Synthesis, characterization and single crystal X-ray structure determination of three cadmium(II) complexes derived from picric acid and p-nitrobenzoic acid in the presence and absence of nitrogen donor ligand N-(hydroxyethyl)ethylenediamine

Abstract

Cadmium, an extremely toxic heavy metal, is of a major public health concern and its efficient removal from the environment is a real challenge. This work aims for a deep understanding of stable cadmium(II) chelation with a tridentate ligand to form complex salts being stabilized by cation–anion hydrogen bonding non-covalent interactions in addition to electrostatic interactions. Three new Cd(II) complexes, [Cd(H2O)6](pic)2·2H2O 1, [Cd(N-hyden)2](pic)22, [Cd(N-hyden)2](pnb)23, (where N-hyden = N-(hydroxyethyl)ethylenediamine, Hpic = picric acid and Hpnb = p-nitrobenzoic acid) using the appropriate acids in the absence and presence of the tridentate N-hyden ligand have been synthesized and fully characterized by elemental analyses, thermogravimetric analyses and spectroscopic (FT-IR, NMR) techniques. The exact ionic structures of complexes 1–3 have been unambiguously determined using single crystal X-ray diffraction studies. They comprise octahedrally surrounded cationic Cd(II) centers, [Cd(H2O)6]2+ in 1 and [Cd(N-hyden)2]2+ in 2 and 3, together with the counter anions pic/pnb, which are stabilized by a mutual interplay of various hydrogen bonding interactions.