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 co-ordinate [Pr(M

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) Å), 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Nprism bond distances (2.583(9), 2.502(9) Å) and PrNcapping (2.645(17) Å). 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) Å) with five THF molecules in an equatorial girdle to give a pentagonal bipyramidal metal geometry PrO (2.467(4)–2.489(3) Å).