Discrepant gas adsorption in isostructural heterometallic coordination polymers: strong dependence of metal identity

Abstract

Two isostructural porous 3d–4d materials [M(cyclam)Pd(2,4-pydc)₂·4H₂O]_n (2,4-H₂pydc = pyridine-2,4-dicarboxylate acid) (1, M = Ni and 2, M = Zn) and five other isostructural complexes {[M′(cyclam)]₂[M(2,5-pydc)₃]·xH₂O}_n (2,5-H₂pydc = pyridine-2,5-dicarboxylate acid) (3, M = Co, M′ = Ni; 4, M = M′ = Ni; 5, M = Zn, M′ = Ni; 6, M = Ni, M′ = Zn and 7, M = M′ = Zn) were synthesized. Both complexes 1′ and 2′ show high selective CO₂ capture over CH₄ and N₂. The comparisons of different gas sorption properties between 1′ and 2′ strongly suggest that metal identity has a great influence on the polarity of frameworks, but just the polar molecules respond to the polarity changes of different frameworks. The comparisons of CO₂ sorption properties between five other isostructural complexes 3′–7′ also strongly suggest that metal identity has great influence on polarity of frameworks and further the CO₂ uptake.