Lanthanide complexes based on a 1,7-diaza-12-crown-4 platform containing picolinate pendants: a new structural entry for the design of magnetic resonance imaging contrast agents

We have synthesized a new macrocyclic ligand, N,N'-Bis[(6-carboxy-2-pyridyl)methyl]-1,7-diaza-12-crown-4 (H 2bp12c4), designed for complexation of lanthanide ions in aqueous solution. The X-ray crystal structure of the Gd (III) complex shows that the metal ion is directly bound to the eight donor atoms of the bp12c4 ligand, the ninth coordination site being occupied by an oxygen atom of a carboxylate group of a neighboring [Gd(bp12c4)] (+) unit, while the structure of the Lu (III) analogue shows the metal ion being only eight-coordinate. The hydration numbers obtained from luminescence lifetime measurements in aqueous solution of the Eu (III) and Tb (III) complexes suggest an equilibrium in aqueous solution between a dihydrated ( q = 2), ten-coordinate and a monohydrated ( q = 1), nine-coordinate species. This has been confirmed by a variable temperature UV-vis spectrophotometric study on the Eu (III) complex. The structure of the complexes in solution has been investigated by (1)H and (13)C NMR spectroscopy, as well as by theoretical calculations performed at the DFT (B3LYP) level. The results indicate that the change in hydration number occurring around the middle of the lanthanide series is accompanied by a change in the conformation adopted by the complexes in solution [Delta(lambdalambdalambdalambda) for q = 2 and Lambda(deltalambdadeltalambda) for q = 1]. The structure calculated for the Yb (III) complex (Lambda(deltalambdadeltalambda)) is in good agreement with the experimental structure in solution, as demonstrated by the analysis of the Yb (III)-induced paramagnetic (1)H shifts.     

Lanthanide directed self-assembly formations of Tb(III) and Eu(III) luminescent complexes from tryptophan based pyridyl amide ligands

The formation of self-assembly complexes between the ligands 1 (SS) and 2 (RR) and terbium or europium was undertaken and shown (using various spectroscopic titrations) to give rise to the exclusive formation of 2:1 (L:Ln) stoichiometry and not the anticipated 3:1 stoichiometry.     

Study of the luminescent and magnetic properties of a series of heterodinuclear [Zn(II)Ln(III)] complexes

Herein, we report the synthesis, structural investigation, and magnetic and photophysical properties of a series of 13 [Zn(II)Ln(III)] heterodinuclear complexes, which have been obtained employing a Schiff-base compartmental ligand derived from o-vanillin [H(2)valpn = 1,3-propanediylbis(2-iminomethylene-6-methoxy-phenol)]. The complexes have been synthesized starting from the [Zn(valpn)(H(2)O)] mononuclear compound and the corresponding lanthanide nitrates. The crystallographic investigation indicated two structural types: the first one, [Zn(H(2)O)(valpn)Ln(III)(O(2)NO)(3)], contains 10-coordinated Ln(III) ions, while in the second one, [Zn(ONO(2))(valpn)Ln(III)(H(2)O)(O(2)NO)(2)]·2H(2)O, the rare earth ions are nine-coordinated. The Zn(II) ions always display a square-pyramidal geometry. The first structural type encompasses the larger Ln ions (4f(0)-4f(9)), while the second is found for the smaller ions (4f(8)-4f(11)). The dysprosium derivative crystallizes in both forms. Luminescence studies for the heterodinuclear compounds containing Nd(III), Sm(III), Tb(III), Dy(III), and Yb(III) revealed that the [Zn(valpn)(H(2)O)] moiety acts as an antenna. The magnetic properties for the paramagnetic [Zn(II)Ln(III)] complexes have been investigated.     

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.     

Epr of luminescent glasses containing chromium(III)

The EPR spectrum at 9 19 GHz has been examined for a series of chromium(III)-doped glasses. The S = $\text{3}\text{2}$ chromium ion site in all the glasses displays two prominent transitions in the g = 6 and g = 2 region. Concentration-dependent broadening observable in the glasses at g = 2 is associated with isotropic spin exchange and provides evidence that the concentration-dependent quenching of chromium luminescence in glasses is due to an ion pairing mechanism     

Synthesis,crystal structures and luminescent properties of two new Ln(III)-dicarboxylate (Ln=Eu,Tb) complexes exhibiting three dimensional networks

Two new coordination polymers, {[Eu₂(L₁)₃(H₂O)₂]?·?H₂O} _n (1), (Cu(II)?···?Cu(II), [Tb(H₂O)]₂(L₂)₃?·?4H₂O (2) (H₂L₁?=?succinic acid, H₂L₂?=?glutaric acid) have been hydrothermally synthesized and characterized by elemental analysis, IR, luminescence spectra and single crystal X-ray diffraction. The complexes are constructed by dicarboxylates bridging chains of edge-sharing EuO₈(H₂O) and TbO₈(H₂O) polyhedra to form 3D network structures. Complexes 1 and 2 exhibit intense red and green photoluminescence upon UV excitation in the solid state at room temperature.     

Redox reactions of V(III) and Cr(III)picolinate complexes in aqueous solutions

Reactions of e_aq⁻, H-atoms, OH, (CH₃)₂COH, and CO₂⁻ radicals with V(III)picolinate and Cr(III)picolinate have been studied by the pulse radiolysis technique. The spectra of V(II)picolinate, V(IV)picolinate, Cr(II)picolinate, OH adduct of Cr(III)picolinate and Cr(IV)picolinate have been obtained and the rate constants of the reactions of various radicals with V(III) and Cr(III)picolinate have been determined. The implications of these results to the chemical decontamination of nuclear reactor systems are discussed.     

High relaxivity supramolecular adducts between human-liver fatty-acid-binding protein and amphiphilic Gd(III) complexes: structural basis for the design of intracellular targeting MRI probes

Gadolinium complexes linked to an apolar fragment are known to be efficiently internalized into various cell types, including hepatocytes. Two lipid-functionalized gadolinium chelates have been investigated for the targeting of the human liver fatty acid binding protein (hL-FABP) as a means of increasing the sensitivity and specificity of intracellular-directed MRI probes. hL-FABP, the most abundant cytosolic lipid binding protein in hepatocytes, displays the ability to interact with multiple ligands involved in lipid signaling and is believed to be an obligate carrier to escort lipidic drugs across the cell. The interaction modes of a fatty acid and a bile acid based gadolinium complex with hL-FABP have been characterized by relaxometric and NMR experiments in solution with close-to-physiological protein concentrations. We have introduced the analysis of paramagnetic-induced protein NMR signal intensity changes as a quantitative tool for the determination of binding stoichiometry and of precise metal-ion-center positioning in protein-ligand supramolecular adducts. A few additional NMR-derived restraints were then sufficient to locate the ligand molecules in the protein binding sites by using a rapid data-driven docking method. Relaxometric and (13)C NMR competition experiments with oleate and the gadolinium complexes revealed the formation of heterotypic adducts, which indicates that the amphiphilic compounds may co-exist in the protein cavity with physiological ligands. The differences in adduct formation between fatty acid and bile acid based complexes provide the basis for an improved molecular design of intracellular targeted probes.     

系列双核Ln(III)配合物的晶体结构和磁性

合成了分子式为[Ln~2(phen)~2L],phen=C~1~2H~8N~2[ALn=Nd,L=(CH~3COO)~4(ONO~2)~2,BLn=Sm,L=(C~6H~5COO)~6,CLn=Eu,L=(C~6H~5COO)~6]3种同双核配合物。用X射线四圆衍射仪测定了3种化合物的结构。在化合物A分子中,2个Nd(III)原子由4个CH~3COO^-基团桥联,以phen和ONO~2^-为端基,构成了一个具有C~2对称性的双核分子。配合物B和C具有完全相同的结构,它们是以4个苯甲酸根为桥,2个phen和2个C~6H~5COO^-为端基的中心对称双核分子,其中6个苯甲酸根的成键状态可分为3种状况。在3种化合物中,每个Ln均为9配位,呈不规则多面体。Ln-Ln距离,A为0.397nm,B和C均为0.405nm。测定了各配合物的变温磁化率,通过对磁性质研究,发现化合物A在低温下具有反铁磁物质行为,并由理论拟合,求得了磁参数g,J值。     

Nucleic acid intercalators and avidin probes derived from luminescent cyclometalated iridium(III)-dipyridoquinoxaline and -dipyridophenazine complexes

Six luminescent cyclometalated iridium(III)-dipyridoquinoxaline and -dipyridophenazine complexes [Ir(ppy)2(N-N)](PF6) (Hppy = 2-phenylpyridine; N-N = dipyrido[3,2-f:2',3'-h]quinoxaline, dpq (1); 2-n-butylamidodipyrido[3,2-f:2',3'-h]quinoxaline, dpqa (2); 2-((2-biotinamido)ethyl)amidodipyrido[3,2-f:2',3'-h]quinoxaline, dpqB (3); dipyrido[3,2-a:2',3'-c]phenazine, dppz (4); benzo[i]dipyrido[3,2-a:2',3'-c]phenazine, dppn (5); 11-((2-biotinamido)ethyl)amidodipyrido[3,2-a:2',3'-c]phenazine, dppzB (6)) have been designed as luminescent intercalators for DNA and probes for avidin. The structure of complex 4 has been studied by X-ray crystallography. The photophysical and electrochemical properties of the complexes have also been investigated. The binding of these complexes to double-stranded calf thymus DNA and synthetic double-stranded oligonucleotides poly(dA) x poly(dT) and poly(dG) x poly(dC) has been investigated by spectroscopic titrations. The interactions between the two biotin-containing complexes and avidin have been studied by 4'-hydroxyazobenzene-2-carboxylic acid (HABA) assays and emission titrations.     

系列双核Ln(III)配合物的晶体结构和磁性

合成了分子式为[Ln~2(phen)~2L],phen=C~1~2H~8N~2[ALn=Nd,L=(CH~3COO)~4(ONO~2)~2,BLn=Sm,L=(C~6H~5COO)~6,CLn=Eu,L=(C~6H~5COO)~6]3种同双核配合物。用X射线四圆衍射仪测定了3种化合物的结构。在化合物A分子中,2个Nd(III)原子由4个CH~3COO^-基团桥联,以phen和ONO~2^-为端基,构成了一个具有C~2对称性的双核分子。配合物B和C具有完全相同的结构,它们是以4个苯甲酸根为桥,2个phen和2个C~6H~5COO^-为端基的中心对称双核分子,其中6个苯甲酸根的成键状态可分为3种状况。在3种化合物中,每个Ln均为9配位,呈不规则多面体。Ln-Ln距离,A为0.397nm,B和C均为0.405nm。测定了各配合物的变温磁化率,通过对磁性质研究,发现化合物A在低温下具有反铁磁物质行为,并由理论拟合,求得了磁参数g,J值。     

High-efficiency poly(p-phenylenevinylene)-based copolymers containing an oxadiazole pendant group for light-emitting diodes

A new series of high brightness and luminance efficient poly(p-phenylenevinylene) (PPV)-based electroluminescent (EL) polymers, poly[2-[4-[5-(4-(3,7-dimethyloctyloxy)phenyl)-1,3,4-oxadiazole-2-yl]phenyloxy]-1,4-phenylenevinylene] (Oxa-PPV), poly[2-[2-((3,7-dimethyloctyl)oxy)phenoxy]-1,4-phenylenevinylene] (DMOP-PPV), and their corresponding random copolymers, poly[[2-[4-[5-(4-(3,7-dimethyloctyloxy)phenyl)-1,3,4-oxadiazole-2-yl]phenyloxy]-1,4-phenylenevinylene]-co-[2-[2-((3,7-dimethyloctyl)oxy) phenoxy]-1,4-phenylenevinylene]] (Oxa-PPV-co-DMOP-PPV), with an electron-deficient 1,3,4-oxadiazole unit on the side groups, were synthesized through the Gilch polymerization method. The newly designed and synthesized asymmetric molecular structures of Oxa-PPV, DMOP-PPV, and Oxa-PPV-co-DMOP-PPV were completely soluble in common organic solvents, and defect-free optical thin film was easily spin-coated onto the indium tin oxide (ITO) substrate. Oxa-PPV shows a high glass transition temperature (T(g)), which might be an advantage for long time operation of polymer light-emitting diodes (PLEDs). Double-layer LEDs with an ITO/PEDOT/polymer/Al configuration were fabricated by using those polymers. Electrooptical properties and device performance could be adjusted by introducing the Oxa-PPV content in the copolymers. The emission colors could be tuned from green to yellowish-orange via intramolecular energy transfer. The improved device performance of Oxa-PPV over DMOP-PPV and Oxa-PPV-co-DMOP-PPV may be due to better electron injection and charge balance between holes and electrons and also efficient intramolecular energy transfer from 1,3,4-oxadiazole units to PPV backbones. The maximum brightness and the luminance efficiency of Oxa-PPV were up to 19395 cd/m(2) at 14 V and 21.1 cd/A at 5930 cd/m(2). The maximum luminance efficiency of Oxa-PPV is ranked the highest value among the PPV derivatives to date.     

Surface-based molecular self-assembly: Langmuir-Blodgett films of amphiphilic Ln(III) complexes

The unique photophysical properties of the Ln(III) series has led to significant research efforts being directed towards their application in sensors. However, for “real-life” applications, these sensors should ideally be immobilised onto surfaces without loss of function. The Langmuir-Blodgett (LB) technique offers a promising method in which to achieve such immobilisation. This mini-review focuses on synthetic strategies for film formation, the effect that film formation has on the physical properties of the Ln(III) amphiphile, and concludes with examples of Ln(III) LB films being used as sensors.     

Synthesis and luminescence studies of aryl substituted tetraamide complexes of europium(III): a new approach to pH responsive luminescent europium probes

DOTA-tetraamide ligands having extended phenol or pyridine substituents have been synthesized. The (5)D(0) --> (7)F(J) deltaJ = 1 and 2 emission bands in the corresponding europium(III) complexes differ in their sensitivity to solution pH. This offers the potential for developing pH responsive probes for in vivo imaging that are independent of probe concentration.     

Ln(III) metal-organic frameworks with 5-nitroisophthalate ligands: Crystal structures and luminescent properties

Two new Ln(III) metal-organic frameworks (MOFs) based on 5-nitroisophthalic acid (H₂L), namely [Pr₄(L)₆(H₂O)₄] _n (I) and [Gd(L)(FA)(H₂O)₂] _n (II) (HFA = formic acid), were prepared by solvothermal reactions and structurally characterized by IR, elemental analysis, XRD, and single crystal X-ray diffraction (CIF files CCDC nos. 971379 (I) and 971380 (II)). A 3D {4.6²}{4¹⁰.6¹⁷.8⁹}{4³}₂ topology framework of I and a 3D {4.6² ₂}{4².6¹⁰.8³} topology network of II are constructed respectively with different synthetic conditions. Four kinds of coordination modes are observed for dicarboxylate in these two MOFs in total. Notably, the in situ hydrolysis of DMF solvates leads to the formation of formate ions that was observed in the structure of II. Moreover, the luminescent properties of both complexes and corresponding ligand have been investigated.     

Europium(III) complex-based luminescent sensing probes for multi-phosphate anions: modulating selectivity by ligand choice

Four tetradentate beta-diketonate-Eu3+ complexes were developed as probes for the luminescent sensing of multi-phosphates. By using an appropriate ligand, the pyrophosphate ion (PPi) could be selectively and sensitively detected.     

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).