Structural and photophysical properties of coordination networks combining [Ru(bipy)(CN)4]2- anions and lanthanide(III) cations: rates of photoinduced Ru-to-lanthanide energy transfer and sensitized near-infrared luminescence

Co-crystallization of K2[Ru(bipy)(CN)4] with lanthanide(III) salts (Ln = Pr, Nd, Gd, Er, Yb) from aqueous solution affords coordination oligomers and networks in which the [Ru(bipy)(CN)4]2- unit is connected to the lanthanide cation via Ru-CN-Ln bridges. The complexes fall into two structural types: [{Ru(bipy)(CN)4}2{Ln(H2O)m}{K(H2O)n}] x xH2O (Ln = Pr, Er, Yb; m = 7, 6, 6, respectively), in which two [Ru(bipy)(CN)4]2- units are connected to a single lanthanide ion by single cyanide bridges to give discrete trinuclear fragments, and [{Ru(bipy)(CN)4}3{Ln(H2O)4}2] x xH2O (Ln = Nd, Gd), which contain two-dimensional sheets of interconnected, cyanide-bridged Ru2Ln2 squares. In the Ru-Gd system, the [Ru(bipy)(CN)4]2- unit shows the characteristic intense (3)metal-to-ligand charge transfer luminescence at 580 nm with tau = 550 ns; with the other lanthanides, the intensity and lifetime of this luminescence are diminished because of a Ru --> Ln photoinduced energy transfer to low-lying emissive states of the lanthanide ions, resulting in sensitized near-infrared luminescence in every case. From the degree of quenching of the Ru-based emission, Ru --> Ln energy-transfer rates can be estimated, which are in the order Yb (k(EnT) approximately 3 x 10(6) sec(-1), the slowest energy transfer) < Er < Pr < Nd (k(EnT) approximately 2 x 10(8) sec(-1), the fastest energy transfer). This order may be rationalized on the basis of the availability of excited f-f levels on the lanthanide ions at energies that overlap with the Ru-based emission spectrum. In every case, the lifetime of the lanthanide-based luminescence is short (tens/hundreds of nanoseconds, instead of the more usual microseconds), even when the water ligands on the lanthanide ions are replaced by D2O to eliminate the quenching effects of OH oscillators; we tentatively ascribe this quenching effect to the cyanide ligands.     

Three-component coordination networks based on [Ru(phen)(CN)4(2-) anions, near-infrared luminescent lanthanide(III) cations, and ancillary oligopyridine ligands: structures and photophysical properties

A series of cyanide-bridged coordination networks has been prepared which contain [Ru(phen)(CN)4](2-) anions, Ln(III) cations, and additional oligopyridine ligands (1,10-phenanthroline, 2,2':6',2'-terpyridine or 2,2'-bipyrimidine) which coordinate to the Ln(III) centres. Five structural types have been identified and examples of each type of structure are described: these are hexanuclear Ru4Ln2 clusters; two-dimensional Ru-Ln sheets with a honeycomb pattern of edge-linked Ru6Ln6 hexagons; one-dimensional chains consisting of two parallel cross-linked strands in a ladder-like arrangement; simple single-stranded chains of alternating Ru/Ln components; and a one-dimensional 'chain of squares' in which Ru2Ln2 squares are linked by bipyrimidine bridging ligands which connect to the Ln(III) corners of adjacent squares in the sequence. The 3MLCT luminescence characteristic of the [Ru(phen)(CN)4](2-) units is quenched in those networks containing Ln(III) which have low-lying near-infrared luminescent f-f states [Pr(III), Nd(III), Er(III), Yb(III)], with sensitised Ln(III)-based near-IR luminescence generated by d --> f energy-transfer. The rate of d --> f energy-transfer, and hence the degree of quenching of the 3MLCT luminescence from the [Ru(phen)(CN)4](2-) units, depends on the availability of f-f levels of an appropriate energy on the Ln(III) centre, with Nd(III) (with a high density of low-lying f-f states) being the most effective energy-acceptor and Yb(III) (with a single low-lying f-f state) being the least effective. Rates of d --> f energy-transfer to different Ln(III) centres could be determined from both the residual (partially quenched) lifetimes of the 3MLCT luminescence, and--in the case of the Yb(III) networks--by a rise-time for the sensitised near-IR luminescence. The presence of the 'blocking' polypyridyl ligands, which reduced the number of cyanide and water ligands that would otherwise coordinate to the Ln(III) centres, resulted in increases in the Ln(III)-based emission lifetimes compared to networks where these blocking ligands were not used.     

Monodisperse lanthanide fluoride nanocrystals: synthesis and luminescent properties

Three types of high-quality, monodisperse lanthanide fluoride colloidal nanocrystals (NCs) including LnF(3) (Ln = La-Pr), NaLnF(4) (Ln = Sm-Er), and Na(5)Ln(9)F(32) (Ln = Tm-Lu) with two crystal phases (hexagonal and cubic) and a rich variety of morphologies have been synthesized in high boiling organic solvents oleic acid and 1-octadecene, via a thermal decomposition pathway. The as-synthesized NCs were well characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), Fourier transform infrared spectroscopy (FT-IR), and photoluminescence (PL) spectra, respectively. It is found that the as-synthesized NCs consist of monodisperse nanoparticles with diverse shapes and narrow size distribution, which can easily disperse in nonpolar cyclohexane solvent. Additionally, a possible mechanism of NC nucleation and growth has been proposed. The results reveal that the formation of monodisperse NCs closely correlates with the inherent nature of lanthanide series from La to Lu. Under 980 nm NIR excitation, as-synthesized Yb(3+)/Ln(3+) (Ln = Er, Tm, Ho)-doped NaGdF(4) and Na(5)Lu(9)F(32) colloidal NCs show the respective characteristic up-conversion (UC) emissions of Er(3+), Tm(3+), and Ho(3+), which are promising for applications in biolabels, bioimaging, displays, and other optical technologies.     

Tuning the photophysical properties of lanthanide(iii)/zinc(ii) ‘encapsulated sandwich’ metallacrowns emitting in the near-infrared range

A family of Zn₁₆Ln(HA)₁₆ metallacrowns (MCs; Ln = Yb^III, Er^III, and Nd^III; HA = picoline- (picHA²⁻), pyrazine- (pyzHA²⁻), and quinaldine- (quinHA²⁻) hydroximates) with an ‘encapsulated sandwich’ structure possesses outstanding luminescence properties in the near-infrared (NIR) and suitability for cell imaging. Here, to decipher which parameters affect their functional and photophysical properties and how the nature of the hydroximate ligands can allow their fine tuning, we have completed this Zn₁₆Ln(HA)₁₆ family by synthesizing MCs with two new ligands, naphthyridine- (napHA²⁻) and quinoxaline- (quinoHA²⁻) hydroximates. Zn₁₆Ln(napHA)₁₆ and Zn₁₆Ln(quinoHA)₁₆ exhibit absorption bands extended into the visible range and efficiently sensitize the NIR emissions of Yb^III, Er^III, and Nd^III upon excitation up to 630 nm. The energies of the lowest singlet (S₁), triplet (T₁) and intra-ligand charge transfer (ILCT) states have been determined. Ln^III-centered total (Q^L_Ln) and intrinsic (Q^Ln_Ln) quantum yields, sensitization efficiencies (η_sens), observed (τ_obs) and radiative (τ_rad) luminescence lifetimes have been recorded and analyzed in the solid state and in CH₃OH and CD₃OD solutions for all Zn₁₆Ln(HA)₁₆. We found that, within the Zn₁₆Ln(HA)₁₆ family, τ_rad values are not constant for a particular Ln^III. The close in energy positions of T₁ and ILCT states in Zn₁₆Ln(picHA)₁₆ and Zn₁₆Ln(quinHA)₁₆ are preferred for the sensitization of Ln^III NIR emission and η_sens values reach 100% for Nd^III. Finally, the highest values of Q^L_Ln are observed for Zn₁₆Ln(quinHA)₁₆ in the solid state or in CD₃OD solutions. With these data at hand, we are now capable of creating MCs with desired properties suitable for NIR optical imaging.

We have created a family of ‘encapsulated sandwich’ Zn₁₆Ln(HA)₁₆ metallacrowns and by detailed quantitative analysis demonstrated how the nature of the hydroximate ligand impacts photophysical properties of these complexes.     

Stable, trinuclear Zn(ii)- and Cd(ii)-metallocycles: TWIM-MS, photophysical properties, and nanofiber formation

A series of trimeric, Zn(ii)- and Cd(ii)-metallocycles is reported. Structural characterization of the highly stable triangles was supported by traveling-wave ion mobility-mass spectrometry (TWIM-MS) and gradient tandem mass spectrometry (gMS(2)). Their unique photophysical properties and self-assembly to form nanofibers are also described.     

Facile preparation and photophysics of near-infrared luminescent lanthanide(III) monoporphyrinate complexes

The synthesis, characterization, and single crystal X-ray diffraction structures of a series of monoporphyrinate, trivalent lanthanide complexes with the monoanionic ligands hydridotris(1-pyrazolyl)borate (Tp) and (cyclopentadienyl)tris(diethylphosphinito)cobaltate (L(OEt)) having the general formulas M(TPP)(L) (M = Yb, Tm, Er, Ho, Nd, Pr; TPP = 5,10,15,20-tetraphenylporphyrinate; L = Tp, L(OEt)) are described. The photophysical properties of these complexes are also presented including their absorption, emission, and transient absorption properties.     

Dual-emissive complexes: Visible and near-infrared luminescence from bis-pyrenyl lanthanide(III) complexes

The syntheses and photophysical attributes of a range of dual-emissive lanthanide complexes are described. The simple ligand architecture is based upon a diethylenetriaminepentaacetic acid (DTPA) core and appended with two aminopyrenyl chromophores to yield the fluorescent free ligand L^pyr. Reaction of the ligand with Ln(tris-trifluoromethanosulfate) gave the mononuclear complexes Ln · L^pyr (Ln = Nd, Er, Yb). Luminescence studies revealed that the complexes were emissive in both the near-IR and UV–Vis, the latter resulting from pyrene localised emission (λ_em = 390 nm), the former from pyrene-sensitised emission of the lanthanide ion (λ_ex = 337 nm). Time-resolved measurements in the near-IR indicated that the number of coordinated solvent molecules for Nd and Yb was <1, confirming the proposed coordination mode of the octadentate L^pyr. The suitability of pyrene as a sensitiser for near-IR emitting lanthanides was further demonstrated in the rare observation of Er^III emission in a non-deuteriated protic medium.     

New lanthanide complexes for sensitized visible and near-IR light emission: synthesis, 1H NMR, and X-ray structural investigation and photophysical properties

We describe the syntheses, the 1H NMR studies in CD3OD and D2O as solvent, the X-ray characterization, and the luminescence properties in D2O solution of the two complexes Eu.1 and Er.1, where 1 is a dipartite ligand that includes (i) a 1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid (DO3A) unit serving as hosting site for the metal center; and (ii) a phenanthroline unit which plays the role of light antenna for the sensitization process of the metal centered luminescence. In a previous report (Inorg. Chem. 2002, 41, 2777), we have shown that for Eu.1 there are no water molecules within the first coordination sphere. X-ray and 1H NMR results reported here are consistent with full saturation of the nine coordination sites within the Eu.1 and Er.1 complexes. In addition, these studies provide important details regarding the conformations, square antiprism (SAP) and twisted square antiprism (TSAP), adopted in solution by these complexes. The luminescence results are consistent with both an effective intersystem crossing (ISC) at the light absorbing phenanthroline unit (lambda(exc) = 278 nm) and an effective energy transfer (en) process from the phenanthroline donor to the cation acceptor (with unit or close to unit efficiency for both steps). In D2O solvent, the overall sensitization efficiency, phi(se), is 0.3 and 5 x 10(-6), for Eu.1 (main luminescence peaks at 585, 612, 699 nm) and Er.1 (luminescence peak at 1530 nm), respectively. The photophysical properties of both complexes are discussed with reference to their structural features as elucidated by the obtained 1H NMR and X-ray results.     

Synthesis, structure and luminescence properties of Cu(ii), Zn(ii) and Cd(ii) complexes with 4'-terphenylterpyridine

The complexes [M(tptpy)(2)](ClO(4))(2) (M = Zn(ii) (1), Cd(ii) (2), and Cu(ii) (3)); tptpy = 4'-[1,1':4',1']terphenyl-4'-yl-[2,2':6',2']terpyridine = 4'-terphenylterpyridine) have been synthesized, structurally characterized by X-ray crystallography and subjected to preliminary luminescence studies. In the crystalline state, all the metal ions have an N(6) coordination sphere of distorted octahedral geometry and the structures of the Zn(ii) and Cd(ii) complexes are isomorphous but differ from that of the Cu(ii) complex, which also differs from the other two in that it is non-emissive. The structure determinations show that aromatic-aromatic interactions involving both the terpyridine heads and the terphenyl tails are important factors influencing the crystalline array. The emission spectra of the Zn(ii) and Cd(ii) complexes are very similar and show a considerable red-shift of the emission maximum compared to that of the free ligand.     

Mononuclear and binuclear lanthanide(III) complexes: syntheses,structural, photophysical and thermal properties

Six new Ln(III) complexes viz., [Gd(tptz)(SCN)₃(CH₃OH)₂OH₂]·CH₃OH (1), [Eu(tptz)(SCN)₃(CH₃OH)₂OH₂]·CH₃OH (2), [Tb(tptz)(SCN)₃(OH₂)₃]₄ (3), [Gd(tptz)(OBz)₂(μ-OBz)OH₂]₂·2H₂O (4), [OH₂(OBz)₂(tptz)Eu₁(μ-OBz)₂Eu₂(tptz)(OBz)₂OH₂]·CH₃OH·7H₂O (5), and {[Tb₁(tptz)(OBz)₂(μ-OBz)]₂·[Tb₂(tptz)(OBz)₃CH₃OH]₂}·2CH₃OH·4H₂O (6) (Ln = Gd, Eu, Tb; tptz = 2,4,6-tris(2-pyridyl)-1,3,5-triazine; BzONa = sodium benzoate), have been synthesized and characterized by physicochemical methods including single-crystal X-ray crystallography. The X-ray studies demonstrate that 1–3 are mononuclear, whereas 4–6 are binuclear. The photophysical properties of 1–6 have been studied with ultraviolet absorption and emission spectral studies. Their thermal properties have been studied by thermogravimetric (TG) and derivative thermogravimetric analysis (DTG), demonstrating that the final product after decomposition was Ln₂O₃ for all these complexes.     

Visible light sensitized attapulgite-based lanthanide composites: microstructure, photophysical behaviour and biological application

Attapulgite, an extremely stable fibrillar mineral present in nature, is a promising new carrier of luminescent lanthanide complexes for further applications. A europium complex Eu(DBM)(3)(H(2)O)(2) (HDBM = dibenzoylmethane) was covalently coupled onto modified attapulgites (or silica nanoparticles) via a ligand exchange reaction, generating attapulgite-based ternary europium complexes. The composites were characterized by CHN elemental analysis, inductively coupled plasma-atomic emission spectroscopy (ICP-AES) for Eu(3+) content, powder X-ray diffraction (XRD), thermogravimetry (TG) and UV-vis absorption spectra. The results indicate that the Eu(3+) complex was grafted covalently to the outer surfaces of attapulgites (or silica nanoparticles) and modifications by coupling agents containing different alkoxide groups (aminopropyltriethoxysilane (APTES) or aminopropylmethyldiethoxysilane (APMDES)) led to different grafting ratios. The structures of these composites were further evidenced by the determination of photophysical behaviours and coordinated water molecules of the complexes linked to matrices. Attapulgite-based lanthanide composites linked by APTES can be excited by visible light, with a wide excitation wavelength range from UV to visible light (a maximum at 398 nm), long luminescence lifetime (503 μs), high quantum yield (48%) and improved exposure durability. When incubated with HeLa cells at 37 °C, the fluorescence of matrix-APTES-cpa-Eu(DBM)(3) is observed on the cell membrane. Moreover, the low cytotoxicity of our present system results in potential applications for cell imaging in biological systems.     

Spectral,luminescent, and photophysical properties of dipyrrolylbenzenes

Dipyrroles with a phenylene bridge, 1,4-bis(pyrrol-2-yl)benzene, 4-(1-vinylpyrrol-2-yl)-1-(pyrrol-2-yl)benzene, and 1,4-bis(1-vinylpyrrol-2-yl)benzene, show intense room-temperature fluorescence in solutions. Analysis of electronic absorption spectra, fluorescence spectra, and results of B3LYP, TD B3LYP, and CIS quantum chemical calculations showed that the introduction of a bulky substituent in position 1 of the pyrrole ring makes the ground-state structures of dipyrrolylbenzenes less planar. Excited-state geometries of all molecules relax to more planar conformations. An increase in the probability of nonradiative transitions has little effect on the quantum yields of fluorescence (Φ_f) of dipyrrolylbenzenes. Even for 1,4-bis(1-vinylpyrrol-2-yl)benzene, where the pyrrole rings deviate from the benzene ring plane by 44°, the fluorescence efficiency remains high enough (Φ_f = 0.7). Substitution at nitrogen atoms has little effect on positions of fluorescence band maxima. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1433–1438, July, 2008.     

Water-soluble monodispersed lanthanide oxide submicrospheres: PVP-assisted hydrothermal synthesis, size-control and luminescence properties

We report a facile hydrothermal synthetic route to prepare a class of monodispersed lanthanide-based compound submicrospheres with controllable size, which employs raw lanthanide oxides as starting material, urea as precipitator and poly(N-vinyl-2-pyrrolidone) (PVP) as surfactant. Dependent on the intrinsic properties of respective lanthanide, the resulting products could be in the form of oxide, hydroxide or basic carbonate. These lanthanide hydroxides or basic carbonates can be easily transformed into their corresponding oxides by calcination, retaining the same morphology and size dispersion. The formation mechanism of these lanthanide-based compound submicrospheres is investigated and PVP plays a critical role in forming uniform and well-dispersed products. Furthermore, this method could be extended to a binary system by using two kinds of lanthanide oxides as starting material, resulting in doped-type lanthanide oxide submicrospheres (such as Y(2)O(3):Eu(3+)). The Y(2)O(3):Eu(3+) submicrospheres exhibit nearly uniform spherical morphology and narrow size distribution as well as good water solubility and sharp spectral emission at 610 nm (corresponding to the 5D(0)-7F(2) transition of Eu(3+)). This makes them attractive materials for applications in fields such as fluorescent lamps, field emission displays (FEDs) or LCDs, or as biomedical labels and molecular probes.     

Structural and photophysical properties of coordination networks combining [Ru(Bpym)(CN)4]2- or [[Ru(CN)4]2(mu-bpym)]4- anions (bpym = 2,2'-bipyrimidine) with lanthanide(III) cations: sensitized near-infrared luminescence from Yb(III), Nd(III), and Er(III) following Ru-to-lanthanide energy transfer

Reaction of the cyanoruthenate anions [Ru(bpym)(CN)4]2- and [[Ru(CN)4]2(mu-bpym)]4- (bpym = 2,2'-bipyrimidine) with lanthanide(III) salts resulted in the crystallization of coordination networks based on Ru-CN-Ln bridges. Four types of structure were obtained: [Ru(bpym)(CN)4][Ln(NO3)(H2O)5] (Ru-Ln; Ln = Sm, Nd, and Gd) are one-dimensional helical chains; [Ru(bpym)(CN)4]2[Ln(NO3)(H2O)2][Ln(NO3)(0.5)(H2O)(5.5)](NO3)(0.5).5.5H2O (Ru-Ln; Ln = Er and Yb) are two-dimensional sheets containing cross-linked chains based on Ru2Ln2(mu-CN)4 diamond units, which are linked into one-dimensional chains via shared Ru atoms; [[Ru(CN)4]2(mu-bpym)][Ln(NO3)(H2O)5]2.3H2O (Ru2-Ln; Ln = Nd and Sm) are one-dimensional ladders with parallel Ln-NC-Ru-CN-Ln-NC strands connected by the bipyrimidine "cross pieces" acting as rungs on the ladder; and [[Ru(CN)4]2(mu-bpym)][Ln(H2O)6](0.5)[Ln(H2O)4](NO3)(0.5).nH2O (Ru2-Ln; Ln = Eu, Gd, and Yb; n = 8.5, 8.5, and 8, respectively) are three-dimensional networks in which two-dimensional sheets of Ru2Ln2(mu-CN)4 diamonds are connected via cyanide bridges to Ln(III) ions between the layers. Whereas Ru-Gd shows weak triplet metal-to-ligand charge-transfer (3MLCT) luminescence in the solid state from the Ru-bipyrimidine chromophore, in Ru-Nd, Ru-Er, and Ru-Yb, the Ru-based emission is quenched, and all of these show, instead, sensitized lanthanide-based near-IR luminescence following a Ru --> Ln energy transfer. Similarly, Ru2-Nd and Ru2-Yb show lanthanide-based near-IR emission following excitation of the Ru-bipyrimidine chromophore. Time-resolved luminescence measurements suggest that the Ru --> Ln energy-transfer rate is faster (when Ln = Yb and Er) than in related complexes based on the [Ru(bipy)(CN)4]2- chromophore, because the lower energy of the Ru-bpym 3MLCT provides better spectroscopic overlap with the low-energy f-f states of Yb(III) and Er(III). In every case, the lanthanide-based luminescence is relatively short-lived as a result of the CN oscillations in the lattice.     

Two trinuclear Ru(II) complexes of hetero-tritopic bridging ligands: synthesis,characterization, theoretical calculations,photophysical and electrochemical properties

Two hetero-tritopic bridging ligands L¹ and L² based on 2,2′-bipyridine and 1,10-phenanthroline moieties, and their corresponding Ru(II) complexes [{Ru(bpy)₂}₃(µ₃?L¹)](PF₆)₆ and [{Ru(bpy)₂}₃(µ₃?L²)](PF₆)₆ (bpy = 2,2′-bipyridine), were synthesized. The molecular structures of both complexes were deduced by ¹H NMR, ESI-MS, ESI-HRMS, elemental analyses, and IR spectroscopy. Quantum calculations on the free bridging ligands and their complexes are also presented. Both complexes display MLCT absorptions at around 454 nm, and emissions at around 613 nm in CH₃CN solution at room temperature and at around 590 nm in EtOH–MeOH glassy matrix at 77 K. Cyclic and differential pulse voltammetry studies of both complexes reveal one reversible Ru(II)-centered oxidation and three reversible ligand-centered reductions, in each case.     

Syntheses, crystal structures and luminescent properties of new lanthanide(III) organoarsonates

The first examples of lanthanide(III) organoarsonates, Ln(L(1))(H(2)O)(3) (Ln = La (1), H(3)L(1) = 4-hydroxy-3-nitrophenylarsonic acid), Ln(L(1))(H(2)O)(2) (Ln = Nd (2), Gd (3)), and mixed-ligand lanthanide(III) organoarsonates, Ln(2)(HL(1))(2)(C(2)O(4))(H(2)O)(2) (Ln = Nd (4), Sm (5), Eu (6)), were hydrothermally synthesized and structurally characterized. Compounds 1-3 feature a corrugated lanthanide arsonate layer, in which 1D lanthanide arsonate inorganic chains are further interconnected via bridging L(1)(3-) ligands. Compounds 4-6 exhibit a complicated 3D network. The interconnection of the lanthanide(III) ions by the bridging arsonate ligand leads to the formation of a novel 3D framework with long narrow 1D tunnels along the a-axis, with the oxalate anions are located at the above tunnels and bridging with lanthanide(III) ions. Compounds 2 and 4 exhibit the characteristic emission bands of the Nd(III) ion, whereas compound 6 displays the characteristic emission bands of the Eu(III) ion. The magnetic properties of compounds 3-6 were also investigated.     

Engineering of highly luminescent lanthanide tags suitable for protein labeling and time-resolved luminescence imaging

The synthesis of a new ligand LH(4) based on a glutamic acid skeleton bis-functionalized on its nitrogen atom by 6-methylene-6'-carboxy-2,2'-bipyridine chromophoric units is described. UV-vis spectrophotometric titrations revealed the formation of 1:1 M:L complexes with lanthanide(III) cations, and complexation of LH(4) with equimolar amounts of hydrated LnCl(3) salts (Ln = Eu, Gd, and Tb) gave water-soluble and stable complexes of the general formula [LnL(H(2)O)]Na, which were characterized by elemental analysis, IR, UV-vis absorption spectroscopy, (1)H NMR (Ln = Eu), and mass spectrometry. The conditional stability constant for formation of the [EuL(H(2)O)]Na complex was determined by competitive complexation experiments to be log K = 16.5 +/- 0.6 in 0.01 M TRIS/HCl buffer (pH = 7.0). In water solution, the [EuL(H(2)O)]Na and [TbL(H(2)O)]Na complexes were highly luminescent with quantum yields of 8% and 31%, respectively, despite the presence of ca. one water molecule in the first coordination sphere of the metal ions. Activation of the appended carboxylate function of the glutamate moiety in the form of an N-hydroxysuccinimidyl ester allows for the covalent linking of the complexes to primary amino groups of biological compounds. Bovine serum albumin (BSA) was labeled with both Eu or Tb complexes, and the Ln-BSA conjugates were characterized by UV-vis absorption and emission spectroscopy and MALDI-TOF mass spectrometry. Labeling ratios (number of complex molecules per BSA) of ca. 8:1 and 7:1 were established for Eu-BSA and Tb-BSA, respectively. The suitability of the tagged compound for use in bioanalytical time-resolved luminescence microscopy was established by comparison with fluorescein-labeled probes.     

Pillaring of CdCl2-like layers in lanthanide metal-organic frameworks: synthesis, structure, and photophysical properties

A hydrothermal reaction of lanthanide salts, pyridine-2,3-dicarboxylic acid, benzene-1,4-dicarboxylic acid, and water gave rise to a new series of three-dimensional mixed carboxylates (homocyclic and heterocyclic) of lanthanides with the general formula [M2(H2O)4][{C5H3N(COO)2}2{C6H4(COO)2}], M=La (I), Pr (II), and Nd (III). The structure consists of M2O14N2 dimeric units connected by pyridine-2,3-dicarboxylate moieties to form two-dimensional layers that are pillared by terephthalate units. The structures also possess two co-ordinated water molecules, which are arranged to form one-dimensional helical chains and can be reversibly adsorbed. The connectivity within the layers closely resembles that of the CdCl2 layered structure with 3(6) topology. To the best of our knowledge, this is the first observation of CdCl2 topology in lanthanide metal-organic framework compounds. Partial substitution of La3+ in I by Eu3+ and Tb3+ (2 and 4 %) gives rise to characteristic red/pink or green emission, which suggests a ligand-sensitized metal-centered emission. The Nd compound III shows interesting UV and blue emission through an up-conversion process.