Cucurbituril (CB[6]) is a hexameric macropolycyclic compound self-assembled from an acid-catalyzed condensation reaction of glycoluril and formaldehyde. 1,2 Its easy synthesis and rigid structure with a hollow core make CB[6] one of the attractive synthetic receptors. Its inclusion properties have been investigated extensively by Mock and co-workers. 3 Enzyme-like behavior of CB[6] effecting a large rate acceleration in a cycloaddition reaction has also been observed. 4 Its ability to bind alkali metal ions at the portals of the cavity allowed us to study molecular container systems capable of reversible encapsulation and release of guest molecules. 5 We also have demonstrated that CB [6] can be used as a molecular "bead" in self-assembly of interlocked structures such as polyrotaxanes and molecular necklaces. 6 CB- [6] is also known to be effective for removal of dyes from waste waters. 7 Although several homologues are available in calixarenes, which are obtained from a base-catalyzed condensation of phenol and formaldehyde, cucurbituril homologues with greater or fewer glycoluril units have not been reported. 8 Here we report the new family of cucurbituril, cucurbit[n]uril (CB[n]) (n ) 5, 7, and 8) containing five, seven, and eight glycoluril units, respectively.Reaction of glycoluril with formaldehyde in 9 M sulfuric acid at ∼75°C for 24 h and then at ∼100°C for 12 h yielded a mixture of CB[n] (n ) 5-11) as evidenced by electrospray ionization mass spectrometry. 9 Although its contents vary from batch to batch, the mixture typically contains ∼60% of CB[6], ∼10% of CB [5], ∼20% of CB [7], and ∼10% of other higher CB homologues. Apparently, the reaction of glycoluril and formaldehyde first generates linear oligomeric products which then cyclize to produce a library of cucurbituril. The cyclization at the lower temperature compared to that employed in the conventional synthesis 2 of CB[6] allows formation of significant amounts of other CB homologues besides CB [6]. The major product CB [6] was separated from the mixture by fractional dissolution of other CB homologues with acetone/water. From the acetone/water soluble portion, CB[5] and CB[7] were isolated by fractional crystallization/precipitation. 9 The homologue CB[8] was isolated from a CB[n] mixture that had been prepared by a modified procedure. Reaction of glycoluril and formaldehyde in the presence of HCl in a high-pressure reactor at 115°C for 24 h produced a white powder which, when treated with dilute sulfuric acid in a way similar to the one described above, yielded a mixture of CB[n] having a similar composition with slightly higher CB[7] and CB[8] contents. Upon standing, crystals of CB[8] were produced from a solution of the CB[n] mixture in 6 M sulfuric acid. 9 The new CB homologues CB[5], CB[7], and CB [8] have been characterized by various spectroscopic methods and X-ray crystallography. In the 1 H NMR spectra, CB homologues show the same peak pattern as that of CB[6], but their chemical shift values are slightly and yet distinctivel...

Thermoelectric energy harvesting-the transformation of waste heat into useful electricity-is of great interest for energy sustainability. The main obstacle is the low thermoelectric efficiency of materials for converting heat to electricity, quantified by the thermoelectric figure of merit, ZT. The best available n-type materials for use in mid-temperature (500-900 K) thermoelectric generators have a relatively low ZT of 1 or less, and so there is much interest in finding avenues for increasing this figure of merit. Here we report a binary crystalline n-type material, In(4)Se(3-delta), which achieves the ZT value of 1.48 at 705 K-very high for a bulk material. Using high-resolution transmission electron microscopy, electron diffraction, and first-principles calculations, we demonstrate that this material supports a charge density wave instability which is responsible for the large anisotropy observed in the electric and thermal transport. The high ZT value is the result of the high Seebeck coefficient and the low thermal conductivity in the plane of the charge density wave. Our results suggest a new direction in the search for high-performance thermoelectric materials, exploiting intrinsic nanostructural bulk properties induced by charge density waves.

Two different molecules are selectively included in cucurbit[8]uril to form a stable 1:1:1 ternary complex, which has been characterized by X‐ray crystallography (see picture). The inclusion of a hetero‐guest pair (a pyridinium derivative (blue) and 2,6‐dihydroxynaphthalene (magenta)) in the molecular host is driven and stabilized by a charge‐transfer interaction between the electron‐rich and electron‐deficient guests.

A one-step oxidative fluorination for carbon–fluorine bond formation from well-defined nickel complexes with oxidant and aqueous fluoride is presented, which enables a straightforward and practical 18F late-stage fluorination of complex small molecules with potential for PET imaging.

A palladium compound facilitates rapid incorporation of radioactive fluoride into prospective tracers for medical imaging.

Separation of acetylene from carbon dioxide and ethylene is challenging in view of their similar sizes and physical properties. Metal-organic frameworks (MOFs) in general are strong candidates for these separations owing to the presence of functional pore surfaces that can selectively capture a specific target molecule. Here, we report a novel 3D microporous cationic framework named JCM-1. This structure possesses imidazolium functional groups on the pore surfaces and pyrazolate as a metal binding group, which is well known to form strong metal-to-ligand bonds. The selective sorption of acetylene over carbon dioxide and ethylene in JCM-1 was successfully demonstrated by equilibrium gas adsorption analysis as well as dynamic breakthrough measurement. Furthermore, its excellent hydrolytic stability makes the separation processes highly recyclable without a substantial loss in acetylene uptake capacity.

The porphyrin boxes (PB-1 and PB-2), which are rationally designed porous organic cages with a large cavity using well-defined and rigid 3-connected triangular and 4-connected square shaped building units are reported. PB-1 has a cavity as large as 1.95 nm in diameter and shows high chemical stability in a broad pH range (4.8 to 13) in aqueous media. The crystalline nature as well as cavity structure of the shape-persistent organic cage crystals were intact even after complete removal of guest molecules, leading to one of the highest surface areas (1370 m(2) g(-1)) among the known porous organic molecular solids. The size of the cavities and windows of the porous organic cages can be modulated using different sized building units while maintaining the topology of the cages, as illustrated with PB-2. Interestingly, PB-2 crystals showed unusual N2 sorption isotherms as well as high selectivity for CO2 over N2 and CH4 (201 and 47.9, respectively at 273 K at 1 bar).

A new approach to the synthesis of hierarchical micro- and mesoporous MOFs from microporous MOFs involves a simple hydrolytic post-synthetic procedure. As a proof of concept, a new microporous MOF, POST-66(Y), was synthesized and its transformation into a hierarchical micro- and mesoporous MOF by water treatment was studied. This method produced mesopores in the range of 3 to 20 nm in the MOF while maintaining the original microporous structure, at least in part. The degree of micro- and mesoporosity can be controlled by adjusting the time and temperature of hydrolysis. The resulting hierarchical porous MOF, POST-66(Y)-wt, can be utilized to encapsulate nanometer-sized guests such as proteins, and the enhanced stability and recyclability of an encapsulated enzyme is demonstrated.