Titanium-oxo Clusters Research Articles

A Large Titanium Oxo Cluster Featuring a Well-Defined Structural Unit of Rutile

Titanium oxo clusters (TOCs) are the well-defined molecular modes for TiO2 materials and provide the opportunity to clarify the relationships between the structures and properties of TiO2. Here, we...

A Titanium Oxo Cluster Model Study of Synergistic Effect of Co-coordinated Dye Ligands on Photocurrent Responses.

The use of multiple sensitizers in dye sensitized solar cells has been attractive as a promising way to achieve highly efficient photovoltaic performance. However, except for the complementary absorption, synergistic effects among the dye components have not been well understood. Herein, using ferrocene-1-carboxylate (FcCO2) and catechol (Cat) as dye ligands, two titanium oxo clusters (TOCs), [Ti3O(OiPr)6(Cat)(FcCO2)2] (1) and [Ti7O4(OiPr)8(Cat)5(FcCO2)2] (2), were synthesized and structurally characterized. Another TOC, [Ti7O3(OiPr)12(Cat)4( o-BDC)] (3) ( o-BDC = o-benzene dicarboxylate), was also prepared as a contrast. Electronic spectra and theoretical calculations showed that charge transfer occurs from ligands FcCO2 and Cat to the TiO cluster core and the contribution of redox active FcCO2 is greater than that of Cat. Using the clusters as TiO-dye pre-anchored precursors, multi-dye sensitized TiO2 electrodes were prepared. Although the two dyes FcCO2 and Cat do not complement each other in spectra, a synergistic effect on the enhancement of photocurrent responses was found and discussed in view of the inter-dyes electron communication.

Modulating the band gap and photoelectrochemical activity of dicarboxylate-stabilized titanium-oxo clusters

The dicarboxylate-stabilized titanium-oxo clusters (TOCs) [Ti6(μ3-O)4(μ2-OiPr)2(OiPr)8(BDC)2(O2CFc)2] (C1), [Ti6(μ3-O)4(μ2-OiPr)2(OiPr)8(TFBDC)2(O2CFc)2] (C2), and [Ti6(μ3-O)4(μ2-OiPr)2(OiPr)8(BDC)2(O2CC6H5)2] (C3) (BDC = 1,2-benzenedicarboxylate, TFBDC = 3,4,5,6-tetrafluoro-1,2-benzenedicarboxylate, Fc = ferrocenyl) were synthesized and structurally characterized. The band gap and photoelectrochemical (PEC) activity of the three Ti6-oxo clusters were effectively modulated by electronic effects of the peripheral carboxylate ligands. Moreover, with the same Ti6O4 core structure, the electronic transitions induced by the functional ligands can be clearly elucidated by combined experimental and computational studies. It is reveal that the low-energy transitions of the ferrocene-containing clusters C1 and C2 mainly involve the Fe 3d → Ti6O4 core metal-to-core charge transfer (MCCT) transition. The introduction of ferrocenecarboxylate ligands into the Ti6-oxo clusters significantly reduced the band gap to 2.2 eV (C1) and 1.9 eV (C2) relative to that of 3.6 eV for the benzoate substituted cluster C3. The electron-withdrawing effect of the TFBDC ligand remarkably promotes the PEC activity of C2.

Dicarboxylate Ligands Oriented Assembly of {Ti3(μ3-O)} Units: From Dimer to Coordination Triangles and Rectangles.

A series of dicarboxylates bridged titanium-oxo clusters with {Ti3(μ3-O)} building units have been synthesized through facile one-step solvothermal reactions. It is interesting to find that the geometric characteristics of the obtained supramolecular structures highly depend on the configuration of the applied dicarboxylate ligands. A linear dimeric [Ti3O]2L2 complex can be constructed using flexible cyclohexanedicarboxylic acid, while the introduction of rigid 2-nitro-1,4-benzenedicarboxylic acid gives rise to a triangular [Ti3O]3L3 structure. Moreover, unusual [Ti3O]4L4 rectangles have been achieved with more symmetric 5-nitro-1,3-benzenedicarboxylic acid or terephthalic acid. Furthermore, a photochromic effect is observed on the obtained complexes upon UV-vis light irradiation in the presence of alcohol.

Titanium-oxo clusters functionalized with catecholate-type ligands: modulating the optical properties through charge-transfer transitions.

Four phenylphosphonate-stabilized titanium-oxo clusters with varying functional ligands, namely, [Ti8(μ3-O)2(μ2-O)2(μ2-OiPr)4(OiPr)8(O3PC6H5)4(cat)2] (cat = catecholate), [Ti8(μ3-O)2(μ2-O)2(μ2-OiPr)4(OiPr)8(O3PC6H5)4(O2C10H6)2] (O2C10H6 = naphthalene-2,3-diolate), [Ti6(μ3-O)2(μ2-O)2(μ2-OiPr)4(OiPr)6(O3PC6H5)2(4-DMAB)2] (4-DMAB = 4-dimethylaminobenzoate), and [Ti6(μ3-O)2(μ2-O)2(μ2-OiPr)4(OiPr)6(O3PC6H5)2(4-CBA)2] (4-CBA = 4-cyanobenzoate) were synthesized and structurally characterized. The introduction of catecholate ligands effectively extended the visible absorption region up to 670 nm and reduced the band gap to 2.1 eV. DFT calculations revealed that the ligand-based energy levels could effectively modify the band structure of titanium-oxo clusters. The ligand-to-core charge transfer (LCCT) transition from the functional ligands to the cluster core is responsible for the low-energy charge transfer states. Photoelectrochemical and photocatalytic experiments show that functional ligands have significant influence on the physicochemical properties of titanium-oxo clusters.

Triphenylamine derived titanium oxo clusters: an approach to effective organic-inorganic hybrid dyes for photoactive electrodes.

Titanium oxo clusters (TOCs) anchored with photoactive triphenylamine (TPA) dyes are reported for the first time. The TiO2 electrodes modified with the TPA dye pre-anchored TOCs showed excellent photocurrent response properties.

Lanthanide–titanium-oxalate clusters and their degradation products, photocurrent response and photocatalytic behaviours

Three Ln–TiO–C2O4 polymers were obtained spontaneously from their titanium oxo-clusters and the advantages of doped TiO materials were discussed based on the experiments of photocurrent conversion and photocatalytic dye degradation.

The structure and photocatalytic activity of the tetranuclear titanium(IV) oxo-complex with 4-aminobenzoate ligands

Titanium oxo-clusters composed of {Ti4O2} and {Ti6O6} cores were synthesized from the direct reaction of Ti(OiBu)4 and 4-aminobenzoic acid (HABZ) in molar ratios 4:1, 2:1, and 1:1 at room temperature. The complex [Ti4O2(OiBu)10(ABZ)2] 0.7iBuOH 0.5C7H8 (1a) has been isolated from the 4:1 reaction mixture. The slow evaporation of the in situ alcohol from 4:1 reaction mixture led to the formation of [Ti4O2(OiBu)10(ABZ)2] (1b). The spectroscopic studies, assisted by DFT methods, of powders isolated from 2:1, 1:1 mother liquor, proved the formation of [Ti4O2(OiBu)10(ABZ)2] (2) and [Ti6O6(OiBu)6(ABZ)6] (3), respectively. The photocatalitic activity of composite foils produced by the dispersion of (1b) complex in the polystyrene matrix, has been estimated by the photodegradation of the methylene blue (MB) under UV light irradiation.

Microporous Cyclic Titanium-Oxo Clusters with Labile Surface Ligands.

By using ethylene glycol and monocarboxylic acid as surface ligands, a series of cyclic Ti-oxo clusters (CTOC) with permanent microporosity are successfully synthesized. With a cyclic {Ti32 O16 } backbone made of eight connected Ti4 tetrahedral cages that are arranged in a zigzag fashion, the clusters have a "donut" shape with an inner diameter of 8.3 Å, outer diameter of 26.9 Å and height of 10.4 Å. While both inner and outer walls of the "donut" clusters are modified by double-deprotonated ethylene glycolates, their upper and lower surfaces are bound by carboxylates and mono-deprotonated ethylene glycolates. The clusters are readily packed into one-dimensional tubes which are further arranged in two different modes into crystalline microporous solids with surface areas over 660 m2 g-1 , depending on the surface carboxylates. The solid with olefin-bearing carboxylates exhibits a superior CO2 adsorption capacity of 40 cm3 g-1 at 273 K under 1 atm. Moreover, the mono-deprotonated ethylene glycolates on the clusters are demonstrated to be highly exchangeable by other alcohols, providing a nice platform for creating microporous solids or films with a wide variety of surface functionalities.

Phosphonate-Stabilized Titanium-Oxo Clusters with Ferrocene Photosensitizer: Structures, Photophysical and Photoelectrochemical Properties, and DFT/TDDFT Calculations.

The metal-to-core charge transfer (MCCT) transition in sensitized titanium-oxo clusters is an important process for photoinduced electron injection in photovoltaic conversion. This process resembles most closely the Type II photoinjection in dye-sensitized solar cells. Herein we report the synthesis and photophysical and photoelectrochemical (PEC) properties of the phosphonate-stabilized titanium-oxo clusters containing the ferrocenecarboxylate ligands. These ferrocene-containing clusters exhibit intense visible absorption extended up to 600 nm along with low optical band gaps of ∼2.2 eV. The low-energy transitions of these clusters were systematically investigated by UV-vis spectroscopy and DFT/TDDFT calculations. The combined experimental and computational studies suggest that the ferrocenecarboxylate-substituted titanium-oxo clusters form a donor-acceptor (D-A) system. The low-energy transition of these clusters primarily involves the MCCT from the iron center to TiO cluster core. The TiO core structure and phosphonate ligands both have great influence on the PEC properties of the clusters. This work provides valuable examples for the sensitized titanium-oxo clusters in which electron injection takes place via MCCT transition.

P-Arsanilic acid stabilizing titanium-oxo clusters with various core structures and light absorption behaviours

A series of p-arsanilic acid stabilizing polyoxo‑titanium clusters (PTCs) have been successfully synthesized through solvothermal method, which present {Ti4}, {Ti5} and {Ti6} cores functionalized by different carboxylic acid ligands. PTC-111 displays a {Ti4} core structure which is stabilized by glycolic acid and esterified p-arsanilic acid. PTC-112, PTC-113 and PTC-114 have isostructural {Ti6} structures, functionalized by isonicotinic acid, 2-chloroisonicotinic acid and benzoic acid, respectively. The {Ti5} core of PTC-115 is functionalized by m-nitrobenzoic acid. It is interesting that the light absorption behaviours of these PTCs are dependent on their core structures and the functionalizing ligands.

Improving the photocatalytic H2 evolution activities of TiO2 by modulating the stabilizing ligands of the nanoscale Ti8O8-cluster precursors

Titanium-oxo clusters (TOCs) are important model complexes and potential precise single-source precursors of TiO2 materials. We report here a series of TiO2 samples derived from TOCs with the same wheel-like Ti8O8 clustercore but different stabilizing ligands. Our results demonstrate that the ligands on TOCs not only influence the phase-transition during themolysis, but more importantly tune the photocatalytic H2 evolution activities of the obtained TiO2 materials. Through 500 °C calcination, the nanosized Ti8O8 cluster stabilized by organic benzoate ligands gives rise to a TiO2 sample with H2 production rate of 611 μmol/h/g. When the stabilizing ligands are changed to inorganic SO42−, a significant improvement of H2 evolution activity has been achieved, resulting in a 7-times higher value of 4527 μmol/h/g. This work provides a new strategy to produce TiO2 with enhanced and tunable photocatalytic activities from titanium-oxo cluster precursors.

Connecting Titanium-Oxo Clusters by Nitrogen Heterocyclic Ligands to Produce Multiple Cluster Series with Photocatalytic H2 Evolution Activities

We herein demonstrate the ability of nitrogen heterocyclic ligands in connecting polyoxotitanium complexes into crystalline multiple cluster series. Moreover, their bandgap and photocatalytic water-splitting behavior were studied. The highest H2 evolution activity reaches up to 42.80 μmol g–1 h–1 for PTC-46.

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.

Construction of molecular rectangles with titanium-oxo clusters and rigid aromatic carboxylate ligands.

Four rectangular molecular architectures have been successfully constructed using {Ti5O7} clusters as inorganic vertical edges and bridging aromatic carboxylates as horizontal edges. The introduced organic ligands show a strong influence on the light absorption behaviors of the obtained hybrid complexes.

Deep eutectic-solvothermal synthesis of titanium-oxo clusters protected by π-conjugated chromophores.

Deep eutectic-solvothermal synthesis has been successfully employed to prepare four polyoxo-titanium clusters (PTCs), with nuclearity up to 28. The cluster cores obtained via this method are completely functionalized by conjugated ligands and display different photocatalytic H2 production activities.

The effects of transition-metal doping and chromophore anchoring on the photocurrent response of titanium-oxo-clusters.

Titanium-oxo-clusters (TOCs), [Ti6O4(OiPr)10(Cat)2(BA)2] (1) and [Ti12M2O10(OEt)22(Cat)2(BA)4] (M = Co, Mn, Ni, 2-4; H2Cat = catechol, HBA = benzoic acid) are prepared in one step in an in situ solvothermal synthesis. Cluster structures of 2-4 can be considered as two 1 moieties merged together by two transition metal atoms. Unlike most TOCs with sphere-like structures, clusters 2-4 feature a unique single layered structure. They are not only transition metal doped TOCs but also charge transfer (CT) TOCs, CT from Cat to the TiO cluster core. Photoelectrodes were prepared by dipping the solution of clusters on a porous TiO2 substrate. Photocurrent response properties of the electrodes were studied in comparison with those of the electrodes of non-metal doped 1 and the non-Cat coordinated Ti6 cluster. The results showed that the photocurrent densities of metal doped clusters are higher than that of non-doped clusters and the highest photocurrent density was found for the redox active Co(ii) doped cluster. Charge transfer also plays an effective role in photocurrent conversion under visible light irradiation.

Water-Soluble Pentagonal-Prismatic Titanium-Oxo Clusters.

By using solubility control to crystallize the prenucleation clusters of hydrosol, a family of titanium-oxo clusters possessing the {Ti18O27} core in which the 18 Ti(IV)-ions are uniquely connected with μ-oxo ligands into a triple-decked pentagonal prism was obtained. The cluster cores are wrapped by external sulfate and aqua ligands, showing good solubilities and stabilities in a variety of solvents including acetonitrile and water and allowing their solution chemistry being studied by means of electrospray ionization mass spectroscopy, (17)O NMR, and vibrational spectroscopy. Furthermore, this study provides new titanium oxide candidates for surface modifications and homogeneous photocatalysis.

A 3.6 nm Ti52-Oxo Nanocluster with Precise Atomic Structure.

We report a 3.6 nm Ti52-oxo cluster with precise atomic structure, which presents a largest size record in the family of titanium-oxo clusters (TOCs). The crystal growth of such large Ti52 is based on a stepwise interlayer assembly approach from Ti6 substructures. The possible growth mechanism of Ti52 could be deduced from crystal structures of two substructures, Ti6 and Ti17, which were also synthesized under similar conditions as Ti52. Moreover, these TOCs show cluster-size-dependent photocatalytic hydrogen evolution activities with Ti52 giving a H2 production rate up to 398 μmol/h/g, which is also the highest record in the family of TOCs. This work not only represents a milestone in constructing large TOCs with comparable sizes as TiO2 nanoparticles but also brings significant advances in improving photocatalytic behaviors of TOCs.

ChemInform Abstract: Small Titanium Oxo Clusters: Primary Structures of Titanium(IV) in Water.

AbstractThree new types of titanium oxo clusters (III), (V), and (VI) are characterized by single crystal XRD, IR, Raman, ESR, and UV/VIS diffuse reflectance spectroscopy.