Chelate ring stacking interactions in the supramolecular assemblies of Zn(ii)and Cd(ii) coordination compounds: a combined experimental and theoretical study

Abstract

The self-assembly of Zn(II) and Cd(II) ions with two isomeric tetradentate ligands, 2-pyridyl-isonicotinoylhydrazone (HL¹) and 2-benzoylpyridyl-picolinoylhydrazone (HL²), was studied by elemental analysis, FT-IR spectroscopy and single-crystal X-ray diffraction. The reaction of zinc(II) and cadmium(II) salts with HL¹ and HL² in methanol under solvothermal conditions produced six monomer and one tetranuclear zinc(II) complexes, namely, Zn(HL¹)Br₂ (1), Zn(HL¹)Cl₂ (2), [Cd(HL¹)₂](NO₃)₂·H₂O (3), Cd(HL²)Br₂(4), Zn(HL²)Cl₂ (5), Zn(HL²)Br₂ (6) and [Zn₄(L²)₄I₂][ZnI₄]·2H₂O (7). The structure of 7 includes a cationic tetranuclear cluster of four zinc ions, four ligands, and two anions, counterbalanced by ZnI₄²⁻ ions. However, the reaction of zinc(II) and cadmium(II) salts with HL¹ under the same conditions produced monomer compounds. Herein, the ligand effects on the complex structures were studied. Hirshfeld surface analysis and fingerprint plots facilitate the comparison of intermolecular interactions in compounds 1–7, which are crucial in building supramolecular architectures.