Homochiral Helical Coordination Architectures Built from Biphenyl-Based Amino Acid Derivatives: Structural Diversity Tuned by Varying Conformation and Configuration of N-Donor Ligands, Sensing of Acidic Amino Acids, and Photoluminescence Properties

Self-assembly of divalent metal ions and designed amino acid derivatives, 4,4′-biphenyl-bis[carbonyl-N-(alanine)] (H2BPBAla) and 4,4′-biphenyl-bis[carbonyl-N-(proline)] (H2BPBPro), as well as ancillary ligands, 1,2-bis(4-pyridyl)ethane (bpea) and N,N′-bis(4-pyridyl)isophthalamide (bpipa), generated seven homochiral coordination polymers [Cu2(BPBAla)2(bpea)(H2O)]·H2O (1), [Co(BPBAla)(bpea)(H2O)2]·2H2O (2), [Ni(BPBAla)(bpea)(H2O)2]·2H2O (3), [Cd(BPBAla)] (4), [Cu(BPBPro)(bpea)(H2O)]·H2O (5), [Cd(BPBPro)(bpipa)(H2O)]·3H2O (6), [Zn(BPBPro)(bpipa)(H2O)]·3H2O (7). All compounds contain different chiral metal-amino acid derivative helixes, which are tuned by varied conformation and configuration of N-donor ligands. 1 exhibits left-handed, double-stranded Cu-BPBAla helical chains tuned by the trans-conformation bpea ligand, whereas isostructural 2 and 3 exhibit right-handed, single-stranded Co/Ni-BPBAla helical chains tuned by the gauche-conformation bpea ligand. In the absence of an ancillary ligand, 4 displays a two-dimensional (2D) Cd-BPBAla layered network made up of left-handed, single-stranded (-Cd-O-)n helical chains and right-handed, double-stranded Cd-BPBPro-fragment helical chains. When H2BPBPro replaces H2BPBAla, 5 becomes a three-dimensional (3D) framework composed of right-handed, single-stranded Cu-BPBPro helical chains and trans-conformation bpea ligand. 6 and 7 are isostructural 3D frameworks and constructed by the coalition of left-handed, single-stranded Cd/Zn-BPBPro and Cd/Zn-bpipa helical chains, and there is an angle of 92.28° between the two Cd/Zn-BPBPro helical chains. The photoluminescence spectra of 4, 6, and 7 reveal the corresponding emission of ligands. More significantly, 6 and 7 can effectively detect the natural acidic amino acids by the enhancement of UV absorption intensity.