Structural study of mono-, di- and tetranuclear complexes of the {Re(CO)3}+ fragment with thiosemicarbazone/thiosemicarbazonate ligands containing benzothiazole or benzoxazole groups

Abstract

Nine thiosemicarbazone ligands (H₂Lⁿ, n = 1–9) containing benzothiazole or benzoxazole groups at the C(2) atom of the thiosemicarbazone have been prepared and characterized. A crystal structure study was performed on six of these free ligands and the role of the π–π interactions in the molecular association was analyzed. The coordination behavior of the thiosemicarbazones towards the {Re(CO)₃}⁺ fragment was investigated and three types of complexes were obtained: mononuclear fac-[ReX(H₂Lⁿ)(CO)₃], X = Cl or Br, with bidentate ligands, dinuclear [Re₂(HLⁿ)₂(CO)₆] with monodeprotonated bridging thiosemicarbazonates yielding Re₂S₂ cores and tetranuclear [Re₄(L²)₂(CO)₁₂(EtOH)₂] with an unusual bideprotonated thiosemicarbazonate ligand. The intermolecular interactions before and after metal coordination were analyzed. In the dinuclear complexes, two different approximate symmetries were observed depending on the relative orientation of the thiosemicarbazonate ligands with respect to the Re₂S₂ diamond. The intramolecular interactions in the dimers and their relationship with the two possible symmetric dispositions were analyzed. The findings, in conjunction with theoretical calculations, allowed the main stabilizing factors for each type of symmetry to be elucidated.