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

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.