Zn(II) and Cd(II) monomer, dimer and polymer compounds coordinated by benzoic acid and 4-acetylpyridine: Synthesis and crystal structures

Abstract

Reaction of MO (MO = Metal oxide, M = Zn(II) or Cd(II)) with benzoic acid (HBz) in H2O/MeOH mixture as solvent yields two benzoate compounds: [Zn(µ-Bz)2]n (1) and [Cd(Bz)2(H2O)3] (2). In addition, the reaction between M(MeCO2)2 (M = Zn(II) or Cd(II)) with HBz and 4-acetylpyridine (4-Acpy) in a 1:2:4 M ratio and in MeOH solution, leads to the formation of [Zn(µ-Bz)2(4-Acpy)]2 (3) and [Cd(µ-Bz)2(4-Acpy)2]2 (4). These four compounds have been fully characterized by analytical and spectroscopic techniques. Besides, their crystal structures have been elucidated revealing a 1D coordination polymer (1), a monomer (2), a paddle-wheel (3) and a dimer (4). In 1, the Zn(II) ion is four-coordinated in a tetrahedral geometry while in 3 is penta-coordinated in a square-pyramidal geometry. By contrast, compounds 2 and 4 exhibit seven-coordinated Cd(II) ions in a pentagonal-bipyramidal geometry. In these set of compounds, the benzoate ligand presents different coordination modes such as bidentate bridged (µ2-η1:η1) (1 and 3), chelate (µ1-η2) (2) and both bridged and chelate (µ2-η2:η1) (4). Besides, their extended structures have been analyzed. Finally, the UV–Vis and fluorescence spectra of all the compounds have been recorded as well as their quantum yields calculated.