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
![](https://www.rsc.org/images/entities/char_200a.gif)
) provided colourless compounds of the generic type
LnSnCl
7
(thf
![](https://www.rsc.org/images/entities/char_200a.gif)
)
6
which have been identified
by X-ray crystallography as ionic salts
[trans-LnCl
2
(thf
![](https://www.rsc.org/images/entities/char_200a.gif)
)
5
][SnCl
5
(thf
![](https://www.rsc.org/images/entities/char_200a.gif)
)]. 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
![](https://www.rsc.org/images/entities/char_200a.gif)
)]
-
anions common to the
series show a two-fold axis of symmetry containing the metal atom, the
oxygen (thf
![](https://www.rsc.org/images/entities/char_200a.gif)
) 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.