Physicochemical and X-ray Crystallographic Properties of the First Rhenium Compound of Benzophenone thiosemicarbazone (bptsc), fac-[Re(CO)3(κ2-Nim,S-bptsc)Cl]

Abstract fac-[Re(CO)3(κ2-Nim,S-bptsc)Cl] (2), isolated from the reaction between Re(CO)5Cl and benzophenone thiosemicarbazone, bptsc, (1) in refluxing toluene in air, is the first Re compound of 1 and is the second Re(CO)3Cl compound of κ2-Nim,S-coordinated ligand (im = imine). The authenticity of 2 was established from the results of its elemental composition, spectroscopic measurements, and X-ray crystallographic analysis. Single crystals of 2 grown from DMF are in the monoclinic space group P21/c. The asymmetric unit of 2 revealed pseudo-octahedral coordination about the Re ion. Two carbonyl C atoms, an imine N atom and a thione S atom from the hydrazonic backbone of 1 occupy the equatorial sites and the axial sites are occupied by a carbonyl C atom and a Cl ion. The κ2-N,S-coordination of 1 to the Re ion forms a semi-planar five-membered [Re-N-N-C-S] metallocyclic ring. The extended structure of 2 disclosed stacks of molecules interlocked via a web of N-H•••X (X = Cl or O), S•••S and C-H•••π interactions. DFT calculations divulged facile delocalization of the electron density in the molecule and interatomic distances and angles in good agreement with the solid state structure. Electrochemical measurements on 2 in CH3CN and DMF revealed sequential irreversible electron transfers pointing to structural changes due to electrochemically induced thione-thiol tautomerization of the thioamide moiety. Plausible mechanisms for the oxidative and reductive electrochemical decomposition of 1 and 2 are reported. The proposed mechanisms are in good agreement with those reported in the literature for closely related compounds.