Series Of Ln Research Articles

Syntheses, structures and near-infrared luminescent properties of a series of Ln(III) coordination polymers

Abstract Using aromatic carboxylic acids as main ligands, four Ln(III) coordination polymers, [Er(CH3C6H4COO)2(Ac)(H2O)]n (1), [Yb(β-C10H7COO)2(Ac)(H2O)]n (2), [Nd(C9H7O2)3]n (3) and [Ho(C9H7O2)3]n (4) (CH3C6H4COO = p-toluylate, Ac = acetate, β-C10H7COO = β-naphthoyloxy, C9H7O2 = cinnamate), were synthesized by hydrothermal method and their structures were studied by single-crystal X-ray diffraction. Polymers 1 and 2 possess 2D layer structures, and polymers 3 and 4 possess 1D chain structures. At room temperature in the solid state, the IR, UV–Vis–NIR spectra and the emission spectra in the visible and near-infrared (NIR) regions of the four polymers were determined. In the NIR region, polymers 1–4 show characteristic emission bands of the corresponding Ln(III) ions which exhibit shift, splitting or broadness in comparison with their theoretical emission bands. This can be confirmed by their UV–Vis–NIR spectra and discussed emphatically.

Synthesis, structure, and photophysical property of series of Ln(III) coordination polymers with different carboxylato ligands (Ln = Sm, Eu)

Four Ln(III) coordination polymers, {[Ln2(1,3-bdc)3(H2O)4]·DMF·H2O}n (Ln = Sm 1, Eu 2) and [Ln2(mal)3(H2O)6]n (Ln = Sm 3, Eu 4) (1,3-H2bdc = isophthalate acid, H2mal = malonate acid), were hydrothermally synthesized and characterized by single-crystal X-ray diffraction, elemental analysis, IR spectra, UV–Vis–NIR absorption spectra, and fluorescence spectra. The structural analyses reveal that polymer 1 is a 3D coordination polymer. Its asymmetry unit contains two crystallographically independent Sm(III) ions, both are eight-coordinated. The 1,3-bdc2− anions show three different coordination modes. The structure of polymer 2 is isomorphous with that of 1. Polymer 3 is also a 3D coordination polymer, its asymmetry unit contains one Sm(III) ion, which is nine-coordinate. The mal2− anions have two different coordination modes. The structure of polymer 4 is isomorphous with that of 3. The luminescent study shows that polymers 1, 2, and 4 exhibit characteristic emission bands in the visible region, corresponding to the transitions of the Ln(III) ions. By comparison and analysis of luminescence, it is found that the incidence of the same ligand on the corresponding spectra of different Ln(III) ions is different, and the influence of different ligands on luminescence of the same Ln(III) ion is also very different.

Unusual High Thermal Stability within a Series of Novel Lanthanide TATB Frameworks: Synthesis, Structure, and Properties (TATB = 4,4′,4″-s-Triazine-2,4,6-triyl-tribenzoate)

A series of multifunctional lanthanide-organic frameworks Ln(TATB)(H2O) (Ln = Y 1, Eu 2, Gd 3, Tb 4, Dy 5, Ho 6, and Er 7; TATB = 4,4′,4″-s-triazine-2,4,6-triyl-tribenzoate) with an unprecedented (4,8)-connected topology have been synthesized and characterized. The structures of these compounds were determined by single crystal X-ray diffraction and their thermal stability, sorption, as well as luminescent and magnetic properties were also investigated. Compounds 1–7 are isomorphic and present an open non-interpenetrated three-dimensional microporous framework constructed by infinite dinuclear-based, rod-shaped lanthanide-carboxylate secondary building units (SBUs) which arranged in nearly mutually perpendicular directions and interwoven by TATB linkers. All these compounds exhibit very high thermal stability and are stable up to 550 °C. The pore characteristics and gas sorption properties of these compounds were studied by experimentally measuring different gases (CO2, N2, and H2) and different solvent m...

Shape-conserving enhancement of vibrational circular dichroism in lanthanide complexes

The VCD spectra of lanthanide chelates with two chiral ligands display conserved sequences of bands throughout the Ln series. Some compounds (Tm, Yb) feature increased bands and strongly improved signal-to-noise ratios, an effect we dub Lanthanide Induced VCD Enhancement (LIVE).

Syntheses and crystal structures of anhydrous Ln(hfac)3(monoglyme). Ln = La, Ce, Pr, Sm, Eu, Gd, Tb, Dy, Er, Tm

The crystal structures of a broad series of anhydrous Ln(hfac)(3)(monoglyme) complexes, prepared in moderate to high yield, are presented: hfac = 1,1,1,5,5,5-hexafluoroacetylacetonato-; Ln = La, Ce, Pr, Sm, Eu, Gd, Tb, Dy, Er, Tm. This study contradicts the general assumption that monoglyme is too small a polyether to act as a partitioning agent displacing coordinated water on the larger lanthanide(III) ions. The structures of an intermediate La(hfac)(3)(monoglyme)(2) species and the hydrated Ce(hfac)(3)(monoglyme)(H(2)O) species are also included. The crystallographic evidence presented herein is supplemented by other characterization techniques (melting point, IR, etc.) and trends are delineated.

Thermal and luminescence characterization of lanthanide 2,6-naphthalenedicarboxylates series

The lanthanide 2,6-naphthalenedicarboxylates series of the formulas Ln 2(ndc) 3·nH 2O, where Ln = lanthanides from La(III) to Lu(III); ndc – C 10H 6(COO) 2 2−; n = 4, 4.5 or 5 have been prepared by the precipitation method. All obtained products were examined and characterized by elemental analysis, FTIR spectroscopy, simultaneous thermal analyses TG-DSC and TG-FTIR, X-Ray diffraction patterns as well as luminescence measurements. The crystalline compounds form three isostructural groups: Ce–Sm; La and Eu–Dy; Ho–Lu. In all complexes, the ndc 2− ligand appears in the deprotonated form. Heating of the complexes resulted in the multi-steps decomposition process. The dehydration process leads to the formation of stable crystalline Ln 2ndc 3 compounds which further decompose to the corresponding lanthanide oxides (air atmosphere). In argon atmosphere they decompose with releasing of water, carbon oxides and naphthalene molecules. The luminescence properties of Eu(III), Nd(III), Tb(III) and Er(III) complexes were investigated. The complexes of Eu(III) and Tb(III) emitted red and green light when excited by ultraviolet light whereas Nd(III) and Er(III) display emissions in the NIR region.

Selective separation of samarium(III) by synergistic extraction with β-diketone and methylphenylphenanthroline carboxamide

Synergistic extraction of trivalent lanthanides (Lns(III)) with pivaloyltrifluoroacetone (HA) and N-methyl-N-phenyl-1,10-phenanthroline-2-carboxamide (MePhPTA) was evaluated across the Ln series. The distribution ratio (D) of Sm(III) under an identical condition was the largest among all Lns(III). The separation factor (SF) between Sm(III) and Nd(III) (SF=DSm/DNd) was 2.0 and SF between Sm(III) and Eu(III), (DSm/DEu) was 1.4. Upon analyzing the extraction data in detail on the basis of mass balance, it was found that the dominant extracted species of light Lns(III) was a stable ternary complex consisting of Ln(III), HA, and MePhPTA (B), namely, LnA3B, while the dominant extracted species of heavy Lns(III) was the ion pair, [LnA2B]+ClO4−.The complex for Pr(III) was very stable (the stability constant, β¯, denoted as [LnA3B]o[LnA3]o−1[B]o−1, was 108.3). It suggests that LnA3 can form two 5-membered rings with MePhPTA, and the size of Pr(III) matches to the distance between the donor atoms in MePhPTA. Although the stability constant decreased with increasing Ln atomic number, the synergistic extraction constant (Kex31=[LnA3B]o[H+]3[Ln3+]−1[HA]o−3[B]o−1) was the largest for Sm(III). Since the constant, Kex31, is given by Kex31=Kex30×β¯ where Kex30=[LnA3]o[H+]3[Ln3+]−1[HA]o−3, the largest Kex31 of Sm(III) is attributable to the difference of the degree of the variation of Kex30 between the light and the heavy Lns(III); the increment of extraction constant of LnA3 (logKex30) for light Lns is larger than the decrement of the stability constant of LnA3B (log⁡β¯), while the increment of logKex30 of post-Sm lessens than the decrement of log⁡β¯. From these results, it is concluded that selective separation of a particular Ln(III) among all Lns(III) is possible using synergistic extraction with a suitable combination of a multidentate β-diketone and a Lewis base.

Preparation, Crystal Structures, and Magnetic Features for a Series of Dinuclear [NiIILnIII] Schiff-Base Complexes: Evidence for Slow Relaxation of the Magnetization for the DyIII Derivative

A series of dinuclear [Ni(II)Ln(III)] Schiff-base complexes (using a Schiff-base dicompartmental ligand derived from o-vanillin [H(2)valpn = 1,3-propanediylbis(2-iminomethylene-6-methoxy-phenol)]) with Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, and a hydroxo-bridged tetranuclear [Ni(II)Yb(III)] are reported. The crystal structures have been solved for 10 dinuclear complexes revealing four arrangements for the dinuclear units, which are modulated by the coordinated solvent molecules and the nitrato-anion interactions. The magnetic behaviors have been investigated, and the nature of the Ni(II)-Ln(III) exchange interaction has been emphasized by comparison with the behavior of the related [Zn(II)Ln(III)] derivatives. This allowed for establishing that the interaction within these compounds is antiferromagnetic with the 4f ions of the beginning of the Ln series and turns ferromagnetic from Gd(III) toward the end of the series. AC susceptibility investigations clearly show the occurrence of slow relaxation processes of the magnetization close to 2 K for the dinuclear [Ni(II)Dy(III)] complex.

NIR-luminescence from ternary lanthanide [Ho III, Pr III and Tm III] complexes with 1-(2-naphthyl)-4,4,4-trifluoro-1,3-butanedionate

The ligand 1-(2-naphthyl)-4,4,4-trifluoro-1,3-butanedionate (Htfnd) has been employed to synthesize six novel ternary–lanthanide complexes in which the synergic ligands were 1,10-phenanthroline-5,6-dione (dione) and 4,5-diazafluoren-9-one (dafone), respectively. Two series of complexes Ln(tfnd) 3dione and Ln(tfnd) 3dafone (Ln=Ho, Pr, Tm) were obtained. These complexes were characterized by elemental analysis, Fourier Transform Infrared spectra and diffused reflectance. After ligand-mediated excitation, Ln(tfnd) 3dione and Ln(tfnd) 3dafone all show the characteristic NIR luminescence of the corresponding Ln 3+ ions (Ln=Ho, Pr, Tm). This can be attributed to the efficient energy transfer from ligands to central Ln 3+ ions, via an antenna effect. The indirect energy transfer in the complexes has been investigated and the differences in the luminescence intensity between Ln(tfnd) 3dione and Ln(tfnd) 3dafone were discussed in detail. The excellent luminescent performances enable these NIR-luminescent complexes to have potential applications in optical amplification operating at 1300 or 1500 nm.

Lanthanide Nitrate Complexes of Tri-Isobutylphosphine Oxide: Solid State and CD2Cl2 Solution Structures

The complexes Ln(NO(3))(3)L(3) between Ln(NO(3))(3) and (i)Bu(3)PO (=L) have been prepared for Ln = La-Lu (excluding Pm). The isolated complexes have been characterized by infrared spectroscopy, mass spectrometry, and elemental analysis. The single crystal X-ray structures have been determined for representative complexes across the series Ln = Ce, Pr, Nd, Sm, Gd, Dy, Ho, Er, Tm, and Yb and show the coordination geometry around the metal to be the same with 9-coordinate lanthanide ions and bidentate nitrates. Subtle changes in the coordination of the nitrate ligand occur from Sm onward. Changes in the infrared spectra correlate well with changes in the X-ray structures. Solution properties have been examined by variable temperature multinuclear ((1)H, (13)C, (15)N, and (31)P) NMR spectroscopy in CD(2)Cl(2). The spectra of complexes of the early lanthanides are consistent with the presence of a single species in solution while those of the heavier lanthanides show that more than one complex is present in solution and that two inequivalent phosphorus environments are observable at low temperature. The fluxional behavior is lanthanide dependent with smaller ions giving static structures at higher temperature. Complexes with tricyclohexylphosphine oxide show that the dynamic NMR behavior is also related to the size of the ligand. Analysis of the lanthanide induced shifts indicates minor changes in solution structure occur from Sm onward which correlate well with the solid state structures.

Europium and terbium ortho-, meta-, and para-methoxybenzoates: Structural peculiarities, luminescence, and energy transfer

A series of methoxybenzoates Ln(MOBA) 3· nH 2O and Ln(MOBA) 3·L (Ln = Eu, Gd, Tb; MOBA – 2-, 3-, and 4-methoxybenzoate anions, L – 1,10-phenanthroline (Phen) and 2,2′-bipyridine (Bpy)) was investigated by methods of optical spectroscopy. The effects of methoxy groups located in different positions of the benzene ring on the structure of Eu 3+ luminescence centers, the lifetimes of 5D 0 (Eu 3+) and 5D 4 (Tb 3+) states, the energies of the lowest singlet and triplet states of the ligands, and on processes of the excitation energy transfer to Eu 3+ and Tb 3+ ions are examined. The spectroscopic data for lanthanide methoxybenzoates are in accordance with known structural peculiarities: the lanthanide–oxygen bond lengths and the Ln 3+ coordination polyhedron distortions. The low-energy ligand–metal charge transfer state was identified in the compound Eu(4-MOBA) 3. It was shown that the distortions of Ln 3+ luminescence centers are the smallest for 2-methoxybenzoates. The enhancement of Tb 3+ luminescence efficiency by 2–2.5 times for terbium methoxybenzoates with phenanthroline Tb(MOBA) 3·Phen in comparison with benzoate Tb(Benz) 3·Phen at 295 K is caused by a decrease in the rate of back energy transfer due to an increase in the energy of the lowest Phen triplet state. The highest luminescence efficiency was observed for Tb(4-MOBA) 3·Phen. Judging from the results presented, the Tb(4-MOBA) 3·Phen can be potentially more preferable for the fabrication of emitter layers in organic light emitting diodes (OLEDs) than the Tb(2-MOBA) 3·Phen·H 2O, which has been tested before.

Relaxometric Study of a Series of Monoaqua GdIII Complexes of Rigidified EGTA‐Like Chelators and Their Noncovalent Interaction with Human Serum Albumin

AbstractThe lanthanide(III) complexes of five EGTA [ethyleneglycol‐bis(2‐aminoethyl) ether‐N,N,N′,N′‐tetraacetic acid] derivatives fused with aromatic (benzene: L1; naphthalene: L2) and functionalized aromatic (L3–L5) moieties on the oxyethylene bridge were investigated in aqueous solution. 1H and 13C NMR spectra of the LaIII and LuIII complexes of L1 and L2 indicate that the structural differences across the Ln series found for the [Ln(EGTA)]– complexes is maintained in the new derivatives. The presence of the aromatic moiety favours an increased stereochemical rigidity, as assessed by VT 13C NMR spectra. Temperature‐dependent 17O NMR spectroscopic data and 1/T1 1H NMRD profiles of the GdIII complexes of L1–L3 were measured and globally analyzed to obtain the parameters influencing the water exchange rate, kex, and rotational dynamics. The kex values are ca. twice as high as the corresponding value of [Gd(EGTA)]– and very close to optimal. The lipophilic complexes [GdL4]– and [GdL5]– form micellar aggregates whose NMRD profiles were measured and analyzed in terms of a model that allows separation of global motion and local rotation. The noncovalent binding interaction of the complexes to human serum albumin and the relaxivity of the macromolecular conjugates were investigated with relaxometric techniques at 20 MHz and 298 K, and the importance of a restricted local motion of the complex at the binding site for attaining large relaxivity enhancement outlined. Theoretical docking simulations and relaxometric competition experiments provided insights into the binding modes of the complexes.

Multi-functional magnetic, ferroelectric, and fluorescent homochiral lanthanide (Ln)–camphorate compounds built on helical {Ln–O}n inorganic substructures

The design and preparation of homochiral metal–organic coordination polymers is presently a topic of intense focus. Herein, we present a series of isomorphous Ln(III)–camphorate compounds with the P65 chiral space group. The overall structural feature is the hex rod-packing architecture, where each helical {Ln–O}n inorganic substructure connects to six analogs via chiral D-cam spacers (D-H2Cam = D-camphoric acid). Moreover, the Ln-related magnetic, fluorescent and chirality-related ferroelectric merits of these compounds are explored.

A series of tetranuclear lanthanide complexes comprising two edge-sharing triangular units with field-induced slow magnetic relaxation for Dy4 species

The syntheses, crystal structures and magnetic studies are reported for a series of Ln(4) clusters formulated as Ln(4)(μ(3)-OH)(2)(php)(2)(OAc)(6)(H(2)O)(2)]·4MeOH·nH(2)O (Ln = Gd (1), Tb (2), Dy (3) (n = 2) and Ho (4) (n = 0); H(2)php = 2,6-(picolinoylhydrazone)pyridine). The overall metal core of each cluster is comprised of two edge-sharing triangular Ln(3) units linked by μ(3)-OH bridges. Direct-current (dc) magnetic susceptibility studies reveal that the Ln(III) ions are very weakly coupled in all four compounds. Alternating-current (ac) magnetic susceptibility studies for 3 indicate that field-induced slow relaxation phenomenon occurs for this compound.

Covalent Lanthanide Chemistry Near the Limit of Weak Bonding: Observation of (CpSiMe3)3Ce−ECp* and a Comprehensive Density Functional Theory Analysis of Cp3Ln−ECp (E = Al, Ga)

Experimental evidence for the existence of two new lanthanide-metalloligand adducts (CpSiMe(3))(3)Ce-ECp* (E = Al, Ga) is presented. Paramagnetic (1)H NMR titration experiments were employed to derive thermodynamic parameters for Ce-Ga dative bond formation, and competition experiments with the U analogue were performed. Density functional theory calculations were undertaken using model complexes Cp(3)Ln-ECp where Ln = La-Lu and E = Al, Ga. The Ln-E bond distances were predicted to decrease more sharply across the Ln series than those involving hard Lewis bases; however, local increases were observed at Eu and Yb. Electronic analyses were performed in the natural bond orbital-natural localized molecular orbital (NBO/NLMO) formalism, indicating that the E→Ln acceptor orbital is primarily of d character in all cases. The Cp(-) ligands donate significant electron density to the Ln d manifold and thus in its bonding interactions with a dative ligand the Ln center may be considered to be Ln(2+) in the f((n-3))d(1) electronic configuration (n = 3 for La, etc.). Molecular dipole moments, NLMO and natural population analyses, bond order indices, measures of E→Ln charge transfer, and calculated Ln-E heterolytic bond disruption enthalpies were found to follow saw-tooth trends, which correlate to varying degrees with the ionization potentials of the Ln(+) ions (corrected for their ground state-to-f((n-3))d(2) excitations). It is proposed that a steric-strain component which increases with the lanthanide contraction in this case balances the Ln-E bond stabilizing effect of core-orbital contraction. All data indicate that the Ln-E bonding interactions are predominantly of covalent or nonpolar donor-acceptor character. However, the formation of a strong covalent bond is not observed because of resistance to reduction of an effectively divalent Ln center.

Synthesis, structures and physical properties of new 3D lanthanide coordination polymers constructed from 1,2,4,5-benzenetetracarboxylic acid

A series of new 3D coordination polymers Ln 2(BTC) 1.5(H 2O)(DMSO) (Ln Eu( 1), Gd( 2), Tb( 3), Dy( 4), Ho( 5)) (H 4BTC = 1,2,4,5-benzenetetracarboxylic acid) have been solvothermal synthesized by the reactions of lanthanide ions with 1,2,4,5-benzenetetracarboxylic acid in a DMSO/H 2O solution. These compounds possess the same 3D architectures based on dinuclear lanthanide SBUs {Tb 2O 4} linked by BTC 4− anions and exhibit unprecedented 3D topological nets. Compounds 1 and 3 are strong luminescent materials which display characteristic Eu 3+ and Tb 3+ emission bands in the visible region. The magnetic properties of 2– 5 have also been investigated through the measurement of their magnetic susceptibilities over the temperature range of 2–300 K.

Several Factors Influencing the Stability of Extracted Species in Synergistic Extraction of Lanthanide(III) with Pivaloyltrifluoro acetone and 2,2′-Bipyridyl

The stability constants and the hydration number of a complex between tris(pivaloyltrifluoroacetonato)lanthanide(III) (LnA(3)) and 2,2'-bipyridyl (B), LnA(3)B, and the complexation heat were determined across the Ln series by a solvent-extraction technique, Karl Fischer coulometry, and calorimetry, successively. The number of water molecules released from LnA(3) upon the complexation with B as well as the values of the stability constant increased along with increasing Ln atomic number to around Dy(III); via a maximum, it decreased. It is concluded that the largest stability constant of the complex of Ho(III) or this vicinity is derived from the strongest bond energy, due to the fitness between LnA(3) and B. This conclusion was supported by the trend of the variation of the entropy change as well as that of the hydration number across the Ln series.

Crystal Structures of the Europium and Yttrium Hydroxychromates Eu(OH)(CrO4) and Y(OH)(CrO4); Structural Evolution as a Function of the Ln3+ Ionic Radius

AbstractThe compounds Eu(OH)(CrO4) and Y(OH)(CrO4) were obtained under hydrothermal conditions and characterized by single‐crystal X‐ray diffraction analysis. They are isostructural and crystallize in the monoclinic system, space group P21/n (no. 14) with lattice parameters a = 8.278(1) Å, b = 11.400(2) Å, c = 8.393(1) Å, β = 93.76(2)°, V = 790.3(2) Å3, Z = 4, d = 4.79 g·cm–3 for Eu(OH)(CrO4) and a = 8.151(1) Å, b = 11.362(2) Å, c = 8.285(1) Å, β = 94.23(1)°, V = 765.2(2) Å3, Z = 4, d = 3.85 g·cm–3 for Y(OH)(CrO4). The [EuO8] polyhedra form infinite double chains along the a direction, which are connected by common edges and corners. These double chains are related together in the two other directions by the [CrO4]2– tetrahedra to form a three‐dimensional network in which channels appear parallel to the [100] direction. We examine the structural evolution, as a function of the Ln3+ ionic radius, in the series Ln(OH)(CrO4) compounds (with Ln = Nd, Eu, Gd, Tb, Er, Yb) and Y(OH)(CrO4). To determine the best coordination number of each lanthanide and yttrium ions, different calculations of bond valence sum were realized.

The lanthanide contraction within the sparkle model

AbstractThe sparkle model has been introduced to allow the a priori quantum chemical calculation of properties, mainly geometries, of lanthanide complexes. In this work, we compute Sparkle/PM3 optimized geometries for the isostructural series of complexes Ln[TREN‐1,2‐HOIQO(H2O)2] and Ln[(H2O)9]3+, with Ln = La‐Lu (except Pm). The results reveal the expected contraction for each series of complexes. We conclude that the lanthanide contraction phenomenon is indeed present within Sparkle/PM3, a fact which can only reinforce the sparkle model as a powerful tool for the prediction and rationalization of the geometric features of lanthanide complexes and for their a priori design. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2010

A study on the NIR-luminescence emitted from ternary lanthanide [Er(III), Nd(III) and Yb(III)] complexes containing fluorinated-ligand and 4,5-diazafluoren-9-one

A series of lanthanide complexes Ln(tfnb) 3dafone, Ln(hfth) 3dafone and Ln(pfnd) 3dafone (Ln = Er, Nd and Yb) with fluorinated-ligand 1-(2-naphthyl)-4,4,4-trifluoro-1,3-butanedionate (Htfnb), 4,4,5,5,6,6,6-heptafluoro-1-(2-thienyl)hexane-1,3-dione (Hhfth) and 4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-pentadecafluoro-1-(naphthalen-2-yl)decane-1,3-dione (Hpfnd) served as main sensitizers, respectively, and 4,5-diazafluoren-9-one (dafone) as the synergistic ligand were synthesized. Upon excitation at the maximum absorption of the ligands, the complexes all show the characteristic near-infrared (NIR) luminescence of the corresponding Ln 3+ ions, which is due to efficient energy transfer from the ligands to the central Ln 3+ ions via an antenna effect. Moreover, an indirect excitation model is proposed and the influence of ligands on the luminescence properties of the complexes is further discussed.