Homochiral coordination architectures based on a series of pyridyl-alanine derivatives with varied configurations: Structural diversity, photoluminescence and magnetic properties

Abstract

Six homochiral coordination polymers based on a series of designed pyridyl-alanine derivatives ligands (x,y-H2PDBAla, x, y ​= ​2, 6; 2, 5; 3, 5) and different divalent cations in the absence/presence of ancillary ligands, including [Zn (2,6-PDBAla)]∙3H2O (1), [Cd (2,6-PDBAla)] (2), [Cd (2,5-PDBAla) (H2O)3]·2H2O (3), [Cu3(2,5-PDBAla)2 (bipy)2(H2O)2]·10H2O (4), [Co(3,5-PDBAla) (bpea) (H2O)] (5), [Ni(3,5-PDBAla) (bpee) (H2O)2]·5H2O (6) (H2PDBAla ​= ​pyridine-dicarbonyl-bis(l-alanine), bipy ​= ​4,4′-bipyridine, bpea ​= ​1,2-bis(4-pyridyl)ethane, bpee ​= ​1,2-bis(4-pyridyl)ethylene), were prepared and characterized. Three kinds of pyridyl-alanine derivatives ligands with versatile coordination modes bridge metal ions to generate the diverse structures. In the absence of ancillary ligand, the 2,6-H2PDBAla ligands and Zn(II)/Cd(II) ions react to get the compounds 1 and 2.1 exhibits a one-dimensional (1D) “loop” chain structure with the 14-membered rings, whereas a 3D framework with the qtz topology was observed in 2, in which the right-handed single-stranded and the left-handed double-stranded helical chains coexist. The 2,5-H2PDBAla ligands coordinate with Cd(II)/Cu(II) ions to yield the compounds 3 and 4.3 shows 1D right-handed single-stranded helical chain, and 4 shows a 2D layer constructed from right-handed single-stranded helical chain. The integration of 3,5-H2PDBAla ligands and Co(II)/Ni(II) ions leads to the compounds 5 and 6.5 displays a 2D wavy layer, consisting of the [Co(3,5-PDBAla)] right-handed single-stranded helical chain and the [Co(bpea)]2+ zigzag chain, and 6 displays a 2D layer with sql topology. The photoluminescence spectra of 1, 2 and 3 reveal the corresponding emissions of organic ligands, their maximum emission peaks appear at 402, 401 and 433 ​nm, respectively. Magnetic susceptibility mensuration of 5 gives the J of −12.35 ​cm−1, indicating strong antiferromagnetic interactions between the Co(II) ions.