Luminescent dinuclear lanthanide complexes of 5-Me-HXTA

The synthesis and characterization of a series of anionic homobimetallic lanthanide complexes of the septadentate chelate 5-Me-HXTA (N,N-(2 hydroxy-5-methyl-1,3-xylylene)bis(N-(carboxymethyl)glycine) is described (Ln = Nd, Sm, Eu, Tb, Dy, Ho, Er, Yb). Single X-ray crystallography confirms that the complexes exist as discrete dimeric pairs in the solid state. Proton NMR, diffusion-ordered spectroscopy, and luminescence solution studies suggest that the binuclear stoichiometry is retained in aqueous solution over a range of analytically useful concentrations. The phenolic chromophores effectively sensitize the visible and near-infrared lanthanide-centered emission in the terbium, neodymium, and ytterbium derivatives, giving rise to particularly long-lived green and near-infrared emission. The terbium complex displays a high quantum yield of around 50% in aqueous solution with a low detection limit of 1 x 10(-12) M, rendering this compound a potential candidate for time-resolved applications.     

Controlled assembly of luminescent racks based on heteroleptic dinuclear lanthanide complexes

Luminescent lanthanide racks are formed in solution through supramolecular assembly of lanthanide ions with a rigid bis-didentate sensitiser ligand and octadentate aminopolycarboxylate ligands.     

Selective reaction based on the linked diamido ligands of dinuclear lanthanide complexes

The dinuclear ytterbium pyridyl diamido complexes [Cp(2)Yb(THF)](2)[mu-eta(1):eta(2)-(NH)(2)(C(5)H(3)N-2,6)] (1a) and [Cp(2)Yb(THF)](2)[mu-eta(1):eta(2)-(NH)(2)(C(5)H(3)N-2,3)] (1b) are easily prepared by protonolysis of Cp(3)Yb with 0.5 equiv of the corresponding diaminopyridine in accepted yields, respectively. Treatment of 1a with 2 equiv of dicyclohexylcarbodiimide (CyN=C=NCy) in THF at low temperature leads to the isolation of the formal double N-H addition product (Cp(2)Yb)(2)[mu-eta(2):eta(2)-(CyN(CyNH)CN)(2)(C(5)H(3)N-2,6)] (2) in 42% yield. Compound 2 is unstable to heat and slowly isomerized to the mixed neutral/dianionic diguanidinate complex (Cp(2)Yb)(2)[mu-eta(2):eta(2)-(CyNH)(2)CN(C(5)H(3)N-2,6)NC(NCy)(2)](THF) (3) at room temperature. Similarly, treatment of 1b with 2 equiv of CyN=C=NCy gives the addition/ isomerization product (Cp(2)Yb)(2)[mu-eta(2):eta(2):eta(1)-(CyNH)(2)CN(C(5)H(3)N-2,3)NC(NCy)(2)] (4). Moreover, the reaction of various ytterbium aryl diamido complexes (prepared in situ from [Cp(2)YbMe](2) and aryldiamine, respectively) with CyN=C=NCy affords the corresponding addition products (Cp(2)Yb)(2)[mu-eta(2):eta(2)-{CyN(CyNH)CN}(2)(C(6)H(4)-1,4)] (5), (Cp(2)Yb)(2)[mu-eta(2):eta(2)-{CyN(CyNH)CN}(2)(C(6)H(4)-1,3)](6), and (Cp(2)Yb)(2)[mu-eta(2):eta(2)-{CyN(CyNH)CN}(2)(C(13)H(8)-2,7)] (7), respectively. In contrast to pyridyl-bridged bis(guanidinate monoanion) complexes, aryl-bridged bis(guanidinate monoanion) complexes 5-7 are stable even with prolonged heating at 110 degrees C. All the results not only demonstrate that the presence of the pyridyl bridge can impart the diamido complexes with a unique reactivity and initiate the unexpected reaction sequence but also indicate evidently that the number and distribution of negative charges of the diguanidinate ligand is tunable from double monoanionic units to mixed neutral/dianionic isomers. All the complexes are characterized by elemental analysis and IR spectroscopies. The structures of complexes 1a, 3, 5, 6, and 7 are also determined through X-ray single-crystal diffraction analysis.     

Synthesis and characterisation of dinuclear and mononuclear Cobalt (II) benzoate complexes

Aqua-bridged binuclear cobalt (II) benzoate complexes having pyridine as auxiliary ligands are synthesised through solid state reactions and characterised. The binuclear core in these complexes comprise of two bridging benzoates and an aqua bridge. Each of the cobalt (II) centre is further co-ordinated to one benzoate and two pyridine ligands. The aqua-bridged cobalt (II) benzoate complex [Co₂(μ-H₂O)(μ-OBz)₂(OBz)₂(Py)₄] ·  (C₆H₆)(BzOH) (1a) is inclusion compounds with benzoic acid and benzene (where OBz  =  benzoate, py  =  pyridine). Analogous complex [Co₂(μ-H₂O)(μ-OBz)₂(OBz)₂(Py)₄] · 1.5(C₆H₆) without benzoic acid included is also prepared by an alternative method and structurally characterised. Analogous aqua-bridged complex derived from p-chlorobenzoic acid in unsolvated form is characterised. The Co–O–Co separation in these complexes is in the range of 3.55–3.64 Å with angles Co–O–Co varying from 111.8° to 116.4°. While similar reaction in solution leads to the formation of mononuclear complex having composition [Co(OBz)₂(Py)₂(H₂O)]. The unsubstituted benzoate complex 1a can be easily oxidised to form a tetrameric cobalt (III) complex having benzoate and oxo-bridged structure with a Co₄O₄ core.     

Synthesis and characterisation of mono- and dinuclear diethyldithiocarbamatonickel(II) organochalcogenide complexes

The reaction of Ni(dtc)(PR₃)Cl (dtc=diethyldithiocarbamate, R=Ph or Bu) with HSC₆H₄Cl-4 or HSCH₂C₆H₄Cl-4 and Et₃N gave two types of complex. For PPh₃, the products were [Ni(dtc)(μ-SC₆H₄Cl-4)]₂ (1) and [Ni(dtc)(μ-SCH₂C₆H₄Cl-4)]₂ (2); whilst PBu₃ gave Ni(dtc)(PBu₃)(SC₆H₄Cl-4) (3). The structure of freshly prepared 3 was determined to be monomeric, as indicated by X-ray diffraction studies. However, at room temperature in solution, 3 was observed to slowly convert to 1. Structural identification of 1 and 2 and similar dimers, and structural identification of 3 and analogous monomers, were investigated by mass spectrometry. Electron impact mass spectrometry (EIMS) failed to confirm the proposed structures due to extensive decomposition in the mass spectrometer. In the electron impact (EI) mode, all complexes invariably decomposed to Ni(dtc)₂; on the other hand, fast atom bombardment (FAB) ionisation gave the expected molecular ions for all compounds.     

Synthesis and characterisation of a new class of phosphine-phosphonite ferrocenediyl dinuclear rhodium complexes

We previously reported the easy access to mixed ferrocenediyl ligands bearing phosphine and phosphonite moieties. Using this strategy, a new enantiopure phosphine-menthylphosphonite ferrocenediyl has been synthesised. This mixed ligand leads to original unsymmetrical dinuclear rhodium coordination-complexes. One example of this new class of “quasi-close bridging A frame” dinuclear rhodium complexes, fully characterised by multinuclear ¹H, ¹³C, ³¹P and ¹⁰³Rh NMR and optical rotation measurements, is presented. Preliminary tests have shown an activity improvement in the hydroformylation of oct-1-ene using the phosphine-menthylphosphonite ferrocenediyl auxiliary compared to known phosphine-phosphonite ligands.     

Synthesis and characterisation of phenoxo bridged dinuclear complexes of copper(II)

A series of model complexes for the type III site, in oxidised hemocyanin, containing Cu₂(μ-0Ph)³⁺ core have been synthesised using a heptadentate ligand (H₃L) formed from the Schiff base condensation of triethylenetetramine and salicylaldehyde. The ligand provides one imine and one inbuilt imidazole nitrogen and two phenolic oxygen donors with both five- and six-membered chelate rings to each metal centre. In the pentacoordinated complexes [Cu₂(L)X]·nH₂O, a third exogenous bridging ligand is present. The TG curve indicates the loss of lattice water molecules between 70 and 125°C. The residue after decomposition is CuO above 550°C. Theg values of theX-band EPR spectrum of [Cu₂L(μ-OAc)]·2H₂O in methanol glass (77 K) are typical of a variety of bridged copper(II) dimers. The copper-copper magnetic interaction is dependent on the presence and nature of X in these complexes.     

Synthesis and magnetism of μ-isophthalato dinuclear lanthanide(III) complexes

Seven new μ-isophthalato dinuclear lanthanide(III) complexes, namely [Ln₂(IPHTA)(Me₂-phen)₄-(ClO₄)₂](ClO₄)₂ (Ln=La, Nd, Sm, Eu, Gd, Ho, Er), where Me₂-phen denotes 2,9-dimethyl-1,10-phenanthroline (Me₂-phen), IPHTA represents isophthalate dianion, have been synthesized and characterized by elemental analyses, molar conductance measurements, IR, ESR and electronic spectra. The variable-temperature magnetic susceptibilities of [ Gd₂ (IPHTA) (Me₂-phen)₄ ( ClO₄ )₂ ] ((ClO₄ )₂ complex were measured in the temperature range of 4–300 K and the observed data were successfully simulated by the equation based on the spin Hamiltonian operator, H = -2JS₁. J₂. giving the exchange parameter J = -0.19 cm^?1. This result is commensurate with a weak antiferromagnetic spin-exchange interaction between Gd(III)-Gd(III) im within the complex.     

Highly luminescent bis-diketone lanthanide complexes with triple-stranded dinuclear structure

A new bis-β-diketone, 3,3'-bis(4,4,4-trifluoro-1,3-dioxobutyl)biphenyl (BTB), has been designed and prepared for the synthesis of a series of dinuclear lanthanide complexes [Ln(2)(BTB)(3)(C(2)H(5)OH)(2)(H(2)O)(2)] [Ln = Eu (1), Gd (2)], [Ln(2)(BTB)(3)(DME)(2)] [Ln = Nd (3), Yb (4); DME = ethylene glycol dimethyl ether] and [Eu(2)(BTB)(3)(L)(2)] [L = 2,2-bipydine (5); 1,10-phenanthroline (6); 4,7-diphenyl-1,10-phenanthroline (7)]. Complexes 1-7 have been characterized by various spectroscopic techniques and their photophysical properties are investigated. X-ray crystallographical analysis reveals that complexes 1, 3 and 4 adopt triple-stranded dinuclear structures which are formed by three bis-bidentate ligands with two lanthanide ions. The complexes 1 and 3-7 display strong visible red or NIR luminescence upon irradiation at ligand band around 372 nm, depending on the choice of the lanthanide. The solid-state photoluminescence quantum yields and the lifetimes of Eu(3+) complexes are determined and described.     

Interaction between f-electronic systems in dinuclear lanthanide complexes with phthalocyanines

The first detection and characterization of the interactions between the f-electronic systems in the dinuclear complexes of paramagnetic trivalent Tb, Dy, Ho, Er, Tm, and Yb ions with phthalocyanine ligands are presented. The molar magnetic susceptibilities, chi(m), were measured for PcLnPcLnPc* ([Ln, Ln]; Pc = dianion of phthalocyanine, Pc* = dianion of 2,3,9,10,16,17,23,24-octabutoxyphthalocyanine) and PcLnPcYPc* ([Ln, Y]) in the range from 1.8 K to room temperature. The selective synthetic method previously reported for the heterodinuclear complex [Y, Ln] was used to prepare [Ln, Ln] and [Ln, Y] with a modification on the choice of starting materials. The f-f interaction contributions to the magnetic susceptibility are evaluated as Delta(chi)(m)T = chi(m)([Ln, Ln])T - chi(m)([Ln, Y])T - chi(m)([Y, Ln])T, where T refers to temperature on the kelvin scale. The homodinuclear complexes having f(8)-f(10)-systems, namely [Tb, Tb], [Dy, Dy], and [Ho, Ho], show positive Delta(chi)(m)T values in the 1.8-50 K range, indicating the existence of ferromagnetic interaction between the f-systems. The magnitude of the Delta(chi)(m)T increases in the descending order of the number of f-electrons. [Er, Er] gives negative Delta(chi)(m)T values in the 1.8-50 K range, showing the antiferromagnetic nature of the f-f interaction. [Tm, Tm] exhibits small and negative Delta(chi)(m)T values, which gradually decline in the negative direction as the temperature decreases in the range 13-50 K and sharply rise in the positive direction as the temperature falls from 10 to 1.8 K. [Yb, Yb] has extremely small Delta(chi)(m)T values, whose magnitude at 2 K is less than 1% of that of [Tb, Tb]. The ligand field parameters of the ground-state multiplets of the six [Ln, Y] complexes are determined by simultaneous fitting to both the magnetic susceptibility data and paramagnetic shifts of (1)H NMR. The theoretical analysis successfully converged by assuming that each ligand field parameter is a function of the number of f-electrons in each ion. Using these parameters as well as the previously obtained corresponding parameters for the [Y, Ln] series, the interactions between the f-systems in [Ln, Ln] are investigated. All the characteristic observations above are satisfactorily reproduced with the assumption that the magnetic dipolar term is the sole source of the f-f interaction.     

Synthesis and characterisation of dimeric eight-coordinate lanthanide(III) complexes of a macrocyclic tribenzylphosphinate ligand

The macrocyclic ligand 1,4,7,10-tetraazacyclododecane-1,4,7-triyl(methylenebenzyl-phosphinic acid) H3L3, has been prepared and its complexes with Eu, Gd and Tb(III) studied by NMR, relaxometry, luminescence and single crystal X-ray crystallography. In solution and in the crystal, the complexes have eight-coordinate metal centres with bridging phosphinate groups linking the two twisted square antiprismatic coordination polyhedra. A single stereoisomer crystallises from solution with an RRR and SSS configuration at the P centres in each sub-unit. The relaxivity of [GdL3]2 is low (1.9 mM-1 s-1, 298 K, 20 MHz), consistent with the absence of any proximate water molecules. The terbium dimer possesses a relatively long excited state lifetime (2.47 ms, 298 K).     

Synthesis and structural characterization of nonanuclear lanthanide complexes

A series of nonanuclear lanthanide oxo-hydroxo complexes of the general formula [Ln(9)(mu(4)-O)(2)(mu(3)-OH)(8)(mu-BA)(8)(BA)(8)](-)[HN(CH(2)CH(3))(3)](+).(CH(3)OH)(2)(CHCl(3)) (BA = benzoylacetone; Ln = Sm, 1; Eu, 2; Gd, 3; Dy, 4; Er, 5) were prepared by the reaction of hydrous lanthanide trichlorides with benzoylacetone in the presence of triethylamine in methanol and recrystallized from chloroform/methanol (1:10) at room temperature. These five compounds are isomorphous. Crystal data for 1: cubic, Pn3n; T = 180 K; a = 33.8652(4) A; V = 38838.4(8) A(3); Z = 6; D(calcd) = 1.125 g cm(-)(3); R1 = 3.37%. Crystal data for 2: cubic, Pn3n; T = 180 K; a = 33.8252(8) A; V = 38700.9(16) A(3); Z = 6; D(calcd) = 1.133 g cm(-)(3); R1 = 4.97%. Crystal data for 3: cubic, Pn3n; T = 180 K; a = 33.7061(6) A; V = 38293.5(12) A(3); Z = 6; D(calcd) = 1.157 g cm(-)(3); R1 = 5.13%. Crystal data for 4: cubic, Pn3n; T = 180 K; a = 33.5900(7) A; V = 37899.2(14) A(3); Z = 6; D(calcd) = 1.182 g cm(-)(3); R1 = 4.03%. Crystal data for 5: cubic, Pn3n; T = 180 K; a = 33.5054(8) A; V = 37613.6(16) A(3); Z = 6; D(calcd) = 1.202 g cm(-)(3); R1 = 4.86%. The core of the anionic cluster comprises two vertex-sharing square-pyramidal [Ln(5)(mu(4)-O)(mu(3)-OH)(4)](9+) units. The compounds were characterized by elemental analysis, IR, fast atom bombardment mass spectra, thermogravimetry, and differential scanning calorimetry. The thermal analysis indicated that the nonanuclear species were stable up to 150 degrees C. Luminescence spectra of 2 and magnetic properties of 1-5 were also studied.     

Synthesis and characterisation of highly emissive and kinetically stable lanthanide complexes suitable for usage "in cellulo"

The synthesis and photophysical characterisation are reported of a series of cationic, neutral and anionic europium and terbium complexes based on structurally related, nonadentate ligands based on the cyclen macrocycle. Each complex incorporates a tetraazatriphenylene moiety and overall absolute emission quantum yields are in the range 15-40% in aerated aqueous media. Dynamic quenching of the lanthanide excited state occurs with electron-rich donors, e.g. iodide, ascorbate and urate, and a mechanistic interpretation is put forward involving an electron transfer process. The cationic lanthanide complexes are taken up by NlH/3T3 cells and tend to localise inside the cell nucleus.     

Synthesis, characterisation and biological evaluation of lanthanide(III) complexes with 3-acetylcoumarin-o-aminobenzoylhydrazone (ACAB)

Lanthanide(III) complexes of the general formula [Ln(ACAB)(2)(NO(3))(2)(H(2)O)(2)].NO(3).H(2)O where Ln=La(III), Pr(III), Nd(III), Sm(III), Eu(III), Gd(III), Tb(III), Dy(III) and Y(III), ACAB=3-acetylcoumarin-o-aminobenzoylhydrazone have been isolated and characterised based on elemental analyses, molar conductance, IR, (1)H- and (13)C-NMR, UV, TG/DTA and EPR spectral studies. The ligand behaves in bidentate fashion coordinating through hydrazide >C=O and nitrogen of >C=N. A coordination number of ten is assigned to the complexes. Antibacterial and Antifungal studies indicate an enhancement of activity of the ligand on complexation.     

Optically active,mesogenic lanthanide complexes: design,synthesis and characterisation

The synthesis, molecular structural characterisation and mesomorphic behaviour of lanthanidomesogens with the formula [LnL(LH)₂ ][X]₂ are reported. These mesogens were derived from ligands (LH- n ) formed by covalently linking the pro-mesogenic cholesterol segment with the N-(n-decyl)salicylaldimine core through either an even-parity (4-oxybutanoyloxy/6-oxyhexanoyloxy/8-oxyoctanoyloxy) or an odd-parity (5-oxypentano-yloxy) spacer. These ligands were designed based on the recently conceived concept of decoupling the anisometric segment from the metal-coordinating site by a flexible spacer to account for the stabilisation of nematic and/or smectic phases at lower temperatures. The even parity spacer ligands are polymesomorphic whereas the odd parity analogue exhibits only the chiral nematic phase. In contrast, the complexes display solely the smectic A phase indicating that the variation in the nature of lanthanide has no influence on the general phase behaviour of the complexes. The clearing temperatures of both the ligands and the complexes display an odd-even effect; the even members show relatively higher transition temperatures.     

Synthesis of a novel dinucleating aminocarboxylate macrocycle and structures of its dinuclear complexes with di- and trivalent transition and lanthanide metal ions

The synthesis of the new ligand L1(H4L1= 3,8,16,21-tetrakis(carboxylmethyl)-3,8,16,21,27,28-hexaazatricyclo[21.3.1.1(10,14)]octacosa-1(27),10,12,14(28),23,25-hexaen-5,18-diine) is reported. The solid-state structures of the four homodinuclear chelate complexes, [Zn2(L1)(H2O)2] x 6H2O, [Fe2(L1)(mu-O)] x 4H2O, [La2(L1)(NO3)2(H2O)2] x 6H2O and Na[Eu2(L1)(mu-AcO)3] x 3H2O, were determined by single-crystal X-ray structural analysis.     

Hydrothermal syntheses,crystal structures and luminescence properties of two lanthanide dinuclear complexes with hexafluoroglutarate

Two complexes [Ln₂(hfga)₂(phen)₄(H₂O)₆] · hfga · 2H₂O (H₂hfga = hexafluoroglutaric acid, phen = 1, 10-phenanthroline, Ln=Tb, 1; Eu, 2) were synthesized under hydrothermal conditions and their structures determined by X-ray crystallography. The complexes consist of dinuclear units with an inversion center. Each Ln(III) is nine-coordinate with two carboxylate oxygens from two hfga ligands, three oxygens from water and four nitrogens from two phen molecules. Two carboxylate groups of one hfga adopt monodentate coordination to Ln(III) as a long bidentate bridge linking two Ln(III) ions to form a dimer. Ln(III) ··· Ln(III) distances of 9.027(3) Å for 1 and 9.043(3) Å for 2 were observed. Both complexes emit strong fluorescence and show characteristic emission of Tb(III) and Eu(III) ions, respectively.     

Synthesis,characterization and fluorescence of lanthanide Schiff-base complexes

Six new lanthanide Schiff-base complexes were synthesized by reactions of hydrated lanthanide nitrates with H₂L (H₂L?=?N,N′-bis(salicylidene)-1,2-cyclohexanediamine) and characterized by elemental analysis, DTA–TG, IR, UV and luminescence spectra. The microanalyses and spectroscopic analyses indicate a 1D polymeric structure with the formula of [Ln(H₂L)(NO₃)₃(MeOH)₂] _n [Ln?=?La (1), Ce (2), Pr (3), Sm (4), Gd (5) & Dy (6)]. The fluorescence spectrum of complex 4 exhibited Sm³⁺ centered, Schiff-base sensitized orange fluorescence, indicating that energy levels of the triplet state of H₂L match closely to the lowest excited state (⁴G_5/2) of Sm³⁺ ion.     

Spontaneous formation of novel luminescent dinuclear lanthanide complexes that emit in the visible and near-IR regions

The reaction of tetrasodium-4,4',6,6'-tetracarboxy-2,2'-bipyridine (Na(4)L) with various lanthanide ions yields a family of isostructural supramolecular {Na(2)[Ln(2)L(2)]} complexes (1-4), where Ln(III) = Eu, Nd, Gd, and Tb. Strikingly, these complexes luminesce in buffered H(2)O or D(2)O solutions in either the visible or near-IR regions, despite their high hydration states.     

Synthesis and characterization of lanthanide complexes of DO3A-alkylphosphonates

Eight DO3A-based lanthanide(III) complexes bearing ester protected and unprotected phosphonate groups at variable distances from the macrocyclic moiety have been synthesized and analyzed. The ligands were made by straightforward four-step synthetic procedures and purified with preparative RP-HPLC, after which they were used to prepare gadolinium(III) and europium(III) complexes. Relaxometric experiments were performed on the Gd(III) complexes at 300 MHz, varying the pH of the solutions or the concentration of human serum albumin (HSA). It was found that when the pH of the medium was changed from neutral to pH 4 the longitudinal relaxivity of GdDO3A-ethylphosphonate and GdDO3A-propylphosphonate complexes increased by 50% and 60%, respectively. Diethyl esters of these complexes did not change longitudinal relaxivity in the same pH range but their transverse relaxivity increased upon binding to HSA. 31P NMR experiments on Eu(III) complexes showed a change in the chemical shift of both acid complexes in the same region where the highest relaxivity changes were observed and proved the stability of the complexes in the investigated pH range, while no shift was observed for the diester complexes. Luminescence studies on europium(III) complexes additionally supported observations obtained by NMR methods. The change in the form of the luminescence emission spectra, and the reduction in the q value upon addition of HSA proved the ternary adduct formation between the charge neutral diester complexes and HSA. Similarly, the change in the emission spectra showing a phosphonate bound structure at pH 7 to a species where the phosphonate oxygen is not coordinated at pH 4 in parallel with the increase of q value is supporting the hypothesis that the deprotonation of phosphonates is the main reason for the distinct relaxivity change from slightly acidic to the neutral solution media.