Recent advances in heterometallic polyoxotitanium clusters

Unveiling Synergetic Photocatalytic Activity from Heterometallic Ti/Ce Clusters

Titanium-oxo clusters, with their robust structure and suitable optical and electronic properties, have been widely investigated as photocatalysts. Heterometallic Ti/M-oxo clusters provide additional tunability and functionality, which enable systematic structure-activity investigations to elucidate the reaction mechanisms and improve the catalyst design. Incorporating cerium into Ti-oxo clusters can provide additional redox (CeIV/CeIII) and oxygen harvesting ability, but to date, only a limited number of structurally defined titanium-cerium (Ti/Ce) clusters have been reported due to their synthetic challenges. Herein, we report the synthesis and photocatalytic properties of two structurally defined Ti/Ce-oxo clusters, Ti8Ce2(BA)16 and Ti9Ce4(BA)20, as well as a TiCe-BA cluster with a calculated formula of Ti20Ce9O36(BA)42. Photocatalytic study of these clusters demonstrates that the amount of Ce3+ species greatly impacts its photocatalytic oxidation performance, and their superior photocatalytic reactivity toward aerobic alcohol oxidation can be contributed to the synergistic effects of the multiple radical species generated upon light absorption. This work represents a significant milestone in the construction of stable Ti/Ce-oxo clusters, enriching the current library of known heterometallic Ti/M-oxo clusters, and providing a series of crystalline materials with great promise of photoluminescence and photovoltaic chemistry.

Structural Chemistry of Titanium (IV) Oxo Clusters, Part 2: Clusters without Carboxylate or Phosphonate Ligands

Homometallic titanium oxo clusters (TOC) are one of the most important groups of metal oxo clusters. In a previous article, TOC structures with carboxylato and phosphonato ligands were reviewed and categorized. This work is now extended to clusters with other ligands. Comparison of the different cluster types shows how the interplay between condensation of the titanium polyhedra by means of bridging oxygen atoms and the coordination characteristics of the ligands influences the cluster structures and allows working out basic construction principles of the cluster core.

Phenanthroline-Mediated Photoelectrical Enhancement in Calix[4]arene-Functionalized Titanium-Oxo Clusters

Incorporating two organic ligands with different functionalities into a titanium-oxo cluster entity simultaneously can endow the material with their respective properties and provide synergistic performance enhancement, which is of great significance for enriching the structure and properties of titanium-oxo clusters (TOCs). However, the synthesis of such TOCs is highly challenging. In this work, we successfully synthesized a TBC4A-functionalized TOC, [Ti2(TBC4A)2(MeO)2] (Ti2; MeOH = methanol, TBC4A = tert-butylcalix[4]arene). By adjusting the solvent system, we successfully introduced 1,10-phenanthroline (Phen) and prepared TBC4A and Phen co-protected [Ti2(TBC4A)2(Phen)2] (Ti2-Phen). Moreover, when Phen was replaced with bulky 4,7-diphenyl-1,10-phenanthroline (Bphen), [Ti2(TBC4A)2(Bphen)2] (Ti2-Bphen), which is isostructural with Ti2-Phen, was obtained, demonstrating the generality of the synthetic method. Remarkably, Ti2-Phen demonstrates good stability and stronger light absorption, as well as superior photoelectric performance compared to Ti2. Density functional theory (DFT) calculations reveal that there exists ligand-to-core charge transfer (LCCT) in Ti2, while an unusual ligand-to-ligand charge transfer (LLCT) is present in Ti2-Phen, accompanied by partial LCCT. Therefore, the superior light absorption and photoelectric properties of Ti2-Phen are attributed to the existence of the unusual LLCT phenomenon. This study not only deeply explores the influence of Phen on the performance of the material but also provides a reference for the preparation of materials with excellent photoelectric performance.

Enhancing the photocatalytic performance of a rutile unit featuring a titanium-oxide cluster by Pb2+ doping

Titanium-oxide clusters (TOCs) are well-defined molecular models for TiO2 materials and provide the opportunity to study the structure-activity relationships of TiO2. Here, we report a new Pb-doped TOC, Ti12Pb2, which resembles a two-layer decker of the {TiTi6} structural units of rutile TiO2 with two Ti4+ ions replaced by two Pb2+ ions. Its electronic structure, photoresponse, and photocatalytic performances were investigated and compared with those of the Ti14 cluster, which is isostructural to Ti12Pb2. Our results indicate that Pb2+ does not affect the electronic structure, but it greatly enhances the photocatalytic activity by improving the charge-separation and interfacial charge-transfer properties of the TOC. The successful synthesis of Ti12Pb2 highlights the roles of closed-shell heterometal ions in the construction of new TOCs. Our mechanism may be an inspiration for understanding the structure-activity relationships of closed-shell heterometal-doped TiO2.

Ligation of Titanium-oxide and {Mo2} Units for Solar CO2 Storage

Two Mo-Ti-mixed oxide clusters, Ti6Mo4 and Ti4Mo4, which contain the {Mo2V} unit commonly observed in many polyoxomolybdates, were successfully synthesized. The introduction of a {Mo2V} dopant into a titanium-oxide cluster (TOC) results in a red shift of the absorption edge, hence leading to a substantial enhancement of visible-light absorption. The band gap electron transition mainly involves the ligand-to-metal charge transfer (LMCT, benzoate-to-Mo) and MoV d-d transition. Both clusters show favorable visible-light responsiveness and charge-separation efficiency. Both serve as heterogeneous photocatalysts and exhibit excellent catalytic activity in CO2/epoxide cycloadditions under very mild conditions. The mechanism study suggests that the catalytically active sites are mainly MoV, and the photogenerated electrons and holes are both involved. Ti6Mo4 exhibits better photocatalytic activity than Ti4Mo4, demonstrating the crucial role of the titanium-oxide core, which corresponds to improved light absorption and charge-separation efficiency. Our findings highlight the potential of the {Mo2V} unit in constructing Mo-Ti-mixed oxide clusters with interesting topologies and excellent solar-light-harvesting activity.

Divalent Heterometal Doped Titanium-Oxide Cluster Polymers: Structures, Photoresponse, and Photocatalysis

Five cluster polymers based on heterometal-doped titanium-oxide cluster (TOC) monomers are reported. The monomers feature Ti10-oxide cluster cores and are connected to the divalent closed-shell heterometal anchors by salicylate ligands. The Sr2+, Ba2+, and Pb2+ dopants cause the monomers to bind head-to-head and generate linear chains, while the Ca2+ and Cd2+ lead to head-to-tail connections and zigzag chains. The cluster polymers are responsive to visible-light up to 565 nm and photo-catalytically active in both H2 evolution and CO2/epoxide cycloaddition reactions. The photo-absorption, photo-charge separation, and photocatalytic properties of the cluster polymers are dependent on the heterometal dopants in order Cd > Pb > Ba > Sr > Ca. Heterometals serve as the catalytic sites in the cluster polymers, which depending on the contribution of the pCB bottom, facilitate photo-charge separation and interfacial charge transfer, further enhancing catalytic activity. The tunable compositions and topologies of the cluster polymers shown herein may inspire the design and synthesis of more multidimensional functional metal-oxide cluster materials for a variety of applications in the future.

A butterfly-like lead-doped titanium-oxide compound with high performance in photocatalytic cycloaddition of CO2 to epoxide

The cycloaddition reaction of CO₂ to epoxides is quite promising for CO₂ capture and storage as well as the production of value-added fine chemicals. Herein, a novel atomically precise lead-doped titanium-oxide cluster with the formula Ti₁₀Pb₂O₁₆(phen)₄(Ac)₁₂(DMF)₂ (denoted as Ti10Pb2; phen = 1,10-phenanthroline; Ac = acetate; DMF = dimethylformamide) was synthesized through a facile solvothermal process, and is a molecular photocatalyst with surface-anchored main-group metal active sites. Its structure was characterized by single-crystal X-ray diffraction and other complementary techniques. Ti10Pb2 showed high photo-response and charge-separation efficiency under simulated sunlight irradiation. Ti10Pb2 was successfully used in the cycloaddition reaction of CO₂ with epoxides under solvent-free conditions. While its catalytic activity due to the Lewis acidity was moderate, simulated solar light irradiation further enhanced the reaction rate, demonstrating the synergistic effect of photocatalysis and Lewis-acid thermocatalysis.

Lead-Decorated Titanium Oxide Compound with a High Performance in Catalytic CO2 Insertion to Epoxides

The CO₂ cycloaddition to epoxides is an efficient method for CO₂ capture and storage, important not only for reducing greenhouse gas emission but also for producing cyclic carbonates, which are valuable industrial materials. In this study, we report a novel high-nuclearity titanium oxide cluster (TOC) inlayed with main-group element Pb²⁺, H₂Ti₁₆Pb₉O₂₄(SA)₁₈(DMF)₁₀(OH₂)₂ (denoted as 1; SA = salicylate; DMF = N,N-dimethylformamide), which has the property of visible-light absorption and has shown high catalytic activities for cycloadditions of CO₂ under visible-light irradiation. The cluster was synthesized in a high yield in a facial solvothermal process. Its structure and electronic structure were characterized by single-crystal X-ray diffraction, density functional theory calculations, and complementary techniques. The cycloaddition reactions were performed under solvent-free conditions. While the catalytic activity due to the Lewis acidity was moderate, visible-light irradiation further folded the reaction rates. The turnover number reached 3400 with a turnover frequency of 120 h^-1. Mechanism studies indicated a synergistic effect of the Lewis acidity and photogenerated charge carriers. The performance of 1 in reversible I₂ uptake was also investigated. This study demonstrates the high potential of heterometal-decorated TOCs in the cost-effective and efficient CO₂ cycloaddition reaction under mild conditions.

Platonic and Archimedean solids in discrete metal-containing clusters

Metal-containing clusters have attracted increasing attention over the past 2-3 decades. This intense interest can be attributed to the fact that these discrete metal aggregates, whose atomically precise structures are resolved by single-crystal X-ray diffraction (SCXRD), often possess intriguing geometrical features (high symmetry, aesthetically pleasing shapes and architectures) and fascinating physical properties, providing invaluable opportunities for the intersection of different disciplines including chemistry, physics, mathematical geometry and materials science. In this review, we attempt to reinterpret and connect these fascinating clusters from the perspective of Platonic and Archimedean solid characteristics, focusing on highly symmetrical and complex metal-containing (metal = Al, Ti, V, Mo, W, U, Mn, Fe, Co, Ni, Pd, Pt, Cu, Ag, Au, lanthanoids (Ln), and actinoids) high-nuclearity clusters, including metal-oxo/hydroxide/chalcogenide clusters and metal clusters (with metal-metal binding) protected by surface organic ligands, such as thiolate, phosphine, alkynyl, carbonyl and nitrogen/oxygen donor ligands. Furthermore, we present the symmetrical beauty of metal cluster structures and the geometrical similarity of different types of clusters and provide a large number of examples to show how to accurately describe the metal clusters from the perspective of highly symmetrical polyhedra. Finally, knowledge and further insights into the design and synthesis of unknown metal clusters are put forward by summarizing these "star" molecules.

Heterometallic Molecular Architectures Based on Fluorinated β-Diketone Ligands

This review summarizes the data on the synthesis of coordination compounds containing two or more different metal ions based on fluorinated β-diketonates. Heterometallic systems are of high interest in terms of their potential use in catalysis, medicine and diagnostics, as well as in the development of effective sensor devices and functional materials. Having a rich history in coordination chemistry, fluorinated β-diketones are well-known ligands generating a wide variety of heterometallic complexes. In this context, we focused on both the synthetic approaches to β-dicarbonyl ligands with additional coordination centers and their possible transformations in complexation reactions. The review describes bi- and polynuclear structures in which β-diketones are the key building blocks in the formation of a heterometallic framework, including the examples of both homo- and heteroleptic complexes.

Crystal structure of bis(μ2-2-oxido-2-phenylacetato-κ3 O,O′:O′)-bis(N-oxido-benzamide-κ2 O,O′)-bis(propan-2-olato-κ1 O)dititanium(IV), C36H38N2O12Ti2

C36H38N2O12Ti2, monoclinic, P21/n (no. 14), a = 10.3151(7) Å, b = 15.8747(11) Å, c = 11.5020(8) Å, β = 98.471(3)°, V = 1862.9(2) Å3, Z = 2, R gt(F) = 0.0386, wR ref(F 2) = 0.1075, T = 296(2) K.

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.

"Three-in-One" Structural-Building-Mode-Based Ti16-Type Titanium Oxo Cluster Entirely Protected by the Ligands Benzoate and Salicylhydroxamate

Titanium oxo clusters (TOCs) with accurate molecular structures have potential applications in photocatalysis, such as photocatalytic degradation, hydrogen production, and water oxidation. The hydrolytic stability and light absorption ability of TOCs have important impacts on photocatalysis, where the selection of peripheral organic ligands plays a significant role. In this regard, salicylhydroxamic acid (abbreviated as H₃L) attracts our attention, acting as a ligand for its multidentate and dye-functional features, which can increase the hydrolytic stability and broaden light absorption for TOCs. Herein, two TOCs were solvothermally synthesized and structurally characterized using H₃L, formulated as [Ti₈(μ₂-O)₂(μ₃-O)₂(OⁱPr)₁₂(L)₄]·2CH₃CN (1) and [Ti₁₆(μ₂-O)₁₀(μ₃-O)₄(PhCOO)₁₄(L)₆(HL)₂]·4CH₃CN·2ⁱPrOH (2). Complex 2 was obtained by adding excessive benzoic acid over the reaction system of 1, resulting in enhanced hydrolytic stability via the replacement of all alkoxy ligands by multidentate ligands for protection. Interestingly, for the first time, the "three-in-one" structural building mode with {Ti₆} + {Ti₄} + {Ti₆} by the common subunits in 2 was observed among all reported TOCs. Moreover, complex 2 can strongly absorb visible light reaching up to 700 nm and exhibit obvious activity for the photodegradation of methyl orange.

Organic-Inorganic High-Valence Sn18-oxo Clusters: Direct Utilization of an Inorganic Sn(IV) Source to Improve the Nuclearity and Electrocatalytic CO2 Reduction Properties

The high-valence tin-oxo clusters are of great significance because of their structural diversity and potential applications in many fields, e.g., catalysis, extreme ultraviolet (EUV) lithography, and so on. The synthesis of high-nuclearity tin-oxo clusters remains a great challenge currently, since the key inorganic Sn_xO_y core with Sn⁴⁺ ions could not be obtained only by the in situ Sn-C bond cleavage in organic tin sources. In this context, we synthesize three organic-inorganic hybrid Sn₁₈-oxo clusters, [(BuSn)₁₂Sn₆(μ₃-O)₂₀(ba)₁₂(PhPO₃)₄] (Bu = butyl, Hba = benzoic acid), [(BuSn)₁₂Sn₆(μ₃-O)₂₀(pmba)₁₂(PhPO₃)₄]·2CH₃CN·2H₂O (Hpmba = p-toluic acid), and [(BuSn)₁₂Sn₆(μ₃-O)₂₀(ptba)₁₂(PhPO₃)₄]·2CH₃CN·2iPrOH·2H₂O (Hptba = p-tert-butyl benzoic acid), as well as one Sn₆-oxo cluster [(BuSn)₆(μ₃-O)₂(μ₂-OH)₄(pnba)₆(PhPO₃)₂] (Sn₆) (Hpnba = p-nitrobenzoic acid) by combining an inorganic precursor (SnCl₄) with an organic one (butyltin hydroxide oxide). It is shown that an inorganic dicyclo-chain-like Sn₆O₈ core encapsulated in a U-shaped dodecanuclear butyltin-oxo ring plays an important role in the construction of Sn₁₈-oxo clusters and that the use of a ligand with an electron-withdrawing group reduces the nuclearity of clusters to Sn₆. Moreover, electrocatalytic CO₂ reduction studies confirm that the electrocatalytic activities of the Sn₁₈ clusters are superior to those of the Sn₆ cluster, probably due to the hybrid organotin-inorganotin structures. Our work not only opens a new way for constructing high-nuclearity tin-oxo clusters but also is helpful in deeply revealing the structure-properties relationship of tin-oxo clusters.

Preparation and Visible-Light Response of Salicylate-Stabilized Heterobimetallic Pb-Ti-Oxo Clusters Initiated via Auxiliary Quaternary Ammonium Salts and a Solvent Effect

In this study, with the assistance of quaternary ammonium salts we have successfully prepared a new family of salicylate-stabilized heterobimetallic Pb-Ti-oxo clusters, including H(TEA)[Pb₂Ti₆(μ₂-O)₂(μ₃-O)₂(OⁱPr)₄(PA)₂(Sal)₆(NO₃)₂] (PTC-321; TEA = tetraethylammonium; HOⁱPr = isopropanol; H₂PA = phenylphosphonic acid; H₂Sal = salicylic acid), {PbTi₃(μ₂-O)(μ₃-O)(OⁱPr)₂(PA)(Sal)₃(DMF)·CH₃CN}_n (PTC-322; DMF = dimethylformamide), {PbTi₅(μ₃-O)₆(Sal)₃(CH₃COO)₂(DMF)(OⁱPr)₂}_n (PTC-323), [Pb₂Ti₄(Sal)₆(EtO)₂(OⁱPr)₆(HOⁱPr)₂]·CH₃NH₂ (PTC-324; EtOH = CH₃CH₂OH), H[Pb₄Ti₉(μ₂-O)₂(μ₃-O)(μ₄-O)₆(Sal)₇(OⁱPr)₁₃] (PTC-325), and Pb₂Ti₁₂(μ₂-O)₃(μ₃-O)₃(μ₄-O)₄(Sal)₄(OEt)₂₄ (PTC-326). Single-crystal X-ray diffraction studies demonstrate that the {Ti₃Pb(Sal)₃} unit acts as the building block to constitute the diverse assembly of PTC-321-PTC-323. Thereinto, the clusters in PTC-322 and PTC-323 are connected into infinite one-dimensional chains. Furthermore, the solvent effects have facilitated the heterobimetallic Pb-Ti-oxo clusters into various configurations in PTC-323-PTC-326. Solid-state ultraviolet-visible spectroscopy analysis indicates that the optical absorption bands of these compounds shift effectively toward the visible-light region, and they were also employed as electrode precursors to investigate their visible-light-driven photocurrent response.

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...

Transition-metal doped titanium-oxo clusters with diverse structures and tunable photochemical properties

Transition metal doping effectively tuned the photochemical properties of titanium-oxo clusters {Ti2Mn4}, {Ti8Co5} and {Ti12Cd5}.

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.

A Mesoporous Lead-Doped Titanium Oxide Compound with High Performance and Recyclability in I2 Uptake and Photocatalysis

A three-dimensional (3D) mesoporous material with an atomically precise structure, Ti₁₆Pb₅O₁₆(C₆H₅CO₂)₂(OCH₃)₄₀ (Ti₁₆Pb₅), comprised of a novel high-nuclearity Pb-doped titanium oxide cluster (TOC), was synthesized. Ti₁₆Pb₅ exhibited a surface area of 45 m² g^-1 and a pore diameter of 3.5 nm. It exhibited an uptake capacity of I₂ of ≤2.2 g g^-1 in vapor, and the performance was maintained after seven uptake-release cycles. Ti₁₆Pb₅ also showed a high adsorption ratio and capacity (93% and 3.1 g g^-1) in hexane. The characterization data, including Fourier transform infrared, Raman, and powder X-ray diffraction, suggested the lattice structure of Ti₁₆Pb₅ was rigid and I₂ was accommodated in the pores of Ti₁₆Pb₅. To the best of our knowledge, this is the first example of using a TOC in I₂ adsorption. In addition, Ti₁₆Pb₅ showed excellent activity and recyclability in visible-light degradation of dye pollutants and photocurrent generation. Our structural analysis suggested the alkoxide ligands within the channels of Ti₁₆Pb₅ build up a confined polar environment and thereby facilitate I₂ accommodation, and meanwhile, the improved performances and stabilities of Ti₁₆Pb₅ are correlated with its cluster-based, 3D hierarchical structure.

A Cyclic Titanium-Oxo Cluster with a Tetrathiafulvalene Connector as a Precursor for Highly Efficient Adsorbent of Cationic Dyes

Titanium-oxo clusters (TOCs) have been studied for applications in catalysis, energy storage and transfer, light emission, and so on; however, use of TOCs for the selective adsorption of dyes has not yet been reported. Herein, a TOC compound formulated as [Ti₆O₃(OⁱPr)₁₄(TTFTC)]₄ (1, TTFTC = tetrathiafulvalene-tetracarboxylate) was successfully prepared and crystallographically characterized. Compound 1 has a cyclic structure assembled by four Ti₆ clusters and four rodlike TTFTC connectors. Red compound 1 self-condenses to form a black polymeric organic-inorganic hybrid material (denoted as B-1), which was characterized by various techniques. B-1 is an amorphous TiO material that is formed by the irregular condensation of 1 by the removal of alkoxyl groups. B-1 exhibits high dye adsorption efficiency toward cationic dyes with a q_e value of 651.3 mg/g at 298 K for methylene blue (MB). Moreover, B-1 can be used to selectively remove MB not only from mixed cationic-anionic dye solutions but also from some mixed cationic dyes, which is related to their structures. Kinetic, isotherm, and thermodynamic studies demonstrated that the pseudo-second-order kinetic model and Freundlich model show a good fit to the experimental data. The adsorption process involves an exothermic and entropy decreasing process. In addition, dye-adsorbed B-1 can be further used as a photocurrent-responsive material. The work opens up a new field for the application of TOCs in the selective adsorption and removal of dyes.

Mono- and Bismetalphenanthroline-Substituted Ti12 Clusters: Structural Variance and the Effect on Electronic State and Photocurrent Property

Despite the numerous titanium-oxo clusters (TOCs) which have been reported, the nature of small clusters (nuclearity < 10) as model compounds showed large deviation from that of nanoscale TiO materials. Therefore, theoretical and experimental studies for large TOCs merit more attention. We recently prepared and crystallographically characterized a series of large TOCs: Ti₁₁O₁₅(OⁱPr)₁₆(Cophen) (1), Ti₁₁O₁₅(OⁱPr)₁₆(Mnphen) (2), Ti₁₀O₁₄(OEt)₁₆(Mnphen)₂ (3), and Ti₁₀O₁₄(OEt)₁₆(Mnphphen)₂ (4) (phen = 1,10-phenanthroline, phphen = 4,7-biphenyl-phen). These compounds are derivatives of a Ti₁₂ parent cluster by replacing one or two of the five-coordinated titanium atoms of the Ti₁₂ cluster with a transition metal M, Co(II) and Mn(II), that is chelated by a phen group. The effects of mono- and bis-substituted Mphen on the charge and structure of the clusters are discussed. Theoretical evaluation of the frontier orbitals of the clusters is carried out on the basis of the precisely defined crystal structures. Different from the dye molecule to TiO core charge transfer for the dye-modified TOCs, charge transfer in these clusters is from TiO/TiOM to phen/Mphen. The effects of different metal ions and the number of substituted Mphen moieties on the photocurrent properties are evaluated. The results will be of interest to research on cluster chemistry, especially on the TOC chemistry.

Titanium-Oxo Clusters with Bi- and Tridentate Organic Ligands: Gradual Evolution of the Structures from Small to Big

Homometallic titanium oxo clusters are one of the most important groups of metal oxo clusters, with more than 300 examples characterized by X-ray structure analyses. Most of them are uncharged and are obtained by partial hydrolysis and condensation of titanium alkoxo derivatives. The cluster cores, ranging from 3 to >50 titanium atoms, are stabilized by organic ligands. Apart from residual OR groups, carboxylato and phosphonato ligands are most frequent. The article critically reviews and categorizes the known structures and works out basic construction principles by comparing the different cluster types.

Assembly of a Titanium-Oxo Cluster and a Bismuth Iodide Cluster, a Single-Source Precursor of a p-n-Type Photocatalyst

Titanium oxides and bismuth halides or oxyhalides have been known to be excellent semiconductors with both excellent photocatalytic and photoelectric properties. The design of supersalts assembled by titanium-oxo clusters (TOCs) and bismuth iodide clusters is a hopeful strategy for exploring the chemistry and application of new titanium-oxo clusters. We report herein a series of unusual ionic TOCs with Ti₁₂ oxo cluster cations and bismuth iodide anions, [Ti₁₂O₁₅(OⁱPr)₁₇]₃[Bi₃I₁₂] (Bi₃), [Ti₁₂O₁₄(OⁱPr)₁₈][Bi₄I₁₄(THF)₂] (Bi₄), and [Ti₁₂O₁₄(OⁱPr)₁₈][Ti₁₁BiO₁₄(OⁱPr)₁₇][Bi₆I₂₂] (Bi₆). Single-crystal X-ray analysis revealed that the type and charge of the Ti₁₂ clusters varied with the charges of different bismuth iodide clusters. Taking advantage of the easy hydrolysis of the TOCs and BiI clusters in water, we used these supersalt crystals as single-source precursors to prepare a p-n-type BiOI-TiO photocatalyst. The heterojunction materials were carefully characterized by powder X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, high-resolution transmission electron microscopy, etc. The synergistic effect of the two components of BiOI and TiO on the photocatalytic degradation of RhB in water is demonstrated. This is a very convenient method for obtaining a p-n-type BiOI-TiO heterojuction photocatalyst by just placing the ground TOC crystals into water.

Threefold Collaborative Stabilization of Ag14 -Nanorods by Hydrophobic Ti16 -Oxo Clusters and Alkynes: Designable Assembly and Solid-State Optical-Limiting Application

Ag nanoclusters have received increasing attention due to their atomically precise and diverse structures and intriguing optical properties. Nevertheless, the inherent instability of Ag nanoclusters has seriously hindered their practical application. In this work, for the first time, Ag clusters are collaboratively protected by hydrophobic Ti-oxo clusters and alkyne ligands. Initially, a pyramidal Ag₅ cluster terminated with ^t BuC≡C^- and CH₃ CN was inserted into the cavity of a Ti₈ -oxo nanoring to form Ag₅ @Ti₈ . To overcome the instability of acetonitrile-terminated silver site, such two Ag₅ @Ti₈ clusters could sandwich an Ag₄ unit to form Ag₁₄ -nanorod@Ti₁₆ -oxo-nanoring (Ag₁₄ @Ti₁₆ ), which is peripherally protected by fluorophenyl groups and alkyne caps. This threefold protected (hydrophobic fluorinated organic layer, Ti-O shell, and terminal alkyne ligands) Ag₁₄ @Ti₁₆ exhibits superhydrophobicity and excellent ambient stability, endowing it with solid-state optical limiting characteristics.

Calixarene-Protected Titanium-Oxo Clusters and Their Photocurrent Responses and Photocatalytic Performances

Three photosensitive tert-butylcalix[n]arene (TBC[n], n = 4, 6, 8)-protected titanium-oxo clusters (TOCs), formulated as [Ti₄(μ₃-O)₂(TBC[4])₂(OⁱPr)₄(DEF)₂]·DEF (1, TBC[4]-Ti₄, DEF = N,N-diethylformamide), [Ti₄(μ₄-O)TBC[6](OCH₃)₉]·H₂O (2, TBC[6]-Ti₄), and [Ti₄(μ₃-O)₂(OⁱPr)₄TBC[8](DEF)₂]·DEF (3, TBC[8]-Ti₄), were successfully synthesized and characterized. Because of the generation of charge transfer from TBC[n] to the TiO core, the three TBC[n]-decorated TOCs show a broadened visible-light absorption and narrowed optical band gap based on the UV-visible spectra and density functional theory calculations. The corresponding photosensitive electrodes prepared using these three TOCs exhibit stable photocurrent responses. Furthermore, their photocatalytic performances for hydrogen evolution and methylene blue degradation were evaluated, and all of the materials display excellent photocatalytic activity and stability. The calixarene-Ti coordination is therefore an effective strategy to enlarge the visible-light absorption band of Ti-O materials and improve their photoelectric/photocatalytic performances.

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.

Pentasulfurated benzene-cored asterisks: relationship between crystal structure and luminescence properties

Pentasulfurated benzene chromophores are not luminescent in fluid solution and are phosphorescent in the solid state; in particular, the cyano-derivative which displays a bright orange luminescence.