Synthesis, Structural Characterization, and Water Vapor Sorption Behavior of Two Ligand Ratio-Dependent Supramolecular Networks, [Cd(2,2′-bpym)_1.5(BDC)]·0.5(2,2′-bpym)·5H₂O and [Cd(2,2′-bpym)_0.5(BDC)(H₂O)₃]

Abstract

Two ligand ratio-dependent supramolecular networks, [Cd(2,2′-bpym) 1.5 (BDC)]·0.5(2,2′-bpym)·5H 2 O ( 1 ) and [Cd(2,2′-bpym) 0.5 (BDC)(H 2 O) 3 ] ( 2 ), (BDC 2– = dianion of terephthalic acid and 2,2′-bpym = 2,2′-bipyrimidine) have been synthesized and structurally characterized by the single-crystal X-ray diffraction method. Structural determination reveals that compound 1 is a two-dimensional (2D) layered metal–organic framework (MOF) constructed via the bridges of Cd(II) ions with 2,2′-bpym and BDC 2– ligands, and compound 2 is a zero-dimensional (0D) 2,2′-bpym-bridged di-Cd(II) monomeric complex. When the thermally dehydrated powders of 1 (at 100 °C) were immersed into water solution, most of the dehydrated powders of 1 underwent structural transformation back to rehydrated 1 , but very little amounts of the dehydrated powders of 1 were decomposed to light-brown crystals of 2 or colorless crystals of a new coordination polymer (CP), [Cd(2,2′-bpym)(BDC)(H 2 O)]·3H 2 O ( 3 ), with its one-dimensional (1D) zigzag chain-like framework being constructed via the bridges of Cd(II) ions with the BDC 2– ligand. Structural analysis reveals that all 3D supramolecular networks of 1–3 are further constructed via strong intermolecular interactions, including hydrogen bonds and π–π stacking interactions. Compounds 1 and 2 both exhibit significant water vapor hysteresis isotherms, and their cyclic water de-/adsorption behavior accompanied with solid-state structural transformation has been verified by de-/rehydration TG analyses and powder X-ray diffraction (PXRD) measurements.