Lanthanide chelates containing pyridine units with potential application as contrast agents in magnetic resonance imaging

A new pyridine-containing ligand, N,N'-bis(6-carboxy-2-pyridylmethyl)ethylenediamine-N,N'-diacetic acid (H(4)L), has been designed for the complexation of lanthanide ions. (1)H and (13)C NMR studies in D(2)O solutions show octadentate binding of the ligand to the Ln(III) ions through the nitrogen atoms of two amine groups, the oxygen atoms of four carboxylates, and the two nitrogen atoms of the pyridine rings. Luminescence measurements demonstrate that both Eu(III) and Tb(III) complexes are nine-coordinate, whereby a water molecule completes the Ln(III) coordination sphere. Ligand L can sensitize both the Eu(III) and Tb(III) luminescence; however, the quantum yields of the Eu(III)- and Tb(III)-centered luminescence remain modest. This is explained in terms of energy differences between the singlet and triplet states on the one hand, and between the 0-phonon transition of the triplet state and the excited metal ion states on the other. The anionic [Ln(L)(H2O)]- complexes (Ln=La, Pr, and Gd) were also characterized by theoretical calculations both in vacuo and in aqueous solution (PCM model) at the HF level by means of the 3-21G* basis set for the ligand atoms and a 46+4 f(n) effective core potential for the lanthanides. The structures obtained from these theoretical calculations are in very good agreement with the experimental solution structures, as demonstrated by paramagnetic NMR measurements (lanthanide-induced shifts and relaxation-rate enhancements). Data sets obtained from variable-temperature (17)O NMR at 7.05 T and variable-temperature (1)H nuclear magnetic relaxation dispersion (NMRD) on the Gd(III) complex were fitted simultaneously to give insight into the parameters that govern the water (1)H relaxivity. The water exchange rate (k(298)(ex)=5.0 x 10(6) s(-1)) is slightly faster than in [Gd(dota)(H2O)]- (DOTA=1,4,7,10-tetrakis(carboxymethyl)-1,4,7,10-tetraazacyclododecane). Fast rotation limits the relaxivity under the usual MRI conditions.     

The first self-assembled trimetallic lanthanide helicates driven by positive cooperativity

The segmental tris-tridentate ligand L7 reacts with stoichiometric quantities of Ln(III) (Ln=La-Lu) in acetonitrile to give the complexes [Ln(2)(L7)(3)](6+) and [Ln(3)(L7)(3)](9+). Formation constants point to negligible size-discriminating effects along the lanthanide series, but Scatchard plots suggest that the self-assembly of the trimetallic triple-stranded helicates [Ln(3)(L7)(3)](9+) is driven to completion by positive cooperativity, despite strong intermetallic electrostatic repulsions. Crystallization provides quantitatively [Ln(3)(L7)(3)](CF(3)SO(3))(9) (Ln=La, Eu, Gd, Tb, Lu) and the X-ray crystal structure of [Eu(3)(L7)(3)](CF(3)SO(3))(9).(CH(3)CN)(9).(H(2)O)(2) (Eu(3)C(216)H(226)N(48)O(35)F(27)S(9), triclinic, P1, Z=2) shows the three ligand strands wrapped around a pseudo-threefold axis defined by the three metal ions rigidly held at about 9 A. Each metal ion is coordinated by nine donor atoms in a pseudo-trigonal prismatic arrangement, but the existence of terminal carboxamide units in the ligand strands differentiates the electronic properties of the terminal and the central metallic sites. Photophysical data confirm that the three coordination sites possess comparable pseudo-trigonal symmetries in the solid state and in solution. High-resolution luminescence analyses evidence a low-lying LMCT state affecting the central EuN(9) site, so that multi-metal-centered luminescence is essentially dominated by the emission from the two terminal EuN(6)O(3) sites in [Eu(3)(L7)(3)](9+). New multicenter equations have been developed for investigating the solution structure of [Ln(3)(L7)(3)](9+) by paramagnetic NMR spectroscopy and linear correlations for Ln=Ce-Tb imply isostructurality for these larger lanthanides. NMR spectra point to the triple helical structure being maintained in solution, but an inversion of the magnitude of the second-rank crystal-field parameters, obtained by LIS analysis, for the LnN(6)O(3) and LnN(9) sites with respect to the parameters extracted for Eu(III) from luminescence data, suggests that the geometry of the central LnN(9) site is somewhat relaxed in solution.     

Tethered dinuclear europium(III) macrocyclic catalysts for the cleavage of RNA

Dinuclear europium(III) complexes of the macrocycles 1,3-bis[1-(4,7,10-tris(carbamoylmethyl)-1,4,7,10-tetraazacyclododecane]-m-xylene (1), 1,4-bis[1-(4,7,10-tris(carbamoylmethyl)-1,4,7,10-tetraazacyclododecane]-p-xylene (2), and mononuclear europium(III) complexes of macrocycles 1-methyl-,4,7,10-tris(carbamoylmethyl)-1,4,7,10-tetraazacyclododecane (3), 1-[3'-(N,N-diethylaminomethyl)benzyl]-4,7,10-tris(carbamoylmethyl)-1,4,7,10-tetraazacyclododecane (4), and 1,4,7-tris(carbamoylmethyl)-1,4,7,10-tetraazacyclododecane (5) were prepared. Studies using direct excitation ((7)F0 --> (5)D0) europium(III) luminescence spectroscopy show that each Eu(III) center in the mononuclear and dinuclear complexes has two water ligands at pH 7.0, I = 0.10 M (NaNO3) and that there are no water ligand ionizations over the pH range of 7-9. All complexes promote cleavage of the RNA analogue 2-hydroxypropyl-4-nitrophenyl phosphate (HpPNP) at 25 degrees C (I = 0.10 M (NaNO3), 20 mM buffer). Second-order rate constants for the cleavage of HpPNP by the catalysts increase linearly with pH in the pH range of 7-9. The second-order rate constant for HpPNP cleavage by the dinuclear Eu(III) complex (Eu2(1)) at pH 7 is 200 and 23-fold higher than that of Eu(5) and Eu(3), respectively, but only 7-fold higher than the mononuclear complex with an aryl pendent group, Eu(4). This shows that the macrocycle substituent modulates the efficiency of the Eu(III) catalysts. Eu2(1) promotes cleavage of a dinucleoside, uridylyl-3',5'-uridine (UpU) with a second-order rate constant at pH 7.6 (0.021 M(-1) s(-1)) that is 46-fold higher than that of the mononuclear Eu(5) complex. Methyl phosphate binding to the Eu(III) complexes is energetically most favorable for the best catalysts, and this supports an important role for the catalyst in stabilization of the developing negative charge on the phosphorane transition state. Despite the formation of a bridging phosphate ester between the two Eu(III) centers in Eu2(1) as shown by luminescence spectroscopy, the two metal ion centers are only weakly cooperative in cleavage of RNA and RNA analogues.     

Direct excitation luminescence spectroscopy of Eu(III) complexes of 1,4,7-tris(carbamoylmethyl)-1,4,7,10- tetraazacyclododecane derivatives and kinetic studies of their catalytic cleavage of an RNA analog

The macrocycles 1,4,7-tris(carbamoylmethyl)-1,4,7,10-tetrazacyclododecane (1), 1,4,7-tris[(N-ethyl)carbamoylmethyl]-1,4,7,10-tetraazacyclododecane (2), 1,4,7-tris[(N,N-diethyl)carbamoylmethyl]-1,4,7,10-tetraazacyclododecane (3) and their Eu(III) complexes are prepared. Studies using direct Eu(III) excitation luminescence spectroscopy show that all three Eu(III) complexes exhibit only one predominant isomer with two bound waters under neutral to mildly basic conditions (Eu(X)(H(2)O)(2) for X = 1-3). There are no detectable ligand ionizations over the pH range 5.0-8.0 for Eu(3), 5.0-8.5 for Eu(2) or 5.0-9.5 for Eu(1). The three Eu(III) complexes show a linear dependence of second-order rate constants for the cleavage of 4-nitrophenyl-2-hydroxyethylphosphate (HpPNP) on pH in the range 6.5-8.0 for Eu(3), 7.0-8.5 for Eu(2) and 7.0-9.0 for Eu(1). This pH-rate profile is consistent with the Eu(III) complex-substrate complex being converted to the active form by loss of a proton and with Eu(III) water pK(a) values that are higher than 8.0 for Eu(3), 8.5 for Eu(2) and 9.0 for Eu(1). Inhibition studies show that Eu() binds strongly to the dianionic ligand methylphosphate (K(d) = 0.28 mM), and more weakly to diethylphosphate (K(d) = 7.5 mM), consistent with a catalytic role of the Eu(III) complexes in stabilizing the developing negative charge on the phosphorane transition state.     

Synthesis, structures, and luminescence properties of lanthanide complexes with structurally related new tetrapodal ligands featuring salicylamide pendant arms

To explore the relationships between the structures of ligands and their complexes, we have synthesized and characterized a series of lanthanide complexes with two structurally related ligands, 1,1,1,1-tetrakis{[(2'-(2-benzylaminoformyl))phenoxyl]methyl}methane (L(I)) and 1,1,1,1-tetrakis{[(2'-(2-picolyaminoformyl))phenoxyl]methyl}methane (L(II)). A series of zero- to three-dimensional lanthanide coordination complexes have been obtained by changing the substituents on the Pentaerythritol. Our results revealed that, complexes of the L(I) ligand, {Ln(4)L(I)(3)(NO(3))(12).nC(4)H(10)O}(infinity) (Ln = Nd, Eu, Tb, Er, n = 3 or 6)] show the binodal 3,4-connected three-dimensional interpenetration coordination polymers with topology of a (8(3))(4)(8(6))(3) notation. Compared to L(I), complexes of L(II) present a cage-like homodinuclear [Ln(2)L(II)(2)(NO(3))(6).2H(2)O].nH(2)O (Ln = Nd, Tb, Dy, n = 0 or 1) or a helical one-dimensional coordination {[ErL(II)(NO(3))(3).H(2)O].H(2)O}(infinity) polymer. The luminescence properties of the resulting complexes formed with ions used in fluoroimmunoassays (Ln = Eu, Tb) are also studied in detail. It is noteworthy that subtle variation of the terminal group from benzene to pyridine not only sensibly affects the overall molecular structures but also the luminescence properties as well.     

Luminescence tuning of imidazole-based lanthanide(III) complexes [Ln = Sm, Eu, Gd, Tb, Dy

To tune the lanthanide luminescence in related molecular structures, we synthesized and characterized a series of lanthanide complexes with imidazole-based ligands: two tripodal ligands, tris{[2-{(1-methylimidazol-2-yl)methylidene}amino]ethyl}amine (Me(3)L), and tris{[2-{(imidazol-4-yl)methylidene}amino]ethyl}amine (H(3)L), and the dipodal ligand bis{[2-{(imidazol-4-yl)methylidene}amino]ethyl}amine (H(2)L). The general formulas are [Ln(Me(3)L)(H(2)O)(2)](NO(3))(3)·3H(2)O (Ln = 3+ lanthanide ion: Sm (1), Eu (2), Gd (3), Tb (4), and Dy (5)), [Ln(H(3)L)(NO(3))](NO(3))(2)·MeOH (Ln(3+) = Sm (6), Eu (7), Gd (8), Tb (9), and Dy (10)), and [Ln(H(2)L)(NO(3))(2)(MeOH)](NO(3))·MeOH (Ln(3+) = Sm (11), Eu (12), Gd (13), Tb (14), and Dy (15)). Each lanthanide ion is 9-coordinate in the complexes with the Me(3)L and H(3)L ligands and 10-coordinate in the complexes with the H(2)L ligand, in which counter anion and solvent molecules are also coordinated. The complexes show a screw arrangement of ligands around the lanthanide ions, and their enantiomorphs form racemate crystals. Luminescence studies have been carried out on the solid and solution-state samples. The triplet energy levels of Me(3)L, H(3)L, and H(2)L are 21?000, 22?700, and 23?000 cm(-1), respectively, which were determined from the phosphorescence spectra of their Gd(3+) complexes. The Me(3)L ligand is an effective sensitizer for Sm(3+) and Eu(3+) ions. Efficient luminescence of Sm(3+), Eu(3+), Tb(3+), and Dy(3+) ions was observed in complexes with the H(3)L and H(2)L ligands. Ligand modification by changing imidazole groups alters their triplet energy, and results in different sensitizing ability towards lanthanide ions.     

Eu(III) macrocyclic complexes promote cleavage of and bind to models for the 5'-cap of mRNA. Effect of pendent group and a second metal ion

The interaction of three Eu(III) macrocyclic complexes Eu(THED)3+, Eu(ATHC)3+, and Eu(ATHC)3+, and Eu(S-THP)3+ with two 5'-cap model compounds, GpppG and m7GpppG is studied (THED = 1,4,7,10-tetrakis(2-hydroxyethyl)-1,4,7,-10-tetraazacyclododecane, ATHC = 1-(carbamoylmethyl)-4,7,10-tris(2-hydroxyethyl)-1,4,7,10- tetraazacyclododecane, S-THP = 1S,4S,7S,10S-tetrakis(2-hydroxypropyl)-1,4,7,10-tetraazacyclododecane). Laser-induced excitation luminescence spectroscopy is used to study the binding of Eu(S-THP)3+ to GpppG (K = 5.9 x 10(4) M-1) and to characterize the Eu(S-THP)-GpppG complex. Both Eu(THED)3+ and Eu(S-THP)3+ bind to m7GpppG as monitored by use of fluorescence spectroscopy with binding constants of 5.9 x 10(3) and 4.4 x 10(4) M-1, respectively. The kinetics of cleavage of GpppG by two macrocyclic complexes is studied. Cleavage of GpppG by Eu(THED)3+ is accelerated by 15-fold in the presence of an equivalent of Zn(NO3)2 at pH 7.3, 37 degrees C, suggesting that two metal ions accelerate the cap cleavage reaction. Eu(ATHC)3+ promotes cleavage of GpppG with a pseudo-first-order rate constant of 2.6 x 10(-5) s-1 at pH 7.3, 37 degrees C, and 0.30 mM complex.     

Structures and properties of porous coordination polymers based on lanthanide carboxylate building units

A series of 3-D lanthanide porous coordination polymers, [Ln(6)(BDC)(9)(DMF)(6)(H(2)O)(3)·3DMF](n) [Ln = La, 1; Ce, 2; Nd, 3], [Ln(2)(BDC)(3)(DMF)(2)(H(2)O)(2)](n) [Ln = Y, 4; Dy, 5; Eu, 6], [Ln(2)(ADB)(3)(DMSO)(4)·6DMSO·8H(2)O](n) [Ln = Ce, 7; Sm, 8; Eu, 9; Gd, 10], {[Ce(3)(ADB)(3)(HADB)(3)]·30DMSO·29H(2)O}(n) (11), and [Ce(2)(ADB)(3)(H(2)O)(3)](n) (12) (H(2)BDC = benzene-1,4-dicarboxylic acid and H(2)ADB = 4,4'-azodibenzoic acid), have been synthesized and characterized. In 1-3, the adjacent Ln(III) ions are intraconnected to form 1-D metal-carboxylate oxygen chain-shaped building units, [Ln(4)(CO(2))(12)](n), that constructed a 3-D framework with 4 × 7 ? rhombic channels. In 4-6, the dimeric Ln(III) ions are interlinked to yield scaffolds with 3-D interconnecting tunnels. Compounds 7-10 are all 3-D interpenetrating structures with the CaB6-type topology structure. Compound 11 is constructed by ADB spacers and trinulcear Ce nodes with a NaCl-type topology structure and a 1.9-nm open channel system. In 12, the adjacent Ce(III) ions are intraconnected to form 1-D metal-carboxylate oxygen chain-shaped building units, [Ln(4)(CO(2))(12)](n), and give rise to a 3-D framework. Moreover, 6 exhibits characteristic red luminescence properties of Eu(III) complexes. The magnetic susceptibilities, over a temperature range of 1.8-300 K, of 3, 6, and 7 have also been investigated; the results show paramagnetic properties.     

Structural and photophysical properties of heterobimetallic 4f-zn iminophenolate cryptates

Lanthanide complexes with the Schiff base axial macrobicyclic ligand L(1) react with Zn(II) nitrate in the presence of CaH(2) to yield Ln(III)-Zn(II) heterodinuclear cryptates with the formula [Ln(NO(3))(L(1)-3H)Zn](NO(3)).xH(2)O.yMeOH. The macrobicyclic receptor L(1) is an azacryptand N[(CH(2))(2)N=CH-R-CH=N-(CH(2))(2)](3)N (R = 1,3-(2-OH-5-Me-C(6)H(2))). The crystal structures of the Pr(III), Yb(III), and Lu(III) complexes, chemical formulas [Ln(NO(3))(L(1)-3H)Zn](NO(3)).xSolv (monoclinic, C2/c, Z = 8), as well as that of [Zn(2)(L(1)-3H)](NO(3)).H(2)O (15) (triclinic, P(-)1, Z = 2), have been determined by X-ray crystallography. The ligand is helically wrapped around the two metal ions, leading to pseudo-C(3) symmetries around the metals. The Ln(III)-Zn(II) distances lie in the range 3.3252(13) to 3.2699(14) A, while the Zn(II)-Zn(II) distance in 15 amounts to 3.1037(18) A. The three five-membered chelate rings of the ligand backbone coordinating the Ln(III) ion adopt a (lambdalambdadelta)(5) (or (deltadeltalambda)(5)) conformation while the three pseudochelate rings formed by the coordination of the ligand to the Zn(II) ion adopt a (lambda'lambda'lambda')(5) (or (delta'delta'delta')(5)) conformation. Thus in the solid state the conformation of the three cations is Lambda(deltadeltalambda)(5)(delta'delta'delta')(5) or its enantiomeric form Delta(lambdalambdadelta)(5)(lambda'lambda'lambda')(5). In solution, the helicates present a time-averaged C(3) symmetry, as shown by (1)H NMR, and the conformation of the cations is described as Lambda(deltadeltadelta)(5)(delta'delta'delta')(5) (or Delta(lambdalambdalambda)(5)(lambda'lambda'lambda')(5)). The photophysical properties of the cryptates depend on the nature of the Ln(III) ion, and (L-3H)(3)(-) is revealed to be a good sensitizer for Eu(III) and Tb(III) at low temperatures, but the emission at room temperature is limited by the low energy of the ligand (3)pipi state. While Eu(III) is most effectively sensitized by the ligand triplet state, the Tb(III) ((5)D(4)) sensitization occurs via the singlet state. The quantum yield of the metal-centered luminescence in the Eu-Zn cryptate amounts to 1.05% upon ligand excitation. The low energy of the ligand (3)pipi state allows efficient sensitization of the Nd(III) and Yb(III) cryptates, which emit in the near-infrared.     

The first enantiomerically pure helical noncovalent tripod for assembling nine-coordinate lanthanide(III) podates

Decomplexation of the trivalent lanthanide, Ln(III), from the racemic bimetallic triple-stranded helicates [LnCr(L8)(3)](6+) provides the inert chiral tripodal nonadentate receptor [Cr(L8)(3)](3+). Elution of the latter podand with Na(2)Sb(2)[(+)-C(4)O(6)H(2)](2).5H(2)O through a cation exchange column allows its separation into its inert helical enantiomers M-(+)(589)-[Cr(L8)(3)](3+) and P-(-)(589)-[Cr(L8)(3)](3+), whose absolute configurations are assigned by using CD spectroscopy and exciton theory. Recombination with Ln(III) restores the original triple-stranded helicates [LnCr(L8)(3)](6+), and the associated thermodynamic parameters unravel the contribution of electrostatic repulsion and preorganization to the complexation process. Combining M-(+)(589)-[Cr(L8)(3)](3+) with Eu(III) produces the enantiomerically pure d-f helicate MM-(-)(589)-[EuCr(L8)(3)](CF(3)SO(3))(6).4CH(3)CN, whose X-ray crystal structure (EuCrC(113)H(111)N(25)O(21)S(6)F(18), monoclinic, P2(1), Z = 2) unambiguously confirms the absolute left-handed configuration for the final helix. The associated ligand-centered and metal-centered chiro-optical properties recorded for the complexes MM-[LnCr(L8)(3)](6+) and PP-[LnCr(L8)(3)](6+) (Ln = Eu, Gd, Tb) show a strong effect of helicity on specific rotary dispersions, CD and CPL spectra.     

Positively charged lanthanide complexes with cyclen-based ligands: synthesis, solid-state and solution structure, and fluoride interaction

The syntheses of a new cyclen-based ligand L(2) containing four N-[2-(2-hydroxyethoxy)ethyl]acetamide pendant arms and of its lanthanide(III) complexes [LnL(2)(H(2)O)]Cl(3) (Ln = La, Eu, Tb, Yb, or Lu) are reported, together with a comparison with some Ln(III) complexes of a previously reported analogue L(1) in which two opposite amide arms have been replaced by coordinating pyridyl units. The structure and dynamics of the La(III), Lu(III), and Yb(III) complexes in solution were studied by using multinuclear NMR investigations and density functional theory calculations. Luminescence lifetime measurements in H(2)O and D(2)O solutions of the [Ln(L(2))(H(2)O)](3+) complexes (Ln = Eu or Tb) were used to investigate the number of H(2)O molecules coordinated to the metal ion, pointing to the presence of an inner-sphere H(2)O molecule in a buffered aqueous solution. Fluoride binding to the latter complexes was investigated using a combination of absorption spectroscopy and steady-state and time-resolved luminescence spectroscopy, pointing to a surprisingly weak interaction in the case of L(2) (log K = 1.4 ± 0.1). In contrast to the results in solution, the X-ray crystal structure of the lanthanide complex showed the ninth coordination position occupied by a chloride anion. In the case of L(1), the X-ray structure of the [(EuL(1))(2)F] complex features a bridging fluoride donor with an uncommon linear Eu-F-Eu entity connecting two almost identical [Eu(L(1))](3+) units. Encapsulation of the F(-) anion within the two complexes is assisted by π-π stacking between the pyridyl rings of two complexes and C-H···F hydrogen-bonding interactions involving the anion and the pyridyl units.     

In situ formed white-light-emitting lanthanide-zinc-organic frameworks

Five novel 3D heterometallic lanthanide-zinc-organic frameworks, [H(H(2)O)(8)][LnZn(4)(imdc)(4)(Him)(4)] [Ln = La (1), Pr (2), Eu (3), Gd (4), Tb (5); H(3)imdc = 4,5-imidazoledicarboxylic acid; Him = imidazole], were synthesized via an in situ hydrothermal reaction, and tunable luminescence from yellow to white was obtained through the doping of Eu and Tb ions in the La-Zn framework.     

Anion-directed self-assembly of lanthanide-notp compounds and their fluorescence, magnetic, and catalytic properties

Reactions of 1,4,7-triazacyclononane-1,4,7-triyl-tris(methylenephosphonic acid) [notpH(6), C(9)H(18)N(3)(PO(3)H(2))3] with different lanthanide salts result in four types of Ln-notp compounds: [Ln{C(9)H(20)N(3)(PO(3)H)(2)(PO(3))}(NO(3))(H(2)O)].4H2O (1), [Ln = Eu (1 Eu), Gd (1 Gd), Tb (1 Tb)], [Ln{C(9)H(20)N(3)(PO(3)H)(2)(PO(3))}(H2O)]Cl.3H2O (2) [Ln = Eu (2 Eu), Gd (2 Gd), Tb (2 Tb)], [Ln{C(9)H(20)N(3)(PO(3)H)(2)(PO(3))}(H2O)]ClO4.8H2O, (3) [Ln = Eu (3 Eu), Gd (3 Gd)], and [Ln{C(9)H(20)N(3)(PO(3)H)(2)(PO(3))}(H2O)]ClO4.3H2O (4), [Ln = Gd (4 Gd), Tb (4 Tb)]. Compounds within each type are isostructural. In compounds 1, dimers of {Ln2(notpH4)2(NO3)2(H2O)2} are found, in which the two lanthanide atoms are connected by two pairs of O-P-O and one pair of mu-O bridges. The NO3- ion serves as a bidentate terminal ligand. Compounds 2 contain similar dimeric units of {Ln2(notpH4)2(H2O)2} that are further connected by a pair of O-P-O bridges into an alternating chain. The Cl- ions are involved in the interchain hydrogen-bonding networks. A similar chain structure is also found in compounds 3; in this case, however, the chains are linked by ClO4- counterions through hydrogen-bonding interactions, forming an undulating layer in the (011) plane. These layers are fused through hydrogen-bonding interactions, leading to a three-dimensional supramolecular network with large channels in the [100] direction. Compounds 4 show an interesting brick-wall-like layer structure in which the neighboring lanthanide atoms are connected by a pair of O-P-O bridges. The ClO4- counterions and the lattice water molecules are between the layers. In all compounds the triazamacrocyclic nitrogen atoms are not coordinated to the Ln(III) ions. The anions and the pH are believed to play key roles in directing the formation of a particular structure. The fluorescence spectroscopic properties of the Eu and Tb compounds, magnetic properties of the Gd compounds, and the catalytic properties of 4 Gd were also studied.     

Complexing mechanism of the lanthanide cations Eu3+, Gd3+, and Tb3+ with 1,4,7,10-tetrakis(carboxymethyl)-1,4,7,10-tetraazacyclododecane (dota)-characterization of three successive complexing phases: study of the thermodynamic and structural properties of the complexes by potentiometry, luminescence spectroscopy, and EXAFS

Complexation of the lanthanides Eu3+, Gd3+, and Tb3+ with 1,4,7,10-tetrakis(carboxymethyl)-1,4,7,10-tetraazacyclododecane (dota) has been studied in solution by using potentiometry, luminescence spectrometry, and EXAFS. Three series of successive complexes were characterized by at least two of these methods: the immediate [LnHn(dota)](n-1)+** and intermediate [LnHn(dota)](n-1)+* complexes with 0 相似文献   

Synthesis of diamondoid lanthanide-polyoxometalate solids as tunable photoluminescent materials

The reaction between polyoxometalate (POM) [TBA](12)[WZn{Zn(H(2)O)}(2)(ZnW(9)O(34))(2)] (TBA = tetrabutyl ammonium) and lanthanide (Ln) nitrate (Ln = La, Eu and Tb) in a mixed solvent of CH(3)CN and DMF yielded three noncentrosymmetric diamondoid Ln-POM solid materials, {[Ln(2)(DMF)(8)(H(2)O)(6)][ZnW(12)O(40)]}·4DMF (Ln-POM; Ln = La, Eu and Tb). In these compounds, the {ZnW(12)O(40)} unit, transferred from the metastable [WZn{Zn(H(2)O)}(2)(ZnW(9)O(34))(2)] cluster, acts as a tetradentate ligand to connect with four Ln nodes, while the Ln ion links up two {ZnW(12)O(40)} units. These compounds generated interesting luminescence emissions that are dependent on the Ln ions and their ratios. White light emission was obtained by a doped approach with a rational ratio of the Eu(3+) and Tb(3+) ions.     

Structural and photophysical properties of visible- and near-IR-emitting tris lanthanide(III) complexes formed with the enantiomers of N,N'-bis(1-phenylethyl)-2,6-pyridinedicarboxamide

The enantiomers of N,N'-bis(1-phenylethyl)-2,6-pyridinedicarboxamide (L), namely, (R,R)-1, and (S,S)-1, react with Ln(III) ions to give stable [LnL(3)](3+) complexes in an anhydrous acetonitrile solution and in the solid state, as evidenced by electrospray ionization mass spectrometry, NMR, luminescence titrations, and their X-ray crystal structures, respectively. All [LnL(3)](3+) complexes [Ln(III) = Eu, Gd, Tb, and Yb; L = (R,R)-1 and (S,S)-1] are isostructural and crystallize in the cubic space group I23. Although the small quantum yields of the Ln(III)-centered luminescence clearly point to the poor efficiency of the luminescence sensitization by the ligand and the intersystem crossing and ligand-to-metal energy transfers, the ligand triplet-excited-state energy seems relatively well suited to sensitize many Ln(III) ion's emission for instance, in the visible (Eu and Tb), near-IR (Nd and Yb), or both regions (Pr, Sm, Dy, Er, and Tm).     

Synthesis, characterizations and luminescent properties of three novel aryl amide type ligands and their lanthanide complexes

Three new aryl amide type ligands, N-(phenyl)-2-(quinolin-8-yloxy)acetamide (L(1)), N-(benzyl)-2-(quinolin-8-yloxy)acetamide (L(2)) and N-(naphthalene-1-yl)-2-(quinolin-8-yloxy)acetamide (L(3)) were synthesized. With these ligands, three series of lanthanide(III) complexes were prepared: [Ln(L(1))(2)(NO(3))(2)]NO(3), [Ln(L(2))(2)(NO(3))(2)(H(2)O)(2)]NO(3).H(2)O and [Ln(L(3))(2)(NO(3))(2)(H(2)O)(2)]NO(3).H(2)O (Ln=La, Sm, Eu, Gd). The complexes were characterized by the elemental analyses, molar conductivity, (1)H NMR spectra, IR spectra and TG-DTA. The fluorescence properties of complexes in the solid state and the triplet state energies of the ligands were studied in detail, respectively. It was found that the Eu(III) complexes have bright red fluorescence in solid state. The energies of excited triplet state for the three ligands are 20325 cm(-1) (L(3)), 21053 cm(-1) (L(2)) and 22831 cm(-1) (L(1)), respectively. All the three ligands sensitize Eu(III) strongly and the order of the emission intensity for the Eu(III) complexes with the three ligands is L(3)>L(2)>L(1). It can be explained by the relative energy gap between the lowest triplet energy level of the ligand (T) and (5)D(1) of Eu(III). This means that the triplet energy level of the ligand is the chief factor, which dominates Eu(III) complexes luminescence.     

Connecting terminal carboxylate groups in nine-coordinate lanthanide podates: consequences on the thermodynamic,structural, electronic,and photophysical properties

The hydrolysis of terminal (t)butyl-ester groups provides the novel nonadentate podand tris[2-[N-methylcarbamoyl-(6-carboxypyridine-2)-ethyl]amine] (L13) which exists as a mixture of slowly interconverting conformers in solution. At pH = 8.0 in water, its deprotonated form [L13 - 3H](3-) reacts with Ln(ClO(4))(3) to give the poorly soluble and stable podates [Ln(L13 - 3H)] (log(beta(110)) = 6.7-7.0, Ln = La-Lu). The isolated complexes [Ln(L13 - 3H)](H(2)O)(7) (Ln = Eu, 8; Tb, 9; Lu, 10) are isostructural, and their crystal structures show Ln(III) to be nine-coordinate in a pseudotricapped trigonal prismatic site defined by the donor atoms of the three helically wrapped tridentate binding units of L13. The Ln-O(carboxamide) bonds are only marginally longer than the Ln-O(carboxylate) bonds in [Ln(L13 - 3H)], thus producing a regular triple helix around Ln(III) which reverses its screw direction within the covalent Me-TREN tripod. High-resolution emission spectroscopy demonstrates that (i) the replacement of terminal carboxamides with carboxylates induces only minor electronic changes for the metallic site, (ii) the solid-state structure is maintained in water, and (iii) the metal in the podate is efficiently protected from interactions with solvent molecules. The absolute quantum yields obtained for [Eu(L13 - 3H)] (Phi(Eu)(tot)= 1.8 x 10(-3)) and [Tb(L13 - 3H)] (Phi(Eu)(tot)= 8.9 x 10(-3)) in water remain modest and strongly contrast with that obtained for the lanthanide luminescence step (Phi(Eu) = 0.28). Detailed photophysical studies assign this discrepancy to the small energy gap between the ligand-centered singlet ((1)pi pi*) and triplet ((3)pi pi*) states which limits the efficiency of the intersystem crossing process. Theoretical TDDFT calculations suggest that the connection of a carboxylate group to the central pyridine ring prevents the sizable stabilization of the triplet state required for an efficient sensitization process. The thermodynamic and electronic origins of the advantages (stability, lanthanide quantum yield) and drawbacks (solubility, sensitization) brought by the "carboxylate effect" in lanthanide complexes are evaluated for programming predetermined properties in functional devices.     

Lanthanide class of a trinuclear enantiopure helical architecture containing chiral ligands: synthesis, structure, and properties

The pinene-bipyridine carboxylic derivatives (+)- and (-)-HL, designed to form configurationally stable lanthanide complexes, proved their effectiveness as chiral building blocks for the synthesis of lanthanide-containing superstructures. Indeed a self-assembly process takes place with complete diastereoselectivity between the enantiomerically pure ligand L(-) and Ln(III) ions (La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er), thus leading to the quantitative formation of a trinuclear supramolecular architecture with the general formula [Ln(3)(L)(6)(mu(3)-OH)(H(2)O)(3)](ClO(4))(2) (abbreviated as tris(Ln[L](2))). This class of C(3)-symmetrical compounds was structurally characterized in the solid state and solution. Electrospray (ES) mass spectrometric and (1)H NMR spectroscopic analyses indicated that the trinuclear species are maintained in solution (CH(2)Cl(2)) and are stable in the investigated concentration range (10(-2)-10(-6) m). The photophysical properties of the ligand HL and its tris(Ln[L](2)) complexes were studied at room temperature and 77 K, thus demonstrating that the metal-centered luminescence is well sensitized both for the visible and near-IR emitters. The chiroptical properties of tris(Ln[L](2)) complexes were investigated by means of circular dichroism (CD) and circularly polarized luminescence (CPL). A high CD activity is displayed in the region of pi-pi* transitions of bipyridine. CPL spectra of tris(Eu[(+)-L](2)) and tris(Tb[(+)-L](2)) present large dissymmetry factors g(em) for the sensitive transitions of Eu(III) ((5)D(0)-->(7)F(1), g(em)=-0.088) and Tb(III) ((5)D(4)-->(7)F(5), g(em)=-0.0806). The self-recognition capabilities of the system were tested in the presence of artificial enantiomeric mixtures of the ligand. (1)H NMR spectra identical to those of the enantiomerically pure complexes and investigations by CD spectroscopic analysis reveal an almost complete chiral self-recognition in the self-assembly process, thus leading to mixtures of homochiral trinuclear structures.     

Structure and photoluminescence tuning features of Mn(2+)- and Ln(3+)-activated Zn-based heterometal-organic frameworks (MOFs) with a single 5-methylisophthalic acid ligand

In attempts to investigate whether the photoluminescence properties of the Zn-based heterometal-organic frameworks (MOFs) could be tuned by doping different Ln(3+) (Ln = Sm, Eu, Tb) and Mn(2+) ions, seven novel 3D homo- and hetero-MOFs with a rich variety of network topologies, namely, [Zn(mip)](n) (Zn-Zn), [Zn(2)Mn(OH)(2)(mip)(2)](n) (Zn-Mn), [Mn(2)Mn(OH)(2)(mip)(2)](n) (Mn-Mn), [ZnSm(OH)(mip)(2)](n) (Zn-Sm), [ZnEu(OH)(mip)(2)](n) (Zn-Eu1), [Zn(5)Eu(OH)(H(2)O)(3)(mip)(6)·(H(2)O)](n) (Zn-Eu2), and [Zn(5)Tb(OH)(H(2)O)(3)(mip)(6)](n) (Zn-Tb), (mip = 5-methylisophthalate dianion), have been synthesized hydrothermally based on a single 5-methylisophthalic acid ligand. All compounds are fully structurally characterized by elemental analysis, FT-IR spectroscopy, TG-DTA analysis, single-crystal X-ray diffraction, and X-ray powder diffraction (XRPD) techniques. The various connectivity modes of the mip linkers generate four types of different structures. Type I (Zn-Zn) is a 3D homo-MOF with helical channels composed of Zn(2)(COO)(4) SBUs (second building units). Type II (Zn-Mn and Mn-Mn) displays a nest-like 3D homo- or hetero-MOF featuring window-shaped helical channels composed of Zn(4)Mn(2)(OH)(4)(COO)(8) or Mn(4)Mn(2)(OH)(4)(COO)(8) SBUs. Type III (Zn-Sm and Zn-Eu1) presents a complicated corbeil-like 3D hetero-MOF with irregular helical channels composed of (SmZnO)(2)(COO)(8) or (EuZnO)(2)(COO)(8) heterometallic SBUs. Type IV (Zn-Eu2 and Zn-Tb) contains a heterometallic SBU Zn(5)Eu(OH)(COO)(12) or Zn(5)Tb(OH)(COO)(12), which results in a 3D hetero-MOF featuring irregular channels impregnated by parts of the free and coordinated water molecules. Photoluminescence properties indicate that all of the compounds exhibit photoluminescence in the solid state at room temperature. Compared with a broad emission band at ca. 475 nm (λ(ex) = 380 nm) for Zn-Zn, compound Zn-Mn exhibits a remarkably intense emission band centered at 737 nm (λ(ex) = 320 nm) due to the characteristic emission of Mn(2+). In addition, the fluorescence intensity of compound Zn-Mn is stronger than that of Mn-Mn as a result of Zn(2+) behaving as an activator for the Mn(2+) emission. Compound Zn-Sm displays a typical Sm(3+) emission spectrum, and the peak at 596 nm is the strongest one (λ(ex) = 310 nm). Both Zn-Eu1 and Zn-Eu2 give the characteristic emission transitions of the Eu(3+) ions (λ(ex) = 310 nm). Thanks to the ambient different crystal-field strengths, crystal field symmetries, and coordinated bonds of the Eu(3+) ions in compounds Zn-Eu1 and Zn-Eu2, the spectrum of the former compound is dominated by the (5)D(0) → (7)F(2) transition (612 nm), while the emission of the (5)D(0) → (7)F(4) transition (699 nm) for the latter one is the most intense. Compound Zn-Tb emits the characteristic Tb(3+) ion spectrum dominated by the (5)D(4) → (7)F(5) (544 nm) transition. Upon addition of the different activated ions, the luminescence lifetimes of the compounds are also changed from the nanosecond (Zn-Zn) to the microsecond (Zn-Mn, Mn-Mn, and Zn-Sm) and millisecond (Zn-Eu1, Zn-Eu2, and Zn-Tb) magnitude orders. The structure and photoluminescent property correlations suggest that the presence of Mn(2+) and Ln(3+) ions can activate the Zn-based hetero-MOFs to emit the tunable photoluminescence.