The structural features of a tetrahedral 1,3-monothiolate complex: The crystal and molecular structure of Bis(ethyl 3-mercaptobut-2-enoato)zinc(II)

Abstract

The crystal and molecular structure of bis(ethy 3-mercaptobut-2- enoato)zinc(II) has been determined by single-crystal X-ray diffraction techniques. Solved by conventional Patterson and Fourier methods the structure was refined by a least-squares method employing anisotropic thermal parameters to all non-hydrogen atoms to R and R_w values of 0.040 and 0.046 respectively. The complex crystallizes in the monoclinic space group P2₁/c with four molecules in a unit cell of dimensions a 11.107(1), b 18.239(2) and c 8.438(1) Ǻ and β 107.7(1)°. The intensities of 2274 independent and statistically significant [I ≥ 3σ(I)] reflections with θ values ≤ 70° were measured by counter methods using nickel- filtered Cu Kα radiation. The crystals comprise discrete monomeric molecules with the zinc atom bonded to two sulphur atoms and two oxygen atoms giving a coordination arrangement which is substantially distorted from an ideal tetrahedron. The mean values for the Zn-S and Zn-O bond distances are 2.247(1) and 2.007(3) Ǻ respectively and the average S-Zn-O intraligand bond angle is 99.25(8)°. The geometries of the ligands differ in two ways. Firstly, the two ethyl groups adopt differing conformations and secondly, while one ligand moiety is essentially planar with the zinc atom displaced about 0.1 Ǻ from that plane, the displaced atom in the other ligand is the carbon bonded to the sulphur atom and not the metal which is, in this instance, coplanar with the other members of the ring. Bond distances in each chelate ring indicate aromatic character with a lone pair of electrons on the ethoxy-oxygen participating in the delocalization.