Synthesis, supramolecular assemblies and luminescence of nickel(II) complexes based on a series of N-(2-pyridylmethyl) amino acid derivatives

N-(2-Pyridylmethyl)-l-alanine (l-Hpana), and N-(2-pyridylmethyl)-aspartic acid (l-H2pasp) have been solvothermally prepared and structurally characterized by X-ray single-crystal diffraction. Complexes 1 and 2 crystallize in the monoclinic P21/c and orthorhombic C2221 space groups, respectively, due to the dissimilar ligand features (chirality of l-Hpana). They show similar mononuclear coordination structures with two kinds of five-member chelating rings, which are assembled into 2D supramolecular networks through multiple N–H⋯O and O–H⋯O interactions. For complex 3, the formation of a Ni–O bond between Ni(II) and the side-chain carboxylate lead to a left-handed helical coordination polymer with helical water chains inclusion. The most striking feature is that the helical hydrogen-bonding motif represents rare hydrated hydronium aggregation that formed by strong interactions between hydronium ions and guest water molecules. This helical aggregate is further stabilized by multiple hydrogen bonds with other lattice water molecules and chloride counteranions. The thermal and luminescent properties of these complexes have also been investigated.