Gas permeation in a molecular crystal and space expansion.
A novel single-crystal membrane [Cu(II)2(4-F-bza)4(2-mpyz)]n (4-F-bza = 4-fluorobenzoate; 2-mpyz = 2-methylpyrazine) was synthesized and its identical permeability in any crystal direction in the correction for tortuosity proved that gas diffuses inside the channels without detour. H2 permeated by 1.18 × 10(-12) mol m m(-2) s(-1) Pa(-1) with a high selectivity (Fα: 23.5 for H2/CO and 48.0 for H2/CH4) through its 2D-channels having a minimum diameter of 2.6 Å, which is narrower than the Lennard-Jones diameter of H2 (2.827 Å), CO (3.690 Å), and CH4 (3.758 Å). The high rate of permeation was well explained by a modified Knudsen diffusion model based on the space expansion effect, which agrees with the observed permselectivity enhanced for smaller gases in considering the expansion of a channel resulting from the collision of gas molecules or atoms onto the channel wall. An analysis of single-crystal X-ray data showed the expansion order to be H2 > Ar > CH4, which was expected from the permeation analysis. The permselectivity of a porous solid depends on the elasticity of the pores as well as on the diameter of the vacant channel and the size of the target gas.
Department of Nanosystem Science, Graduate School of Nanobioscience, Yokohama City University , 22-2 Seto, Kanazawa-ku, Yokohama, Kanagawa 236-0027, Japan.
Yuichi
Y
Takasaki
Satoshi
S
Takamizawa
D001565:Benzoates / Q000138:chemical synthesis / Q000737:chemistry*; D002248:Carbon Monoxide / Q000737:chemistry; D003300:Copper / Q000737:chemistry*; D018360:Crystallography, X-Ray; D004058:Diffusion; D005740:Gases / Q000737:chemistry*; D006859:Hydrogen / Q000737:chemistry; D008567:Membranes, Artificial; D008697:Methane / Q000737:chemistry; D008958:Models, Molecular; D010539:Permeability; D011719:Pyrazines / Q000138:chemical synthesis / Q000737:chemistry
D001565:Benzoates; D005740:Gases; D008567:Membranes, Artificial; D011719:Pyrazines; D003300:Copper; D002248:Carbon Monoxide; D006859:Hydrogen; D008697:Methane; C022893:4-fluorobenzoic acid