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give the cationic [Zn(H
2
O)
6
]
21
and the anionic [Ni(NCS)
6
]
4
species. Upon
calcination of the silica-supported compound, ZnO and NiO particles form
that are of smaller sizes hence more active in water gas shift reaction than
the reference material. Another cationic-anionic complex, [Cu(H
2
O)
6
]-
[Ni(dipic)
2
], was prepared from the reaction of (NH
4
)
2
[Ni(dipic)
2
] with
Cu(NO
3
)
2
3H
2
O and also supported on silica and calcined.
11
In this case, a
mixed Ni
0.75
Cu
0.25
O phase was observed in addition to CuO and NiO. Again,
it displayed higher activity than the commercial Sud-Chemie MDC-7 catalyst
and the reference catalyst prepared by a conventional impregnation method.
d
n
9
r
4
n
g
|
5
3.2.3 Heterometallic Complexes with Bridging Ligands
Heterometallic complexes with no formal M-M
0
bond but stabilized through
bridging ligands have also been used as precursors of bimetallic catalysts.
For example, the group of C. M. Lukehart used a chloro-bridged Pt-Ru
complex (Figure 3.2a) for the preparation of Pt
1
Ru
1
/C nanocomposite.
12
The
complex immobilized on Vulcan carbon was activated by rapid microwave
heating and gave supported nanoparticles presenting the nominal ratio of
(a)
(c)
NMe
2
Pt
O
CF
3
Cl
Cl
Ru
O
Pt
Ru
C
2
H
4
Cl
Cl
.
F
3
C
2+
CH
3
CH
3
(b)
(d)
N
N
N
O
O
O
N
O
+
M
2
Ru
M
N
+
M
2
Pt
Pd
Co
N
L
O
O
N
S
N
S
N
O
O
L = H
2
O, acetate
N
N
H
3
C
CH
3
S
Figure 3.2 Example of hetero-bimetallic complexes exempt of M-M
0
bond pre-
senting bridging ligands.
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