A new series of homoleptic,paramagnetic organochromium derivatives: synthesis,characterization, and study of the magnetic properties

The synthesis and characterization of the triad of organochromium derivatives Cr(C(6)Cl(5))(4)](n-) (n=0, 1, 2) are described. By treating CrCl(3)(thf)(3)] with LiC(6)Cl(5) in 1:5 molar ratio, the salt Li(thf)(4)]Cr(III)(C(6)Cl(5))(4)] (1) was obtained as a violet solid in 57 % yield. Oxidation of 1 with N(4-BrC(6)H(4))(3)]SbCl(6)] yielded the neutral complex Cr(IV)(C(6)Cl(5))(4)] (2) as a brown solid in 71 % yield. The arylation of CrCl(2)(thf)] with LiC(6)Cl(5) under similar conditions as above gave Li(thf)(3)](2)(mu-Cl)](2)Cr(II)(C(6)Cl(5))(4)] (3) as an extremely air- and water-sensitive red solid in 47 % yield. The crystal and molecular structures of 1 and 3 have been established by X-ray diffraction methods. Complex 3 contains the unusual cation Li(thf)(3)](2)(mu-Cl)](+) with an almost linear Li-Cl-Li unit (174.2(6)degrees). All four C(6)Cl(5) groups are sigma-bonded to the Cr(II) center, which is located in a square-planar environment. The local geometry around the Cr(III) center in 1 is, in turn, pseudo-octahedral, since two of the C(6)Cl(5) groups act as standard sigma-bonded monodentate ligands, while the other two act as small-bite didentate ligands coordinated through both the ipso-C and one of the ortho-Cl atoms. Compounds 1-3 are paramagnetic with maximum spin multiplicity each (EPR and magnetization measurements).