Crystal structures, phase transition, and Hirshfeld surface analyses of the bromide and chloride congeners of aqua[2,4,6‐tris(pyridin‐4‐yl)‐1,3,5‐triazine]zinc(II) halide

During the course of exploring crystallization conditions in generating metal–organic frameworks (MOFs) for use in the crystalline sponge method, two discrete metal–organic complexes, namely, aqua[2,4,6‐tris(pyridin‐4‐yl)‐1,3,5‐triazine]zinc(II) bromide, [Zn(C18H12N6)(H2O)]Br2, and aqua[2,4,6‐tris(pyridin‐4‐yl)‐1,3,5‐triazine]zinc(II) chloride, [Zn(C18H12N6)(H2O)]Cl2, were encountered. Structures in the orthorhombic space group Pnma (No. 62) for the bromide congener at 299 K and the chloride congener at 100 K were obtained. A phase transition for the bromide congener occurred upon cooling from 299 to 100 K, yielding a crystal polymorph with four domains that exhibits monoclinic P21/m space‐group symmetry (No. 11), which arises from conformational changes. The main intramolecular contacts that contribute to the crystal packing in all observed structures are H…H, Halide…H/H…Halide, C…H/H…C, and N…H/H…N. Intramolecular hydrogen bonding between the Zn‐bound water and non‐Zn‐bound pyridyl N atoms is a prominent feature within the three‐dimensional networks. Aromatic π‐stacking between the non‐Zn‐bound pyridine rings and contacts involving the halide ligands further stabilize the crystal packing. The crystallization conditions leading to the production of the title metal–organic complexes aqua[2,4,6‐tris(pyridin‐4‐yl)‐1,3,5‐triazine]zinc(II) bromide and chloride, along with the structural characterization, temperature‐induced phase transition of the bromide congener, supramolecular analysis using Hirshfeld surfaces, and two‐dimensional fingerprint plots, are reported. In both structures, intermolecular hydrogen bonding involving the zinc‐bound water and pyridyl N atoms is a key interaction that underpins the three‐dimensional supramolecular network.