Mononuclear zinc(II) and mercury(II) complexes of Schiff bases derived from pyrrolealdehyde and cysteamine containing intramolecular NH⋯S hydrogen bonds

Two neutral group 12 metal complexes, bis(pyrrol-2-ylmethyleneaminoethylthio)zinc(II) (1) and bis(pyrrol-2-ylmethyleneaminoethylthio)mercury(II) (2), with the (Nimine)2S2 coordination mode were synthesized by using metal-templated Schiff base condensation, and their molecular structures were determined by X-ray diffraction analysis. Complex 1 exhibits a distorted tetrahedral geometry around the metal, whereas the metal center has a bisphenoidal configuration in complex 2. Both mononuclear complexes possess intramolecular NH⋯S hydrogen bonds, as evidenced by IR, 1H NMR and X-ray crystallography. The hydrogen-bond donor (H–Npyrrole) and acceptor (S atom) are coming from different ligands within a single molecule. Complex 2 represents the first example of a mercury complex in the N2S2 coordination mode with intramolecular NH⋯S hydrogen-bond interactions. An investigation of the effects of the NH⋯S hydrogen bonding on the stability of 1 and 2, using an N-methyl pyrrolyl analogue, demonstrated that the N–H hydrogen-bond donor from the pyrrolyl moiety probably played a role in the stability of 1, but not 2.

Graphical abstractThe extensive intermolecular N–H⋯S hydrogen bonds in the structure of bis(2-aminoethanethiolate)zinc(II) were substituted by new intramolecular N–H⋯S hydrogen bonds by using the pyrrole moiety as an extension of cysteamine. Similarly, a new Hg(N2S2) complex was successfully prepared. The (pyrrole)NH⋯S interactions of both new complexes were evidenced by IR, 1H NMR spectra and X-ray analysis.Figure optionsDownload full-size imageDownload as PowerPoint slide