CROWN THIOETHER COMPLEXES OF TRIVALENT TRANSITION-METAL IONS - THE CRYSTAL-STRUCTURE OF [CR(18S6)CL-3]

The structure of the macrocyclic complex, [Cr(18S6)Cl-3] (18S6 = 1,4,7,10,13,16-hexathiacyclooctadecane), has been determined by single-crystal X-ray diffraction, the first Cr(III)-thioether coordination complex to be structurally characterized. An octahedral environment of three sulfur atoms and three chlorine atoms around the Cr(III) center is observed in the complex, and the stereoisomer obtained in our case is the one in which only three adjacent sulfur atoms in the 18S6 ligand are bonded to the CrCl3 moiety. This is also the first reported structure of this atypical coordination mode for the 18S6 ligand which typically coordinates in hexadentate fashion or as a bridging ligand. The syntheses, characterization, and electronic spectra of a series of eleven additional thioether complexes of Cr(III) are described. All twelve Cr complexes have the general formula CrLCl(3) and potentially tetra-, penta- and hexadentate thioether ligands all function as tridentate ligands coordinating to a single metal center. The electronic spectra for the Cr complexes are all similar and enable ligand field parameters readily to be calculated. The thioethers function as weak field ligands, and there is a substantial reordering in their spectrochemical series when compared to the series obtained with softer metal ions such as Ni(II) or Fe(II). In addition, the synthesis and characterization of two novel V(III) complexes with the general formula VLCl(3) where L = 1,4,7-trithiacyclononane (9S3) or 1,4,7-trithiacyclodecane (10S3) are described. These are the first two reported examples of thioether complexes of vanadium(III). The reaction between 9S3 and the anion [Re2Cl8](2-) has also been investigated.