Sensitized near-IR luminescence of Ln(III) complexes with benzothiazole derivatives

Lanthanide complexes with benzothiazole derivatives (Btz-R, R = OCH(3) and OH) and terpyridine (tpy) ligands were synthesized, and their photophysical properties were precisely investigated. The free Btz-OCH(3) ligand in toluene, excited with UV light, produced the normal emission bands around 410 nm, whereas Btz-OH produced a strong excited-state intramolecular proton transfer (ESIPT) band at 510 nm. The Ln(III) complexes (Ln = Nd, Er, and Yb) exhibited sensitized near-IR luminescence when the Btz-R ligands were excited. The sensitized luminescence quantum yields (Phi(Ln)) of the lanthanide complexes were markedly enhanced by ESIPT: for [Nd(Btz-R)(tpy)] in toluene solution, Phi(Ln) = 0.04% for Btz-OCH(3) and 0.39% for Btz-OH. The sensitized luminescence of the Er(III) complexes (Phi(Ln) = 0.002% for Btz-OCH(3) and 0.009% for Btz-OH) was less efficient than that of the Nd(III) complexes. This difference is due to the smaller energy gap between the emitting and ground levels of the Er(III) ion. The rate constants for the energy transfer from Btz-R to Ln(III) were about approximately 10(9) s(-1), as evaluated by the F?rster resonance energy transfer mechanism.     

Bimodal system (luminophore and paramagnetic contrastophore) derived from Ln(III) complexes based on a bipyridine-containing macrocyclic ligand

The synthesis of a new 15-membered polyaza-macrocyclic ligand L3H3, which is based on a 2,2'-bipyridine moiety and a diethylenetriaminetriacetic acid core, is reported. The lanthanide chelates of this octadentate ligand were programmed for bimodal probes, luminescent agents (Sm, Eu, Tb, Dy), and magnetic resonance imaging agents (Gd3+). The neutral 1:1 complexes with these Ln3+ ions were prepared and studied in aqueous solution by luminescence and NMR techniques. The main photophysical characteristics of these complexes (i.e., the absorption and luminescence spectra, the metal-centered lifetimes, and the overall luminescence yields, Phi) were measured. In addition, the role played by nonradiative pathways (vibrational energy transfer involving coordinated water molecules, involvement of ligand-to-metal charge-transfer excited states, or metal --> ligand back transfer) is discussed. The L3.Eu and L3.Tb complexes show very bright luminescence when photoexcited from the lowest-energy absorption band of the bipyridine chromophore. The luminescence quantum yields in an air-equilibrated water solution at room temperature are 0.10 and 0.21, respectively, despite the presence of one water molecule in the first coordination sphere of the metal ion. NMR data show that L3.Gd contains also one H2O molecule in the inner sphere. The proton longitudinal relaxivity, r1, of this complex is 3.4 s(-1) mM(-1) (0.47 T, 310 K) and the rotational correlation time, tau(R), is 57 ps (310 K). These values are comparable to those of the clinically used Gd-DTPA. Interestingly, the water exchange rate between the coordination site and the bulk solvent is slow (tau(M) = 3.5 micros at 310 K). The presence of water molecules in the second sphere and in rapid exchange with the solvent is discussed. Finally, it was found by luminescence and NMR experiments that these lanthanide complexes are stable versus transmetalation by several cations (especially Ca2+ and Zn2+) at physiological pH and have no interaction with blood proteins.     

Re(I) sensitised near-infrared lanthanide luminescence from a hetero-trinuclear Re2Ln array

The trinuclear complexes Re2Ln (Ln = Nd, Yb or Er) contain two Re(I) tricarbonyl units linked to a DTPA binding site via 2,2'-bipyridyl ligands; Ln(III)-centred emission is sensitised by the Re(I) MLCT excited states.     

Two-color luminescence from a tetranuclear Ir(III)/Ru(II) complex

A new tetranuclear compound containing Ru(II) and Ir(III) polypyridine subunits exhibits two independent emissions at room temperature, as a consequence of weak interchromophoric coupling; in contrast, at 77 K energy transfer from Ir-based chromophores to the Ru-based ones is quantitative.     

Carboxylate-free Mn(III)2Ln(III)2 (Ln = lanthanide) and Mn(III)2Y(III)2 complexes from the use of (2-hydroxymethyl)pyridine: analysis of spin frustration effects

The initial employment of 2-(hydroxymethyl)pyridine for the synthesis of Mn/Ln (Ln = lanthanide) and Mn/Y clusters, in the absence of an ancillary organic ligand, has afforded a family of tetranuclear [Mn(III)(2)M(III)(2)(OH)(2)(NO(3))(4)(hmp)(4)(H(2)O)(4)](NO(3))(2) (M = Dy, 1; Tb, 2; Gd, 3; Y; 4) anionic compounds. 1-4 possess a planar butterfly (or rhombus) core and are rare examples of carboxylate-free Mn/Ln and Mn/Y clusters. Variable-temperature dc and ac studies established that 1 and 2, which contain highly anisotropic Ln(III) atoms, exhibit slow relaxation of their magnetization vector. Fitting of the obtained magnetization (M) versus field (H) and temperature (T) data for 3 by matrix diagonalization and including only axial anisotropy (zero-field splitting, ZFS) showed the ground state to be S = 3. Complex 4 has an S = 0 ground state. Fitting of the magnetic susceptibility data collected in the 5-300 K range for 3 and 4 to the appropriate van Vleck equations revealed, as expected, extremely weak antiferromagnetic interactions between the paramagnetic ions; for 3, J(1) = -0.16(2) cm(-1) and J(2) = -0.12(1) cm(-1) for the Mn(III)···Mn(III) and Mn(III)···Gd(III) interactions, respectively. The S = 3 ground state of 3 has been rationalized on the basis of the spin frustration pattern in the molecule. For 4, J = -0.75(3) cm(-1) for the Mn(III)···Mn(III) interaction. Spin frustration effects in 3 have been quantitatively analyzed for all possible combinations of sign of J(1) and J(2).     

Enantiopure sandwich-type nonanuclear Ln(III)3Mn(III)6 clusters

Three enantiopure isostructural sandwich-type clusters, Ln(III)(3)Mn(III)(6) (Ln = Dy (1), Tb (2) and Gd (3)) have been synthesized through reactions of a chiral Schiff-base ligand ((S,E)-4-(2-hydroxybenzylideneamino)-2-hydroxybutanoic acid, H(3)L) with manganese and lanthanide ions, showing intramolecular antiferromagnetic interaction.     

Optimization Studies of An(III) and Ln(III) Extraction and Back-Extraction from a PUREX Raffinate by BisDGA Compounds

A family of compounds based on bis-diglycolamide (bisDGA) estructure has been recently developed to be applied for the trivalent actinides and lanthanides (An(III) and Ln(III)) co-extraction by means of DIAMEX process [1], [2]. It has been shown that these bisDGA compounds are efficient extractants of An(III) and Ln(III) regarding to extraction and loading capacity, as well as it has been proved their stability against hydrolysis and radiolysis [3]. For process development, it is necessary to study their selectivity towards An(III) and Ln(III) in the extraction and back-extraction steps in presence of the other elements, such as fission and activation products (FP and AP), in the high active raffinate (HAR) issued from the PUREX process.     

Cerium(III) and neodymium(III) amides derived from a chelating 2-pyridyl amido ligand

Homoleptic Ce(III) and Nd(III) triamides [LnL(3)] [Ln = Ce(1) or Nd(2)] and the heterobimetallic amide-alkoxide derivatives [LnL(2)(mu-OBu(t))2M(tmeda)] [Ln = Ce, M = Na (3); Ln = Nd, M = Na (4); Ln = Nd, M = K (5)] supported by the bulky [N(SiBu(t)Me2)(2-C(5)H(3)N-6-Me)]- ligand (L-) have been successfully synthesized and characterized. Complexes 1-3 and 5 show a high activity toward the ring-opening polymerization of epsilon-caprolactone.     

Rare earth trisoxalatocobaltates(III) a precursor for rare earth cobaltites(III)

Rare earth cobalties, LnCoO₃, can be conveniently prepared by the thermal decomposition of the precursor LnCo(C₂O₄)₃·nH₂O (La, Ce, n=9; Pr, Nd, n=8). CeCo(C₂O₄)₃·8H₂O, unlike the other oxalato compounds thermally decompose to a mixture of CeO₂ and Co₃O₄. Although LnCoO₃are formed from the precursors at a temperature lower than 800°C, thermal analysis of a mixture of La₂(C₂O₄)₃·10H₂O and CoC₂O₄·2H₂O at 900·C shows the residue containing mainly La₂O₃ and Co₃O₄ with a small amount of LaCoO₃.     

Synthesis of Ln(III) chloride tetraphenylporphyrin complexes

The isolation and identification of the first examples of anhydrous lanthanide chloride tetraphenylporphyrin complexes have been described. The purple complexes were generated by the reaction of dilithiotetraphenylporphyrin bis(dimethoxyethane) with lanthanide trichloride tris(tetrahydrofuran) salts to yield the products in up to 85% yield. The crystal structures for the holmium and ytterbium complexes are also presented.     

Synthesis and luminescence studies on lanthanoid(III) complexes of aSchiff base derived from 2-acetylpyridine andtris-(2-aminoethyl)-amine

Summary A potentially heptadentated ligand (apytren) was obtained by condensation of 2-acetylpyridine andtris-(2-aminoethyl)-amine in the presence of lanthanoid(III) cations. Complexes of the formulaLn(apytren)(NO₃)₃·H₂O (Ln=La, Eu, Gd, and Tb) have been isolated and characterized, both in the solid state and in solution, by means of vibrational and electronic spectroscopy and of conductometric measurements. Their photophysical properties, including emission quantum yields and lifetimes, were studied and are discussed.

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Synthese und Lumineszenzuntersuchungen an Lanthanoid(III)-Komplexen mit einer aus 2-Acetylpyridin undtris-(2-Aminoethyl)-amin hergeleitetenSchiffschen Base

Zusammenfassung Durch Kondensation von 2-Acetylpyridin undtris-(2-Aminoethyl)-amin in der Gegenwart von Lanthanoid(III)-Kationen wurde ein potentiell siebenzähniger Ligand (apytren) erhalten. Komplexe der ZusammensetzungLn(apytren)(NO₃)₃·H₂O (Ln=La, Eu, Gd und Tb) wurden isoliert und sowohl im festen Zustand als auch in Lösung mittels IR-und UV-Vis-Spektroskopie und Leitfähigkeitsmessungen charakterisiert. Ihre photophysikalischen Eigenschaften, einschließlich Emissionsquantenausbeute und Lebensdauer, wurden untersucht und werden diskutiert.

     

Structure and properties of new mixed-valent [Mn(III)2Mn(IV)3Ln(III)5O5] complexes (Ln(III) = Tm(III), Lu(III), and Yb(III))

By using 2'-hydroxyacetophenoxime, a new family of complexes with an [Mn(III)(2)Mn(IV)(3)Ln(5)O(5)] core was obtained with Ln = Tm (1), Lu (2), and Yb (3). Heterometallic Mn/Tm and Mn/Lu combinations have had no precedence so far. Studies of the magnetic properties indicate the presence of intracomplex antiferromagnetic interactions in 1 and 3, as well as a dominating ferromagnetic interaction between Mn(III) and Mn(IV) spins in 2, leading to an S(T) = 5/2 ground state.     

SCMEH-MO calculations on lanthanide systems. III. Ln(CO)6, Ln(OC)6 (Ln = Nd,Sm)

The SCMEH-MO method with average relativistic and spin-orbit effects has recently been applied to study the electronic structure and bonding in samarium pentamethylcyclopentadienyls. In this report the same approach has been utilized in studying the electronic structures of Nd and Sm hexacarbonyls. In contrast to the stable transition metal d-block carbonyls, these lanthanide carbonyls are found to be quite unstable. These findings are based on calculated electronic structures and bond energies. © 1996 John Wiley & Sons, Inc.     

Lanthanum(III) and praseodymium(III) derivatives with dithiocarbamates derived from alpha-amino acids

Lanthanum(III) and praseodymium(III) complexes with dithiocarbamates have been synthesized by the reactions of lanthanum(III) and praseodymium(III) chloride with barium dithiocarbamate and complexes of type [LnCl(L)H2O]n have been obtained (where Ln=La(III) or Pr(III); L=barium salt of dithiocarbamate derived from glycine, L-leucine, L-valine, DL-alanine). The complexes have been characterized by elemental analysis, molar conductance, electronic absorption and fluorescence, infrared, far infrared, 1H NMR spectral studies. The presence of coordinated water molecule is inferred from thermogravimetric analysis which indicates the loss of one water molecule at 150-170 degrees C. The oscillator strength, Judd-Ofelt intensity parameter, stimulated emission cross-section, etc. have been obtained for different transitions of Pr3+.     

Synthesis and photophysical properties of new Ln(III) (Ln = Eu(III), Gd(III), or Tb(III)) complexes of 1-amidino-O-methylurea

Three new solid lanthanide(III) complexes, [Ln(1-AMUH)₃] · (NO₃)₃ (1-AMUH = 1-amidino-O-methylurea; Ln = Eu(III), Gd(III), or Tb(III)) were synthesised and characterised by elemental analysis, infrared spectra, magnetic moment measurement, and electron paramagnetic resonance (EPR) spectra for Gd(III) complex. The formation of lanthanide(III) complexes is confirmed by the spectroscopic studies. The photophysical properties of Gd(III), Eu(III), and Tb(III) complexes in solid state were investigated. The Tb(III) complex exhibits the strongest green emission at 543 nm and the Eu(III) complex shows a red emission at 615 nm while the Gd(III) complex shows a weak emission band at 303 nm. Under excitation with UV light, these complexes exhibited an emission characteristic of central metal ions. The powder EPR spectrum of the Gd(III) complex at 300 K exhibits a single broad band with g = 2.025. The bi-exponential nature of the decay lifetime curve is observed in the Eu(III) and Tb(III) complexes. The results reveal them to have potential as luminescent materials.     

The thermodynamics of complexing of Ln(III) and Am(III) by chloroacetates

The thermodynamic parameters of complexation of Ce(III), Eu(III), Tm(III) and Am(III) by ClCH₂CO₂⁻, Cl₂CHCO₂⁻ and Cl₃CCO₂⁻ have been measured by potentiometry, solvent extraction and calorimetry in a medium of 2.0 M (NaClO₄). The log of the stability constants of any particular cation correlated linearly with the ligand pK_a. From comparison of the entropy data it is proposed that the ratio of inner to outer sphere nature of the complexes varies in the order LnClAc²⁺ > LnCl₂Ac²⁺ > LnCl₃Ac²⁺.     

Sensitized near-infrared lanthanide luminescence from Nd(III)- and Yb(III)-based cyclen-ruthenium coordination conjugates

The development of novel mixed lanthanide-transition-metal (f-d) based supramolecular self-assemblies made from neodymium- and ytterbium-based tetraamide-functionalized cyclen complexes bearing a single 1,10-phenanthroline moiety coordinating to a RuII(bipy)2 (bipy = bipyridine) unit is described. Excitation of the Ru(II) metal-to-ligand charge-transfer band in water gave rise to long-wavelength sensitized emission from the Yb(III) or Nd(III) centers, observed in the near-infrared.     

Liquid state membrane electrode sensitive to Ln(III)

A liquid ion-exchange electrode containing a chloroform solution of the complex of Ln(III) (Gd, La) with tetraphenyl ester of imidodiphosphoric acid is described. The slope of the calibration graph (electrode potential vs concentration) is 18.5 mV/pLn in the pLn range 4.7-2 (pH = 5). Fe(III), Al(III), Co(II), Ni(II) and Ca(II) ions do not interfere, unlike ions of other lanthanides. It was found that the electrode might be applied to detect the end point of the titration of Ln(3+) ions.     

Mixed-ligand cobalt(III) complexes derived from bis(dehydroacetato)ethylenediimine

Summary A hydroxocobalt(III) complex (1a), has been obtained by reaction of bis(dehydroacetato)ethylenediimine (H₂dhaen) with cobalt(II) hydroxide or acetate in the presence of air. Addition of a second complexing agent leads to the formation of a series of mixed-ligand complexes (2)-(26) having either the trans- or cis- configuration. In the cis- complexes, the quadridentate ligand dhaen adopts a nonplanar conformation. Configurations are distinguishable from characteristic differences in the electronic and n.m.r. spectra.