Homo- and heteronuclear compounds with a symmetrical bis-hydrazone ligand : synthesis, structural studies, and luminescent properties

Abstract

Nine new coordination compounds have been synthesized by the reaction of salts of bivalent metal ions (a=ZnII, b=CuII, c=NiII, d=CoII) with the bis(benzoylhydrazone) derivative of 4,6-diacetylresorcinol (H4L). Three kinds of complexes have been obtained: homodinuclear compounds [M2(H2L)2]⋅nH2O (1 a, 1 b, 1 c, and 1 d), homotetranuclear compounds [M4(L)2]⋅n(solv) (2 a and 2 c), and heterotetranuclear compounds [Zn2M2(L)2]⋅n(solv) (2 ab, 2 ac, and 2 ad). The structures of the free ligand H4L⋅2 DMSO and its complexes [Zn2(H2L)2(DMSO)2] (1 a*), [Zn4(L)2(DMSO)6] (2 a*), and [Zn0.45Cu3.55(L)2(DMSO)6]⋅2 DMSO (2 ab*) were elucidated by single-crystal X-ray diffraction. The ligand shows luminescence properties and its fluorimetric behavior towards MII metals (M=Zn, Cu, Ni and Co) has been studied. Furthermore, the solid-state luminescence properties of the ligand and compounds have been determined at room temperature. 1H NMR spectroscopic monitoring of the reaction of H4L with ZnII showed the deprotonation sequence of the OH/NH groups upon metal coordination. Heteronuclear reactions have also been monitored by using ESI-MS and spectrofluorimetric techniques.