The vapor absorbency of the series of alcohols methanol, ethanol, 1-propanol, 1-butanol, and 1-pentanol was characterized on the single-crystal adsorbents [M(II)2(bza)4(pyz)]n (bza = benzoate, pyz = pyrazine, M = Rh (1), Cu (2)). The crystal structures of all the alcohol inclusions were determined by single-crystal X-ray crystallography at 90 K. The crystal-phase transition induced by guest adsorption occurred in the inclusion crystals except for 1-propanol. A hydrogen-bonded dimer of adsorbed alcohol was found in the methanol- and ethanol-inclusion crystals, which is similar to a previous observation in 2 x 2EtOH (S. Takamizawa, T. Saito, T. Akatsuka, E. Nakata, Inorg. Chem. 2005, 44, 1421-1424). In contrast, an isolated monomer was present in the channel for 1-propanol, 1-butanol, and 1-pentanol inclusions. All adsorbed alcohols were stabilized by hydrophilic and/or hydrophobic interactions between host and guest. From the combined results of microscopic determination (crystal structure) and macroscopic observation (gas-adsorption property), the observed transition induced by gas adsorption is explained by stepwise inclusion into the individual cavities, which is called the "step-loading effect." Alcohol/water separation was attempted by a pervaporation technique with microcrystals of 2 dispersed in a poly(dimethylsiloxane) membrane. In the alcohol/water separation, the membrane showed effective separation ability and gave separation factors (alcohol/water) of 5.6 and 4.7 for methanol and ethanol at room temperature, respectively.

A single crystal adsorbent, [Rh(II)(2)(bza)(4)(2,3-empyz)](n) (2,3-empyz = 2-ethyl-3-methylpyrazine) (1), was synthesized by self-assembly reaction of a Rh(2) benzoate complex and substituted pyrazine linker. The compound consists of one-dimensional zigzag chains, which generated a closed-pore structure without channels. The cavities were statistically generated by the static disorder of substituents on pyrazine and are separated by long intervals within the crystal. The property of CO(2) absorption was characterized in this closed-pore system. The CO(2) inclusion structure was determined by single-crystal X-ray diffraction measurements. These studies suggest that CO(2) molecules were adsorbed and diffused in the nonporous crystal with the isolated cavities.

The crystalline one-dimensional compound, [Rh(II)2(bza)4(pyz)]n (1) (bza = benzoate, pyz = pyrazine) demonstrates gas adsorbency for N2, NO, NO2, and SO2. These gas-inclusion crystal structures were characterized by single-crystal X-ray crystallography as 1 x 1.5 N2 (298 K), 1 x 2.5 N2 (90 K), and 1 x 1.95 NO (90 K) under forcible adsorption conditions and 1 x 2 NO2 (90 K) and 1 x 3 SO2 (90 K) under ambient pressure. Crystal-phase transition to the P1 space group that correlates with gas adsorption was observed under N2, NO, and SO2 conditions. The C2/c space group was observed under NO2 conditions without phase transition. All adsorbed gases were stabilized by the host lattice. In the N2, NO, and SO2 inclusion crystals at 90 K, short interatomic distances within van der Waals contacts were found among the neighboring guest molecules along the channel. The adsorbed NO molecules generated the trans-NO...NO associated dimer with short intermolecular contacts but without the conventional chemical bond. The magnetic susceptibility of the NO inclusion crystal indicated antiferromagnetic interaction between the NO molecules and paramagnetism arising from the NO monomer. The NO2 inclusion crystal structure revealed that the gas molecules were adsorbed in the crystal in dimeric form, N2O4.

To develop the application of the adsorption ability of our flexible single-crystal host [Cu(2)(bza)(4)(pyz)](n) (1) (bza = benzoate; pyz =pyrazine) possessing a 1D channel, we study the separation ability of a 1 packed column for various organic vapors and inorganic gases. A 1 packed column can detect various organic molecules with sharp signals although steric or nonpolar molecules give broad signals. Interestingly, 1 separates various organic mixtures even if the mixture contains nonpolar molecules. Comparing the separation properties with columns of other separation media, including zeolite, activated carbon, activated alumina, and silica gel, suggests that a 1 packed column separates various gaseous molecules under moderate conditions. Additionally, the eluted order of similar molecules, such as N(2)/O(2) and methanol/ethanol using the 1 packed column is different from the others (zeolite, activated carbon, activated alumina, and silica gel), which suggests a difference in the separation mechanism of 1. From GC measurements, the estimated changes in Gibbs free energy by gas adsorption, under diluted gas conditions, exhibits a large entropy dependence caused by regularity in the generated adsorption state, which enables the dynamic control of gas adsorption selectivity. Therefore, it is suggested that single-crystal host 1, because of its flexibility, can separate various gases by adjusting its channel structure according to the features of the guest gaseous molecules. This generates active controllability of the adsorption potential in addition to the intrinsic adsorption interaction.

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