Crown ether complexation of scandium(III), yttrium(III) and lanthanum(III) halides. Synthesis and spectroscopic characterisation of anhydrous cationic metal-oxacrown species and crystal structure of a scandium benzocrown
Abstract
Halide abstraction reactions of MCl3(M = Sc, Y or La) with SbCl5 in the presence of a crown ether provided a series of anhydrous cationic MIII-crown compounds of the types [MCl2(crown)][SbCl6][M = Sc, crown = 1, 4, 7, 10, 13, 16- hexaoxacyclooctadecane (18-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-pentaoxacyclo- pentadecane (15-crown-5)], [ScCl2(12-crown-4)(MeCN)][SbCl6](12-crown-4 =1,4,7,10-tetraoxacyclododecane),[M(18-crown-6)(MeCN)3][SbCl6]3(M = Y or La) and [M(12-crown-4)(MeCN)5]-[SbCl6]3(M = Y or La). Analytical and spectroscopic (1H and 13C 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)Å and Z= 8. The cation has a threaded structure with an essentially linear ScCl2+ unit [Sc–Cl (mean) 2.395 Å, Cl–Sc–Cl 175.5°]. 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)Å, (mean) 2.188 Å with the benzene ring titled out of this plane at an angle of 24.9°. The resulting geometry of the seven-co-ordinate scandium atom is pentagonal bipyramidal.