Assembly of Two Flexible Metal–Organic Frameworks with Stepwise Gas Adsorption and Highly Selective CO2 Adsorption

[Co3(bpydc)2­(HCOO)2­H2O]­·2DMF (JLU-Liu3) and [Zn3(bpydc)2­(HCOO)2]­·H2O­·DMF (JLU-Liu4), two kinds of chiral flexible metal–organic frameworks, have been synthesized using 2,2′-bipyridyl-5,5′-dicarboxylate ligand (H2bpydc) and trinuclear clusters. The two materials reveal ant topology and exhibit uncommon stepwise N2 and CO2 adsorption behaviors with large hysteresis loops. The three-dimensional frameworks of JLU-Liu3 and JLU-Liu4 undergo structural transformation upon the removal of the guest molecules in the pores, which is indicated by the shift of powder X-ray diffraction peaks and the alteration of the peak intensity. These two flexible metal organic frameworks can be switched between the unique “closed” and “opened” forms via the removal of guest molecules. Moreover, after activation, both samples show high selective CO2 uptake over N2 and CH4.