FORMATION OF CATIONIC MONOCYCLOPENTADIENYL METAL(IV) COMPOUNDS FOLLOWING HALIDE ABSTRACTION FROM [M(ETA-5-C5H5)-CL3(MECN)2] (M=ZR OR HF) - CRYSTAL AND MOLECULAR-STRUCTURE OF [HF(ETA-5-C5H5)(MECN)6][SBCL6]3-CENTER-DOT-CH2CL2

Treatment of [M(eta5-C5H5)Cl3(MeCN)2] (M = Zr or Hf) with antimony(V) chloride in acetonitrile solution provides a convenient route to catio nic monocyclopentadienyl metal(IV) species following halide abstractio n. The hexachloroantimonate(V) salts [M(eta5-C5H5)Cl2(MeCN)3][SbCl6], [M(eta5-C5H5)Cl(MeCN)4][SbCl6]2 and [M(eta5-C5H5)(MeCN)6][SbCl6]3 have been isolated and characterised by micro-analytical and spectroscopic (IR, H-1 NMR) data. The presence of geometrical isomers in solution i s discussed. The structure of [Hf(eta5-C5H5)(MeCN)6][SbCl6]3.CH2Cl2 ha s been established by X-ray crystallographic studies: monoclinic, spac e group P2(1)/n, a = 22.627(7), b = 18.956(8), c = 22.699(7) angstrom, beta = 98.80(7)-degrees. The structure shows two independent [Hf(eta5 -C5H5)(MeCN)6]3+ cations, six [SbCl6]-anions and two lattice solvent ( CH2Cl2) molecules. The two cations show equivalent dimensions within e xperimental error and feature a seven-co-ordinate, pentagonal-bipyrami dal metal geometry in which the cyclopentadienyl ligand occupies an ax ial position: Hf-C(ring) 2.38(2)-2.53(2) (molecule 1) and 2.43(2)-2.51 (2) angstrom (molecule 2).