Two Isoreticular 2D Zn(II) Coordination Polymers (CPs) Based on a Flexible Tripodal Thioether-Based Pyridyl Ligand and Two V-Shaped Dicarboxylate Ligands: Structural Characterization, CO2 Uptakes, and Water Ad-/Desorption Isotherms

Two Zn-based mixed-ligand coordination polymers (CPs) constructed by a tripodal thioether-based pyridyl ligand, 1,3,5-tris(4-pyridylsulfanylmethyl)-2,4,6-trimethylbenzene (L¹), and two V-shaped 5-R-1,3-isophthalate ligands, {[Zn(L¹)(5-nipa)]·C₂H₅OH·H₂O}_∞ (1) and {[Zn(L¹)(5-bipa)]·2C₂H₅OH·H₂O}_∞ (2) (5-nipa^2– = dianion of 5-nitroisophthalic acid, and 5-bipa^2– = dianion of 5-bromoisophthalic acid), have been synthesized and structurally characterized. CPs 1 and 2 are isoreticular, in which L¹ acts as a bridging ligand with a bis-monodentate coordination mode in a cis–cis–cis structural configuration, connecting the Zn(II) ions to form a 1D helical chain. Two helical chains are entwined together to generate a 1D double-helical chain, and neighboring double-helical chains are interlinked via the connectivity between Zn(II) ions and 5-nipa^2– in 1 and 5-bipa^2– in 2 with bis-monodentate coordination modes and arranged orderly in an ABAB··· manner to create 2D layered-like CPs. Adjacent 2D layers are then assembled in an ABAB··· fashion to fulfill their 3D supramolecular networks. Compounds 1 and 2 displayed reversible solvent (H₂O, MeOH, and EtOH) de-/adsroption behaviors by cyclic de-/resolvation TG analyses. Significant CO₂ sorption occurs at 195 K for pretreated 1′ and 2′, indicating that structural transformation happens to accumulate the adsorbed CO₂ molecules. Water vapor adsorption/desorption isotherms for pretreated 1′ and 2′ show maximum values of 59.54 cm³ g^–1 at a relative pressure P/P₀ of 1.02 for 1′ and 91.37 cm³ g^–1 at a relative pressure P/P₀ of 1.01 for 2′, corresponding to adsorption of approximately two and three water molecules per asymmetric unit (ASU).