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

Abstract

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.