Low-dimensional compounds containing bioactive ligands. Part XVIII: Design, synthesis and crystal structural investigations of ionic heteroleptic Pd(II) complexes based on halo and nitro 8-hydroxyquinoline derivatives

Abstract

The construction of coordination compounds with desired properties and fascinating structures is a topic of a great interest. In this context, noncovalent interactions can play a dominant role in synthesis, catalysis and design of materials. Here, new heteroleptic palladium(II) coordination compounds bearing 8-hydroxyquinolinium (8-HQH) as cation and [PdCl2(XQ)]- as anion, where HXQ = 5-chloro-7-iodo-8-hydroxyquinoline (1), 5-chloro-8-hydroxyquinoline (2), 5-nitro-8-hydroxyquinoline (3) or 5,7-dibromo-8-hydroxyquinoline (4), have been synthesized via one-pot reaction. Single crystal structure analysis reveals that Pd(II) is coordinated via the N- and O- donor atoms of the XQ ligands besides two cis-chlorido ligands. Both the anions and cations are connected by ionic interaction as well as hydrogen bonds to form infinite chains. The formed chains are assembled into 3D structures by π-π interactions between the aromatic quinoline rings. In addition, complexes 1 and 4 contain two water molecules of crystallization that are involved in the hydrogen bond system. Furthermore, elemental analysis and FT-IR spectroscopy were employed to prove the compositions of the produced compounds. The 1H and 13C NMR spectra measured in DMSO‑d6 confirm the presence of quinoline moieties in all the complexes and give a remarkable distinction between the coordinated and non-coordinated quinoline moieties. Collectively, this study provides a concrete starting point for the design and construction of ionic complexes of Pd(II) with 8-HQ derivatives including covalent and different non-covalent interactions and thus tuning the conformation, properties, and finally the functions of the compounds.