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

A porous and photoactive Ti-MOF based on a novel tetranuclear [Ti2Tb2] cluster

A robust and porous titanium metal-organic framework (Ti-MOF; LCU-505) has been solvothermally synthesized based on an unprecedented tetranuclear Ti2(μ3-O)2Tb2(μ2-CH3COO)2(H2O)4(OOC-)8 cluster (abbreviated as [Ti2Tb2]) and tritopic 4,4',4''-s-triazine-2,4,6-triyl-tribenzoic acid ligand (H3TATB). LCU-505 shows remarkable water stability and permanent porosity for N2 and CO2 gas adsorption. Moreover, LCU-505 demonstrates n-type semiconductor behavior and good photocatalytic activity in the degradation of organic dyes.

Heterometallic Polyoxotitanium Clusters as Bifunctional Electrocatalysts for Overall Water Splitting

Incorporating heterometal into titanium-oxygen clusters (TOCs) is an effective way to improve its catalytic activity. Herein, we synthesize three novel heterometallic TOCs with the formula of [Ti₆Cu₂O₇(Dmg)₂(OAc)₄(ⁱPrO)₆][H₂Ti₆Cu₂O₇(Dmg)₂(OAc)₄(ⁱPrO)₈] ({Ti₆Cu₂}), [Ti₈Cu₂O₉(Dmg)₂(OAc)₂(ⁱPrO)₁₂] ({Ti₈Cu₂}), and [Ti₁₀Co₂O₆(Dmg)₂(Pdc)₄(ⁱPrO)₁₈Cl₃] ({Ti₁₀Co₂}, DmgH₂ = dimethylglyoxime; PdcH₂ = pyridine-2,3-dicarboxylic acid) using dimethylglyoxime and different carboxylates as the synergistic ligands. By depositing the clusters {Ti₆Cu₂} and {Ti₁₀Co₂} on carbon cloth as electrodes, we investigated the electrocatalytic performance of TOCs for full water splitting for the first time. To reach a 10 mA cm^-2 current density in an alkaline solution, the {Ti₁₀Co₂}@CC electrode needs an overpotential as low as 120 and 400 mV for the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER), respectively. In addition, full water-splitting equipment with {Ti₁₀Co₂}@CC as a cathode and an anode need only 1.67 V to deliver a current density of 10 mA cm^-2. Our work confirmed the potential of noble metal-free TOCs as bifunctional cluster-based electrocatalysts for water splitting, and their activities can be tuned by doping with different metal ions.

Photoluminescence of Lanthanide-Titanium-Oxo Clusters and 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.

Visible and near-infrared emitting heterotrimetallic lanthanide-aluminum-sodium 12-metallacrown-4 compounds: discrete monomers and dimers

The luminescence properties of two types of heterotrimetallic aluminum-lanthanide-sodium 12-metallacrown-4 compounds are presented here, LnNa(ben)₄[12-MC_{Al(III)N(shi)}-4] (LnAl4Na) and {LnNa[12-MC_{Al(III)N(shi)}-4]}₂(iph)₄ (Ln2Al8Na2), where Ln = Gd^III, Tb^III, Er^III, and Yb^III, MC is metallacrown, ben^- is benzoate, shi^3- is salicylhydroximate, and iph^2- is isophthalate. The aluminum-lanthanide-sodium metallacrowns formed with benzoate are discrete monomers while, upon replacement of the benzoate with the dicarboxylate isophthalate, two individual metallacrowns can be joined to form a dimer. In the solid state, the terbium version of each structure type displays emission in the visible region, and the erbium and ytterbium complexes emit in the near-infrared. The luminescence lifetimes (τ_obs) and quantum yields have been collected under ligand excitation (QLLn) for both LnAl4Na monomers and Ln2Al8Na2 dimers. Several of these values tend to be shorter (luminescence lifetimes) and smaller (quantum yields) than the corresponding values recorded for the structurally similar gallium-lanthanide monomer and dimer 12-MC-4 molecules. However, the quantum yield value recorded for the visible emitting Tb2Al8Na2 dimer, 43.9%, is the highest value observed in the solid state to date for a Tb^III based metallacrown.

Assembly of Cyclic Ferrocene-Sensitized Titanium-Oxo Clusters with Excellent Photoelectrochemical Activity

The development of crystalline titanium-oxo clusters has made great progress in recent years. However, the geometric assembly of titanium-oxo clusters is still very challenging. Herein, we report the assembly of...

Ferrocene-Sensitized Titanium-Oxo Clusters with Effective Visible Light Absorption and Excellent Photoelectrochemical Activity

Sensitized Ti-oxo clusters have attracted growing attention as analogous molecular mode compounds of dye-sensitized titanium dioxide solar cells. However, reports on the introduction of metal complexes as photosensitizers into Ti-oxo...

A family of oxime-based titanium-oxo clusters: synthesis, structures, and photoelectric responses

A family of oxime-based titanium-oxo clusters was successfully synthesized, and their photoelectrochemical performances were observed.

Metal-Directed Self-Assembly of {Ti8L2} Cluster-Based Coordination Polymers with Enhanced Photocatalytic Alcohol Oxidation Activity

Cooperative assembly of the neutral cluster {Ti₈O₅(OEt)₁₈L₂} (L = pyrazine-2,3-dicarboxylic acid) with different metal units of Mn(NO₃)₂, CuCl₂, Zn(OEt)₂, Cd(NO₃)₂, Ce(NO₃)₃, Lu(NO₃)₃, and Lu(NO₃)₂(OEt), or the [Cu₂I₂] cluster, generates a family of titanium-oxygen cluster (TOC)-based coordination polymers. These one-dimensional (1D) linear structures contain the same {Ti₈L₂} cluster but with variable bridging metal units. The regulation of the heterometal not only affects the chain geometries of the {MTi₈} but also affects the way the 1D chains are stacked in the crystal lattice. Investigation of the catalytic activities toward alcohol oxidation demonstrated the synergetic effect of combining the metal site and the photosensitive {Ti₈L₂} cluster in the tailored structure. Under light illumination, the {MTi₈} with dual catalytic sites shows greatly enhanced catalytic activity in the selective oxidation of alcohols to aldehydes. Because the compositions and structures of {MTi₈} are highly tunable, this work spotlights the potential of utilizing such metal-bridged multidimensional Ti-oxo materials for cooperative photoredox catalysis for organic transformation.

Modification of Multi-Component Building Blocks for Assembling Giant Chiral Lanthanide-Titanium Molecular Rings

Building blocks with multiple components are promising for the synthesis of complex molecular assemblies, but are rarely available. Herein, we report a modification procedure for a multi-component building block [Ln₃ Ti(HSA)₆ (SA)₄ (H₂ O)]^- ({Ln₃ Ti-SA}, H₂ SA=salicylic acid, Ln=Eu/Gd) to form new building blocks {Ln₃ Ti_x -MSA} (H₂ MSA=5-methoxysalicylic acid, x=1, 2, 3) by constructing [Ti(MSA)₃ ]^2- units. The obtained {Ln₃ Ti_x -MSA} can further assemble into a chiral Ln₂₂ Ti₁₄ ring with the formulae [Eu₂₂ Ti₁₄ (MSA)₄₈ (HMSA)₂₂ (CH₃ COO)₄ (H₂ O)₁₀ (iPrOH)] and [Gd₂₂ Ti₁₄ (MSA)₄₆ (HMSA)₂₆ (CH₃ COO)₄ (H₂ O)₈ ]. Parallel experiments without Ti⁴⁺ result in linear Ln chains. Detailed analysis shows that the [Ti(MSA)₄ ]^4- unit makes the originally variable Ln chains become available building blocks and the modified [Ti(MSA)₃ ]^2- further triggers interesting chiral-sorting behavior. Finally, the electronic adsorption and magneto-optic responses of these molecular rings are investigated.

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 Cu^I -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.

Heterometallic Group 4-Lanthanide Oxo-alkoxide Precursors for Synthesis of Binary Oxide Nanomaterials

In this study, an efficient procedure for the synthesis of uncommon group 4-lanthanide oxo-alkoxide derivatives was developed. Heterometallic clusters with the structures [La₂Ti₄(μ₄-O)₂(μ₃-OEt)₂(μ-OEt)₈(OEt)₆(Cl)₂(HOEt)₂] (1), [La₂Zr₂(μ₃-O)(μ-OEt)₅(μ-Cl)(OEt)₂(HOEt)₄(Cl)₄]_n (2), [La₂Hf₂(μ₃-O)(μ-OEt)₅(μ-Cl)(OEt)₂(HOEt)₄(Cl)₄]_n (3), [Nd₂Ti₄(μ₄-O)₂(μ₃-OEt)₂(μ-OEt)₈(OEt)₆(HOEt)₂(Cl)₂] (4), [Nd₄Zr₄(μ₃-O)₂(μ-OEt)₁₀(μ-Cl)₄(OEt)₈(HOEt)₁₀(Cl)₂] (5), and [Nd₄Hf₄(μ₃-O)₂(μ-OEt)₁₀(μ-Cl)₄(OEt)₈(HOEt)₁₀(Cl)₂] (6) were synthesized via the reaction of a metallocene dichloride, Cp₂M'Cl₂ (where M' = Ti, Zr, and Hf), and metallic lanthanum or neodymium in the presence of excess ethanol. This procedure gave crystalline precursors with molecular stoichiometries suitable for obtaining group 4-lanthanide oxide materials. Compounds 1-6 were examined by analytical and spectroscopic techniques and single-crystal X-ray diffraction. The magnetic properties of 5 and 6 were investigated by using direct and alternating current (dc and ac) susceptibility measurements. The results indicated weak antiferromagnetic interactions between Nd^III ions and a field-supported slow magnetic relaxation. Lanthanum-titanium compound 1 decomposed at 950 °C to give the perovskite compound La_0.66TiO₃ and small amounts of rutile TiO₂. Under the same conditions, 4 decomposed to give a mixture of Nd₄Ti₉O₂₄ and Nd_0.66TiO₃. When 4 was calcined at 1300 °C, decomposition of Nd₄Ti₉O₂₄ to Nd_0.66TiO₃ and TiO₂ was observed. Calcination of 2, 3, 5, and 6 at 950-1500 °C led to the selective formation of heterometallic La₂Zr₂O₇, La₂Hf₂O₇, Nd₂Zr₂O₇, and Nd₂Hf₂O₇ phases, respectively.

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.

Eu-phen Bonded Titanium Oxo-Clusters, Precursors for a Facile Preparation of High Luminescent Materials and Films

Incorporation of Eu complexes into various organic or inorganic matrixes is one of the acceptable strategies to obtain displaying materials having practical applications. In this work, we report a convenient approach to preparing high luminescent organic-inorganic hybrid materials and films from the europium-titanium oxo-clusters (EuTOCs) having photoactive antenna ligands. Three Eu₂Ti₄ oxo-clusters were synthesized and crystallographically characterized. They are the first reported lanthanide-TOCs coordinated with 1,10-phenanthroline (phen) and 2,2'-bipyridine (bpy) as photoactive ligands, Eu₂Ti₄O₆(phen)₂(pa)₁₀ (1) (pa = propionate), Eu₂Ti₄O₆(bpy)₂(pa)₁₀ (2), and Eu₂Ti₄O₆(phen)₂(MA)₁₀ (3) (MA = methacrylate). Benefitting from the photoactive antenna ligands and the rigid cluster structures, these clusters showed bright red luminescence with quantum yield in the range of 60-80% and long lifetime up to 3.0 ms. Unlike those physically mixed polymeric materials, the MA coordinated compound 3 can be self-polymerized to form a brilliant luminescent film. The film coated slide was used to develop a fluorescence sensor for biomolecule ascorbic acid (AA). The low detection limit and reusable properties suggest great potential for such EuTOC films in real applications.

Accurate Regulating of Visible-Light Absorption in Polyoxotitanate-Calix[8]arene Systems by Ligand Modification

With use of a macrocyclic polyphenol, tert-butylcalix[8]arene (TBC[8]), as ligands, a series of TBC[8]-stabilized {Ti₄O₂}clusters, containing penta- and hexacoordinated Ti centers, were synthesized. Such complexes are "core-shell" shaped containing a {Ti₄O₂} core arranged in a zigzag fashion. While outer walls of the clusters are decorated by deprotonated TBC[8], their upper and lower surfaces can be modified by various O- or N-donor ligands, and the ratio of the penta- and hexacoordinated Ti(IV) centers in the {Ti₄O₂} core can be precisely regulated from 4:0, to 3:1, to 2:2, to 1:3, and finally to 0:4. The combined coordination of different ligands in the axial direction shows significant influence on the adsorption of the TBC[8]-Ti₄ system in the visible-light region, and their absorption edge can be precisely regulated from 600 to 700 nm. The above structural functionalization in the TBC[8]-Ti₄ system also tunes their photocatalytic H₂ production activities and oxidative desulfurization ability. Thus, for the first time, by confining the polyoxotitanium cluster in macrocyclic molecules, we provide an example of understanding the structure-property relationship of titanium-oxygen materials by ligand modification.