Chemistry Reference
In-Depth Information
the other cluster giving the central
6
-oxo ligand. The Mo
6
O
19
core is of course
reminiscent of the transition metal isopolyanions.
Another structural motif was exhibited by the structure of the mixed ligand hexa-
nuclear molecule [Mo
6
O
6
3
-O
2
-OEt
6
-Cl
2
Cl
6
] with a cyclic array of six
Mo(
V
) atoms in a chair conformation. The six valence electrons are paired off in three
Mo-Mo bonds (2.665 A, 2.672 A, 2.741 A) alternating around the ring. The
3
-oxo
ligands are in planar three-coordination (T-shaped).
162
The
[Mo
8
O
16
4
-O
2
3
-O
4
-O
2
-
octanuclear
Mo(
VI
)
complex
anion
OMe
2
OMe
2
]
4
has
an
Mo
8
O
28
framework
similar
to
that
found
in
various
substituted octamolybdates.
52
Another octanuclear Mo(
V
) complex [Mo
8
O
8
-O
8
-OMe
8
PMe
3
4
] contains
a puckered ring of eight Mo atoms. The molecule comprises a tetramer of the
[Mo
2
O
2
-O
2
-OMe
2
PMe
3
] moiety which involves Mo-Mo bonds (2.567 A)
between the Mo
-O
2
Mo pairs. Four of the metals which have coordinated PMe
3
ligands are octahedrally coordinated and the other four are five-coordinated (square
pyramidal).
163
In the octanuclear Mo(
VI
) anion [Mo
8
O
14
-O
6
3
-OMe
2
OMe
2
f
OCH
2
3
CMeg
2
]
2
the centrosymmetric species may be viewed as two [Mo
4
O
7
-O
2
3
-
OMe
3
OMe
f
OCH
2
3
CMeg]
units joined by two (
-O) bridges (Fig. 5.19).
58
A most remarkable mixed ligand heterometallic oxide-alkoxide anion
[Ag
2
Mo
10
O
8
5
-O
2
-O
16
-OMe
8
NO
2
]
4
has been characterized.
167a
The
centrosymmetrical anions consist of two Mo
5
O
4
5
-O
-O
8
-OMe
4
NO
units
connected by four Mo
-O
Ag
-O
Mo bridges involving square planar AgO
4
with a
short Ag
....
Ag distance (2.873 A). All of the molybdenums are in distorted octahedral
configurations.
The pentanuclear Mo
5
O
13
OMe
4
NO
moiety was earlier found in the salts
of the heterometallic alkali metal complexes
NBu
4
2
[Mo
5
O
4
5
-O
-O
8
-
OMe
4
NO
Na
,
MeOH
], K
2
[Mo
5
O
4
5
-O
-O
8
-OMe
4
NO
fNa
H
2
O
MeOH
g],
NMe
4
2
[Mo
5
O
4
5
-O
-O
8
-OMe
4
NO
Na
,
H
2
O
]and[NBu
4
2
[Mo
5
O
4
5
-
O
-O
8
-OMe
4
Na
,
DMF
].
167b
Each complex has a square pyramid of Mo atoms
with the apical metal bonded to a linear NO ligand
trans
to the
5
-oxo and the basal
Figure 5.19
Structure of [Mo
8
O
14
-
O
6
3
-OMe
2
OMe
2
f
OCH
2
3
CMeg
2
]
2
(
ΕΎ
D Mo; H atoms omitted).
