2(Por-).     

Molecular structure of diatomic lanthanide compounds

The molecular constants of selected diatomic lanthanide compounds (LaH, LaO, LaF, EuH, EuO, EuF, EuS, GdO, GdF, GdH, YbH, YbO, YbF, YbS, LuH, LuO and LuF) have been calculated by using relativistic small-core pseudopotentials and optimized (14s13p10d8f6g)/ [6s6p5d4f3g] valence basis sets. The results are in good agreement with available experimental data, with exception of YbO and LuF. The reasons for the discrepancies in case of YbO are due to a complicated mixing of configurations in the ground state, whereas in case of LuF the binding energy estimated by experimentalists appears to be too low.     

Synthesis and characterization of some new lanthanide(III) chelates with 1,4-bis-(2′-hydroxyphenylazomethine) phenylene

Summary The chelates formed between 1,4-bis(2-hydroxyphenylazomethine) phenylene with La, Ce, Pr, Nd, Sm, Gd, Dy, Er, Yb, and Lu ions have been investigated in solution using conductometric, potentiometric, and spectrophotometric methods. The studies revealed the formation ofM ₂ L andML complexes. The solid chelates have been characterized by elemental and thermal analysis, molar conductance, IR,¹H NMR (for La and Lu chelates), and electronic spectra. The bonding takes place through the coordination of nitrogen in the -CH=N- group and the oxygen of the hydroxyl group by proton displacement.

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Synthese und Charakterisierung einiger neuer Lanthanid(III)-Chelate mit 1,4-bis-(2-Hydroxyphenylazomethin)-phenylen

Zusammenfassung Chelate von 1,4-bis-(2-Hydroxyphenylazomethin)-phenylen mit La, Ce, Pr, Nd, Sm, Gd, Dy, Er, Yb und Lu in Lösung wurden konduktometrisch, potentiometrisch und spektrophotometrisch untersucht. Die Bildung von Komplexen der FormM ₂ L undML wurde festgestellt. Die festen Chelate wurden mittels Elementaranalyse. Thermoanalyse, molarer Leitfähigkeit, IR-, UV/Vis-und im Fall von La und Lu-NMR-Spektroskopie charakterisiert. Die Komplexbindung erfolgt durch Koordination des Stickstoffs der -CH=N- Gruppe und des Sauerstoffs der Hydroxylgruppe unter Protonenverschiebung.

     

Asymmetric synthesis of (–)-leiocarpin A via (–)-(S)-goniothalamin employing Julia–Kocienski olefination

A concise and enantioselective syntheses of antileukemic natural products such as (–)-(S)-goniothalamin and (–)-leiocarpin A has been accomplished in excellent yields. By employing reported conditions on suitable substrates via Julia–Kocienski olefination, intramolecular lactonization, and subsequently dehydroxylative olefination, (–)-(S)-goniothalamin was synthesized. Then Sharpless asymmetric dihydroxylation–intramolecular Michael addition on (–)-(S)-goniothalamin provided (–)-leiocarpin A.     

Pyrolysis kinetics of ethylene–propylene (EPM) and ethylene–propylene–diene (EPDM)

The thermal degradation kinetics of several ethylene–propylene copolymers (EPM) and ethylene–propylene–diene terpolymers (EPDM), with different chemical compositions, have been studied by means of the combined kinetic analysis. Until now, attempts to establish the kinetic model for the process have been unsuccessful and previous reports suggest that a model other than a conventional nth order might be responsible. Here, a random scission kinetic model, based on the breakage and evaporation of cleavaged fragments, is found to describe the degradation of all compositions studied. The suitability of the kinetic parameters resulting from the analysis has been asserted by successfully reconstructing the experimental curves. Additionally, it has been shown that the activation energy for the pyrolysis of the EPM copolymers decreases by increasing the propylene content. An explanation for this behavior is given. A low dependence of the EPDM chemical composition on the activation energy for the pyrolysis has been reported, although the thermal stability is influenced by the composition of the diene used.     

Lanthanide contraction in linear lanthanide–oxygen clusters

Five coordination polymers containing linear lanthanide–oxygen clusters 1–5 have been synthesized by a hydrothermal reaction of 3-(quinolin-8-yloxy) phthalic acid (H₂L) with the respective lanthanide salt. The X-ray single crystal structural analyses revealed that these five crystalline materials belong to two isostructures with formulas [LnHL₂(H₂O)₂]_n (Ln1, where Ln = La 1, Ce 2, Pr 3) and [Ln(HL)(L)(H₂O)]_n (Ln2, where Ln = Nd 4, Sm 5), respectively, which are attributed to the effect of lanthanide contraction. In both structures, the lanthanide cations were bridged by two carboxyl groups of L^2? through Ln–O bonds to form 1-D linear lanthanide–oxygen clusters, which were further connected by intermolecular π–π stacking interactions between quinolinyl units to generate 3-D supramolecular polymers with moderate luminescence and high thermal stability.     

Improved Synthesis of (–)-Agelastatin A

Optimization of key steps in the synthesis of the architecturally unique tetracyclic antitumor alkaloid (–)-agelastatin A (1) improved the overall yield of the 11-step process (eight operations) from 9% to 23%. Changing the solvent and using a more efficient N-benzyl deprotecting-group procedure enhanced the yields of the C-ring and D-ring intermediates, (–)-4 and (–)-7, respectively. Bromination of (–)-7 with 1,3-dibromo-5,5-dimethylhydantoin, rather than N-bromosuccinimide (NBS), increased the yield of (–)-1 from 69% to more than 94% yield.     

Hydro(solvo)thermal synthesis and structural characterization of three lanthanide–carboxylate coordination polymers based on BDC and/or EDTA

Three lanthanide coordination polymers, [Ln₄(BDC)₆(H₂O)₂] _n (Ln = Er, 1; Ln = Tm, 2; BDC = 1,2-benzenedicarboxylate) and {[Nd₂(BDC)(EDTA)(H₂O)₂] · 1.5H₂O} _n , 3, were prepared by hydrothermal synthesis and characterized by elemental analysis, IR spectra, as well as single-crystal X-ray diffraction. The isostructural coordination polymers 1 and 2 exhibit four different coordination modes, which are rarely found in one lanthanide complex. Complex 3 displays a 2-D wave-like network assembled by two polycarboxylate ligands.     

Synthesis of Bis 〔bis (tert-butylcyclopentadienyl) neodymium chloride〕 and Structural trend of Bis〔bis(tertbutylcyclopentadienyl) lanthanide chloride〕

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Affinity of lanthanide(III) ions for oxygen- and mixed oxygen–nitrogen-donor ligands in dimethylsulfoxide: a thermodynamic and spectroscopic investigation

The interactions of lanthanide(III) ions with the following oxygen- and mixed oxygen–nitrogen-donor ligands: 2-methoxyethylamine (L1), 2-aminoethanol (L2), 2-methoxyethylether (L3), di(ethyleneglycol) (L4), 2,2′-oxydiethylamine (L5) and 1,5-diaminopentane (L6) have been investigated in dimethylsulfoxide (DMSO) at 298 K and I=0.1 mol dm⁻³ (Et₄NClO₄). Calorimetric and ¹H NMR results show that L1–L4 and L6 are not able to complex Ln(III) ions. L5 is shown to be able to bind heavier Ln(III) ions (LnHoLu). Potentiometric and calorimetric measurements have been carried out to obtain the Ln(III)–L5 thermodynamic parameters of complexation. All the complexes are formed in exothermic reactions being the entropy terms generally negative or slightly positive. Comparison between the complexing abilities of L1 and L5 shows that at least two CH₂CH₂NH₂ side-arms added to an ether function are needed to promote effective interaction between an ether O atom and Ln(III) ions in the high coordinating solvent DMSO. The results are discussed in terms of different donor properties and solvation of NR and O groups towards metal ions. A comparison with data previously obtained in DMSO for the complex formation of Ln(III) with the purely N donor diethylenetriamine (dien) is made.