Lanthanide-titanium Oxo Clusters Research Articles

Photoluminescence of Lanthanide-Titanium-Oxo Clusters Eu9Ti2 and Tb9Ti2 Based on a β-Diketone Ligand.

A series of acetylacetone-protected lanthanide-titanium-oxo clusters (LTOCs), formulated as [La6Ti(μ3-OH)8(acac)12(CH3O)2(CH3OH)6] (La6Ti; Hacac = acetylacetone) and [Ln9Ti2(μ4-O)(μ3-OH)14(acac)17(CH3O)2(CH3OH)3] [Ln = Eu (Eu9Ti2) and Tb (Tb9Ti2)], were synthesized through the reactions of LnCl3·6H2O (Ln = La, Eu, and Tb), Hacac, Ti(OiPr)4, and triethylamine in methanol. Crystal structural analysis shows that La6Ti exhibits an hourglass-like structure consisting of two La3Ti cubane subunits by sharing one Ti4+ ion, while Eu9Ti2 can be viewed as a combination of four Eu3Ti cubane subunits by sharing three corners and one side. The photoluminescence (PL) measurements show that Tb9Ti2 exhibits excellent PL properties with a high quantum yield (QY) of 34.8%, while Eu9Ti2 only has a QY of 1.4% because of the different photosensitizations of ligands to Eu3+ and Tb3+ ions in the photophysical process.

Studies of high-nuclearity lanthanide-titanium oxo clusters: Structure and properties

Three new lanthanide-titanium oxo clusters (LnTOCs), namely, Ti4Gd2, Ti13Gd2 and Ti14Gd4 were synthesized by reactions of different lanthanide salts with salicylic acid (H2sal) in different solvents. Crystallographic studies reveal that both Ti4Gd2 and Ti13Gd2 are composed by a oxo-centred triangular motif {Ti2Gd(μ3-O)}, while Ti14Gd4 has a heart-shaped heterometallic core {Ti12Gd2O13(OH)6}, which represents the second highest nuclearity LnTOC reported to date. In addition, these compounds exhibit a strong absorption in visible light region and a fast photocurrent response owing to the existence of salicylate ions.

Preparation of a Lanthanide-Titanium Oxo Cluster-Polymer Composite by CuI -Catalyzed Click Chemistry.

Incorporating metal clusters within the skeleton of the organic polymers through a click reaction cannot only effectively prepare cluster-polymer composites, but also effectively avoid the cluster aggregation. Herein, an azide-containing lanthanide-titanium oxo cluster of Eu8 Ti10 -N3 (Eu8 Ti10 -N3 =[Eu8 Ti10 (μ3 -O)14 (H2 O)4 (OAc)2 (tbba)30 (paza)4 (THF)2 ]⋅4 THF⋅8 H2 O (1), Htbba=4-tert-butylbenzoic acid, Hpaza=4-azidobenzoate, HOAc=acetic acid, THF=tetrahydrofuran) through an in situ solvothermal reaction of 4-azidobenzoic acid and 4-tert-butylbenzoic acid. Reaction of 1 with PEG (PEG=methoxypoly(ethyleneglycol)alkyne, 2000 g mol-1 ) through CuI -catalyzed click chemistry generates a lanthanide-polymer composite of Eu8 Ti10 -N3 @PEG (2). Investigation with IR, 1 H NMR and ICP-OES of 2 indicates that the structural integrity of 1 is maintained in 2. Study of the luminescent properties of 1 and 2 reveals that the quantum yield of 1 itself basically remains unchanged in 2. Significantly, the formation of 2 cannot only effectively prevent the cluster 1 from aggregation, but also greatly enhance its solubility and adhesion to the substrate. Owing to the solubility and adhesion of luminescent materials being the key to their practical application, present work is thus of great significance for the development of metal cluster-polymer composite luminescent materials.

Lanthanide-Titanium Oxo Clusters as the Luminescence Sensor for Nitrobenzene Detection.

A luminescent lanthanide-titanium oxo cluster of Eu2Ti4(μ2-O)2(μ3-O)4(phen)2(tbza)10·4CH3CN (1, Eu2Ti4-phen-tbza, phen = 1,10-phenanthroline, Htbza = 4-tert-butylbenzoic acid) was prepared through the reaction of phen, Htbza, Eu(Ac)3·xH2O, and Ti(OiPr)4 in acetonitrile. Its overall absolute quantum yield is 65.4% in solid state and 30.2% in CH2Cl2, and the detection limit of 1 for the nitrobenzene (NB) is 10.5 ppb. When the concentration of NB is 40 ppm, the luminescence quenching of 1 can be observed with the naked eye. Time-resolved excited-state decay measurements indicate that the static quenching process is dominated across the NB concentration of 0-9 ppm. The distinguishable shifts in 1H NMR spectra of NB together with 1 confirm the presence of π···π stacking interactions between the organic ligands in 1 and the NB, which plays a key contribution for the quenching of luminescence.

Lanthanide-titanium oxo-clusters, new precursors of multifunctional colloids for effective imaging and photodynamic therapy

Multifunctional biomaterials with functions of effective imaging and photogenerated reactive oxygen species (ROS) are highly desirable for effective photodynamic therapy (PDT). This work reports a convenient method to prepare colloids with low-energy light activatable PDT nanoparticles from lanthanide‑titanium oxo-clusters (LnTOCs). Two LnTOCs, formulated as [Ln2Ti8(μ3-O)6(Ac)18(OiPr)8]·4CH3CN, Ln = Eu (1), Gd (2), were synthesized and crystallographically characterized, in which the Ln and Ti ions are pre-bonded covalently at atomic level. Using the LnTOCs, aqueous sol solution with nano particles 1-n and 2-n were obtained by an organic-inorganic phase transfer technique. The biocompatible 1-n showed effective fluorescent labeling property in Hela cells. Another important progress of this work is that photosensitizer, 5,10,15,20-tetra(p-benzoato) porphyrin (TBP), was incorporated with the 2-n and the red light excitable nano-particles, 2-n-TBP, were obtained. To evaluate the PDT efficiency, concentrations of ROS produced by the nanoparticles and the toxicity under red laser irradiation were examined in vitro using Hela cells. The results confirm that in comparison with the pure TBP and 2-n the 2-n-TBP had the capacity to produce a large amount of ROS and hence had the potential as the PDT materials.

Ligand-Dependent Luminescence Properties of Lanthanide-Titanium Oxo Clusters.

A series of lanthanide-titanium oxo clusters (LnTOCs), Ln2Ti8-Ac, Ln2Ti8-p-Toluic, and Ln2Ti8-Anthra (Ln = Eu and Tb), were prepared based on acetic acid (HAc), p-toluic acid (Hp-Toluic), and anthracene-9-carboxylic acid (HAnthra). Crystal structural analysis showed that these clusters possess the same metal topology framework, in which eight Ti4+ ions form a cube and two Ln3+ ions are located on the opposite faces of the cube. The luminescence investigation discovered that the Eu2Ti8-Ac displays the highest quantum yields with 15.6%, and the conjugation effect of ligand substituents can lower the triplet state energy of ligands, thus regulating the luminescence quantum yield of the Ln2Ti8 clusters. These results suggest that the triplet excited-state energy of the ligands should match well with the energy levels of Ln3+ to enhance the luminescence.

Water-Soluble Lanthanide-Titanium-Oxo Cluster, a Precursor for Biocompatible Nanomaterial.

Titanium-oxo clusters (TOCs) are attractive as a rapidly growing class of molecular materials due to their use as molecular models and precursors of nano-titanium-oxide. However, most TOCs can only be dissolved in nonaqueous solvents, which largely limits their potential applications in biological or environmental situations. Very few water-soluble TOCs were reported, which can be used directly in aqueous biomedical systems. However, until now, no research studies of such TOCs involved in biomedical fields have been documented. We report here a series of lanthanide-titanium-oxo clusters (LnTOCs) formulated as {H2@[Ln2Ti8(μ3-O)8(μ2-O)4(Ac)16]}3·24CH3CN·23H2O (Ln = Eu(III) 1, Tb(III) 2, and Yb(III) 3). The compounds are easily soluble in water and form a stable solution of the cluster aggregates (LnTOC-a). Therefore, nano-biocompatible TiO materals can be prepared from these LnTOCs just by dissolving them in water. The nanoscale aggregates in water solutions were characterized by SEI-MS, 1H NMR, XPS, IR, and EDS mapping. Using the EuTOC-a solution, excellent fluorescence sensor properties for biomolecule ascorbic acid were found. Furthermore, biocompatibility and fluorescent labeling properties of the EuTOC-a for HeLa cells were evaluated. The results indicated that water-soluble LnTOCs can be used to prepare biocompatible fluorescent Ln-Ti-O nanomaterials.

The Effect on the Luminescent Properties in Lanthanide-Titanium OXO Clusters.

Two lanthanide-titanium oxo clusters (LTOCs), formulated as [Eu3Ti3(μ3-O)2(μ3-OH)(CH3O)2(Ac)2(CH3OH)(tbba)12]·CH3OH (1) and [Eu6Ti8(μ3-O)13(μ2-OH)(μ3-OCH3)2(μ2-OCH3)2(H2O)(CH3OH)2(tbba)19]·Htbba·10H2O (2), were synthesized through the solvothermal reaction of 4-tert-butylbenzoate ligand, Eu(Ac)3·3H2O, and Ti(OiPr)4 in methanol. Single-crystal structural analysis reveals that 1 crystallized in the orthorhombic space group Pnn2, and 2 crystallized in the triclinic space group P1. Structurally, the core of 1 can be viewed as a coplanar unit of [Eu3Ti3(μ3-O)2(μ3-OH)]16+ formed through each μ3-O2- and μ3-OH- bridging one Ti4+ and two Eu3+ ions, while that of 2 can be viewed as two units of [Eu3Ti3(μ3-O)3(μ2-O)4(μ2-OCH3)2(CH3OH)]5+ and [Eu3Ti5(μ3-O)6(μ2-OH)(μ3-OCH3)2(H2O)(CH3OH)]14+ connected through four μ2-O units from the [Eu3Ti3(μ3-O)3(μ2-O)4(μ2-OCH3)2(CH3OH)]5+ unit to respectively coordinate two Eu3+ and two Ti4+ ions from the [Eu3Ti5(μ3-O)6(μ2-OH)(μ3-OCH3)2(H2O)(CH3OH)]14+ unit. Measurement of their luminescence properties shows that the luminescence lifetime and quantum yield are 1212 μs and 69.6% for 1 and 857 μs and 56.2% for 2. When F- was introduced into 1 in a molar ratio of F- to 1 of 1:3, its quantum yield was increased 1.3 times, and the lifetime increased from 1.2 to 1.4 ms. However, no obvious enhancement in the emission intensity was observed in 2; even the molar ratio of F- to 2 is in the range from 2 to 1/4. Investigation on the structures of 1 and 2 reveals that the luminescence lifetime and quantum yield in 1 is significantly larger than that in 2 are attributed to the vibration of the nonradiative O-H vibration groups in 1 being significantly smaller than that in 2.

Assembly of a Wheel-Like Eu24 Ti8 Cluster under the Guidance of High-Resolution Electrospray Ionization Mass Spectrometry.

A building blocks strategy is an effective approach for constructing the large molecular systems. Herein, we demonstrate that high-resolution electro-spray ionization mass spectrometry (HRESI-MS) provides an effective chance to insight the assemble process of the building blocks and guides the construction of high-nuclearity metal clusters on the basis of the reaction of Ti(Oi Pr)4 , Eu(acac)3 , and salicylic acid. The time-dependent HRESI-MS indicates that not only a Eu3 Ti building block can be formed, but that it can further assemble into a Eu24 Ti8 compound. Temperature-dependent HRESI-MS reveals that increase of the reaction temperature favors the formation and crystallization of the stable Eu24 Ti8 structure. Single-crystal structural analysis demonstrates that the Eu24 Ti8 has a wheel-like structure with diameter of ca. 4.1 nm and is the highest nuclearity lanthanide-titanium oxo cluster reported to date.

High-Nuclearity Lanthanide-Titanium Oxo Clusters as Luminescent Molecular Thermometers with High Quantum Yields.

Three heterometallic lanthanide-titanium oxo clusters (LnTOCs) formulated as Eu2Ti4(μ3-O)4(tbba)12(acac)2 (Eu2Ti4, 1, Hacac = acetylacetone), Eu5Ti4(μ3-O)6(tbba)20(Htbba)(THF)2 (Eu5Ti4, 2), and Eu8Ti10(μ3-O)14(Ac)2(tbba)34(H2O)4(THF)2(Htbba)2 (Eu8Ti10, 3) were prepared through the reactions of 4-tert-butylbenzoate (Htbba), rare-earth salts, and Ti(OiPr)4. The solution luminescence investigation discovered a size-dependent quantum yield phenomenon in solution. A solid-state luminescence study showed that these three LnTOCs display temperature-dependent photoluminescent properties. Interestingly, the Eu5Ti4 cluster exhibited the highest quantum yield of 94.9% in the solid state among the reported 3d-4f clusters.

Heterometallic Lanthanide-Titanium Oxo Clusters: A New Family of Water Oxidation Catalysts.

We report the synthesis and photoelectrochemical activity of three lanthanide-titanium oxo clusters (LTOCs), formulated as [Ln8Ti10(μ3-O)14(tbba)34(Ac)2(H2O)4(THF)2]·2Htbba [Ln = Eu (1), Sm (2), and Gd (3); Htbba = 4-tert-butylbenzoic acid; Ac- = acetate]. These stable compounds are efficient catalysts of photoelectrochemical water oxidation with high turnover numbers (7581.0 for 1, 5172.4 for 2, and 5413.0 for 3) and high turnover frequencies (2527.0 for 1, 1724.1 for 2, and 1804.0 for 3). The differences in the photoelectrochemical activity among these three compounds may be related to the differences in their band gaps. This work shows that the heterometallic LTOCs provide a tunable platform for the design of highly effective water oxidation catalysts.

Fluorescence and energy transfer properties of heterometallic lanthanide-titanium oxo clusters coordinated with anthracenecarboxylate ligands.

Two 9-anthracenecarboxylate (9-AC) coordinated heterometallic TOC compounds, [Ln2Ti10O14(ClO4)2(O(i)Pr)14(9-AC)2(CH3CN)2]·2H2O, Ln = Nd 1() and Eu (2), along with two benzoate (bza) analogues, [Ln2Ti10O14(ClO4)2(O(i)Pr)14(bza)2(HO(i)Pr)2], Ln = Nd (3) and Eu (4), were prepared by one step in situ solvothermal synthesis, and characterized by single crystal analysis. To date, only about ten lanthanum-titanium oxo clusters have been reported. Except for two Ti28 clusters, the compounds are all small clusters (Ti ≤ 4). The cluster structures of 1-4 adopt a Ti10Ln2 core structure with pseudo-Ci symmetry, which is similar to the fundamental structure of Ti12 clusters. Furthermore, except for their structures, the properties of lanthanum-titanium oxo clusters have never been studied. Herein, the fluorescence properties of these compounds are studied in detail. The metal centered emission of Eu(III) is completely quenched by 9-AC due to the lower triplet energy of the coordinated ligand. Enhanced ligand centered fluorescence is found for 2 in comparison with that of 1.