Ancillary ligand-mediated syntheses and fluorescence properties of zinc(ii) complexes based on flexible benzene dicarboxylic acid

Abstract

This work presents a well-defined synthetic system exemplifying the effect of N-donor ancillary ligands on the formation of complex architectures in a zinc(II)-H₂hmph-H₂O system by the mild hydrothermal route (H₂hmph = homophthalic acid). The single-crystal X-ray diffractions reveal that structure variation of isolated three complexes spans the range of dimensionalities from 2D lamella [Zn(hmph)(bpe)]_n (1), 2D thick-layer [Zn(hmph)(bpp)]_n (2) to 3D microporous framework {[Zn₂(hmph)(trz)₂]·H₂O}_n (3), showing the marked sensitivity of the structures to the flexibility of varied N-donor ancillary ligands (bpe = 1,2-di(4-pyridyl)ethylene, bpp = 1,3-di(4-pyridyl)propane, and Htrz = 1,2,4-triazole). The structures of three complexes can be considered as the assembly of various chain-like structure motifs. The 2D lamella structure of 1 features hmph-bridged binuclear zinc(II) chains joined by less flexible trans-bpe ligands, whereas the 2D thick-layer of 2 manifests hmph-bridged mononuclear zinc(II) chains cross-linked further by flexible bpp legands along two different directions. The alternate opposite chiral helixes, featuring rigid trz-bridged mononuclear zinc(II), and additional binuclear zinc(II) units are cohered together by hmph linkers yielding a 3D microporous coordination network of 3 with new framework topology. It is shown that the structures, packing densities, and thermal stabilities of all these complexes are markedly sensitive to the molecule size, conformation, and flexibility of varied N-donor ancillary ligands. Furthermore, fluorescence properties of complexes 1–3 are also investigated.