Octadentate Ligand Research Articles

Synthesis, characterization, and electrochemical study of two new macroacyclic Schiff bases and their copper(II) and zinc(II) complexes

Two new potentially octadentate N2O6 Schiff-base ligands 2-((E)-(2-(2-(2-((E)-2-hydroxy-3-methoxybenzylideneamino)phenoxy)phenoxy)phenylimino)methyl)-6-methoxyphenol H2L1 and 2-((E)-(2-(2-(2-((E)-2-hydroxy-3-methoxybenzylideneamino)phenoxy)-4-tert-butylphenoxy)phenylimino)methyl)-6-methoxyphenol H2L2 were prepared from the reaction of O-Vaniline with 1,2-bis(2′-aminophenoxy)benzene or 1,2-bis(2′-aminophenoxy)-4-t-butylbenzene, respectively. Reactions of H2L1 and H2L2 with copper(II) and zinc(II) salts in methanol in the presence of N(Et)3 gave neutral [CuL1] · 0.5CH2Cl2, [CuL2], [ZnL1] · 0.5CH2Cl2, and [ZnL2] complexes. The complexes were characterized by IR spectra, elemental analysis, magnetic susceptibility, ESI–MS spectra, molar conductance (Λm), UV-Vis spectra and, in the case of [ZnL1] · 0.5CH2Cl2 and [ZnL2], with 1H- and 13C-NMR. The crystal structure of [ZnL1] · 0.5CH2Cl2 has also been determined showing the metal ion in a highly distorted trigonal bipyramidal geometry. The electrochemical behavior of H2L2 and its Cu(II) complex, [CuL2], was studied and the formation constant of [CuL2] was evaluated using cyclic voltammetry. The logarithm value of formation constant of [CuL2] is 21.9.

Eu(III) Complexes of Functionalized Octadentate 1-Hydroxypyridin-2-ones: Stability, Bioconjugation, and Luminescence Resonance Energy Transfer Studies

The synthesis, stability, and photophysical properties of several Eu(III) complexes featuring the 1-hydroxypyridin-2-one (1,2-HOPO) chelate group in tetradentate and octadentate ligands are reported. These complexes pair highly efficient emission with exceptional stabilities (pEu ∼ 20.7-21.8) in aqueous solution at pH 7.4. Further analysis of their solution behavior has shown the observed luminescence intensity is significantly diminished below about pH ∼ 6 because of an apparent quenching mechanism involving protonation of the amine backbones. Nonetheless, under biologically relevant conditions, these complexes are promising candidates for applications in Homogeneous Time-Resolved Fluorescence (HTRF) assays and synthetic methodology to prepare derivatives with either a terminal amine or a carboxylate group suitable for bioconjugation has been developed. Lastly, we have demonstrated the use of these compounds as the energy donor in a Luminescence Resonance Energy Transfer (LRET) biological assay format.

Two distinct manganese molybdenum(V) phosphates directed by different organic amines

By employing different organic amines as structure-directing agents, two new distinct 3D porous inorganic frameworks based on molybdenum(V) phosphates and Mn II, (H 2en) 2{[Mn(H 2O)] 2[MnMo 12O 24(OH) 6(H 2PO 4) 2(HPO 4) 4(PO 4) 2]}·7H 2O (en = ethylenediamine) (1) and (H 3dien) 2{[Mn(H 3O) 2][Mn 3Mo 12O 24(OH) 6(HPO 4) 2(PO 4) 6]}·5H 2O (dien = diethylenetriamine) (2), have been hydrothermally synthesized, and characterized by routine physical methods. In compound 1, Mn II all adopt octahedral coordination mode and each sandwich cluster Mn[Mo 6P 4O 31] 2 (abbreviated as Mn[Mo 6P 4] 2) acts as an octa-dentate ligand linking eight Mn II, which result in a 3D inorganic (4, 8)-connected framework with the (4 6)(4 10·6 12·8 6) topology. Compound 2 shows a 3D (4, 10)-connected framework with the (3 1·4 4·6 1)(3 4·4 9·5 7·6 17·7 4·8 4) topology, in which Mn II ions exhibit both tetrahedral and octahedral coordination modes, and each Mn[Mo 6P 4] 2 links ten Mn II. Interestingly, there exist channels along the a and b axes in 1, while along the a and c axes in 2. The differences between the two compounds should be ascribed to the distinctions of the organic amines. Primary de-/rehydration behaviors and electrochemistry properties have also been studied for the two compounds.

1-Methyl-3-hydroxy-pyridin-2-one Complexes of Near Infra-Red Emitting Lanthanides: Efficient Sensitization of Yb(III) and Nd(III) in Aqueous Solution

The synthesis, X-ray structure, solution stability, and photophysical properties of several trivalent lanthanide complexes of Yb(III) and Nd(III) using both tetradentate and octadentate ligand design strategies and incorporating the 1-methyl-3-hydroxy-pyridin-2-one (Me-3,2-HOPO) chelate group are reported. Both the Yb(III) and Nd(III) complexes have emission bands in the Near Infra-Red (NIR) region, and this luminescence is retained in aqueous solution (Phi(tot)(Yb) approximately 0.09-0.22%).Furthermore, the complexes demonstrate very high stability (pYb approximately 18.8-21.9) in aqueous solution, making them good candidates for further development as probes for NIR imaging. Analysis of the low temperature (77 K) photophysical measurements for a model Gd(III) complex were used to gain an insight into the electronic structure, and were found to agree well with corresponding time-dependent density functional theory (TD-DFT) calculations at the B3LYP/6-311G++(d,p) level of theory for a simplified model monovalent sodium complex.

Structural Changes in CuII Complexes of Potential Octadentate Ligands by Coordination with Carboxylate/Carboxylic Acid: DFT, TD-DFT, and Experimental Studies

The structural and spectroscopic studies of N,N,N′,N′,N′-pentakis-(benzimidazol-2-yl-methyl)diethylenetriamine (L1) and N,N,N′,N′-tetrakis-(benzimidazol-2-yl-methyl)-N′-(carboxylmethyl)diethylenetriamine (L2H) and [CuL1]2+, [CuL2H]2+, and [CuL2]+ were carried out by density functional theory (DFT) and time-dependant (TD)-DFT techniques. The results show that a geometrical change occurs when carboxylate/carboxylic acid coordinates with the metal ion. For example, the ligand L2H forms an octahedral geometry with CuII and in the structure, four nitrogens (N3, N13, N44, N47) are equatorially coordinated with the metal ion, and atoms O50 (–COOH) and N41, which are weakly bonded at the axial positions, are in competition in the formation of an axial bond with CuII; however, for the ligand L2, only a square pyramidal (SP) geometry results with CuII because of the formation of a strong axial bond by O50 (–COO–) with CuII, which dictates non-bonding at its trans position. Molecular orbital analysis proves that both HOMO and HOMO – 1 are localized over the carboxylate ion that favours a strong axial bond with the metal ion; thus, the SP geometry results in the X-ray structure of [CuL2]ClO4. Furthermore, for the complexes, since the electronic spectroscopic bands were unseparated in the spectra, the TD-DFT was used to identify the bands.

Dramatic Increase of Selectivity for Heavy Lanthanide(III) Cations by Tuning the Flexibility of Polydentate Chelators

Two novel octadentate ligands have been synthesized by attaching two terminal iminodiacetic groups to either 1,4-diazepane (BCAED) or piperazine (BCAEP) as central scaffold. The introduction of the seven- or six-membered ring into the ligand backbone is expected to modify their overall flexibility and then to affect the stability of the corresponding lanthanide(III) complexes. In this work, thermodynamic stability data are determined for the formation of the complexes of BCAED and BCAEP with La(3+), Nd(3+), Eu(3+), Gd(3+), Ho(3+), and Lu(3+). The ligand BCAED shows a strong binding affinity for Lu(3+) (logK = 20.99), moderate for Gd(3+) (logK = 17.15) and rather weak for La(3+) (logK = 12.77). Thus, the variation of logK across the Ln series assumes the remarkable value of 8.22, the largest so far reported. This points to a predominant role of a suitable size match between the metal ion and the ligand cavity, determined by its structure and flexibility. The ligand BCAEP forms less stable complexes with lanthanide(III) cations although it retains a good selectivity (DeltalogK(La-Lu) = 5.66). The Gd(III) complexes have been investigated in aqueous solution by measuring their relaxivity as a function of pH, at 20 MHz and 25 degrees C. The results can be interpreted very well in terms of the species distribution curves calculated from the thermodynamic data and indicate that in these complexes Gd(3+) is octacoordinated, without any bound water molecule. This coordination geometry is maintained in the solid state as shown by the X-ray crystal structure of [Na(H(2)O)(2)][Gd(BCAED)] where the metal ion is at the center of a bicapped-trigonal prism. Finally, the (13)C NMR spectra (9.4 T, 25 degrees C) of the diamagnetic La(3+), Y(3+), and Lu(3+) complexes show that a pronounced stereochemical rigidity is associated with the thermodynamically more stable complexes.

Selective Chelation of Cd(II) and Pb(II) versus Ca(II) and Zn(II) by Using Octadentate Ligands Containing Pyridinecarboxylate and Pyridyl Pendants

Herein we report the coordination properties toward Cd(II), Pb(II), Ca(II), and Zn(II) of a new octadentate ligand (py-H(2)bcpe) based on a ethane-1,2-diamine unit containing two picolinate and two pyridyl pendants, which is structurally derived from the previous reported ligand bcpe. Potentiometric studies have been carried out to determine the protonation constants of the ligand and the stability constants of the complexes with these cations. The introduction of the pyridyl pendants in bcpe provokes a very important increase of the logK(ML) values obtained for the Pb(II) and Cd(II) complexes, while this effect is less important in the case of the Zn(II) analogue. As a result, py-bcpe shows a certain selectivity for Cd(II) and Pb(II) over Zn(II) while keeping good Pb(II)/Ca(II) and Cd(II)/Ca(II) selectivities, and the new receptor py-bcpe can be considered as a new structural framework for the design of novel Cd(II) and Pb(II) extracting agents. Likewise, the stabilities of the Cd(II) and Pb(II) complexes are higher than those of the corresponding EDTA analogues. The X-ray crystal structure of [Zn(py-bcpe)] shows hexadentate binding of the ligand to the metal ion, the coordination polyhedron being best described as a severely distorted octahedron. However, the X-ray crystal structure of the Pb(II) analogue shows octadentate binding of the ligand to the metal ion. A detailed investigation of the structure in aqueous solution of the complexes by using nuclear magnetic resonance (NMR) techniques and density functional theory (DFT) calculations (B3LYP) shows that while in the Zn(II) complex the metal ion is six-coordinated, in the Pb(II) and Ca(II) analogues the metal ions are eight-coordinated. For the Cd(II) complex, our results suggest that in solution the complex exists as a mixture of seven- and eight-coordinated species. DFT calculations performed both in the gas phase and in aqueous solution have been also used to investigate the role of the Pb(II) lone pair in the structure of the [Pb(py-bcpe)] complex.

Synthesis and Characterization of Novel Heterobinuclear Mercury(II)-DTPA-M(II) Complexes: Electrocatalytic and Sensor Applications

Hg(II) metal complex is synthesized using octadentate ligand diethylene triamine penta acetic acid (DTPA) and the interaction of second metal ions viz. Cu(II), Pb(II), Mg(II) and Ca(II) is studied for the formation of novel heterobinuclear complexes. Heterobinuclear complexes are formed by taking 1:1 ratio of metal ions with Hg(II)-DTPA in aqueous solution at pH above 7. Heterobinuclear Hg(II)-DTPA-M(II) complexes are characterized using electrochemical technique and stability constant is calculated by pH-titration technique. Electroactive and stable Hg(II)-DTPA-Pb(II) complex is found to be suitable for the electrocatalytic application and demonstrated for the detection of glutathione in the wide range of concentration from 10 μ g/L to 10 mg/L.

Structures and Properties of Closed Ladderanes C24H24, Laddersilanes Si24H24, and Their Nitrogen-Containing Isoelectronic Equivalents: A G3(MP2) Investigation

An investigation has been undertaken to study the large closed ladderanes C(24)H(24) and their analogs. Thirteen isoelectronic species have been identified as local minima on the MP2(FU)/6-31G(d) potential energy surface, including three C(24)H(24), four Si(24)H(24), two N(24,) and four C(24-x)H(24-x)N(x) (x = 6, 8, 12) isomers. Of these 13 species, 11 are reported for the first time. Their structures, stabilities, HOMO-LUMO gaps, and G3(MP2) heats of formations are computationally obtained and discussed. These results are also compared with those of the related species already available in the literature. Our results show that molecules with 12-membered rings are highly energetic and much less stable than their corresponding isomers that do not have such rings. Isomer II of Si(24)H(24) with anticonformations has a very small HOMO-LUMO gap of 2.56 eV, approaching the semiconductor range. Therefore, it is a candidate of potential semiconductor materials. Meanwhile, the N(24) and other nitrogen-containing species are candidates for high-energy density materials. Our results also indicate that C(18)H(18)N(6) and C(16)H(16)N(8) may be good hexa- and octadentate ligands for metal cations.

Biomimetic Modelling of Copper Enzymes: Synthesis, Characterization, EPR Analysis and Enantioselective Catalytic Oxidations by a New Chiral Trinuclear Copper(II) Complex

AbstractThe new octadentate ligand (R)‐(+)‐N,N′‐dimethyl‐N,N′‐bis{‐2‐[bis(1‐methyl‐2‐benzimidazolylmethyl)]‐2‐methylaminoethyl}‐1,1′‐binaphthyl‐2,2′diamine [(R)‐(+)‐DABN‐L‐Ala‐Bz4; L] was employed for the synthesis of dinuclear and trinuclear copper(II) complexes. The ligand design is based on the insertion of chiral residues derived from L‐alanine between the diaminobinaphthyl (R)‐(+)‐DABN spacer and the aminobis(benzimidazole) metal binding units. The chiroptical properties of the ligand and the complexes are described. EPR experiments were performed on [Cu2L]4+ and [Cu3L]6+ at low temperatures. In the case of [Cu2L]4+, a weak dipolar interaction between the two spin centres was found. A similar weak spin interaction occurred in the trinuclear copper cluster, which could be treated likewise as a weakly coupled three‐spin system. The analysis was substantiated by studying the complex EPR temperature behaviour, where population of the quartet state occurred only at high temperature (77 K), whereas at cryogenic temperatures (4 K) the system adopted a doublet state as a ground‐state spin configuration. Titration with sodium azide of [Cu2L]4+ was consistent with terminal binding of one N3– molecule to each copper ion. Furthermore, dipolar interactions between spin centres were strongly suppressed in this case. For [Cu3L]6+, the adduct formed by the interaction with two azido molecules induced formation of a μ‐azido bridges among the three Cu2+ ions and led to population of the quartet state even at cryogenic temperatures. This bridged configuration was, however, lost upon further addition of azido molecules. The copper(II) complexes were tested as catalysts in the oxidation of biogenic catechols and flavonoids by dioxygen to give the corresponding quinones, which were trapped as adducts with MBTH. The dinuclear complex [Cu2L]4+ displays poor substrate enantiodifferentiating ability, even though it exhibits catalytic activity comparable to that of [Cu3L]6+. The trinuclear complex [Cu3L]6+ exhibits significant enantioselectivity in the oxidations of the catecholamines L‐/D‐dopa methyl ester and L‐/D‐norepinephrine. The origin of this enantioselectivity must be associated with the mode of substrate binding, as it depends almost entirely on KM.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Eu(III) Complexes of Octadentate 1-Hydroxy-2-pyridinones: Stability and Improved Photophysical Performance[

The luminescence properties of lanthanoid ions can be dramatically enhanced by coupling them to antenna ligands that absorb light in the UV/visible and then efficiently transfer the energy to the lanthanoid center. The synthesis and the complexation of Ln(III) cations (Ln=Eu; Gd) for a ligand based on four 1-hydroxy-2-pyridinone (1,2-HOPO) chelators appended to a ligand backbone derived by linking two L-lysine units (3LI-bis-LYS) is described. This octadentate Eu(III) complex ([Eu(3LI-bis-LYS-1,2-HOPO)](-)) has been evaluated in terms of its thermodynamic stability, UV/visible absorption and luminescence properties. For this complex the conditional stability constant (pM) is 19.9, which is an order of magnitude higher than diethylenetriaminepentacetic acid (DTPA) at pH= 7.4. This Eu(III) complex also shows an almost two-fold increase in its luminescence quantum yield in aqueous solution (pH= 7.4) when compared to other octadentate ligands. Hence, despite a slight decrease of the molar absorption coefficient, a much higher brightness is obtained for [Eu(3LI-bis-LYS-1,2-HOPO)](-). This overall improvement was achieved by saturating the coordination sphere of the Eu(III) cation, yielding an increased metal centered efficiency by excluding solvent water molecules from the metal's inner sphere.

Homonuclear and heteronuclear complexes of a four-armed octadentate ligand: synthetic control based on matching ligand denticity with metal ion coordination preferences

The octadentate ligand 1,2,4,5-tetrakis-[3-(2-pyridyl)pyrazol-1-yl]benzene (L), with four bidentate arms radiating from a central phenyl ring, combines with 6-coordinate and 4-coordinate metal ions (as their tetrafluoroborate salts) in different ways according to the coordination number preferences of the metal ions. The four bidentate arms are not ideally matched to the requirement of octahedral metal ions, such that complexes with Cd(ii), such as tetranuclear [Cd(4)L(2)(micro-F)(2)(solv)(4)](BF(4))(6) (solv = MeOH or MeCN), and Co(ii)/Ni(ii), such as hexanuclear [Co(6)L(4)(micro-F)(2)][BF(4)](10), require monodentate ancillary ligands (solvent molecules or fluoride ions) to provide coordinative saturation. In contrast, a mixture of octahedral [M = Co(ii) or Ni(ii)] and tetrahedral [Ag(i)] metal ions reacts with L to afford the simpler trinuclear heterometallic complexes [Co(2)AgL(2)](BF(4))(5) in which the requirements of the metal ions (for 3 + 3 + 2 bidentate arms) are matched by two four-armed ligands. The maximum site occupancy principle can accordingly be used to direct self-assembly of heterometallic complexes.

Water-Soluble 2-Hydroxyisophthalamides for Sensitization of Lanthanide Luminescence

A series of octadentate ligands featuring the 2-hydroxyisophthalamide (IAM) antenna chromophore to sensitize Tb(III) and Eu(III) luminescence has been prepared and characterized. The length of the alkyl amine scaffold that links the four IAM moieties has been varied to investigate the effect of the ligand backbone on the stability and photophysical properties of the Ln(III) complexes. The amine backbones utilized in this study are N,N,N',N'-tetrakis-(2-aminoethyl)-ethane-1,2-diamine [H(2,2)-], N,N,N',N'-tetrakis-(2-aminoethyl)-propane-1,3-diamine [H(3,2)-], and N,N,N',N'-tetrakis-(2-aminoethyl)-butane-1,4-diamine [H(4,2)-]. These ligands also incorporate methoxyethylene [MOE] groups on each of the IAM chromophores to increase their water solubility. The aqueous ligand protonation constants and Tb(III) and Eu(III) formation constants were determined from solution thermodynamic studies. The resulting values indicate that at physiological pH the Eu(III) and Tb(III) complexes of H(2,2)-IAM-MOE and H(4,2)-IAM-MOE are sufficiently stable to prevent dissociation at nanomolar concentrations. The photophysical measurements for the Tb(III) complexes gave overall quantum yield values of 0.56, 0.39, and 0.52 respectively for the complexes with H(2,2)-IAM-MOE, H(3,2)-IAM-MOE, and H(4,2)-IAM-MOE, while the corresponding Eu(III) complexes displayed significantly weaker luminescence, with quantum yield values of 0.0014, 0.0015, and 0.0058, respectively. Analysis of the steady state Eu(III) emission spectra provides insight into the solution symmetries of the complexes. The combined solubility, stability, and photophysical performance of the Tb(III) complexes in particular make them well suited to serve as the luminescent reporter group in high sensitivity time-resolved fluoroimmunoassays.

Preparation and characterization of new Mn 6 and Mn 8 clusters obtained from the in situ formation of an unprecedented octadentate ligand

The use of 1,3,5-trihydroxybenzene (thbH 3) in manganese carboxylate chemistry has been investigated. The reactions of thbH 3 with 4 and 6 equivalents of Mn(O 2CEt) 2 in MeOH afford the complexes [Mn 6(O 2CEt) 8(L)(MeOH) 4(H 2O) 2] ( 1) and [Mn 8O 2(O 2CEt) 14(MeOH) 4] ( 2), respectively. In the case of complex 1, the product of the in situ organic ligand transformation has been observed, namely the conversion of the tridentate thbH 3 group to a new octadentate ligand L 4−; the latter has never been previously reported. Both complexes possess rare topologies, with 1 containing 6Mn II ions, whereas 2 is mixed-valent 6Mn II, 2Mn III. The core of 1 consists of two [Mn 3(μ 3-OR)] 5+ triangles linked by the bulky octadentate ligand L. The [Mn 8(μ 4-O) 2(μ-OR) 8] 6+ core of 2 can be considered an extension of the common [Mn 6(μ 4-O) 2] 10+ (4Mn II, 2Mn III) core, comprising two edge-sharing tetrahedra, with two additional Mn atoms at one end. Peripheral ligation in both 1 and 2 is provided by eight and fourteen bridging EtCO 2 - groups, respectively. Variable-temperature, solid-state dc and ac magnetization studies were carried out on complexes 1 and 2 in the 1.8–300 K range. The magnetic susceptibility data for 1 were fit to the theoretical χ M vs T expression, derived by the use of an isotropic Heisenberg spin Hamiltonian and the Van Vleck equation, for two essentially non-interacting triangular [Mn 3(μ 3-OR)(μ-OR) 2] 3+ units. The fitting procedure revealed the two pairwise exchange parameters to be weakly ferromagnetic ( J basal = J′ = + 0.79(3) cm −1) and antiferromagnetic ( J side = J = −2.04(3) cm −1), respectively, resulting in an S = 5/2 spin ground state. In contrast, the data for 2 revealed dominant antiferromagnetic interactions and a resulting S = 0 ground state; the latter value is rationalized in terms of the strong antiferromagnetic coupling within the central Mn 2 III O 2 unit.

Enantiopure, octadentate ligands as sensitizers for europium and terbium circularly polarized luminescence in aqueous solution.

Tb and Eu complexes of enantiopure ligands with a new modular design show strong overall luminescence and CPL activity in aqueous solution.

An Octadentate Luminescent Eu(III) 1,2-HOPO Chelate with Potent Aqueous Stability

The synthesis, characterization, and photophysical properties of two novel ligands, 5LINMe-1,2-HOPO (1) and H(2,2)-1,2-HOPO (2), which utilize the 1,2-HOPO chelate as a sensitizer for Eu(III) are reported. In addition, the former ligand was structurally characterized as the Eu(III) complex by X-ray crystallography. The [Eu(1)2]- complex of the tetradentate ligand (1) is stable in aqueous solution, to a limiting concentration of ca. 7x10(-9) M, and retains the superior photophysical performance noted for the 1,2-HOPO sensitizer. By contrast, the octadentate ligand (2) has vastly improved stability as the [Eu(2)]- complex upon further dilution, to a limiting concentration of ca. 5x10(-17) M, which is beyond the minimum detectable concentration of most fluorimeters. The presence of a single coordinated water molecule for the latter complex reduces the overall metal-centered luminescence.

Synthesis and crystal structure of manganese(II) complexes with high-denticity ligands derived from azacrowns

The hepta- and octa-dentate ligands N, N′-bis(2-aminobenzyl)-1,10-diaza-15-crown-5 ( L 1) and N, N′-bis(2-aminobenzyl)-1,10-diaza-18-crown-6 ( L 2), respectively, form stable mononuclear Mn(II) complexes. Spectrophotometric titrations performed in acetonitrile solution indicate the formation of mononuclear Mn(II) complexes with both ligands, and no evidence for the formation of binuclear complexes was obtained. The optimal architecture of L 1 allows it to impose the less usual pentagonal bipyramidal geometry on the Mn(II) guest, and the X-ray crystal structure of [Mn(L 1)](ClO 4) 2 shows that the Mn(II) ion is deeply buried in the receptor cavity, coordinated to the seven available donor atoms, with the perchlorate anions remaining outside the metal coordination sphere. In spite of its higher denticity, the receptor L 2 is unable to form the expected binuclear complexes. The X-ray crystal structure of [Mn(L 2)](NO 3) 2 consists of the [Mn(L 2)] 2+ cation and nitrate anions involved in hydrogen-bonding interactions with the aniline groups. In [Mn(L 2)] 2+ the metal ion is also placed in the crown hole, but as a result of the large size of the macrocyclic cavity only six of the eight available donor atoms of the receptor form part of the Mn(II) coordination sphere, with the Mn(II) ion found in a distorted octahedral coordination environment.

Allosteric deprogramming of a trinuclear heterometallic helicate

Two multidentate ditopic ligands L1 and L2 which contain both N-donor and crown ether units have been synthesised. The potentially octadentate ligand L1 forms a trinuclear heterometallic double helicate with Cu(I) and Zn(II) ([Zn2Cu(L1)2](5+)), whereas L2 forms a tetranuclear heterometallic double helicate with the same metal ions ([Zn2Cu2(L2)2](6+)). Both species have been characterised by (1)H NMR, ESI-MS and single crystal X-ray crystallography. Reaction of [Zn2Cu2(L2)2](6+) with Ba(2+) results in the coordination of the crown ether units giving the simple barium coordinated species [Zn2Cu2(L2)2Ba2](10+). However, reaction of [Zn2Cu(L1)2](5+) with Ba(2+) deprograms the ligand and results in the formation of a mixture of species.

Luminescent properties of an Yb podate in sol–gel silica films, solution, and solid state

In search of IR emitting materials a complex of Yb III with an octadentate ligand bearing four bidentate 8-hydroxyquinolinate subunits connected to a N, N, N′, N′-tetra-aminopropyl-1,2-ethylenediamine anchor [S. Comby, D. Imbert, A.S. Chauvin, J.C.G. Bünzli, Inorg. Chem. 45 (2006) 732.] has been incorporated into silica glasses obtained by a special two-step, catalyzed sol–gel method. Photophysical properties of the resulting thin films are investigated and compared to those of an aqueous solution 10 −3 M in HBS buffer (pH 7.4) and of a solid state sample, at room temperature and 10 K. They point to the chelate withstanding the sol–gel process; moreover the lifetime and quantum yield are comparable and even slightly better than in aqueous solution.

Lanthanide Complexes of a Picolinate Ligand Derived from 1,4,7‐Triazacyclononane with Potential Application in Magnetic Resonance Imaging and Time‐Resolved Luminescence Imaging

The new potentially octadentate ligand, 1-(carboxymethyl)-4,7-bis[(6-carboxypyridin-2-yl)methyl]-1,4,7-triazacyclononane (H(3)bpatcn), in which two picolinate arms and one acetate arm are connected to the 1,4,7-triazacyclonane core, has been prepared. Potentiometric studies show an increased stability of the Gd(III) complex of H(3)bpatcn (logK(GdL)=15.8(2)) with respect to the Gd(III) complex of the analogous ligand 1,4,7-triazacyclononane-N,N',N''-triacetic acid (H(3)nota) (logK(GdL)=13.7), associated with an increased selectivity of H(3)bpatcn for gadolinium over calcium. The H(3)bpatcn ligand sensitises the terbium ion very efficiently, leading to a long-lived and highly luminescent terbium complex (quantum yield=43 %), in spite of the presence of a coordinated water molecule. (1)H proton NMR studies indicate that the metal ion is rigidly encapsulated by the three arms of the octadentate ligand H(3)bpatcn and that the macrocycle framework remains bound (through the five nitrogen and the three oxygen atoms) even at high temperature. A new theoretical method for interpreting the water proton relaxivity is presented. It is based on recent progresses in the description of the electronic spin relaxation and on an auxiliary probe solute. It replaces the Solomon, Bloembergen and Morgan (SBM) framework, which is questionable at low field, while avoiding resorting to simulations and/or sophisticated theories with additional unknown zero-field splitting (ZFS) parameters. The inclusion of two picolinate groups on a triazacyclononane framework affords the mono-aquo gadolinium complex [Gd(bpatcn)(H(2)O)] with favourable electron-relaxation properties (tau(eff)(S0)=125 ps). The optimisation of the electronic relaxation by ligand design is especially important to achieve high relaxivity in the new generation macromolecular complexes with long rotational correlation times.