Enantioselective Assembly Structures of Copper(II) and Zinc(II) Complexes with the 1:1 Condensation Products of Imidazole-4-carbaldehyde Derivatives and Dl-Phenylalanine

Abstract

Abstract Copper(II) complexes with tridentate ligands H2LR (R = H, 2-Me, and 5-Me) derived from 1:1 condensation products of Dl-phenylalanine and imidazole-4-carbaldehyde derivatives (imidazole-4-carbaldehyde, 2-methylimidazole-4-carbaldehyde, and 5-methylimidazole-4-carbaldehyde), [CuClHLH] (1), [CuClHL2-Me] (2), [CuClHL5-Me]·MeOH (3), [CuBrHLH] (4a and 4b), and [CuBrHL2-Me] (5), were prepared. Two types of crystals in the reaction vessel, 4a and 4b, were obtained in the reaction between CuBr2 and H2LH. Their assembled structures were determined by single-crystal analysis. Except for 4b, the complexes assumed a homochiral chain structure constructed by intrachain imidazole–carboxylato hydrogen bonds between the adjacent two molecules, and the adjacent chains are linked by interchain Cu–X (X = Cl or Br) interactions. 3 exhibited a shorter interchain Cu–X distance and crystallized in the acentrosymmetric space group C2221 representing a spontaneous resolution (conglomerate), while 1, 2, 4a, and 5 gave a stacking of the adjacent chains with opposite chiralities to give racemic crystals. 4b assumed a homochiral chain structure constructed by a coordination bond between a copper(II) ion and an oxygen atom of the carboxyl group of the adjacent complex. A zinc(II) complex, [ZnClHLH] (6), showed a similar racemic crystal to that of 4b.