Chemistry Reference
In-Depth Information
The hexanuclear [La
2
Mo
4
O
4
4
-O
4
-OPr
i
8
OPr
i
6
] has a tetragonal bipyra-
midal configuration of metal atoms with the lanthanums
trans
to each other. Each Mo
atom has one terminal oxo ligand and the
4
-oxo ligands are each bonded to two
La and two Mo atoms. The bridging isopropoxo groups span the LaMo edges of the
polyhedron and each metal has one terminal isopropoxo group.
116
5.3.2 Actinides
Among the actinides a few structures of uranium oxo-alkoxides have been reported.
The trinuclear [U
3
3
-O
3
-OBu
t
-OBu
t
3
OBu
t
6
] uranium(
IV
) complex has
the familiar M
3
O
11
core structure but there is no U
....
U bonding in contrast
to [Mo
3
O
OCH
2
Bu
t
10
], which exhibits metal - metal bonding.
117
The trinuclear
uranium(
VI
) compound [U
3
O
2
-O
2
-OBu
t
2
OBu
t
8
] has a central uranium
containing a linear UO
2
group bridged by unsymmetrical
-O oxo groups and
-OBu
t
groups to the outer U atoms.
64
The mononuclear [UO
2
OBu
t
2
Ph
3
PO
2
] has the linear
UO
2
group and
cis
phosphine oxide ligands.
44
5.4 Titanium Sub-group Metal-containing Oxo-alkoxides (Including
Heterometallic Compounds) (Table 5.4)
5.4.1 Titanium
Numerous titanium oxo-alkoxides have been structurally characterized including
[Ti
7
O
4
OEt
20
],
9
,
118
[Ti
10
O
8
OEt
24
]
9
and [Ti
16
O
16
OEt
32
]
118
which with the
unhydrolysed crystalline tetrameric ethoxide [Ti
4
OEt
16
] conform to a general formula
[Ti
4C3
x
O
4
x
OEt
4
x
C4
](
x
D 0, 1, 2, 4) implying an increment of Ti
3
O
4
OEt
4
between
each member of the series. Interestingly this is very similar to the series proposed by
Bradley
et al
.
5
[Ti
3C3
x
O
4
x
OEt
4
x
C3
] based on the analysis of the variation of number
average degree of polymerization with degree of hydrolysis of the tetraethoxide in boiling
ethanolic solution. The actual structures of the oxo-ethoxides obtained to date all involve
octahedra. In the heptanuclear [Ti
7
4
-O
2
3
-O
2
-OEt
8
OEt
12
] the central TiO
6
octahedron shares six edges through two
cis
-
4
-oxo ligands, two
trans
-
3
-oxo ligands,
and two
cis
-
-ethoxo ligands to six other octahedra (Fig. 5.7).
118
Figure 5.7
Structure of [Ti
7
4
-
O
2
3
-O
2
-OEt
8
OEt
12
]( D
4
-oxo,
D
3
-oxo,
ΕΎ
D Ti;
H
atoms omitted).
