Chemistry Reference
In-Depth Information
Figure 4.30
Structure of [CefOC
CF
3
2
CH
2
C
Me
D
NC
2
H
4
N
D
C
Me
CH
2
C
CF
3
2
Og
2
]
(H and F atoms omitted).
complex [CefOC
CF
3
2
CH
2
C
Me
D
NC
2
H
4
N
D
C(Me)CH
2
C
CF
3
2
Og
2
] (Fig. 4.30)
was obtained using the tetradentate functionalized diolate ligand obtained by template
condensation of ethylene diamine and 5,5,5-trifluoro-4-hydroxy-4-trifluoromethyl-2-
pentanone.
125
The structure involves a distorted square antiprism with the two diolate
ligands occupying meridional configurations. The triphenylsiloxo ligand gave rise to
the mononuclear [Ce(OSiPh
3
3
thf
3
]
126
isostructural with the yttrium and lanthanum
analogues (Table 4.7). The unsolvated compound [Ce
2
-OSiPh
3
2
OSiPh
3
4
]hasthe
familiar dimeric structure with a distorted tetrahedral structure. There appears to be
interaction between the
ipso
-carbon atom of one phenyl group of the bridging OSiPh
3
group with a cerium atom (Ce
....
C D 2
.
982
9
A).
117
2.7.3
Praseodymium
Some structures of praseodymium(
III
) complexes with fluorinated tertiary alkoxo
ligands have been reported. The tris-trifluoro-
tert
-butoxide adopts the trinuclear
structure [Pr
3
3
-tftb
2
-tftb
3
(tftb)
2
](tftb D OCMe
2
CF
3
))
127
with the three metals
in an isosceles triangle capped above and below by two
3
-OCMe
2
CF
3
ligands. The
-ligands span the edges of the triangle, and one Pr atom, which has two terminal
alkoxo groups, is in a distorted octahedral coordination while the other two, with one
terminal ligand apiece, are five-coordinated. However, the five-coordinated metals are
close enough to fluorine atoms of CF
3
groups (Pr
....
F, 2.756, 2
.
774 A) to suggest
distorted six- and seven-coordination (Fig. 4.31). This trinuclear structure is clearly
related to the other [M
3
3
-OR
2
-OR
3
(OR)
4
L
2
] structures (Fig. 4.5) but without
the neutral donor ligands L. With the even more acidic hftb group the ammonia
produced in a side reaction was captured by the praseodymiums to give the dimeric
ammine [Pr
2
-hftb
2
(hftb)
4
NH
3
4
]. The centrosymmetric molecule has the typical
edge-shared octahedral structure (
cf
. Fig. 4.20) but with one hftb and one ammonia in
the Pr
2
O
2
plane and the other hftb at right angles to the Pr
2
O
2
plane and
trans
to the
second ammonia on each praseodymium.
128
This is a different arrangement from that
found in [Sc
2
-hfip
2
(hfip)
4
NH
3
4
].
103
