Diorganotin(IV) complexes of imidazole-2-carbaldehyde thiosemicarbazone (H2ImTSC). The crystal and molecular structures of the “free” ligand and of [SnMe2(ImTSC)]

Abstract

The compounds [SnR₂(ImTSC)] (R = Me, ⁿBu or Ph; H₂ImTSC = imidazole-2-carbaldehyde thiosemicarbazone) were synthesized by treating the appropriate diorganotin(IV) oxide with the ligand in ethanol. The structures of H₂ImTSC·0.5H₂O and [SnMe₂(ImTSC)]·EtOH were determined by X-ray diffractometry. The thiosemicarbazone chain of the former has E,E,E configuration and is almost coplanar with the imidazole ring. A rich network of hydrogen bonds involving all potential donor and acceptor groups of H₂ImTSC and the water molecule stabilizes the crystal lattice. The crystal of the dimethyltin(IV) complex is composed of discrete molecules that are likewise linked by hydrogen bonds. The Sn is bound to the two methyl groups and to an N,N,S-tridentate thiosemicarbazonato dianion (ImTSC²⁻) in a highly distorted trigonal bipyramidal arrangement with the thioamide sulfur and the imidazole nitrogen apical. The Sn–N bond lengths [2.129(5) and 2.174(5) Å] are close to the sum of the covalent radii and dominate the metal–ligand interaction. The Sn–S bond length [2.659(2) Å] suggests a weak bond. The unusual co-ordination mode of the ImTSC²⁻ anion creates four- and six-membered stannole rings. The EtOH is bound to the complex via hydrogen bonds involving the nitrogen of the imidazole that is not co-ordinated to the tin and the thiosemicarbazone NH₂ group. The IR spectra of the ⁿBu and Ph derivatives suggest that they are structurally similar to the methyl complex. ¹H, ¹³C and ¹¹⁹Sn NMR spectroscopy indicates that the structure of the complexes in the solid state persists in CDCl₃ solution. For H₂ImTSC, ¹⁵N NMR data are presented in addition to IR and ¹H and ¹³C NMR data.