Variable Water Adsorption in Amino Acid Derivative Based Homochiral Metal Organic Frameworks

Six new Cd-containing homochiral metal–organic framework materials [{Cd­(L1)­(Cl)}­(H₂O)]_∞ (1a), [Cd­(L1)­(Br)]_∞ (1b), [Cd­(L2)­(Cl)]­(H₂O)]_∞ (2a), [{Cd₂(L2)₂(Br)₂}­(H₂O)₃]_∞ (2b) [{Cd­(L3)­(Cl)}­(H₂O)₂]_∞ (3a), and [{Cd­(L3)­(Br)}­(H₂O)₂]_∞ (3b) [L1 = 2-((pyridin-4-yl)­methylamino)-4-methylpentanoic acid], [L2 = 2-(pyridin-4-yl)­methylamino)-3-hydroxypropanoic acid], and [L3 = 2-((pyridin-4-yl)­methylamino)-3-hydroxybutanoic acid] have been synthesized using pyridine functionalized amino acid (l-leucine, l-serine, and l-threonine) homochiral links and Cd­(CH₃COO)₂·2H₂O and characterized via single crystal X-ray diffraction (XRD), powder X-ray diffraction (PXRD), variable temperature powder X-ray diffraction (VTPXRD), thermogravimetric analysis and water adsorption experiments. Side chains in different amino acid derivatives and anions (Cl^–, Br^–) have been identified to play an important role in structural diversity (from porous to nonporous) as well as physical properties. These metal–organic frameworks (MOFs) exhibit a distinct water adsorption nature and capacity, e.g., high adsorption at low partial pressure based on architectural diversities.