Halide abstraction from Pr(III) chloride by Sn(IV): formation and crystal structures of [Pr(MeCN)(9)][SnCl5(THF)](2.5)[SnCl5(MeCN)](0.5), [Pr(MeCN)(9)][SnCl5(MeCN)](3) and [PrCl2(THF)(5)][SnCl5(THF)]: identification of structural isomers of the nine

摘要

Treatment of PrCl3 with SnCl4 and dibenzo-24-crown-8 in MeCN/THF (60/40) afforded [Pr(MeCN)(9)][SnCl5-(THF)](2.5)[SnCl5(MeCN)](0.5) (I) as the only isolated product. From the crystal structure determination (X-ray diffraction) the nine co-ordinate Pr atom adopts a tricapped trigonal prismatic geometry with Pr-N bond distances in the range (2.577(4)-2.615(5) Angstrom), whilst one of the three Sn(IV) counteranions has half-occupancy between THF and MeCN at the solvent position. Subsequent investigation of the PrCl3/SnCl4/S (solvent) system reveals that with S = MeCN complete halide abstraction leads to the formation of [Pr(MeCN)(9)][SnCl5 (MeCN)](3) (II), regardless of the stoichiometry employed. In this case the cationic Pr metal centre adopts a slightly distorted mono-capped square prismatic geometry with Pr-N-prism bond distances (2.583(9), 2.502(9)Angstrom) and Pr-N-capping (2.645(17) Angstrom). Conversion of the (idealised) monocapped square prismatic isomer (II) to the tricapped trigonal prismatic isomer (I) is discussed. Treatment of PrCl3 with SnCl4 with S = THF leads to the formation of [trans-PrCl2(THF)(5)][SnCl5(THF)] (III) in which the cation is seven co-ordinate and features a trans-PrCl2 unit (axial) Pr-Cl (2.6767(9) Angstrom) with five THF molecules in an equatorial girdle to give a pentagonal bipyramidal metal geometry Pr-O (2.467(4)-2.489(3) Angstrom). (C) 2001 Elsevier Science B.V. All rights reserved. [References: 35]