Structural Diversity of Cadmium(II) Coordination Polymers Induced by Tuning the Coordination Sites of Isomeric Ligands

When the coordination sites of ligands were shifted, the solvothermal reactions of four positional isomeric asymmetrical pyridyldicarboxylatic acids with Cd(NO3)(2) generated four new coordination polymers, [Cd(L1)-(DMF)(3)]DMF.H2O (1), [H2N(CH3)(2)](2)[Cd(L2)(2)].3DMF. H2O (2), [Cd(L3)(H2O)(2)] (3), and [Cd(L4)].1.5DMF (4), where DMF = N,N-dimethylformamide, H(2)L1 = 2-(3'-carboxylphenyl)isdnicotinic acid, H(2)L2 = 2-(4'-carboxylphenyl)isonicotinic acid, H(2)L3 = S-(3'-carboxylphenyOnicotic acid, and H(2)L4 = 2-(3'-pyridyl)terephthalic acid. 1 shows a rare 2D fabric structure. 2 discloses a grid-layer structure with heterochiral helical chains and in which three sets of layers stack in different directions, affording an unprecedented 2D + 2D + 2D -> 3D polycatenating framework with 3D intersecting porous systems. 3 also displays a 2D layer possessing strong intralayer pi...pi interactions and interlayer hydrogen bonds. 4 contains a rare Cd-2(COO)(4) paddle-wheel unit and forms a 3D framework with 1D open channels. The carboxyl and pyridyl groups of the positional isomeric H(2)L1 H(2)L4 ligands show distinct bridging fashions, which leads to the production of versatile architectures of 1-4, and their effects on the crystal structures are discussed. 1-4 reveal solid-state photoluminescence stemming from intraligand charge transfer. 2 and 4 show high selectivity for CO2 over CH4 but with different CO2 adsorption enthalpies. Grand canonical Monte Carlo simulations identified the multiple adsorption sites in 2 for CO2.