Tetranuclear Zn(II) complexes with ditopic picolinohydrazone ligands: Synthesis, crystal structure, spectroscopic studies, and Hirschfeld surface analysis

Abstract

Two N- and O-donor hydrazone ligands, (E)-N'-(1-(4‑hydroxy-6-methyl-2-oxo-2H-pyran-3-yl)ethylidene)picolinohydrazide (H2L1) and (E)-N'-(4-oxo-4-phenylbutan-2-ylidene)picolinohydrazide (H2L2), were synthesized by the reaction of picolinohydrazide and dehydroacetic acid or benzolyacetone in methanol solvent. The ligands were characterized by spectroscopic methods and were employed in preparing Zn(II) complexes. Two new tetranuclear Zn(II) complexes, [Zn4(L)2(µ-OAc)4(CH3OH)2] (1) and [Zn4(L2)2(µ-OAc)4(CH3OH)2] (2), were synthesized by the reaction of Zn(OAc)2·H2O with H2L1 and H2L2 in methanol, respectively. These complexes were also characterized by elemental analysis, spectroscopic methods, and single crystal X-ray analysis. Structural studies indicated both 1 and 2 are acetato-bridged tetranuclear Zn(II) complexes and in both of them, the picolinohydrazone ligands are coordinated to the metal ions as both bridging and chelating ligand to fill the coordination environments of Zn(II) ions. In compound 1 four Zn(II) ions have an almost linear arrangement, while in compound 2 they show square arrangement. This matter can be attributed to the steric and electronic difference of the beta-diketone moiety in the structure of ligand. Intermolecular interactions in compounds 1 and 2 were investigated by Hirschfeld surface analysis.