CROWN-ETHER COMPLEXATION OF SCANDIUM(III), YTTRIUM(III) AND LANTHANUM(III) HALIDES - SYNTHESIS AND SPECTROSCOPIC CHARACTERIZATION OF ANHYDROUS CATIONIC METAL OXACROWN SPECIES AND CRYSTAL-STRUCTURE OF A SCANDIUM BENZOCROWN

Halide abstraction reactions of MCI, (M = Sc, Y or La) with SbCl5 in the presence of a crown ether provided a series of anhydrous cationic M(III)-crown compounds of the types [MCl2(crown)][SbCl6] [M = Sc, crown = 1,4,7,10,13,16-hexaoxacyclooctadecane (1 8-crown-6), 2,3,5,6,8,9,11,12-octahydro-1,4,7,10,13-benzopentaoxacyclopentadecine (benzo-15-crown-5), or 1,4,7,10,13-pentaoxacyclopentadecane (15-crown-5)], [ScCl2(12-crown-4)(MeCN)][SbCl6] (12-crown-4 = 1,4,7,10-tetraoxacyclododecane), [M (1 8-crown-6) (MeCN)3] [SbCl6]3 (M = Y or La) and [M (1 2-crown-4) (MeCN)5]-[SbCl6]3 (M = Y or La). Analytical and spectroscopic (H-1 and C-13 NMR) characterisation of these compounds supports their formulation as hexachloroantimonate(v) salts. The structure of [ScCl2(benzo-15-crown-5)][SbCl6] has been determined by X-ray diffraction. Crystals are orthorhombic, space group Pbca with a = 17.015(10), b = 13.296(8), c = 22.236(12) angstrom and Z = 8. The cation has a threaded structure with an essentially linear ScCl2+ Unit [Sc-Cl (mean) 2.395 angstrom, Cl-Sc-Cl 175.5-degrees]. All the oxygen atoms of the oxacrown ligand are coplanar and are bonded to the central scandium atom, Sc-O 2.166(4)-2.223(4) angstrom, (mean) 2.188 angstrom with the benzene ring tilted out of this plane at an angle of 24.9-degrees. The resulting geometry of the seven-co-ordinate scandium atom is pentagonal bipyramidal.