Chiral Cd(II) Coordination Polymers Based on Amino Acid Derivatives: The Effect of Side Chain on Structure

Homochiral coordination polymers have emerged as promising candidates for a range of chirotechnological applications, including asymmetric catalysis and enantioselective separation. The use of ligands derived from naturally occurring L-amino acids is an inexpensive and effective approach for generating a range of homochiral coordination polymers. To investigate the structure-directing effect of the amino acid side chain, seven homochiral Cd(II) frameworks were synthesized using semirigid dicarboxylates composed of L-amino acids appended to terephthalic acid (H(2)TMXxx, where Xxx = Ala, Val, Phe, Trp, Tyr, and His) and bis(4-pyridyl)ethylene coligands. When Xxx = Val, Tyr, Phe, or Trp, a series of 2D (4,4)-networks were obtained, in which the different intermolecular interactions of the side chains result in subtle changes in crystal packing. Employing Xxx = Ala or Tyr led to 3D frameworks with a {6(5)center dot 8} topology, in which the varying steric bulk of the side chains results in significant differences in framework geometry as well as the shape and volume of the solvent-accessible channels. When Xxx = His, the imidazole side chains coordinate to the metal center to direct the formation of a 3D pillared structure that undergoes 2-fold interpenetration.