The combination of a properly designed organic linker, 3,6-N-ditriazolyl-2,5-dihydroxy-1,4-benzoquinone(trz2An), with CoII ions results in a novel 3D ultramicroporous MOF with high CO2 uptake capacity and separation efficiency, with particular attention to CO2/N2 and CO2/CH4 gas mixtures. This material consists of 1D chains of octahedrally coordinated CoII ions linked through anilato ligands at the equatorial positions and triazole substituents from two neighbouring chains at the two axial positions. This leads to a 3D microporous structure with voids with an affinity for CO2 molecules and channels that enable the selective entry of CO2 but not of molecules with larger kinetic diameters such as N2 or CH4. Adsorption studies revealed that (i) the MOF presents a remarkable carbon dioxide uptake, above 20% in weight; (ii) CO2 adsorptive separation is successfully performed in CO2:N2 and CO2:CH4 gas mixtures, exhibiting high selectivity in a large operation range; (iii) regeneration is easily achieved under mild conditions.