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trigonal bipyramid) and the other two are five-coordinated (lone pair in the vacant
octahedral site).
24
The only copper oxo-alkoxide structure determined to date is the giant
trimethylsiloxo derivative [Cu
18
4
-O
2
OSiMe
3
14
] containg two-coordinated (linear)
copper(
I
).
181
5.9.2
Aluminium
The first structural report of an aluminium oxo-alkoxide concerned the mixed-
ligand complex [H
5
Al
5
5
-O
-OBu
i
8
] containing the novel Al
5
O
9
framework
with a square pyramidal array of aluminium atoms. The apical Al is octahedrally
coordinated by one terminal hydride
trans
to the
5
-oxo ligand and connected to
the four basal Al atoms by
-isobutoxo ligands. Each basal Al is five-coordinated
(TBP) by one terminal hydride in an axial position
trans
to the
5
-oxo ligand
and three
-isobutoxo bridges in the equatorial positions to the apical Al and two
adjacent basal aluminiums.
182
Several years later the corresponding oxo-isobutoxide
[
Bu
i
O
5
Al
5
5
-O
-OBu
i
8
] (Fig. 5.22) was isolated and characterized and shown to
have the same Al
5
O
9
framework.
79
Meanwhile the scandium, yttrium, and lanthanide
species [
RO
5
M
5
5
-O
3
-OR
4
-OR
4
] had been characterized in which all five
metals were six-coordinated.
16
A remarkable decanuclear oxo-ethoxide [Al
10
4
-O
2
3
-O
2
-OEt
14
OEt
8
]was
reported which contained aluminium in four-, five-, and six-coordination (Fig. 5.23).
183
The average Al-O bond distance for the
4
-oxo ligand was significantly longer
(1.880 A)
(1.801 A).
than
for
the
3
-oxo
ligand
In
the
tetranuclear
compound
[Al
4
4
-O
-OBu
i
5
OBu
i
5
Bu
i
OH
]
the
four
aluminiums
are
in
a
distorted
(Fig. 5.24).
184
tetrahedral
configuration
around
the
4
-oxo
ligand
Although
the
OH
hydrogen
in
the
isobutanol
ligand
was
not
located
it
was
clearly
present
Figure 5.22
Structure of [Al
5
5
-
O
-OBu
i
8
OBu
i
5
](
ΕΎ
D
5
-oxo;
H atoms omitted).
