Three stable dinuclear [M2(OH)0.5(NO3)0.5(RCOO)2(RN)4] (M = Cu, Ni) based metal-organic frameworks with high CO2 adsorption and selective separation for O2/N2 and C3H8/CH4

Three highly porous MOFs with dinuclear [M-2(OH)(0.5)(NO3)(0.5)(RCOO)(2)(RN)(4)] SBUs (secondary building units), [Cu-4(L-1)(4)(OH)(NO3)]center dot 2(NO3)center dot 4DMF (compound Cu-L-1, HL1 = 5-imidazol-1-yl-nicotinic acid, DMF = N,N-dimethylformamide), [Ni-4(L-1)(4)(OH)(NO3)(3)(DMF)(2)]center dot 3DMF center dot 4H(2)O (compound Ni-L-1) and [Ni-4(L-2)(4)(OH)(NO3)(3)(DMF)(2)]center dot 3DMF (compound Ni-L-2, HL2 = 5-[1,2,4]triazol-1-yl-nicotinic acid), have been solvothermally constructed using a heterofunctional ligand motif with carboxylate and azolate groups. All three compounds show high thermal and chemical stability, not only in water but also in acidic and basic solutions (pH = 2-11). Due to the presence of accessible open metal sites (OMSs), compounds Cu-L-1, Ni-L-1, and Ni-L-2 exhibit significant ability to capture CO2 (114.8, 88.3 and 93.7 cm(3) g(-1), respectively, under 1 bar at 273 K). Interestingly, gas adsorption results show that all three compounds exhibit high selectivity toward O-2 over N-2 at 77 K and C3H8 over CH4 at 298 K, which indicates that the three materials have potential for gas separation applications.