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) aZn(Pip)(2)(H2O)(2)] (1c)), two of Cd(II) ([Cd(mu-Pip)(2)(H2O)](n) (2) and [Cd-3(mu-Pip)(6)(MeOH)(2)](n) (3)), and one of Hg(II) ([Hg(mu-Pip)(2)](n) (4)). The obtention of compounds lc 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 squareantiprism 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: mu(1)-eta(1) (1c); mu(2)-eta(1):eta(1) and mu(2)-eta(2):eta(1) (2); mu(2)-eta(1):eta(1), mu(2)-eta(2):eta(1) and mu(3)-eta(2):eta(1):eta(1) (3); mu(1)-eta(2) and mu(2)-eta(2):eta(1) (4). The extended structures were also analyzed. Their photoluminescence properties have been examined, and the quantum yields have been calculated.