Diverse Structures and Dimensionalities in Zn(II), Cd(II), and Hg(II) Metal Complexes with Piperonylic Acid

Reaction of M­(MeCO2)2 (M = Zn­(II), Cd­(II), and Hg­(II)) with 1,3-benzodioxole-5-carboxylic acid (HPip) in methanol (MeOH) yields four piperonylate compounds, one of Zn­(II) ([Zn­(Pip)2­(H2O)2] (1c)), two of Cd­(II) ([Cd­(μ-Pip)2­(H2O)] n (2) and [Cd3(μ-Pip)6­(MeOH)2] n (3)), and one of Hg­(II) ([Hg­(μ-Pip)2] n (4)). The obtention of compounds 1c and 4 was independent of the M/L ratio. These four compounds were characterized by analytical and spectroscopic techniques. In addition, the thermal stability of 1c, 2, and 4 has been studied, and the structure of all the complexes has been determined by the single crystal X-ray diffraction method. The Zn­(II) compound displayed a monomeric structure, while Cd­(II) and Hg­(II) complexes exhibited three polymeric arrays. The Zn­(II) (1c) and Hg­(II) (4) centers are four- and eight-coordinated in a tetrahedral or square-antiprism geometry, respectively. Furthermore, the Cd­(II) ions are either six- (2) or six- and seven- (3) coordinated in a octahedral or both octahedral and pentagonal bipyramid geometries, respectively. In these compounds, the Pip ligand presents different coordination modes: μ1-η1 (1c); μ2-η1:η1 and μ2-η2:η1 (2); μ2-η1:η1, μ2-η2:η1 and μ3-η2:η1:η1 (3); μ1-η2 and μ2-η2:η1 (4). The extended structures were also analyzed. Their photoluminescence properties have been examined, and the quantum yields have been calculated.