Exceptional sensitivity to the synthetic approach and halogen substituent for Zn(ii) coordination assemblies with 5-halonicotinic acids

Abstract

Seven Zn(II) coordination complexes with 5-halonicotinic acids (HL-X, X = F, Cl, or Br) have been synthesized with different synthetic approaches, including layer diffusion or stirring method in an ambient environment and solvothermal synthesis at 100 °C. Assembly of HL-F with Zn(II) under different conditions will yield the same 2D network of [Zn(L-F)₂]_n (1). Interestingly, three distinct complexes, a 3D framework {[Zn₂(L-Cl)₄(H₂O)](H₂O)₆}_n (2) and two 2D pseudo-polymorphic isomers {[Zn(L-Cl)₂](H₂O)_1.5}_n (3) and {[Zn₂(L-Cl)₄](H₂O)}_n (4) can be obtained by reacting HL-Cl with Zn(II) under layer diffusion, stirring, and solvothermal conditions, respectively. Furthermore, replacing the –Cl substituent with –Br on the HL-X ligand will also afford three diverse coordination assemblies of 3D {[Zn₂(L-Br)₄(H₂O)](CH₃OH)_2.5}_n (5), mononuclear [Zn(HL-Br)₂(H₂O)₄][L-Br]₂ (6), and 2D {[Zn(L-Br)₂](H₂O)_1.15}_n (7) depending on the synthetic pathways. Beyond the significant influence of the synthetic approach, which will lead to the formation of various crystalline products, the halogen substitution effect of HL-X ligands on the coordination motifs has also been demonstrated. In addition, thermal stability and fluorescence for these crystalline materials will be presented.