Microporous Cyclic Titanium-Oxo Clusters with Labile Surface Ligands

Hierarchical assembly of Ag40 nanowheel ranging from building blocks to diverse superstructure regulation

Achieving precise and controllable hierarchical self-assembly of functional nanoclusters within crystal lattices to create distinct architectures is of immense significance, yet it creates considerable challenges. Here we successfully synthesized a silver nanowheel Ag40, along with its optically pure enantiomers S-/R-Ag40. Each species possesses an internal nanospace and exhibits host-guest interactions. These structures are constructed from primary building blocks (Ag9). By manipulating the surface anions and guest molecules, the nanowheels function as secondary building blocks, spontaneously organizing into complex double- and triple-helical crystalline superstructures or one-dimensional chains {Ag41}n through conformational matching and diverse noncovalent interactions. Moreover, we demonstrate that the water-mediated complex specifically assembled with uridine monophosphate nucleotides, resulting in chiral assemblies of Ag40 that exhibit chiroptical activity for specific recognition. Our findings provide insights into the efficient construction of assemblies with hollow frameworks and propose strategies for superstructure engineering by manipulating surface motifs.

Advancements in calixarene-protected titanium-oxo clusters: from structural assembly to catalytic functionality

This review explores calixarenes, a prominent family of third-generation supramolecules celebrated for their distinct hollow, cavity-shaped structures. These macrocycles are intricately assembled by linking multiple phenolic units orthogonally through methylene (-CH2-), sulfur (-S-), or sulfonyl (-SO2-) bridges. This structural framework plays a pivotal role in the intricate assembly of nanoclusters, significantly advancing the field of cluster chemistry. A key focus of current research is the remarkable ability of calixarenes to stabilize titanium-oxo clusters. Our review details the application of calixarenes in constructing titanium-oxo cluster structures, emphasizing how these clusters, when encapsulated within calixarenes, exploit flexible coordination sites for structural modifications and serve as foundational units for more complex assemblies. Additionally, we investigate how these calixarene-stabilized metal-oxo clusters function as versatile scaffolds for catalytically active metal ions, facilitating the creation of bimetallic nanoclusters. These clusters not only exhibit unique structural diversity but also demonstrate exceptional catalytic efficiency. This review aims to inspire ongoing exploration and innovation in the use of calixarenes for the synthesis and application of advanced cluster materials.

Modulated assembly and structural diversity of heterometallic Sn-Ti oxo clusters from inorganic tin precursors

Through modulating the multidentate ligands, solvent environments, and inorganic tin precursors during the synthesis processes, we have successfully prepared a series of unprecedented heterometallic Sn-Ti oxo clusters with structural diversity and different physiochemical attributes. Initially, two Sn6Ti10 clusters were synthesized using trimethylolpropane as a structure-oriented ligand and SnCl4·5H2O as a tin source. Then, when a larger pentadentate ligand di(trimethylolpropane) was used instead of trimethylolpropane and aprotic acetonitrile solvent was introduced into the reaction system, four low-nuclearity Sn-Ti oxo clusters were discovered, including two Sn1Ti1, one Sn2Ti2 and one Sn2Ti6. Finally, two mixed-valence state clusters, SnII4SnIV2TiIV14 and SnII4SnIV4TiIV20, were obtained by transforming the tin precursor from SnCl4·5H2O to SnCl2·2H2O and adjusting the acetonitrile solution with trace acetic acid/formic acid. Sn8Ti20 is the highest-nuclearity heterometallic Sn-Ti oxo cluster to date. Moreover, comparative electrocatalytic CO2 reduction experiments were carried out, and it was concluded that the Sn8Ti20-decorated electrode showed the most satisfactory performance due to the influence of mixed-valence states of the Sn atoms and the charging effects provided by 20 Ti4+ ions. This study presents important guiding significance for the design, synthesis and application optimization of functional heterometallic nanoclusters.

Hydrogen-Bonded Mesoporous Frameworks with Tunable Pore Sizes and Architectures from Nanocluster Assembly Units

Construction of mesoporous frameworks by noncovalent bonding still remains a great challenge. Here, we report a micelle-directed nanocluster modular self-assembly approach to synthesize a novel type of two-dimensional (2-D) hydrogen-bonded mesoporous frameworks (HMFs) for the first time based on nanoscale cluster units (1.0-3.0 nm in size). In this 2-D structure, a mesoporous cluster plate with ∼100 nm in thickness and several micrometers in size can be stably formed into uniform hexagonal arrays. Meanwhile, such a porous plate consists of several (3-4) dozens of layers of ultrathin mesoporous cluster nanosheets. The size of the mesopores can be precisely controlled from 11.6 to 18.5 nm by utilizing the amphiphilic diblock copolymer micelles with tunable block lengths. Additionally, the pore configuration of the HMFs can be changed from spherical to cylindrical by manipulating the concentration of the micelles. As a general approach, various new HMFs have been achieved successfully via a modular self-assembly of nanoclusters with switchable configurations (nanoring, Keggin-type, and cubane-like) and components (titanium-oxo, polyoxometalate, and organometallic clusters). As a demonstration, the titanium-oxo cluster-based HMFs show efficient photocatalytic activity for hydrogen evolution (3.6 mmol g-1h-1), with a conversion rate about 2 times higher than that of the unassembled titanium-oxo clusters (1.5 mmol g-1h-1). This demonstrates that HMFs exhibited enhanced photocatalytic activity compared with unassembled titanium-oxo clusters units.

Precise Modulation of CO2 Sorption in Ti8Ce2-Oxo Clusters: Elucidating Lewis Acidity of the Ce Metal Sites and Structural Flexibility

Investigating the structure-property correlation in porous materials is a fundamental and consistent focus in various scientific domains, especially within sorption research. Metal oxide clusters with capping ligands, characterized by intrinsic cavities formed through specific solid-state packing, demonstrate significant potential as versatile platforms for sorption investigations due to their precisely tunable atomic structures and inherent long-range order. This study presents a series of Ti8Ce2-oxo clusters with subtle variations in coordinated linkers and explores their sorption behavior. Notably, Ti8Ce2-BA (BA denotes benzoic acid) manifests a distinctive two-step profile during the CO2 adsorption, accompanied by a hysteresis loop. This observation marks a new instance within the metal oxide cluster field. Of intrigue, the presence of unsaturated Ce(IV) sites was found to be correlated with the stepped sorption property. Moreover, the introduction of an electrophilic fluorine atom, positioned ortho or para to the benzoic acid, facilitated precise control over gate pressure and stepped sorption quantities. Advanced in situ techniques systematically unraveled the underlying mechanism behind this unique sorption behavior. The findings elucidate that robust Lewis base-acid interactions are established between the CO2 molecules and Ce ions, consequently altering the conformation of coordinated linkers. Conversely, the F atoms primarily contribute to gate pressure variation by influencing the Lewis acidity of the Ce sites. This research advances the understanding in fabricating metal-oxo clusters with structural flexibility and provides profound insights into their host-guest interaction motifs. These insights hold substantial promise across diverse fields and offer valuable guidance for future adsorbent designs grounded in fundamental theories of structure-property relationships.

Sulfur atom-directed metal-ligand synergistic catalysis in zirconium/hafnium-oxo clusters for highly efficient amine oxidation

The performance applications (e.g., photocatalysis) of zirconium (Zr) and hafnium (Hf) based complexes are greatly hindered by the limited development of their structures and the relatively inert metal reactivity. In this work, we constructed two ultrastable Zr/Hf-based clusters (Zr9-TC4A and Hf9-TC4A) using hydrophobic 4-tert-butylthiacalix[4]arene (H4TC4A) ligands, in which unsaturated coordinated sulfur (S) atoms on the TC4A4- ligand can generate strong metal-ligand synergy with nearby active metal Zr/Hf sites. As a result, these two functionalized H4TC4A ligands modified Zr/Hf-oxo clusters, as catalysts for the amine oxidation reaction, exhibited excellent catalytic activity, achieving very high substrate conversion (>99%) and product selectivity (>90%). Combining comparative experiments and theoretical calculations, we found that these Zr/Hf-based cluster catalysts accomplish efficient amine oxidation reactions through synergistic effect between metals and ligands: (i) The photocatalytic benzylamine (BA) oxidation reaction was achieved by the synergistic effect of the dual active sites, in which, the naked S sites on the TC4A4- ligand oxidize the BA by photogenerated hole and oxygen molecules are reduced by photogenerated electrons on the metal active sites; (ii) in the aniline oxidation reaction, aniline was adsorbed by the bare S sites on ligands to be closer to metal active sites and then oxidized by the oxygen-containing radicals activated by the metal sites, thus completing the catalytic reaction under the synergistic catalytic effect of the proximity metal-ligand. In this work, the Zr/Hf-based complexes applied in the oxidation of organic amines have been realized using active S atom-directed metal-ligand synergistic catalysis and have demonstrated very high reactivity.

All-catecholate-stabilized black titanium-oxo clusters for efficient photothermal conversion

The controlled synthesis of titanium-oxo clusters (TOCs) completely stabilized by organic dye ligands with high stability and superior light absorption remains a significant challenge. In this study, we report the syntheses of three atomically precise catechol (Cat)-functionalized TOCs, [Ti2(Cat)2(OEgO)2(OEgOH)2] (Ti2), [Ti8O5(Cat)9(iPrO)4(iPrOH)2] (Ti8), and [Ti16O8(OH)8(Cat)20]·H2O·PhMe (Ti16), using a solvent-induced strategy (HOEgOH = ethylene glycol; iPrOH = isopropanol; PhMe = toluene). Interestingly, the TiO core of Ti16 is almost entirely enveloped by catechol ligands, making it the first all-catechol-protected high-nuclearity TOC. In contrast, Ti2 and Ti8 have four weakly coordinated ethylene glycol ligands and six weakly coordinated iPrOH ligands, respectively, in addition to the catechol ligands. Ti16 is visually evident in its distinctively black appearance, which belongs to black TOCs (B-TOCs) and exhibits an ultralow optical band gap. Furthermore, Ti16 displays exceptional stability in various media/environments, including exposure to air, solvents, and both acidic and alkaline aqueous solutions due to its comprehensive protection by catechol ligands and rich intra-cluster supramolecular interactions. Ti16 has superior photoelectric response qualities and photothermal conversion capabilities compared to Ti2 and Ti8 due to its ultralow optical band gap and remarkable stability. This discovery not only represents a huge step forward in the creation of all-catecholate-protected B-TOCs with ultralow optical band gaps and outstanding stability, but it also gives key valuable mechanistic insights into their photothermal/electric applications.

Structure and optical limiting effects of heterometallic Ag6@Ti12 and Ag8@Ti12 oxo clusters regulated by alkynyl ligands

Heterometallic Ag6@Ti12 and Ag8@Ti12 oxo clusters were prepared through a strategy of protecting polynuclear silver cores by a hollow Ti-O module. The introduction of alkyne ligands has shown significant influence on their structures and optical limiting effects.

Structural Regulation and Transformation of Oxalate-Bridged Polyoxo-Titanium Nanoclusters: Intercluster Docking Strategy and Polyiodides Induced Rearrangement

Although significant progress has been made in the synthetic and structural chemistry of polyoxo-titanium clusters (PTCs), the rational regulation of their geometric and electronic configurations is rather difficult. Meanwhile, it is also challenging to induce their systematic structural transformation, thereby customizing their physicochemical properties. In this work, we illustrate the intercluster docking strategy, which utilizes oxalates as multidentate ligands to connect and regulate the modular assembly of polynuclear Ti-O subunits into nanoclusters Ti24(μ3-O)26(μ2-O)4(OiPr)34(Oxal) (PTC-361), Ti28(μ4-O)2(μ3-O)28(μ2-O)8(OtBu)22(PA)12(Oxal) (PTC-362), Ti10(μ3-O)6(OtBu)14(PA)6(Oxal)2(tBC)2 (PTC-363), and Ti24(μ3-O)20(μ2-O)12(PA)12(Oxal)2(Hoxal)8(PyA)8 (PTC-364) (H2Oxal = oxalic acid; HOiPr = isopropanol; HOtBu = t-butanol; H2tBC = 4-tert-butylcatechol; HPA = propionic acid; and HPyA = 2-picolinic acid). Furthermore, the stepwise addition of iodine gives rise to polyiodide I3- to assist the controllable structure transformation of PTC-361 to [Ti12(μ-O)15(OiPr)17]I3 (PTC-365) and even to [Ti24(μ2-O)2(μ3-O)30(OiPr)30](I3)2 (PTC-366) with increasing polyiodide content. Moreover, modification with 4-tert-butylcatecholate as light absorbent material on the surface layers of PTCs and polyiodide I3- incorporation in PTCs expand their light response to the visible region and reduce their highest occupied molecular orbital-lowest unoccupied molecular orbital gaps. This work successfully develops an intercluster docking strategy and gives precise modulation on the geometry of nanoclusters as well as the optimization of their desired properties.

Atomically accurate site-specific ligand tailoring of highly acid- and alkali-resistant Ti(iv)-based metallamacrocycle for enhanced CO2 photoreduction

Skillfully engineering surface ligands at specific sites within robust clusters presents both a formidable challenge and a captivating opportunity. Herein we unveil an unprecedented titanium-oxo cluster: a calix[8]arene-stabilized metallamacrocycle (Ti16L4), uniquely crafted through the fusion of four "core-shell" {Ti4@(TBC[8])(L)} subunits with four oxalate moieties. Notably, this cluster showcases an exceptional level of chemical stability, retaining its crystalline integrity even when immersed in highly concentrated acid (1 M HNO3) and alkali (20 M NaOH). The macrocycle's surface unveils four specific, customizable μ2-bridging sites, primed to accommodate diverse carboxylate ligands. This adaptability is highlighted through deliberate modifications achieved by alternating crystal soaking in alkali and carboxylic acid solutions. Furthermore, Ti16L4 macrocycles autonomously self-assemble into one-dimensional nanotubes, which subsequently organize into three distinct solid phases, contingent upon the specific nature of the four μ2-bridging ligands. Notably, the Ti16L4 exhibit a remarkable capacity for photocatalytic activity in selectively reducing CO2 to CO. Exploiting the macrocycle's modifiable shell yields a significant boost in performance, achieving an exceptional maximum CO release rate of 4.047 ± 0.243 mmol g-1 h-1. This study serves as a striking testament to the latent potential of precision-guided surface ligand manipulation within robust clusters, while also underpinning a platform for producing microporous materials endowed with a myriad of surface functionalities.

A Thiol-Michael Approach Towards Versatile Functionalized Cyclic Titanium-Oxo Clusters

In expanding our research activities of superlattice engineering, designing new giant molecules is the necessary first step. One attempt is to use inorganic transition metal clusters as building blocks. Efficient functionalization of chemically precise transition metal clusters, however, remains a great challenge to material scientists. Herein, we report an efficient thiol-Michael addition approach for the modifications of cyclic titanium-oxo cluster (CTOC). Several advantages, including high efficiency, mild reaction condition, capability of complete addition, high atom economy, as well as high functional group tolerance were demonstrated. This approach can afford high yields of fully functionalized CTOCs, which provides a powerful platform for achieving versatile functionalization of precise transition metal clusters and further applications.

Stepwise assembly of thiacalix[4]arene-protected Ag/Ti bimetallic nanoclusters: accurate identification of catalytic Ag sites in CO2 electroreduction

The accurate identification of catalytic sites in heterogeneous catalysts poses a significant challenge due to the intricate nature of controlling interfacial chemistry at the molecular level. In this study, we introduce a novel strategy to address this issue by utilizing a thiacalix[4]arene (TC4A)-protected Ti-oxo core as a template for loading Ag1+ ions, leading to the successful synthesis of a unique Ag/Ti bimetallic nanocluster denoted as Ti8Ag8. This nanocluster exhibits multiple surface-exposed Ag sites and possesses a distinctive "core-shell" structure, consisting of a {Ti4@Ag8(TC4A)4} core housing a {Ti2O2@Ag4(TC4A)2} motif and two {Ti@Ag2(TC4A)} motifs. To enable a comprehensive analysis, we also prepared a Ti2Ag4 cluster with the same {Ti2O2@Ag4(TC4A)2} structure found within Ti8Ag8. The structural disparities between Ti8Ag8 and Ti2Ag4 provide an excellent platform for a comparison of catalytic activity at different Ag sites. Remarkably, Ti8Ag8 exhibits exceptional performance in the electroreduction of CO2 (eCO2RR), showcasing a CO faradaic efficiency (FECO) of 92.33% at -0.9 V vs. RHE, surpassing the FECO of Ti2Ag4 (69.87% at -0.9 V vs. RHE) by a significant margin. Through density functional theory (DFT) calculations, we unveil the catalytic mechanism and further discover that Ag active sites located at {Ti@Ag2(TC4A)} possess a higher εd value compared to those at {Ti2O2@Ag4(TC4A)2}, enhancing the stabilization of the *COOH intermediate during the eCO2RR. This study provides valuable insights into the accurate identification of catalytic sites in bimetallic nanoclusters and opens up promising avenues for efficient CO2 reduction catalyst design.

Ligand-dependent structural diversity and optimizable CO2 chemical fixation activities of Cu-doped polyoxo-titanium clusters

Heterometallic oxo clusters have been attracting intensive interest due to their unique properties originating from the synergistic interactions between different components. Herein, we report the construction and catalytic applications of a family of copper-doped polyoxo-titanium clusters (Cu-PTCs) coordinated with different acetate derivative ligands. The solvothermal reactions of metal salts and trimethylacetic acid or 1,2-phenylenediacetic acid in ethanol produced Ti6Cu3(μ3-O)4(μ2-O)(OEt)16(L1)4 (L1 = trimethyl acetate, PTC-367) and H2Ti8Cu2Br2(μ4-O)2(μ2-O)4(OEt)20(L2)2 (L2 = 1,2-phenylenediacetate, PTC-368), respectively. When smaller acetic acid was introduced as a stabilizing ligand, higher nuclei H2Ti16Cu3(μ4-O)5(μ3-O)15(μ2-O)3(OiPr)18(Ac)8 (Ac = acetate, PTC-369) and H3Ti29Cu3(μ4-O)6(μ3-O)30(μ2-O)8(OiPr)17(Ac)20 (PTC-370) were prepared. The number of metal ions exposed on the surface of the four clusters changes due to variations in the steric hindrance of functionalizing ligands, and theoretically, so does their catalytic activity as Lewis acids. In light of this, we conducted a carbon dioxide cycloaddition reaction in an atmospheric environment and the four obtained compounds displayed increasing catalytic activities from PTC-367 to PTC-370. These results provide a feasible synthetic method for modulating the structures of Cu-doped titanium oxide materials and improving their catalytic activities.

Atomically accurate structural tailoring of thiacalix[4]arene-protected copper(II)-based metallamacrocycles

Accurate manipulation of ligands at specific sites in robust clusters is attractive but difficult, especially for those ligands that coordinate in intricate binding patterns. By linking the shuttlecock-like {Cu₄(μ₄-Cl)TC4A} motif and the phenylphosphate (PhPO₃^2-) ligand, we elaborately design and synthesize two Cu(II)-thiacalix[4]arene metallamacrocycles (MMCs), namely Cu₁₂L₃ and Cu₁₆L₄, which have regular triangular and quadrilateral topologies, respectively. While keeping the core intact, the Cl^- and PhPO₃^2- in those two MMCs, which coordinated in a μ₄-bridging fashion, can be accurately substituted with salicylate ligands. Theoretical calculations have been carried out to reveal the effect of ligand tailoring on the electronic structure of clusters. Structural regulation can affect the catalytic activity of these clusters, which has been verified by using the clusters as catalysts for selective sulfide oxidation.

Biocompatible Material-Based Flexible Biosensors: From Materials Design to Wearable/Implantable Devices and Integrated Sensing Systems

Human beings have a greater need to pursue life and manage personal or family health in the context of the rapid growth of artificial intelligence, big data, the Internet of Things, and 5G/6G technologies. The application of micro biosensing devices is crucial in connecting technology and personalized medicine. Here, the progress and current status from biocompatible inorganic materials to organic materials and composites are reviewed and the material-to-device processing is described. Next, the operating principles of pressure, chemical, optical, and temperature sensors are dissected and the application of these flexible biosensors in wearable/implantable devices is discussed. Different biosensing systems acting in vivo and in vitro, including signal communication and energy supply are then illustrated. The potential of in-sensor computing for applications in sensing systems is also discussed. Finally, some essential needs for commercial translation are highlighted and future opportunities for flexible biosensors are considered.

High-Valence Metal-Organic Framework Materials Constructed from Metal-Oxo Clusters: Opportunities and Challenges

Metal-organic framework (MOF), which possesses stable framework structure constructed by highly connected metal-oxo cluster nodes and organic linkers, has shown great promise in gas storage, adsorption, and separation, owing to the high surface areas, tunable pore aperture, and rich functional groups. In this review article, we summarized recent progress made in synthesizing high-valence MOF (e. g., UiO-66, MIL-125, PCN-22, and MIP-207) with metal-oxo cluster as metal source. Of particular note, recent breakthroughs in the preparation of UiO-66 and MIL-125 membranes with the corresponding Zr₆ -oxo and Ti₈ -oxo cluster sources (e. g., Zr₆ O₄ (OH)₄ (OAc)₁₂ and Ti₈ O₈ (OOCR)₁₆ clusters) possessing superior separation performance were highlighted. In the end, an outlook on the preparation of versatile high-valence MOF membranes with the corresponding metal-oxo clusters as metal sources was highlighted.

Gradual Size Enlargement of Aluminum-Oxo Clusters and the Photochromic Properties

Metallic clusters, assembled by functional motifs, possess the attribute of regulating the properties by changing inorganic and organic components. In this work, a series of aluminum-oxo clusters, [Al₆O(dmp)₄(Hdmp)₂]·2ⁱPrOH [Al₆-1, H₃dmp = 2,2-bis(hydroxymethyl)propionic acid], [Al₆(H₂thmmg)₆]·2DMF·2H₂O [Al₆-2, H₅thmmg = N-tris(hydroxymethyl)methylglycine], [Al₈(OH)₄(NAP-OH)₁₂(MeO)₇(MeOH)]Cl·7MeCN·3MeOH (Al₈, HNAP-OH = 3-hydroxy-2-naphthoic acid), and [Al₁₀(NA)₁₀(MeO)₂₀] (Al₁₀, HNA = nicotinic acid), were obtained based on different carboxylic acids, realizing metallic ring size enlargement from 5.91 to 9.32 Å. They all exhibit good chemical stability. Importantly, the Al₈ cluster displays obvious photochromic behavior from pale yellow to orange yellow, originating from the generation of photoinduced radicals in the metal-assisted ligand-ligand electron transfer process of 3-hydroxy-2-naphthoic acid (HNAP-OH). This work enriches the metal ring cluster chemistry and reports the example of the aluminum-oxo cluster-based photochromic material, developing a novel system of photochromic materials.

Black Titanium-Oxo Clusters with Ultralow Band Gaps and Enhanced Nonlinear Optical Performance

A series of catecholate-functionalized titanium-oxo clusters (TOCs), PTC-271 to PTC-277, with atomically precise structures were synthesized and characterized, including distinctive "boat" and "chair" conformations in PTC-273 and PTC-274, respectively. These cluster compounds are prominent for their ultralow optical band gaps, as is visually evident from the rather unusual black TOCs (B-TOCs), PTC-272 to PTC-277. The cluster structures were found to be ultrastable with respect to air, water, organic solvents, and even acidic or basic aqueous solutions in a wide pH range (pH 0-13), owing to the stabilizing effects of catecholate and its derivatives, as well as the carboxylate ligands. Another prominent feature is the occurrence of third-order nonlinear optical (NLO) performance, which has previously been unreported in the field of homometallic titanium-oxo clusters. Open-aperture Z-scan experiments show significant solid-state optical limiting (OL) applications of these B-TOCs, with high laser irradiation stability and low minimum normalized transmittance (T_min) of PTC-273 as ∼0.17. Meanwhile, theoretical calculations indicate that the smaller band gaps of B-TOCs were beneficial for strengthening the NLO response. This work not only represents a significant milestone in the construction of stable low-band gap black titanium oxide materials but also contributes to the mechanism insights into their optical applications.

Inorganic acid influenced formation of Ti26 and Ti44 oxysulfate clusters with toroidal and capsule structures

We herein report the discovery of inorganic toroidal and capsule titanium oxysulfate clusters by ionothermal synthesis. The ratio between geometrically different anions (tetrahedral SO₄^2-vs. pseudo-tetrahedral PO₃^3-) shows an interesting influence on cluster structure formation.

Record Aluminum Molecular Rings for Optical Limiting and Nonlinear Optics

Crystalline cluster materials, a class of functional motif aggregations, provide a great opportunity for tuning the properties stemming from the flexible and accurate variation of inorganic and organic compositions. In this study, we demonstrate the effects of functional ligand and ring size regulation on the structures and third-order nonlinear optical (NLO) properties. Revealed by the single-crystal X-ray analysis results, aluminum molecular ring expansion is achieved by 2×9 and 3×6 strategies. In terms of the given organic shells, we further tuned the aluminum molecular ring sizes from 3.0 nm to 1.7 nm. The picosecond Z-scan measurements results revealed that the third-order NLO performances do not only depend on the general conjugate interactions but are also related to hydrogen bonding, polarizability, and ring sizes. The large nonlinear absorption coefficient and onset prove that the observed samples are promising candidates for the field of nonlinear optics.

Stepwise assembly and reversible structural transformation of ligated titanium coated bismuth-oxo cores: shell morphology engineering for enhanced chemical fixation of CO2

Herein, we report the stepwise assembly and reversible transformation of atomically precise ligated titanium coated bismuth-oxide core nanostructures. The soluble and stable Bi38O45@Ti6-oxo clusters with weakly coordinated surface salicylate ligands were first prepared as precursors. Owing to the high surface reactivity of the Bi38O45 inner core, its shell composition and morphology could be systemically modified by assembly with various Ti ions and auxiliary ligands (L), especially those with different flexibility, bridging ability and steric hindrance. As a result, a series of new core-shell Bi38O44/45@Ti x L-oxo (x = 14, 16, 18 or 20) clusters containing gradually increasing shell Ti atoms were successfully synthesized. Among them, the Bi38Ti20-oxo cluster is the largest one in the family of heterometallic Bi/Ti-oxo clusters to date. In addition, the sensitized titanium outer shell can effectively improve the photocurrent response under visible light irradiation. More remarkably, the obtained core-shell Bi38O44/45@Ti x L-oxo clusters can serve as stable and efficient catalysts for CO2 cycloaddition with epoxides under ambient conditions, whose activity was significantly influenced by the outer ligated titanium shell structure. This work provides a new insight into the construction of atomically precise heterometallic core-shell nanostructures and also an interesting shell engineering strategy for tuning their physicochemical properties.

Synthesis, Structure, and Light Absorption Behaviors of Prismatic Titanium-Oxo Clusters Containing Lacunary Lindqvist-like Species

Exploring new structural types of polyoxotitanium clusters (PTCs), especially those containing classical polyoxometalates structures, has always been the focus of research in the field of metal-oxo clusters. In this work, we present the synthesis and characterization of three prismatic PTCs: namely, Ti₈(μ₂-O)₃(μ₄-O)₂(OnPr)₆(HOnPr)₂(L1)₈ (PTC-237; H₂L1 = 3,5-di-tert-butylcatechol), Ti₁₂(μ₂-O)₆(μ₃-O)₈(OnPr)₆(L2)₁₂(L3)₂ (PTC-238; HL2 = 1-adamantanecarboxylic acid, HL3 = 2-picolinic acid), and [Ti₁₈(μ₂-O)₄(μ₃-O)₁₆(μ₅-O)₂(OiPr)₁₈(L3)₈](L3)₂ (PTC-239). Single-crystal X-ray diffraction analyses indicate that the construction of these prismatic PTCs is based on a stepwise interlayer assembly of {Ti₃} and {Ti₄} substructures. The diameters of their core skeletons are in the range between 0.9 and 1.3 nm. In particular, lacunary Linqvist-like {Ti₄} and {Ti₅} building units are found to exist in the structures of PTC-237 and PTC-239. According to the solid-state UV-vis diffuse reflectance measurements, the absorption band of 3,5-di-tert-butylcatecholate-functionalized PTC-237 shifts toward the visible-light region, giving a smaller optical band gap of 1.56 eV in comparison to PTC-238 (3.36 eV) and PTC-239 (3.25 eV).

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}.

Aluminum molecular rings bearing amino-polyalcohol for iodine capture

Amino-polyalcohol-solvothermal synthesis leads to the isolation of a broad range of aluminum molecular rings, which exhibit considerable affinity towards iodine molecules.

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.

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.

Synthesis, characteristic fragmentation patterns, and antibacterial activity of new azo compounds from the coupling reaction of diazobenzothiazole ions and acetaminophen

In this study, a series of azobenzothiazole dyes 4 were synthesized via diazotization of substituted benzothiazole derivatives followed by azo coupling with acetaminophen. The chemical structures of all synthesized compounds were confirmed using analytical data and spectroscopic techniques, including UV-visible, IR, mass spectra, and 1H- and 13C-NMR. The in situ formed diazobenzothiazole ions regiospecifically react with acetaminophen derivatives in the Hollemann-guided electrophilic aromatic substitution mechanism. The regio-orientations were established, on the one hand, by a rigorous interpretation of 1H-NMR spectra and, on the other hand, by the characteristic fragmentation patterns observed on the electrospray mass spectra. In the cases of 4a and 4b, multisubstitutions occurred. The antimicrobial activity of compound 4, along with all the starting materials, was investigated on Pseudomonas aeruginosa PA01, Staphylococcus aureus 18, Escherichia coli 64R, and S. aureus ATCC 25923. The results showed that this skeletal framework exhibited marked potency as antibacterial agents. The most active antibacterial agent against both targeted organisms was compound 4a′.

Macrocyclic Inorganic Tin-Containing Oxo Clusters: Heterometallic Strategy for Configuration and Catalytic Activity Modulation

In this work, the first examples of inorganic macrocyclic tin-oxo clusters which are stabilized by sulfate ligands are reported. As determined by X-ray diffraction and photoelectron spectroscopy analyses, the prepared inorganic Sn₁₀ -oxo cluster displays interesting mixed valence behaviors, with 8 Sn⁴⁺ located at the cyclic skeleton and two Sn²⁺ encapsulated in the center. When further introducing Ti⁴⁺ and In³⁺ ions to the synthetic systems, heterometallic Sn₂ Ti₆ and SnIn₅ Ti₆ complexes with Ti₆ (SO₄ )₉ and SnIn₅ (SO₄ )₁₂ macrocyclic skeletons were prepared whose configuration and packing models were affected by the ionic radius of incorporated metals. Moreover, comparative CO₂ reduction experiments confirm that such heterometallic composition can significantly improve the catalytic activities of these inorganic macrocyclic oxo clusters. This work represents a milestone in constructing inorganic tin complexes and also macrocyclic metal oxo clusters with tunable configurations and properties.

Ti-Oxo Clusters with Peripheral Alkyl Groups as Cathode Interlayers for Efficient Organic Solar Cells

Three independent Ti-oxo clusters (TOCs) that contain 6, 8, and 12 Ti atoms in the cores and alkyl groups on the surface were developed as cathode interlayers in bulk-heterojunction organic solar cells (OSCs). These TOCs have precise chemical structures with a single crystal, excellent solubility in methanol, and well-aligned work function. Smooth films can be facilely obtained by spin-casting their solution on top of the active layer. Therefore, they can be used as an interlayer in OSCs to provide a high power conversion efficiency (17.29%). Further studies reveal that these TOCs can not only reduce the work function of the silver electrode to provide better energy level alignment but also exhibit a significant n-doping effect with the non-fullerene acceptors to facilitate efficient electron extraction and transport. Our results demonstrate that TOCs as semiconductors have great potential application in OSCs.

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.

A novel series of giant cobalt-calixarene macrocycles: ring-expansion and modulation of pore apertures through recrystallization

The design and synthesis of metallomacrocycles can be quite challenging because the assemblies of such molecular cycles are difficult to control and the products are usually unpredictable. In this work, a novel series of metallomacrocycles, denoted as {Co30-A}, {Co30-B} and {Co32-A} have been synthesized via self-assembly of p-tert-butylthiacalix[4]arene (H4TC4A) and 3,5-pyrazoledicarboxylic acid (H3pdc) with Co2+ ions under solvothermal conditions. Recrystallization of {Co32-A} under different conditions was found to form {Co32-B} and {Co32-C} that have a similar ring structure to that of {Co32-A} but have different molecular packing modes in the lattices, as well as a 40-membered ring {Co40}. These complexes represent the highest-nuclearity metallocalixarene coordination wheels reported to date. Crystallographic studies indicate that all these metallomacrocycles feature wheel-like structures with apertures varing from 11.4 to 20.3 Å. It is noteworthy that {Co32-A} exhibited good efficiency in removing RhB even at low initial concentration (10 ppm) and also excellent adsorption selectivity towards RhB over Na2Fl (RhB = Rhodamine B, Na2Fl = disodium fluorescein). This work not only makes a breakthrough in the synthesis of metallocalixarene macrocycles with high nuclearity and large apertures, but also provides a simple recrystallization approach to realize the ring-expansion and regulation of molecular packing modes of the metallomacrocycles.

Accurate assembly of ferrocene-functionalized {Ti22Fc4} clusters with photocatalytic amine oxidation activity

We report here the synthesis of a ferrocene-functionalized {Ti22Fc4} cluster with a 'dimer-of-clusters' topology, which represents the largest Ti-oxo cluster (TOC) modified with organometallic groups ever reported. The exact assembly path of {Ti22Fc4} can be inferred from its two substructures, {Ti11Fc2} and {Ti5Fc}, which can also be synthesized independently through subtle changes in reaction conditions. Furthermore, we used these clusters as photocatalysts, and have studied, for the first time, the photocatalytic activity of TOCs in the oxidative coupling of amines.

Functional ligand directed assembly and electronic structure of Sn18-oxo wheel nanoclusters

The bilayer hexagonal Sn₁₈-oxo cluster, as the largest tin-oxo wheel, was constructed by a ligand templating method. Moreover, the ligands also show important effects on electronic structure and third-order nonlinear optical property of the wheel.

Rational assembly of metal-oxo clusters into molecular materials via a “wheel mounting” mode

Presented here is the self-assembly of metal-oxo clusters into molecular materials of different shapes and sizes via a “wheel mounting” mode, and molecular transformation was optical-driven.

Tartrate-stabilized titanium–oxo clusters containing sulfonate chromophore ligands: synthesis, crystal structures and photochemical properties

In tartrate-stabilized TOCs, aniline-sulfonate ligands can extend the absorption edge to the visible light region.

Monocarboxylate-driven structural growth in Calix[n]arene-polyoxotitanate hybrid systems: utility in hydrogen production from water

A carboxylate-driven assembly strategy has been developed for the first time to build calix[n]arene-based polyoxotitanate clusters with tuneable nuclearity and structures. Photocatalytic studies revealed that these clusters exhibit structural-dependent H₂ evolution ability with a maximum rate up to 415.11 μmol h^-1 g^-1, which is almost the highest recorded in polyoxotitanate clusters.

Use of a cyclo-P4 building block - a way to networks of host-guest assemblies

Despite the proven ability to form supramolecular assemblies via coordination to copper halides, organometallic building blocks based on four-membered cyclo-P4 ligands find only very rare application in supramolecular chemistry. To date, only three types of supramolecular aggregates were obtained based on the polyphosphorus end-deck complexes CpRTa(CO)2(η4-P4) (1a: CpR = Cp''; 1b: CpR = Cp'''), with none of them, however, possessing a guest-accessible void. To achieve this target, the use of silver salts of the weakly coordinating anion SbF6 - was investigated as to their self-assembly in the absence and in the presence of the template molecule P3Se4. The two-component self-assembly of the building block 1a and the coinage-metal salt AgSbF6 leads to the formation of 1D or 3D coordination polymers. However, when the template-driven self-assembly was attempted in the presence of an aliphatic dinitrile, the unprecedented barrel-like supramolecular host-guest assembly P3Se4@[{(Cp''Ta(CO)2(η4-P4))Ag}8]8+ of 2.49 nm in size was formed. Moreover, cyclo-P4-based supramolecules are connected in a 2D coordination network by dinitrile linkers. The obtained compounds were characterised by mass-spectrometry, 1H and 31P NMR spectroscopy and X-ray structure analysis.

Designable Aluminum Molecular Rings: Ring Expansion and Ligand Functionalization

Presented herein are the Al^III molecular ring architectures from 8-ring to 16-ring. Although there are numerous reported cyclic coordination compounds based on transition metals, gallium, or lanthanides, the Al versions are less developed due to the fast hydrolysis nature of Al³⁺ ion. With the assistant of monohydric alcohols, a series of atomic precisely Al molecular rings based on benzoates are synthesized. The ring expansion of these Al-rings from 8-ring to 16-ring is related to the monohydric alcohol structure-directing agents. Moreover, the organic ligands on the Al-rings can be modified by using various benzoate derivatives, which lead to tunable surface properties of the Al-rings from hydrophilicity to ultra-hydrophobicity. Importantly, 4-aminobenzoic acid bridged 16-ring is soluble in organic solvents and exhibits high solution stability revealed by mass spectroscopy. Ligand substitution also can be performed between these Al-rings, which reveal controllable ligand functionalization of these Al-rings.