Near-IR Luminescent YbIII Coordination Polymers Composed of Pyrene Derivatives for Thermostable Oxygen Sensors

Oxygen-sensitive and near-infrared (NIR) luminescent Yb^III coordination polymers incorporating ligands based on pyrene derivatives were synthesized: Yb^III–TBAPy and Yb^III–TIAPy (TBAPy: 1,3,6,8-tetrakis(p-benzoate)pyrene; TIAPy: 1,3,6,8-tetrakis(3,5-isophthalic acid)pyrene). The coordination structures of these materials have been characterized by means of electrospray ionization mass spectrometry, X-ray diffraction analysis, and thermogravimetric analysis. Moreover, the porous structure of Yb^III–TIAPy has been evaluated by measuring its N₂ adsorption isotherm. The NIR luminescence properties of Yb^III–TBAPy and Yb^III–TIAPy have been examined by acquiring emission spectra and determining emission lifetimes under air or argon and in vacuo. Yb^III–TIAPy exhibited high thermal stability (with a decomposition temperature of 400 °C), intense luminescence (with an emission quantum yield under argon of 6.6 %), and effective oxygen-sensing characteristics. These results suggest that NIR luminescent Yb^III coordination polymers prepared using pyrene derivatives could have applications in novel thermo-stable oxygen sensors.     

(Acetato‐κ2O,O′)dihydroxidoytterbium(III) hemihydrate

The title compound, [Yb(C₂H₃O₂)(OH)₂]·0.5H₂O, was obtained via hydrothermal reaction of Yb(CH₃COO)₃·H₂O with NaOH at 443 K. The compound forms two‐dimensional layers with six crystallographically independent Yb^III atoms. Four of these form YbO₈ coordination polyhedra, while the coordination number of the remaining two Yb^III atoms is 7. Five of these coordination polyhedra are interconnected mainly via hydroxide groups, as they build a narrow inner layer that extends infinitely within the ab plane. The sixth Yb^III atom resides outside this inner layer and builds a terminal YbO₈ coordination polyhedron on the layer surface. Its coordination environment comprises four carboxylate O atoms belonging to three different acetate entities, three hydroxide groups and one water molecule. Adjacent layers experience weak interactions via hydrogen bonds. The Yb—O distances lie in the range 2.232 (4)–2.613 (5) Å.     

Synthesis,Structure, Luminescent and Thermal Properties of Ytterbium(III) and Dysprosium(III) Complexes with 5‐Sulfoisophthalic Acid Sodium Salt

Two rare earth metal‐organic framework compounds [Ybsip(H₂O)₅] · 3H₂O ( 1 ) and [Dysip(H₂O)₄] ( 2 ) (NaH₂sip: 5‐sulfoisophthalic acid sodium salt) were synthesized hydrothermally, and characterized by single‐crystal X‐ray diffraction, elemental analysis, and FT‐IR spectroscopy. In complex 1 , each Yb^III atom is nine‐coordinate with a distorted monocapped tetragonal prismatic arrangement. Two carboxylate groups of each sip^3– molecule adopt the same μ₁‐η¹:η¹ chelating coordination model connecting two Yb^III atoms. The oxygen atoms of the sulfonate group do not participate in coordination with Yb^III. The whole sip^3– molecule acts as a μ₂ bridge to form an one‐dimensional (1D) chain structure. The 1D chains are linked by hydrogen bonding to generate two‐dimensional layers, and are further combined together to form a three‐dimensional structure. In complex 2 , the Dy^III atom is nine‐coordinate with a distorted monocapped tetragonal antiprismatic arrangement. In each sip^3– anion, two carboxylate groups take the same μ₁‐η¹:η¹ chelating coordination mode, only an oxygen atom of sulfonate group bond to Dy^III ion. The whole ligand sip^3– acts as a μ₃ bridge linking three different Dy^III ions to generate a wave‐like two‐dimensional network with (6,3) topological structure. The two‐dimensional networks are further linked by O–H ··· O hydrogen bonds to form a three‐dimensional structure. The thermal and luminescent properties of both complexes are investigated.     

Wavelength-Dependent Singlet Oxygen Generation in Luminescent Lanthanide Complexes with a Pyridine-Bis(Carboxamide)-Terthiophene Sensitizer

Lanthanide ion (Ln^III) complexes, [Ln(3Tcbx)₂]³⁺ (Ln^III=Yb^III, Nd^III, Er^III) are isolated with a new pyridine-bis(carboxamide)-based ligand with a 2,2′:5′,2′′-terthiophene pendant (3TCbx), and their resulting photophysical properties are explored. Upon excitation of the complexes at 490 nm, only Ln^III emission is observed with efficiencies of 0.29 % at 976 nm for Ln^III=Yb^III and 0.16 % at 1053 nm for Ln^III=Nd^III. Er^III emission is observed but weak. Upon excitation at 400 nm, concurrent ¹O₂ formation is seen, with efficiencies of 11 % for the Yb^III and Nd^III complexes and 13 % for the Er^III complex. Owing to the concurrent generation of ¹O₂, as expected, the efficiency of metal-centered emission decreases to 0.02 % for Yb^III and 0.05 % for Nd^III. The ability to control ¹O₂ generation through the excitation wavelength indicates that the incorporation of 2,2′:5′,2′′-terthiophene results in access to multiple sensitization pathways. These energy pathways are unraveled through transient absorption spectroscopy.     

Accessing Lanthanide-to-Lanthanide Energy Transfer in a Family of Site-Resolved [LnIIILnIII′] Heterodimetallic Complexes

The ligand H₃L (6-[3-oxo-3-(2-hydroxyphenyl)propionyl]pyridine-2-carboxylic acid), which exhibits two different coordination pockets, has been exploited to engender and study energy transfer (ET) in two dinuclear [Ln^IIILn^III′] analogues of interest, [EuYb] and [NdYb]. Their structural and physical properties have been compared with newly synthesised analogues featuring no possible ET ([EuLu], [NdLu], and [GdYb]) and with the corresponding homometallic [EuEu] and [NdNd] analogues, which have been previously reported. Photophysical data suggest that ET between Eu^III and Yb^III does not occur to a significant extent, whereas emission from Yb^III originates from sensitisation of the ligand. In contrast, energy migration seems to be occurring between the two Nd^III centres in [NdNd], as well as in [NdYb], in which Yb^III luminescence is thus, in part, sensitised by ET from Nd. This study shows the versatility of this molecular platform to further the investigation of lanthanide-to-lanthanide ET phenomena in defined molecular systems.     

Novel bimetallic Cr<Subscript>3</Subscript>Yb<Subscript>3</Subscript> mixed salt containing a 3<Emphasis Type="Italic">d</Emphasis>-4<Emphasis Type="Italic">f</Emphasis> heterometallic Cr<Subscript>2</Subscript>Yb<Subscript>3</Subscript> cluster

A novel bimetallic Cr₃Yb₃ coordination compound containing a 3d-4f heterometallic Cr₂Yb₃ cationic cluster has been synthesized and structurally characterized. The crystal structure was determined by X-ray analysis. Results denote that the complex consists of an original [Cr ₂ ^III Yb ₃ ^III ]³⁺ moiety with a trigonal-bipyramidal topology of the [Cr₂Yb₃(μ-OOCCH₃)₆(μ-OH)₆(H₂O)₆]³⁺ core, an isolated [Cr^III(CN)₆]^3? anion, and four molecular neutral 4,4′-bipyridene (Bipy) ligands, namely, [Cr₂Yb₃(μ-OOCCH₃)₆(μ-OH)₆(H₂O)₆][Cr(CN)₆] · 4Bipy · 13H₂O.     

Coordinate Structures of PrIII, GdIII, TmIII, and YbIII Complexes with Nitrilotriacetic Acids

The crystal and molecular structures of the [Pr^III(nta)(H₂O)₂]·H₂O (nta = nitrilotriacetic acids), K₃[Gd^III(nta)₂(H₂O)]·6H₂O, and K₃[Yb^III(nta)₂]·5H₂O complexes have been determined by single-crystal X-ray structure analyses. In [Pr^III(nta)(H₂O)₂]·H₂O, the Pr^IIINO₈ part forms a nine-coordinate pseudo-monocapped square antiprismatic structure in which one N and three O atoms are from one nta ligand in the same molecule, three O atoms from another nta ligand in the neighboring molecule and two O atoms from two coordinate water molecules. In K₃[Gd^III(nta)₂(H₂O)]·6H₂O, the [Gd^III(nta)₂(H₂O)^3- complex anion has a nine-coordinate pseudo-monocapped square antiprismatic structure in which each nta acts as a tetradentate ligand with one N atom of the amino group and three O atoms of the carboxylic groups. In K₃[Yb^III(nta)₂]·5H₂O, each nta also acts as a tetradentate ligand with one N atom of amino group and three O atoms of the carboxylic groups, but the [Yb^III(nta)₂ ^3- complex anion has an eight-coordinate structure with a distorted square antiprismatic prism. All the results including those for [Tm^III(nta)(H₂O)₂]·2H₂O confirm the inferences on the coordinate structures and coordination numbers of rare earth metal complexes with the nta ligand.     

Erste Pyridylbenzimidazolate der Lanthanide: Synthese,Kristallstruktur und thermischer Abbau von NH4[Ln(N3C12H8)4] mit Ln = Nd,Yb

The First Pyridylbenzimidazolates of the Lanthanides: Syntheses, Crystal Structure and Thermal Decomposition of NH₄[Ln(N₃C₁₂H₈)₄] with Ln = Nd, Yb Transparent yellow crystals of the compounds NH₄ [Ln^III (N₃C₁₂H₈)₄] with Ln = Nd, Yb were obtained by solvent‐free reactions of the lanthanides neodymium and ytterbium with 2‐(2‐Pyridyl)‐benzimidazole. The bulk syntheses lead to isotypic compounds despite the different ionic radii of Nd^III and Yb^III exhibiting nitrogen coordination of the lanthanides only. Both compounds were investigated IR‐ and Raman‐spectroscopically and in regard to their thermal behaviour. They are the first examples of completely solvent‐free (coordinating and non‐coordinating) compounds of the lanthanides with a complete N‐coordination that were obtained via a solid‐state reaction method.     

Excited State Properties of Lanthanide(III) Complexes with a Nonadentate Bispidine Ligand

Eu^III, Tb^III, Gd^III and Yb^III complexes of the nonadentate bispidine derivative L² (bispidine=3,7-diazabicyclo[3.3.1]nonane) were successfully synthesized and their emission properties studied. The X-ray crystallography reveals full encapsulation by the nonadentate ligand L² that enforces to all Ln^III cations a common highly symmetrical capped square antiprismatic (CSAPR) coordination geometry (pseudo C_4v symmetry). The well-resolved identical emission spectra in solid state and in solution confirm equal structures in both media. As therefore expected, this results in long-lived excited states and high emission quantum yields ([Eu^IIIL²]⁺, H₂O, 298 K, τ=1.51 ms, ϕ=0.35; [Tb^IIIL²]⁺, H₂O, 298 K, τ=1.95 ms, ϕ=0.68). Together with the very high kinetic and thermodynamic stabilities, these complexes are a possible basis for interesting biological probes.     

Synthesis and photophysical properties of Ir<Superscript>III</Superscript>-Ln<Superscript>III</Superscript> (Ln = Nd,Yb, Er) bimetallic complexes containing bipyrimidines as bridging ligands

Bipyrimidines have been chosen as (N∧N)(N∧N) bridging ligands for connecting metal centers. Ir^III-Ln^III (Ln = Nd, Yb, Er) bimetallic complexes [Ir(dfppy)₂(μ-bpm)Ln(TTA)₃]Cl were synthesized by using Ir(dfppy)₂(bpm)Cl as the ligand coordinating to lanthanide complexes Ln(TTA)₃·2H₂O. The stability constants between Ir(dfppy)₂(bpm)Cl and lanthanide ions were measured by fluorescence titration. The obvious quenching of visible emission from Ir^III complex in the Ir^III-Ln^III (Ln = Nd, Yb, Er) bimetallic complexes indicates that energy transfer occurred from Ir^III center to lanthanides. NIR emissions from Nd^III, Yb^III, and Er^III were obtained under the excitation of visible light by selective excitation of the Ir^III-based chromophore. It was proven that Ir(dfppy)₂(bpm)Cl as the ligand could effectively sensitize NIR emission from Nd^III, Yb^III, and Er^III.     

Syntheses and structural determination of eight-coordinate Na[YbIII(Cydta)(H2O)2] · 5H2O and [YbIII(Hegta)] · 2H2O complexes

Na[Yb^III(Cydta)(H₂O)₂] · 5H₂O (1) (H₄Cydta = trans-1,2-cyclohexanediamine-N,N,N′,N′-tetraacetic acid) and [Yb^III(Hegta)] · 2H₂O (2) (H₄egta = ethyleneglycol-bis-(2-aminoethylether)-N,N,N′,N′-tetraacetic acid) were prepared and their composition and structures were determined by elemental analyses and single-crystal X-ray diffraction techniques. Complex 1 crystallized in the triclinic crystal system with space group P 1; the Yb^III is eight-coordinate by a hexadentate Cydta and two water molecules. Complex 2 is a protonated egta complex, crystallized in the monoclinic crystal system with space group P 2 ₁ /c; Yb^III is coordinated only by the octadentate Hegta ligand. Both these complexes adopt a pseudo-square antiprismatic conformation.     

Sensitized near-infrared emission of Yb from an Ir–Yb bimetallic complex

A new cyclometalated ligand 1,3-dimethyl-5-phenyl-1H-[1,2,4]-triazole (pdt) was designed and synthesized. And the corresponding Ir^III complex Ir(pdt)₂(phen5f) (phen5f stands for 4,4,5,5,5-pentafluoro-1-(1′,10′-phenanthrolin-2′-yl)-pentane-1,3-dionate) was obtained. According to the measurement of the lowest triplet state energy level of Ir(pdt)₂(phen5f), it is suitable for sensitizing NIR (near-infrared) lanthanide ions instead of Eu^III. The bimetallic complex [(pdt)₂Ir(μ-phen5f)YbCl₂ · 2CH₃CH₂OH · H₂O]Cl was synthesized by the approach of “complexes as ligands”. Data showed that the emission quenching was observed in the solid state when the Ir^III–Yb^III complex was compared with the Ir^III complex, which implied that energy transfer might occur from Ir^III complex-ligand to Yb^III ion. Upon irradiation of the MLCT (metal-to-ligand charge transfer) absorption of Ir(pdt)₂(phen5f), the characteristic emission of Yb^III was obtained with the peak around 978 nm.     

Solid-State Near-Infrared Circularly Polarized Luminescence from Chiral YbIII-Single-Molecule Magnet

A field-induced chiral Yb^III Single-Molecule Magnet (SMM) displayed an unprecedented near-infrared circularly polarized luminescence (NIR-CPL) in the solid-state. The bridging bis(1,10-phenantro[5,6b])tetrathiafulvalene triad ( L ) allowed an efficient sensitization of the NIR ²F_5/2→²F_7/2 emission while the NIR-CPL is associated to the f-f transitions of the Yb^III ion bearing chiral β-diketonate derived-camphorate ancillary ligands.     

Crystal structures and DNA-binding properties of PrIII complexes derived from 8-hydroxyquinoline-2-carboxaldehyde and three aroylhydrazines

Pr^III and three synthesized ligands, 8-hydroxyquinoline-2-carboxaldehyde-(benzoyl)hydrazone, 8-hydroxyquinoline-2-carboxaldehyde-(2′-hydroxybenzoyl)hydrazone, and 8-hydroxyquinoline-2-carboxaldehyde-(isonicotinyl)hydrazone, respectively, can form binuclear Pr^III complexes with 1?:?1 metal-to-ligand stoichiometry and nine-coordination at Pr^III indicated by X-ray crystal structural analyses. Ligands are dibasic tetradentate, binding to Pr^III through the phenolate oxygen, nitrogen of quinolinato unit, the C=N of methylene, and ^–O–C=N– enolized and deprotonated from O=C–NH– of the aroylhydrazone side chain. One DMF binds orthogonally to the ligand plane from one side to the metal ion, while another DMF and a bidentate nitrate simultaneously bind from the other. Dimerization of the monomeric unit occurs through the phenolate oxygen leading to a central planar four-membered (PrO)₂ ring. The crystal structures are similar to each other and to other nine-coordinate lanthanide complexes with geometry of distorted edge-sharing mono-capped square-antiprism of [LnL(NO₃)(DMF)₂]₂ (Ln = La^III, Nd^III, Sm^III, Eu^III, Tb^III, Dy^III, Ho^III, and Er^III) except for Yb^III with eight-coordinate Yb^III center with distorted edge-sharing dodecahedron of [YbL(NO₃)(DMF)]₂, derived from 8-hydroxyquinoline-2-carboxaldehyde and aroylhydrazines. The ligands and Pr^III complexes can bind to calf thymus DNA through intercalation with binding constants at 10⁵ M^?1 and probably be used as potential antitumor drugs.     

Aqua­tris­(1,10‐phenan­throline)­(trans‐2,3‐di­methyl­acrylato)­ytterbium(III)

The title mononuclear complex, [Yb(C₅H₇O₂)₃(C₁₂H₈N₂)(H₂O)], is a most uncommon carboxylate complex of a rare earth metal. Each Yb^III ion is eightfold coordinated, being bonded to five O atoms of three dimethylacrylate groups, both N atoms of a phenanthroline and one O atom of a water molecule, giving a distorted square antiprismatic coordination polyhedron.     

Lanthanide luminescence efficiency in eight- and nine-coordinate complexes: Role of the radiative lifetime

The photophysical parameters for the sensitization of metal-centred luminescence are analyzed in two series of complexes with tridentate and hexadentate ligands having N_xO_y chelating units. In particular, the radiative lifetime τ_rad is experimentally estimated for 29 nine-coordinate Eu^III complexes and 10 eight- and nine-coordinate Yb^III complexes. The known dependence of τ_rad on refractive index is substantiated by comparing data for solid-state samples and solutions. Moreover, a clear dependence of τ_rad with the coordination environment is evidenced and in the case of Eu^III, a comparison between τ_rad and the nephelauxetic effect generated by the ligands is attempted. Altogether, this extensive analysis points to the importance of having a handle on τ_rad when designing ligands for highly luminescent lanthanide-containing molecular edifices. This, in turn, should stimulate initiating theoretical considerations to unravel a reliable relationship between τ_rad and the electronic structure of the ligands.     

Long-Range LMCT Coupling in EuIII Coordination Polymers for an Effective Molecular Luminescent Thermometer**

A design for an effective molecular luminescent thermometer based on long-range electronic coupling in lanthanide coordination polymers is proposed. The coordination polymers are composed of lanthanide ions Eu^III and Gd^III, three anionic ligands (hexafluoroacetylacetonate), and a chrysene-based phosphine oxide bridges (6,12-bis(diphenylphosphoryl)chrysene). The zig-zag orientation of the single polymer chains induces the formation of packed coordination structures containing multiple sites for CH-F intermolecular interactions, resulting in thermal stability above 350 °C. The electronic coupling is controlled by changing the concentration of the Gd^III ion in the Eu^III-Gd^III polymer. The emission quantum yield and the maximum relative temperature sensitivity (S_m) of emission lifetimes for the Eu^III-Gd^III polymer (Eu:Gd=1:1, Φ_tot=52 %, S_m=3.73 % K⁻¹) were higher than those for the pure Eu^III coordination polymer (Φ_tot=36 %, S_m=2.70 % K⁻¹), respectively. Enhanced temperature sensing properties are caused by control of long-range electronic coupling based on phosphine oxide with chrysene framework.     

Quinoxaline sensitised lanthanide ion luminescence: Syntheses,spectroscopy and X-ray crystal structure of Na{1,4,7-tris[(N-diethyl)carbamoylmethyl]-1,4,7,10-tetraazacyclododecane-10-(2-methylquinoxaline)}I3 C7H8

The synthesis of a quinoxaline-appended aza-macrocyclic ligand together with corresponding Ln^III complexes are described. The luminescence properties of the complexes show that the quinoxaline unit sensitises both visible (Eu^III) and near-IR (Nd^III and Yb^III) emitting lanthanide ions. UV–Vis absorption and time-resolved photophysical studies together with X-ray structural data suggest that as well as contributing chromophorically, the quinoxaline moiety generally participates in the first coordination sphere of Ln^III. The luminescent pH response of the Eu^III complex is also reported. The form of the steady state spectrum changes profoundly in the pH range 2–12, implying a change in the coordination environment, which was confirmed with time-resolved lifetime measurements that suggest an increase in europium inner sphere hydration at acidic pH.     

Syntheses,Structures, Photoluminescence,and Magnetism of a Series of Discrete Lanthanide Complexes based on 2,5‐Dichlorobenzoate and 1,10‐Phenanthroline

The syntheses and crystal structures of eight lanthanide complexes with formula [Ln(2,5‐DCB)_x(phen)_y] are reported, which are characterized via single‐crystal, powder X‐ray diffraction, elemental analysis, IR spectroscopy, thermogravimetric analysis, photoluminescence measurement, and DC/AC magnetic measurement. These eight complexes are isostructural, and possess a discrete dinuclear structure. The adjacent dinuclear molecules are linked by the hydrogen bonding interactions into a one‐dimensional (1D) supramolecular chain. The neighboring 1D chains are further extended into a two‐dimensional (2D) supramolecular layer by the π–π stacking interactions. The photoluminescent properties of complexes 1 (Nd^III), 2 (Sm^III), 3 (Eu^III), 5 (Tb^III), 6 (Dy^III), and 8 (Yb^III) were investigated. Magnetic investigations also reveal the presence of ferromagnetic interactions in complexes 4 (Gd^III), 6 (Dy^III), and 7 (Er^III). Additionally, complex 6 (Dy^III) demonstrates field‐induced slow magnetic relaxation behavior.     

Control of the Single‐Molecule Magnet Behavior of Lanthanide‐Diarylethene Photochromic Assemblies by Irradiation with Light

Lanthanide‐based extended coordination frameworks showing photocontrolled single‐molecule magnet (SMM) behavior were prepared by combining highly anisotropic Dy^III and Ho^III ions with the carboxylato‐functionalized photochromic molecule 1,2‐bis(5‐carboxyl‐2‐methyl‐3‐thienyl)perfluorocyclopentene (H₂dae), which acts as a bridging ligand. As a result, two new compounds of the general formula [{Ln^III₂(dae)₃(DMSO)₃(MeOH)} ? 10 M eOH]_n (M=Dy for 1 a and Ho for 2 ) and two additional pseudo‐polymorphs [{Dy^III₂(dae)₃(DMSO)₃(H₂O)} ? x MeOH]_n ( 1 b ) and [{Dy^III₂(dae)₃(DMSO)₃(DMSO)} ? x MeOH]_n ( 1 c ) were obtained. All four compounds have 2D coordination‐layer topologies, in which carboxylate‐bridged Ln₂ units are linked together by dae^2? anions into grid‐like frameworks. All four compounds exhibited a strong reversible photochromic response to UV/Vis light. Moreover, both 1 a and 2 show field‐induced SMM behavior. The slow magnetic relaxation of 1 a is influenced by the photoisomerization reaction leading to the observation of the cross‐effect: photocontrolled SMM behavior.