Gram quantities of titania (TiO 2) nanotubes, with a typical outside diameter about 9 nm, wall thickness of about 2.5 nm, and length of about 600 nm, were synthesized from anatase nanopowder and micropowder using the hydrothermal method. The crystallization, structure, and phase stability of the nanotubes at high temperatures were studied. A morphology change from nanotube to nanowire was observed at 650 • C. The as-prepared nanotubes were usually contaminated with sodium impurities and were poorly crystallized, but under optimized synthesis conditions the impurity phase was completely removed, resulting in highly crystallized nanotubes. The volume filling fraction of the autoclave as well as the concentration of the acid treatment were found to be particularly important for controlling the purity and crystallinity of the resulting nanotubes. The various TiO 2-derived nanotube phases (sodium titanate and hydrogen titanate) reported previously by different groups were also observed under different synthesis conditions, resolving the contradiction among the previous results.
The crystal method: Single‐crystal‐to‐single‐crystal (SCSC) transformations of two 3D coordination polymers, {[Zn4(μ3‐OH)2(5‐sipa)2(1,4‐bpeb)2]⋅4 H2O}n (see picture; C pale blue, N dark blue, H green) and an analogous cadmium species, gave rise to corresponding linked 3D coordination polymers through photochemical [2+2] cycloaddition reactions.
The investigation of heterometallic Mo(W)-M'-S clusters (M' = transition metals) has its genesis in the late 1970s with the identification of the nitrogenase iron-molybdenum cofactor (FeMoco) featuring a Mo-Fe-S double-cubane cluster core. This has led to the generation of a library of cluster skeletons subsequently used as building blocks for oligomers (OGs) and polymers, merging this field with the fascinating developments in supramolecular chemistry and coordination polymers (CPs). While resembling the general metal-ligand assembly to form CPs in one-pot, cluster-based OGs or CPs are conventionally prepared from Mo(W)-S synthons and Cu(i) salts in the presence of bridging ligands. This review summarizes the synthesis of Mo(W)-Cu-S cluster-supported OGs and CPs through a two-step strategy involving preformed clusters. This stepwise approach facilitates clean conversion, and is amenable to exquisite design protocols and yields products otherwise inaccessible via a direct one-pot method. We review the synthesis of OGs and CPs by cluster core upgrading, downgrading, ligand substitution, and cluster aggregation reactions, together with the optical and host-guest properties of the products. In doing so, we demonstrate the power and generality of this strategy for assembling these unique materials and offer clues on how to adapt this less practiced method to preparing extended molecular assemblies with potentially intriguing properties.
The observation of a reversible chemical transformation corresponding to an external stimulus in the solid state is intriguing in the exploration of smart materials, which can potentially be applied in molecular machines, molecular switches, sensors, and data storage devices. The solid-state photodimerization reaction of 1,3-bis[2-(4-pyridyl)ethenyl]benzene (1,3-bpeb) in a one-dimensional coordination polymer {[Cd(1,3-bpeb)(4-FBA)]·HO} (4-FBA = 4-fluorobenzoate) with 365 nm UV light afforded syn-tetrakis(4-pyridyl)-1,2,9,10-diethano[2.2]metacyclophane (syn-tpmcp) in quantitative yield via a single-crystal-to-single-crystal (SCSC) transformation. Upon irradiation with 254 nm UV light, an SCSC conversion from syn-tpmcp to 1,3-bpeb was also achieved in quantitative yield within the syn-tpmcp-supported coordination polymer {[Cd(syn-tpmcp)(4-FBA)]·HO}. In particular, accompanied by the reversible transformation between 1,3-bpeb and syn-tpmcp, the coordination chain exhibits photocontrollable fluorescence-switching behavior, which makes this intelligent material an appealing candidate for practical applications.
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