Homochiral Layered Coordination Polymers from Chiral N‑Carbamylglutamate and Achiral Flexible Bis(pyridine) Ligands: Syntheses, Crystal Structures, and Properties

Four new homochiral two-dimensional (2D) coordination polymers, namely, [Zn2L­(NCG)2­(H2O)2·4H2O]n (1), [Zn­(bpe)­(NCG)·3H2O]n (2), [Zn­(bpe)­(NCG)­(NaNO3)0.5H2O]n (3), and [Zn­(bpp)­(NCG)·3.5H2O]n (4) (NCG = N-carbamyl­glutamate, L = 1,2-bis­(4′-pyridyl­methyl­amino)­ethane, bpe = 1,2-bis­(4-pyridyl)­ethane, bpp = 1,3-bis­(4-pyridyl)­propane), have been prepared under mild conditions. The structures of CPs 1–4 were determined by single-crystal X-ray diffraction analysis. Complexes 1 and 2 display novel homochiral wavelike networks, with adjacent layers stacked in an AA type arrangement. Complex 3 shows an interesting 2D double-layered framework, which is further connected to form a 3D supermolecular structure through hydrogen bonding and aromatic π–π stacking interactions. The 2D structure of complex 4 contains two uncommon helical chains of bpp and NCG, with two flexures in each single strand. Different layers are stacked in an offset ABAB fashion. The mixed-ligand strategy, cooperation of a chiral and an achiral ligand, is applied to prepare the homochiral neutral layered CPs. Complexes 1–4 display second harmonic generation efficiencies, which are approximately 0.7, 0.9, 0.4, and 0.6 times as much as that of urea powder. In addition, the photoluminescence of all complexes has also been investigated in the solid state.