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.