Planar-chiral macrocyclic host pillar[5]arene: no rotation of units and isolation of enantiomers by introducing bulky substituents

Enantiomers of bulky percyclohexylmethyl-substituted pillar[5]arene (Cy-C1-Pillar) were able to be separated by chiral column chromatography, and the separated enantiomers did not racemize. Even though modified with the bulky cyclohexylmethyl-substituents at both rims, Cy-C1-Pillar was able to capture a guest molecule.     

Planar-chiral pillar[5]arene: chiral switches induced by multiexternal stimulus of temperature, solvents, and addition of achiral guest molecule

We synthesized chiral-substituents modified pillar[5]arene for the first time. The chiral-substituents modified pillar[5]arene showed planar chirality and interconversion between (pS) and (pR) forms took place quickly. The planar chirality was switched by temperature, solvents, and addition of achiral guest. As the measurement temperature increased, the diastereomeric excess was decreased. The diastereomeric excesses were high in low-permittivity solvents, while a low diastereomeric excess was observed in high-permittivity solvents. Addition of achiral guest induced an increase of negative CD intensities.     

A quantum generalization of intrinsic reaction coordinate using path integral centroid coordinates

We propose a generalization of the intrinsic reaction coordinate (IRC) for quantum many-body systems described in terms of the mass-weighted ring polymer centroids in the imaginary-time path integral theory. This novel kind of reaction coordinate, which may be called the "centroid IRC," corresponds to the minimum free energy path connecting reactant and product states with a least amount of reversible work applied to the center of masses of the quantum nuclei, i.e., the centroids. We provide a numerical procedure to obtain the centroid IRC based on first principles by combining ab initio path integral simulation with the string method. This approach is applied to NH(3) molecule and N(2)H(5) (-) ion as well as their deuterated isotopomers to study the importance of nuclear quantum effects in the intramolecular and intermolecular proton transfer reactions. We find that, in the intramolecular proton transfer (inversion) of NH(3), the free energy barrier for the centroid variables decreases with an amount of about 20% compared to the classical one at the room temperature. In the intermolecular proton transfer of N(2)H(5) (-), the centroid IRC is largely deviated from the "classical" IRC, and the free energy barrier is reduced by the quantum effects even more drastically.     

A rectangular Ni-Fe cluster with unusual cyanide bridges

An asymmetric polycyanide iron complex, K(2)[Fe(III)(L1)(CN)(4)](MeOH) (HL1 = 2,2'-(1H-pyrazole-3,5-diyl)bis-pyridine), was synthesized and its complexation compatibility with nickel ions was examined. Two kinds of enantiomeric nickel-iron squares were obtained in the presence of a chiral bidentate capping ligand. The compounds display unusual cyanide bridge geometry and have ferromagnetic interactions between nickel and iron ions.     

Reversibly tunable lower critical solution temperature utilizing host-guest complexation of pillar[5]arene with triethylene oxide substituents

A thermoresponsive macromolecule consisting of 10 outer triethylene oxide groups and a pillar[5]arene core was prepared. The macromolecule showed lower critical solution temperature behavior. Moreover, its clouding point can be reversibly tuned based on the addition of guest and host compounds; the clouding point increased upon addition of a guest didecylviologen salt and decreased when the competitive host cucurbit[7]uril was added.     

Electrical conduction and thermoelectric properties of perovskite-type BaBi1−xSbxO3

To elucidate the thermoelectric properties at high temperatures, the electrical conductivity and Seebeck coefficient were measured at temperatures between 423 K and 973 K for perovskite-type ceramics of BaBi_1?xSb_xO₃ solid solutions with x=0.0–0.5. All the ceramics exhibit p-type semiconducting behaviors and electrical conduction is attributed to hopping of small polaronic holes localized on the pentavalent cations. Substitution of Bi with Sb causes the electrical conductivity σ and cell volume to decrease, but the Seebeck coefficient S to increase, suggesting that the Sb atoms are doped as Sb⁵⁺ and replace Bi⁵⁺, reducing 6s holes conduction from Bi⁵⁺(6s⁰) to Bi³⁺ (6s²). The thermoelectric power factor S ²σ has values of 6×10^?8–3×10^?5 W m^?1 K^?2 in the measured temperature range, and is maximized for an Sb-undoped BaBiO_3?δ, but decreases upon Sb doping due to the decreased σ values.     

An antiferromagnetic {Mn8} ring supported by planar multidentate ligands

Complexation of the planar multidentate ligand 3,5-bis-(2-hydroxyphenyl)pyrazole (H 3 L) with manganese chloride leads to the formation of the polynuclear complex [Mn Ⅲ 8 L 4 O 4 (MeO) 4 (MeOH) 8 ] (1). 1 has an octanuclear macrocyclic core in which the MnⅢ ions are bridged by four L molecules to form a ring type structure. Antiferromagnetic interactions were shown to be operative between metal centers.