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 (N-imine)(2)S-2 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 center dot center dot center dot S hydrogen bonds, as evidenced by IR, H-1 NMR and X-ray crystallography. The hydrogen-bond donor (H-N-pyrrole) 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 center dot center dot center dot S hydrogen-bond interactions. An investigation of the effects of the NH center dot center dot center dot 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. (c) 2009 Elsevier B.V. All rights reserved.