A justification for using NMR model-free methods when investigating the solution structures of rhombic paramagnetic lanthanide complexes

The detailed analysis of the 1H NMR hyperfine shifts according to the model-free methods shows that the semi-rigid monometallic complexes [Ln(L)(NO3)3] (Ln = Eu-Yb) are isostructural in solution. The associated separation of contact and pseudo-contact contributions to the hyperfine NMR shifts in each rhombic lanthanide complex at room temperature provides paramagnetic susceptibility tensors whose principal magnetic axes match the expected symmetry requirements. Moreover, both axial (Delta chi(ax)) and rhombic (Delta chi(rh)) paramagnetic anisotropies display satisfactory linear dependence on Bleaney's factors, a correlation predicted by the approximate high-temperature expansion of the magnetic susceptibility limited to T(-2). Consequently, the simple, and chemically attracting NMR model-free methods are not limited to axial systems, and can be safely used for the investigation of the solution structures of any lanthanide complexes. Molecular-based structural criteria for the reliable estimation of paramagnetic susceptibility tensors by NMR are discussed, together with the assignment of the labels of the crystal-field and magnetic axes within Bleaney's approach.     

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.     

The solution structure of rhombic lanthanide complexes analyzed with a Model-free and crystal-field independent paramagnetic NMR method: application to nonaxial trimetallic complexes [LnxLu(3-x)(TACI-3H)2(H2O)6]3+ (x = 1-3)

The model-free approach has been extended with the derivation of a novel three-nuclei crystal-field independent method for investigating isostructurality in nonaxial (i.e., rhombic) complexes along the lanthanide series. Application of this technique to the heterotrimetallic sandwich complexes [LnLu2(TACI-3H)2(H2O)6]3+, which possess a single C2v-symmetrical paramagnetic center, unambiguously evidences isostructurality for Ln = Pr-Yb, while the variation of the second-rank crystal-field parameters and along the series prevents reliable structural analyses with the classical one-nucleus equation. Extension toward polymetallic magnetically noncoupled rhombic lanthanide complexes in [Ln2Lu(TACI-3H)2(H2O)6]3+ (two paramagnetic centers with Cs microsymmetry) and [Ln3(TACI-3H)2(H2O)6]3+ (three paramagnetic centers with C2v microsymmetry) requires only minor modifications of the original three-nuclei equation. Isostructurality characterizes [Ln2Lu(TACI-3H)2(H2O)6]3+ (Ln = Pr-Yb), while [Ln3(TACI-3H)2(H2O)6]3+ exhibit a structural change between Eu and Tb which results from the concomitant contraction of the three metallic centers. Particular attention has been focused on (i) the stepwise increase of contact (i.e., through-bond) and pseudocontact (i.e., through-space) contributions when the number of paramagnetic centers increases, (ii) the assignment of 13C resonances in the strongly paramagnetic complexes [Ln3(TACI-3H)2(H2O)6]3+ (Ln = Tb-Yb) for which reliable T1 measurements and [1H-13C] correlation spectra are not accessible, and (iii) the combination of crystal-field dependent and independent methods for analyzing the paramagnetic NMR spectra of axial and nonaxial lanthanide complexes.     

A simple thermodynamic model for rationalizing the formation of self-assembled multimetallic edifices: application to triple-stranded helicates

Reaction of the bis-tridentate ligand bis[1-ethyl-2-[6'-(N,N-diethylcarbamoyl)pyridin-2'-yl]benzimidazol-5-yl]methane (L2) with Ln(CF(3)SO(3))(3).xH(2)O in acetonitrile (Ln = La-Lu) demonstrates the successive formation of three stable complexes [Ln(L2)(3)](3+), [Ln(2)(L2)(3)](6+), and [Ln(2)(L2)(2)](6+). Crystal-field independent NMR methods establish that the crystal structure of [Tb(2)(L2)(3)](6+) is a satisfying model for the helical structure observed in solution. This allows the qualitative and quantitative beta23 (bi,Ln1,Ln2)characterization of the heterobimetallic helicates [(Ln(1))(Ln(2))(L2)(3)](6+). A simple free energy thermodynamic model based on (i) an absolute affinity for each nine-coordinate lanthanide occupying a terminal N(6)O(3) site and (ii) a single intermetallic interaction between two adjacent metal ions in the complexes (DeltaE) successfully models the experimental macroscopic constants and allows the rational molecular programming of the extended trimetallic homologues [Ln(3)(L5)(3)](9+).     

Influence of Schiff base and lanthanide metals on the synthesis, stability, and reactivity of monoamido lanthanide complexes bearing two Schiff bases

The monoamido lanthanide complexes stabilized by Schiff base ligand L(2)LnN(TMS)(2) (L = 3,5-Bu(t)(2)-2-(O)-C(6)H(2)CH═N-8-C(9)H(6)N, Ln = Yb (1), Y (2), Eu (3), Nd (4), and La (5)) were synthesized in good yields by the reactions of Ln[N(TMS)(2)](3) with 1.8 equiv of HL in hexane at room temperature. It was found that the stability of 1-5 depends greatly on the size of the lanthanide metals with the increasing trend of Yb ≈ Y < Nd < La. The amine elimination of Ln[N(TMS)(2)](3) with the bulky bidentate Schiff base HL' (L' = 3,5-Bu(t)(2)-2-(O)-C(6)H(2)CH═N-2,6-Pr(i)(2)-C(6)H(3)) afforded the monoamido lanthanide complexes L'(2)LnN(TMS)(2) (Ln = Yb (9), Y (10), Nd (11), and La (12)). While the amine elimination with the less bulky Schiff base HL' (L' = 3,5-Bu(t)(2)-2-(O)-C(6)H(2)CH═N-2,6-Me(2)-C(6)H(3)) yielded the desired monoamido complexes with the small metals of Y and Yb, L'(2)LnN(TMS)(2) (Ln = Yb (13) and Y (14)), and the more stable tris-Schiff base complexes with the large metals of La and Nd, yielded L'(3)Ln as the only product. Complexes 1-14 were fully characterized including X-ray crystal structural analysis. Complexes 1-5, 10, and 14 can serve as the efficient catalysts for addition of amines to carbodiimides, and the catalytic activity is greatly affected by the lanthanide metals with the active sequence of Yb < Y < Eu ≈ Nd ≈ La.     

Lanthanide complexes of chiral 3 + 3 macrocycles derived from (1R,2R)-1,2-diaminocyclohexane and 2,6-diformyl-4-methylphenol

The enantiopure amine macrocycle H(3)L, as well as the parent macrocyclic Schiff base H(3)L1, the 3 + 3 condensation product of (1R,2R)-1,2-diaminocyclohexane and 2,6-diformyl-4-methylphenol, are able to form mononuclear complexes with lanthanide(III) ions. The lanthanide(III) complexes of H(3)L have been studied in solution using NMR spectroscopy and electrospray mass spectrometry. The NMR spectra indicate the presence of complexes of low C(1) and C(2) symmetry. The (1)H and (13)C NMR signals of the Lu(III) complex obtained from H(3)L have been assigned on the basis of COSY, TOCSY, NOESY, ROESY and HMQC spectra. The NMR data reveal unsymmetrical binding of lanthanide(III) ion and the presence of a dynamic process corresponding to rotation of Lu(III) within the macrocycle. The [Ln(H(4)L)(NO(3))(2)](NO(3))(2)(Ln = Sm(III), Eu(III), Dy(III), Yb(III) and Lu(III)) complexes of the cationic ligand H(4)L(+) have been isolated in pure form. The X-ray analysis of the [Eu(H(4)L)(NO(3))(2)](NO(3))(2) complex confirms the coordination mode of the macrocycle determined on the basis of NMR results. In this complex the europium(III) ion is bound to three phenolate oxygen atoms and two amine nitrogen atoms of the monoprotonated macrocycle H(4)L(+), as well as to two axial bidendate nitrate anions. In the presence of a base, mononuclear La(III), Ce(III) and Pr(III) complexes of the deprotonated form of the ligand L(3-) can be obtained. When 2 equivalents of Pr(III) are used in this synthesis Na(3)[Pr(2)L(NO(3))(2)(OH)(2)](2)NO(3).5H(2)O is obtained. The NMR, ES MS and an X-ray crystal model of this complex show coordination of two Pr(III) ions by the macrocycle L. The X-ray crystal structure of the free macrocycle H(3)L1 has also been determined. In contrast to macrocyclic amine H(3)L, the Schiff base H(3)L1 adopts a cone-type conformation resembling calixarenes.     

Enantiomeric self-recognition in homo- and heterodinuclear macrocyclic lanthanide(III) complexes

The controlled formation of lanthanide(III) dinuclear μ-hydroxo-bridged [Ln(2)L(2)(μ-OH)(2)X(2)](n+) complexes (where X = H(2)O, NO(3)(-), or Cl(-)) of the enantiopure chiral macrocycle L is reported. The (1)H and (13)C NMR resonances of these complexes have been assigned on the basis of COSY, NOESY, TOCSY, and HMQC spectra. The observed NOE connectivities confirm that the dimeric solid-state structure is retained in solution. The enantiomeric nature of the obtained chiral complexes and binding of hydroxide anions are reflected in their CD spectra. The formation of the dimeric complexes is accompanied by a complete enantiomeric self-recognition of the chiral macrocyclic units. The reaction of NaOH with a mixture of two different mononuclear lanthanide(III) complexes, [Ln(1)L](3+) and [Ln(2)L](3+), results in formation of the heterodinuclear [Ln(1)Ln(2)L(2)(μ-OH)(2)X(2)](n+) complexes as well as the corresponding homodinuclear complexes. The formation of the heterodinuclear complex is directly confirmed by the NOESY spectra of [EuLuL(2)(μ-OH)(2)(H(2)O)(2)](4+), which reveal close contacts between the macrocyclic unit containing the Eu(III) ion and the macrocyclic unit containing the Lu(III) ion. While the relative amounts of homo- and heterodinuclear complexes are statistical for the two lanthanide(III) ions of similar radii, a clear preference for the formation of heterodinuclear species is observed when the two mononuclear complexes contain lanthanide(III) ions of markedly different sizes, e.g., La(III) and Yb(III). The formation of heterodinuclear complexes is accompanied by the self-sorting of the chiral macrocyclic units based on their chirality. The reactions of NaOH with a pair of homochiral or racemic mononuclear complexes, [Ln(1)L(RRRR)](3+)/[Ln(2)L(RRRR)](3+), [Ln(1)L(SSSS)](3+)/[Ln(2)L(SSSS)](3+), or [Ln(1)L(rac)](3+)/[Ln(2)L(rac)](3+), results in mixtures of homochiral, homodinuclear and homochiral, heterodinuclear complexes. On the contrary, no heterochiral, heterodinuclear complexes [Ln(1)L(RRRR)Ln(2)L(SSSS)(μ-OH)(2)X(2)](n+) are formed in the reactions of two different mononuclear complexes of opposite chirality.     

Tuning facial-meridional isomerisation in monometallic nine-co-ordinate lanthanide complexes with unsymmetrical tridentate ligands

The unsymmetrical tridentate benzimidazole-pyridine-carboxamide units in ligands L1-L4 react with trivalent lanthanides, Ln(III), to give the nine-co-ordinate triple-helical complexes [Ln(Li)3]3+ (i = 1-4) existing as mixtures of C3-symmetrical facial and C1-symmetrical meridional isomers. Although the beta13 formation constants are 3-4 orders of magnitude smaller for these complexes than those found for the D3-symmetrical analogues [Ln(Li)3]3+ (i = 5-6) with symmetrical ligands, their formation at the millimolar scale is quantitative and the emission quantum yield of [Eu(L2)3]3+ is significantly larger. The fac-[Ln(Li)3]3+ <--> mer-[Ln(Li)3]3+ (i = 1-4) isomerisation process in acetonitrile is slow enough for Ln = Lu(III) to be quantified by 1H NMR below room temperature. The separation of enthalpic and entropic contributions shows that the distribution of the facial and meridional isomers can be tuned by the judicious peripheral substitution of the ligands affecting the interstrand interactions. Molecular mechanics (MM) calculations suggest that one supplementary interstrand pi-stacking interaction stabilises the meridional isomers, while the facial isomers benefit from more favourable electrostatic contributions. As a result of the mixture of facial and meridional isomers in solution, we were unable to obtain single crystals of 1:3 complexes, but the X-ray crystal structures of their nine-co-ordinate precursors [Eu(L1)2(CF3SO3)2(H2O)](CF3SO3)(C3H5N)2(H2O) (6, C45H54EuF9N10O13S3, monoclinic, P2(1)/c, Z = 4) and [Eu(L4)2(CF3SO3)2(H2O)](CF3SO3)(C4H4O)(1.5) (7, C51H66EuF9N8O(15.5)S3, triclinic, P1, Z = 2) provide crucial structural information on the binding mode of the unsymmetrical tridentate ligands.     

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.     

Oxidation and coupling of β-diketiminate ligand in lanthanide complexes: novel eight-nuclear lanthanide clusters with μ-, μ3-Cl, and μ4-O bridge

Two novel eight-nuclear lanthanide oxide and chloride clusters Ln(8)(μ-η(2)-L(4))(2)(μ(3)-Cl)(4)(μ-Cl)(10)(μ(4)-O)(3)(THF)(8) (Ln = Er(3), Dy(4); L(4) = [OC{(Me)CN-2,6-(i)PrC(6)H(3)}(2)](2-)) have been synthesized by the reaction of β-diketiminate rare-earth metal chlorides with oxygen, providing a new oxidation and coupling reaction of the β-diketiminate ligand.     

Noncovalent Tagging Proteins with Paramagnetic Lanthanide Complexes for Protein Study

The site‐specific labeling of proteins with paramagnetic lanthanides offers unique opportunities for NMR spectroscopic analysis in structural biology. Herein, we report an interesting way of obtaining paramagnetic structural restraints by employing noncovalent interaction between a lanthanide metal complex, [Ln(L)₃]^n? (L=derivative of dipicolinic acid, DPA), and a protein. These complexes formed by lanthanides and DPA derivatives, which have different substitution patterns on the DPA derivatives, produce diverse thermodynamic and paramagnetic properties when interacting with proteins. The binding affinity of [Ln(L)₃]^n? with proteins, as well as the determined paramagnetic tensor, are tunable by changing the substituents on the ligands. These noncovalent interactions between [Ln(L)₃]^n? and proteins offer great opportunities in the tagging of proteins with paramagnetic lanthanides. We expect that this method will be useful for obtaining multiple angles and distance restraints of proteins in structural biology.     

Solid state and solution studies of lanthanide(III) complexes of cyclohexanetriols, models of the coordination sites found in sugars

This report covers studies in trivalent lanthanide complexation by two simple cyclohexanetriols that are models of the two coordination sites found in sugars and derivatives. Several complexes of trivalent lanthanide ions with cis,cis-1,3,5-trihydroxycyclohexane (L(1)()) and cis,cis-1,2,3-trihydroxycyclohexane (L(2)()) have been characterized in the solid state, and some of them have been studied in organic solutions. With L(1)(), Ln(L)(2) complexes are obtained when crystallization is performed from acetonitrile solutions whatever the nature of the salt (nitrate or triflate) [Ln(L(1)())(2)(NO(3))(2)](NO(3)) (Ln = Pr, Nd); [Ln(L(1)())(2)(NO(3))H(2)O](NO(3))(2) (Ln = Eu, Ho, Yb); [Ln(L(1)())(2)(OTf)(2)(H(2)O)](OTf) (Ln = Nd, Eu). Lanthanum nitrate itself gives a mixed complex [La(L(1)())(2)(NO(3))(2)][LaL(1)()(NO(3))(4)] from acetonitrile solution while [La(L(1)())(2)(NO(3))(2)](NO(3)) is obtained using dimethoxyethane as reaction solvent and crystallization medium. With L(2)(), Ln(L)(2) complexes have also been crystallized from methanol solution [Ln(L(2)())(2)(NO(3))(2)]NO(3), (Ln = Pr, Nd, Eu). Single-crystal X-ray diffraction analyses are reported for these complexes. Complex formation in solution has been studied for several triflate salts (La, Pr, Nd, Eu, and Yb) with L(1 )()and L(2)(), respectively in acetonitrile and in methanol. In contrast to the solid state, both structures Ln(L) and Ln(L)(2) equilibrate in solution, as was demonstrated by low-temperature (1)H NMR and electrospray ionization mass spectrometry experiments. Competing experiments in complexing abilities of L(1)() and L(2)() with trivalent lanthanide cations have shown that only L(2)() exhibits a small selectivity (Nd > Pr > Yb > La > Eu) in methanol.     

Lanthanide coordination with alpha-amino acids under near physiological pH conditions: polymetallic complexes containing the cubane-like [Ln4(mu3-OH)4]8+ cluster core

Tetranuclear lanthanide-hydroxo complexes of the general formula [Ln(4)(mu(3)-OH)(4)(AA)(x)(H(2)O)(y)](8+) (1, Ln = Sm, AA = Gly, x = 5, y = 11; 2, Ln = Nd, AA = Ala, x = 6, y = 10; 3, Ln = Er, AA = Val, x = 5, y = 10) have been prepared by alpha-amino acid controlled hydrolysis of lanthanide ions under near physiological pH conditions (pH 6-7). The core component of these compounds is a cationic cluster [Ln(4)(mu(3)-OH)(4)](8+) whose constituent lanthanide ions and triply bridging hydroxo groups occupy the alternate vertexes of a distorted cube. The amino acid ligands coordinate the lanthanide ions via bridging carboxylate groups. Utilizing L-glutamic acid as the supporting ligand, a cationic cluster complex (4) formulated as [Er(4)(mu(3)-OH)(4)(Glu)(3)(H(2)O)(8)](5+) has been obtained. Its extended solid-state structure is composed of the cubane-like [Er(4)(mu(3)-OH)(4)](8+) cluster building units interlinked by the carboxylate groups of the glutamate ligands. All compounds are characterized by using a combination of spectroscopic techniques and microanalysis (CHN and metal). Infrared spectra of the complexes suggest the coordinated amino acids to be zwitterionic. The presence of mass (MALDI-TOF) envelopes corresponding to the [Ln(4)(mu(3)-OH)(4)](8+) (Ln = trivalent Sm, Nd, or Er) core containing fragments manifests the integrity of the cubane-like cluster unit. Magnetic studies using Evans' method suggest that exchange interactions between the lanthanide ions are insignificant at ambient temperature. The structural identities of all four compounds have been established crystallographically. The tetranuclear cluster core has been demonstrated to be a common structural motif in these complexes. A mechanism responsible for its self-assembly is postulated.     

The first examples of lanthanide selenite-carboxylate compounds: syntheses, crystal structures and properties

[Ln(8)(SeO(3))(4)(2,6-pdc)(8)(H(2)O)(10)].2H(2)O (Ln = La (1), Nd (2), Eu (3); 2,6-pdcH(2) = pyridine-2,6-dicarboxylic acid) represent the first examples of luminescent lanthanide selenite-carboxylate compounds. The compounds have been hydrothermally synthesized and structurally characterized. The structures feature two-dimensional (2D) host frameworks composed of Ln(8)(SeO(3))(4)(2,6-pdc)(8)(H(2)O)(10) clusters connected to each other via inter-cluster Ln(2)O(2) rhombic units along the b-axis and 12-membered Ln(4)O(2)(COO)(2) rings along the c-axis. Inter-layer H-bonding interactions between coordinated water molecules and carboxylate groups lead to three-dimensional architectures. Thermogravimetric analysis (TGA) indicated that the 2D networks were thermostable up to approximately 450 degrees C after losing both coordinated and lattice water molecules and underwent reversible process of dehydration and rehydration. Study on photoluminescent properties revealed that compounds 1, 2 and 3 were new rare-earth materials with violet, near-infrared, and red luminescence, respectively.     

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.     

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.     

Synthesis and luminescence studies of mono- and C3-symmetric, tris(ligand) complexes of Sm(III), Y(III) and Eu(III) with sulfur-bridged binaphtholate ligands

A series of trivalent mono- and tris(ligand) lanthanide complexes of a sulfur-bridged binaphthol ligand [1,1'-S(2-HOC(10)H(4)Bu(t)(2)-3,6)(2)] H(2)L(SN), have been prepared and characterised both structurally and photophysically. The H(2)L(SN) ligand provides an increased steric bulk and offers an additional donor atom (sulfur) as compared with 1,1'-binaphthol (BINOL), a ligand commonly used to complex Lewis acidic lanthanide catalysts. Reaction of the diol H(2)L(SN) with [Sm[N(SiMe(3))(2)](3)] affords silylamido- and amino- derivatives [Sm(L(SN))[N(SiMe(3))(2)][HN(SiMe(3))(2)]] and the crystallographically characterised [Sm(L(SN))[N(SiMe(3))(2)](thf)(2)] with different degrees of structural rigidity, depending on the presence of coordinating solvents. The binaphthyl groups of the L(SN) ligand act as sensitisers of the metal centred emission, which is observed for the Eu(III) and Sm(III) complexes studied. We have therefore sought to use emission spectroscopy as a non-invasive technique to monitor a monomer-dimer equilibrium in these complexes. A dramatic difference between the emission properties of the unreactive dimeric Sm(III) aryloxide complex, the solvated monomeric analogues and the amido adduct demonstrated the potential use of such a technique. For a few representative lanthanides (Ln = Sm, Eu and Y) the reaction of the dilithium salt Li(2)L(SN) with either [Ln[N(SiMe(3))(2]3)] or [LnCl(3)(thf)(3)] affords only the homoleptic complex [Li(S)(3)][LnL(SN)(3)](S = thf or diethyl ether); we report the structural characterisation of the Sm complex. However, the reactions of this dipotassium salt K(2)L(SN) with [Sm[N(SiMe(3))(2)](3)] or [SmCl(3)(thf)(3)] give only [SmL(SN)N(SiMe(3))(2)], or intractable mixtures respectively, in which no (tris)binaphtholate is observed. The only isolable lanthanide-L(SN) halide adduct so far is [YbL(SN)I(thf)].     

Hydrothermal synthesis, crystal structure and properties of Ni(II)-4f complexes based on 1H-benzimidazole-5,6-dicarboxylic acid

Nine novel heterometallic coordination polymers [Ln(2)Ni(Hbidc)(2)(SO(4))(2)(H(2)O)(8)](n) (Ln = Pr (1), Sm (2), Eu (3), Gd (4), Tb (5), Dy (6), Ho (7), Er (8), Yb (9), H(3)bidc = 1H-benzimidazole-5,6-dicarboxylic acid) have been synthesized under hydrothermal conditions and characterized by elemental analysis, FT-IR, TG analysis and single crystal X-ray diffraction. X-ray analysis revealed that all complexes present almost identical three-dimensional (3D) structures with PtS-type topology. Complexes 1-7 are all isomorphous, and the structure variation of polymers 8 and 9 is induced by the lanthanide contraction effect. In additional, the luminescence properties of complexes 2, 3 and 5-7, and the magnetic properties of complexes 4 and 6-8 were investigated.     

Lanthanide(III)-cobalt(II) heterometallic coordination polymers with radical adsorption properties

Two new coordination polymers {[Ln(2)(PDA)(6)Co(3)(H(2)O)(6)] x xH(2)O}(n) [Ln = Nd, x = 7 (1); Ln = Gd, x = 3.25 (2); H(2)PDA = pyridine-2,6-dicarboxylic acid] have been prepared under hydrothermal conditions with Ln(NO(3))(3) x 6H(2)O, CoO, and H(2)PDA in a molar ratio of 2:3:6. X-ray crystallographic analyses reveal that they crystallize in the hexagonal group P6/mcc and exhibit a nanotubular 3D framework. The adsorption experiment shows that 1 and 2 can adsorb radicals, which is proven by electron paramagnetic resonance spectra with the characteristic bands of the radicals at g = 2.006 and 2.005, respectively.