Photoluminescence, magnetic and photocatalytic properties of three overlapping layered homochiral coordination polymers based on semi-rigid alanine ligands

Three homochiral coordination polymers based on semi-rigid alanine ligands and varied auxiliary N-donor ligands, [Cd(TMAla)(bpipa-4)]·2H₂O (1), [Co₂(TMAla)₂(bipy)₂]·2.5H₂O (2), [Co(TBAla)(bpee)(H₂O)₂]·3H₂O (3), (H₂TMAla = terephthaloyl-mono(L-alanine), H₂TBAla = terephthaloyl-bis(L-alanine), bpipa-4 = N,N′-bis(pyridin-4-yl)isophthalamide, bipy = 4,4′-bipyridine and bpee = 1,2-bis(4-pyridyl)ethylene), have been synthesized and structurally characterized. In these structures, the different metal ions are connected into two types of chains by the semi-rigid alanine ligands and various N-donor ligands in different direction, respectively, to generate diverse 2D layered coordination networks, which are further stacked into 3D supramolecular frameworks in an ABAB overlapping mode through interlayered hydrogen bonds. Complex 1 exhibits the 2D squamous sheet constructed by zigzag chains. Complex 2 shows a thick 2D layer motif formed through the looped and ladder-shaped chains. Complex 3 features a (4,4) grid 2D coordination network built via the zigzag and linear chains. Complex 1 displays a strong fluorescent emission at 402 nm in solid state at room temperature. Magnetic susceptibility measurement indicates weak antiferromagnetic interactions between the Co(II) ions in complex 2. Meanwhile, complex 2 shows good photocatalytic activity for the degradation of methylene blue (MB) and methyl orange (MO) dyes under UV light.