Synthesis and structural studies of 1D coordination polymer, tetranuclear and octanuclear coordination compounds of Zn(II) with dihydrazone ligand

An ( ONO ) 2 -donor dihydrazone ligand, H 4 L, was synthesized via the condensation of benzoylacetone and 2,6-dimethylpyridine-3,5-dicarbohydrazide and subsequently utilized in the synthesis of Zn(II) coordination compounds. An acetate-bridged tetranuclear coordination compound, [Zn 4 ( µ -OAc) 2 (HL) 2 (CH 3 OH) 2 ]·6(CH 3 OH) ( 1 ), was prepared by the reaction of H 4 L with Zn(OAc) 2 ·2H 2 O in methanol and by replacing the acetate group with terephthalate (TPA) bridge, as a dicarboxylate ligand, a new 1D Zn(II) coordination polymer with the general formula of {[Zn 4 ( µ -TPA)(HL) 2 (CH 3 OH) 2 ]·2.2(CH 3 OH)]} n ( 2 ), was obtained. An octanuclear Zn(II) coordination compound, [Zn 8 ( µ 3 -OH) 2 (L) 2 (HL) 2 (EtOH) 6 ]·3.8(EtOH) ( 3 ), was synthesized by the reaction of H 4 L with Zn(NO 3 ) 2 ·6H 2 O in ethanol. Compounds 1-3 were obtained in single crystal forms, and they were characterized by various analytical and spectroscopic methods. The crystal structures of 1 - 3 were determined by X-ray diffraction, revealing that the dihydrazone ligand exhibits flexible coordination behavior when binding to Zn(II) ions. Intermolecular interactions in the structures of 1 - 3 were investigated by Hirshfeld surface calculations to evaluate their contribution to the overall crystal stability. The thermal behavior of 1 - 3 was analyzed by TGA, which indicated that the organic ligands undergo decomposition starting at approximately 300 °C. Photoluminescence spectra of 1 - 3 revealed two independent emissions in the 270-380 and 400-600 nm ranges upon excitation at 260 nm, along with a weak emission between 450-600 nm when excited at 420 nm. These results indicate that dihydrazone ligands, by coordinating to several metal ions and acting as both chelating and bridging units, possess high potential to form multinuclear coordination compounds and coordination polymers.