Chemistry Reference
In-Depth Information
EA of
24
(calculated values in brackets): C: 33.09 (34.94), H: 5.98 (6.32), N: 1.23 (1.46).
It is however a relatively fast way of synthesizing the POM-IL and may suffice for
preliminary studies e.g. concerning catalytic activity or chemical behavior of a POM-IL. If
absolutely clean products are needed (e.g. for rheological measurements,
determination of chemophysical properties or electrochemical investigations)
crystallization (and possibly recrystallization) of the functionalized cluster is necessary
prior to its phase transfer. Particular attention has then to be paid that the amount of
crystal bound water is exactly determined e.g. by
Karl-Fischer
titration or TGA, which
makes the alleged simpler one step synthesis rather intricate too.
For the synthesis of the mono-lacunary K
7
[PW
11
O
39
]
·
nH
2
O an aqueous solution of
dodecatungstophosphoric acid has to be brought to a pH of 5 with KHCO
3
,
which
already causes the formation of the cluster at room temperature. Insoluble side
products have to be filtered or centrifuged off before the K
7
PW
11
O
39
·
nH
2
O can directly
be crystallized as white crystals from the concentrated reaction mixture. An additional
recrystallization is recommended.
[79]
During the reaction no metal spatula shall be used
as these can reduce the product (which is seen at hand of a blue coloring).
The reaction with a 3d-heterometal for ligation in the lacuna and the POMs final phase
transfer into toluene works identical to the procedure described for the Si-templated
clusters (see chapter 3.1.1 & 3.1.2.).
Insight into the electronic interaction of the phosphate oxygen with the substituent
metal in the lacuna can be gained at hand of the compounds IR spectra as
Weakley
[80]
and
Rocchicciolo-Deltcheff
[81]
have shown. It is literature known that the P-O stretching
vibration at 1080 cm
-1
in the spectrum of [PW
12
O
40
]
3-
is split by 45 cm
-1
in [PW
11
O
49
]
7-
.
[80]
Examination of the obtained vibrational spectra of (
24
) and (
25
) shows a similar splitting
of 75cm
-1
for the (Q
7
)
5
[PW
11
O
39
Cu(H
2
O)] whereas the spectrum of the
(Q
7
)
4
[PW
11
O
39
Fe(H
2
O)] more closely resembles this of the PW
12
O
40
3-
with one distinct
P-O stretching vibration at 1069 cm
-1
.
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