Adsorption-desorption experiments were carried out to investigate the porous properties of 4a and 4b. As shown in Fig. , 4a and 4b showed adsorption behavior for CO2. These results show the porous properties of 4a and 4b. The BET surface and Langmuir surface area of 4a calculated from CO2 adsorption are 581 and 576 m 2 •g -1 , respectively, are slightly larger than those of 4b (386 and 446 m 2 •g -1 ).