Halide-abstraction reactions of tin(IV) andlanthanide(III) chlorides in tetrahydrofuran: crystal andmolecular structures of[LnCl2(thf)5][SnCl5(thf)] where Ln = Ce, Gd or Yb

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Abstract
It has been established that halide abstraction from several lanthanide(III) chlorides can be effected by tin tetrachloride. Direct treatment (1∶1) of LnCl 3 where Ln = Ce, Gd or Yb with SnCl 4 in tetrahydrofuran (thf) provided colourless compounds of the generic type LnSnCl 7 (thf) 6 which have been identified by X-ray crystallography as ionic salts [trans-LnCl 2 (thf) 5 ][SnCl 5 (thf)]. The individual seven-co-ordinate cations feature a regular pentagonal-bipyramidal metal geometry in which a trans-LnCl 2 unit is surrounded by five thf molecules arranged in an equatorial plane. These co-ordinated solvent molecules adopt the familiar ‘propeller-like’ arrangement indicative of a skew as opposed to envelope ligand conformation. For Ln = Ce, Ce–Cl 2.697(2), Ce–O mean 2.495(5) Å; for Ln = Gd, Gd–Cl 2.608(2), Gd–O mean 2.415(4) Å; for Ln = Yb, Yb–Cl 2.5375(13), Yb–O mean 2.346(4) Å. The six-co-ordinate [SnCl 5 (thf)] - anions common to the series show a two-fold axis of symmetry containing the metal atom, the oxygen (thf) atom and a chloride atom mutually trans to the latter. Bond distances for Ln = Ce, i.e. Sn–O 2.276(7), Sn–Cl mean 2.399(2) Å, are typical for the series.

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