Two novel metal-organic frameworks [Ni2(μ2-Cl)(BTBA)2·DMF]·Cl·3DMF (JLU-MOF56, BTBA = 3,5-bis(triazol-1-yl)benzoic acid) and [Co2(μ2-Cl)(BTBA)2·DMF]·Cl·3DMF (JLU-MOF57) have been successfully synthesized under solvothermal conditions. Crystallographic analysis indicates that the two compounds with different metal ions are isoreticular and both are constructed from binuclear [M2(μ2-Cl)(COO)2N4] (M = Co, Ni) and a 3-connected hetero-N,O donor ligand. The overall framework possesses a (3,6)-connected dag topology. Furthermore, both of them feature ultramicroporous channels of 3.5 Å× 3.4 Å, which are suitable for adsorbing smaller carbon dioxide (CO2) gas molecules but not larger nitrogen (N2) gas molecules. Therefore, JLU-MOF56 and JLU-MOF57 exhibit good performance for CO2/N2 separation, and are promising materials for gas adsorption and purification.