Syntheses and structures of four- and five-coordinate bio-related zinc complexes containing dithiolate–diamine ligands

Two new zinc complexes, namely, [{Zn(N2H2S2)}2] (3) [N2H2S22− = N,N-bis(2-mercaptophenyl)ethylendiamine (2−)] and [Zn(N2Me2S2)] (4) [N2Me2S22− = N,N′-dimethyl-N,N′-bis(2-mercaptophenyl)ethylendiamine) (2−)] have been synthesized and structurally characterized by X-ray structure analyses. The structure of 3 consists of a bis(μ-thiolato) binuclear unit, in which each zinc center was found to reside in an N2S3 array between square-pyramidal and trigonal-bipyramidal environment. The two zinc centers are bridged by one of the two thiolates of an [N2S2] ligand. In the crystal packing, the neighboring binuclear units interact with each other by H-bonding interaction, which extends the binuclear unit into a 3D network. In contrast to 3 complex 4 is mononuclear, where each zinc center now was found to reside in an N2S2 distorted tetrahedral environment with a large S–Zn–S bite angle. The relevance of these compounds in biological systems is discussed. Unlike 3, the formation of hydrogen bridges in 4 is no longer possible and instead the molecular packing is determined by π-stacking between the phenyl rings.