Structural susceptibility of gas inclusion crystal to external gas pressure and temperature: force guide role of channel.

In order to investigate the methane-included condition in porous materials and its response to external stimuli, the methane adsorption state of a single-crystal adsorbent, [Cu(ii)(2)(bza)(4)(pyz)](n), was studied by single-crystal X-ray analysis and adsorption measurement as functions of temperature (90-298 K) and pressure (3.2-42 MPa). The included methane molecule was encapsulated into the channel of the adsorbent and stabilized through the interactions between the surrounding aromatic rings. The single-crystal host readily adsorbed methane gas and easily achieved the saturated condition with the included amount of 2 methane molecules per Cu(2) unit. The results from the gas adsorption measurements were consistent with the results from the crystallographic structures. Single-crystal X-ray analysis showed that the methane-saturated crystal has a critical temperature of the crystal phase transition from the C2/c to the P1 space group between 150 and 200 K. In temperature swinging, the thermal factors of the atoms of the guest methane and host skeleton monotonically decreased as the temperature decreased. In contrast, in pressure swinging at 298 K, the thermal factors gradually decreased as the pressure increased, after passing 11 MPa only the thermal factor of the guest methane decreased in response to an increase in gas pressure while those of the host skeleton remained almost constant. It is suggested that the channel acts as "force guide," propagating the outside gas pressure into the crystal inside through a guest-guest interaction in the included gas array. In addition, the difference in the pressure dependencies of the thermal factors on the host and guest suggested that the structural susceptibility to external gas pressure and temperature is different between open porous solids and non-porous solids.

Structural and magnetic study of O2 molecules arranged along a channel in a flexible single-crystal host family.

We report the magnetic behaviors of O(2) molecules, which aligned in the channels of four types of single-crystal adsorbents, [M(2)(bza)(4)(pyz)](n) (bza = benzoate; pyz = pyrazine; M = Rh(II) (1a) and Cu(II) (1b)) and [M(2)(bza)(4)(2-mpyz)](n) (2-mpyz = 2-methylpyrazine; M = Rh(II) (2a) and Cu(II) (2b)). The X-ray single-crystal structures at various temperatures from 10 to 298 K were determined for O(2)-included crystals of 1a and 2a. All adsorbed O(2) molecules exhibited abnormal magnetic phases above 4 T in the temperature range around 55-105 K. The magnetic behaviors of adsorbed O(2) molecules between four inclusions were discussed. The existence of the metastable state, which was also suggested by hysteresis on the M-H curves, was revealed by analysis of the time course of the magnetization. Considering that the abnormal magnetic behavior occurred at relatively high temperatures and a low magnetic field, it was suggested that these behaviors were induced because of the changes of magnetic interaction of included O(2) aggregates involving transformation which is supported by the surrounding of the channels of the single-crystal hosts under the applied magnetic field.

Generation of a plastic crystal including methane rotator within metal-organic cavity by forcible gas adsorption.

The structural determination of saturated adsorbed methane inside a metal-organic cavity by the forcible pressure swing adsorption method (ca. 13 MPa) through a gas-adsorption equilibrium state gives a methane inclusion crystal even at 298 K. The adsorbed methane molecules regularly locate in the pocket-like narrow corners of the necks of the 1-D channel without disorder. The thermal motion of the pseudo-spherical methane molecules seems to be effectively suppressed in its translation mode but allowed rotation. In cooling to 90 K, the crystal structure remained essentially unchanged while the thermal motion decreased, indicating that a lower temperature reduces the rotation of the adsorbed pseudo-spherical methane. The observed crystal structure could also be influenced by a reduction of the vibrational magnitude, and a phase transition from a static disordered structure to an ordered state might occur. The observed crystal state at a higher temperature should have a plastic crystal nature in terms of the randomness of the orientation of incorporated guests. The single-crystal adsorbent is effective for crystallographic observation of the thermal activated guest forced into regular alignment in the crystal lattice, which can be used as a model of the supercritical fluid.

Selective generation of organic aggregates included within metal-organic micropores through vapor adsorption.

The ethanol vapor adsorption behavior and the inclusion crystal structure of a 1D-transformable coordination polymer host were characterized. The adsorption jump was observed during phase transition or two-phase equilibrium with abnormal adsorption enthalpy caused by the nature of "mass induced phase transition." The included ethanol guests selectively form O-H...O hydrogen bonded pairs inside channels, suggesting selective construction of a specific cluster/aggregate in pores under control of thermodynamic factors and cooperative intermolecular interactions among the guest and channel surface.