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Russ.Chem.Bull., Int.Ed., Vol. 54, No. 8, August, 2005
Pai et al.
various anions (1Aa with F–, 1Ab, 1Bb, and 1Cb with Cl–,
and 1Bc with Br–). As can be seen from Table 2 and
Fig. 1, the absorption bands in the IR spectra of complex
compounds 2Aa, 2Ab, and 2Bb prepared with the use of
quaternary ammonium fluoride (QAF) or chloride (QAC)
correspond to the {PO4[WO(O2)2]4}3– anion and agree
well with our results11 and the published data.3,4,10
spond to the K2[W2O3(O2)4(H2O)2] (956, 851, 619, 568,
558, 331, and 318 cm–1) and [Bu4N]3{PO4[WO(O2)2]4}
(980, 860, 591, 578, 534, 330, 298, and 259 cm–1) comꢀ
pounds and are consistent with the results of the study.9
In the synthesis of complex 2Bc with the use of quaꢀ
ternary ammonium bromide (QAB) 1Bc, the reaction mixꢀ
ture warmed up and vigorous foaming occurred in the
step of precipitation of the peroxo complex. These pheꢀ
nomena were not observed in reactions with the use of
QAF and QAC. In the IR spectrum of the yellow crystalꢀ
line compound (2Bc) prepared by precipitation of the
peroxo complex with QAB (1Bc), the absorption bands of
The IR spectrum of complex compound 2Aa (see
3–
Fig. 1) shows absorption bands of the PO4 ion (1085,
1052, and 1038 (sh) cm–1), the W=O bond (971 cm–1),
the O—O bond (856 and 845 cm–1), and antisymmetꢀ
ric and symmetric vibrations of W—O—O (590 and
521 cm–1). The spectrum also has other absorption bands
(722, 736, 651, 577, and 550 cm–1) associated with abꢀ
sorption of the cation.
3–
the PO4 ion (1089, 1069, and 1032 (sh) cm–1) only
partially consistent with the published data.9,10 Other abꢀ
sorption bands in the spectrum do not correspond to
the catalyst [C5H5N(CH2)15Me]3{PO4[WO(O2)2]4} (see
Fig. 1, d).
The IR spectrum of complex compound 2Ab shows
3–
absorption bands of the PO4 ion (1082, 1051, and
1036 (sh) cm–1), the W=O bond (970 cm–1), the O—O
bond (855, 844 cm–1), antisymmetric and symmetric viꢀ
brations of W—O—O (591 and 521 cm–1), and absorption
bands at 721, 735, 650, 574, and 549 cm–1 characterizing
the cation.
The observed influence of QAB (1Bc) on decomposiꢀ
tion of the peroxo complex can be attributed to the higher
reducing power of the bromine salts compared to QAF
and QAC (QBr > QCl > QF), which is also true for the
series of halogens F2 > Cl2 > Br2, whose standard redox
potentials (E°)12 are 2.87, 1.359, and 1.065 V, respecꢀ
The IR spectrum of compound 2Bb has absorption
bands of the PO43– ion (1088, 1061, and 1038 (sh) cm–1),
the W=O bond (988 and 961 cm–1), the O—O bond
(856 and 844 cm–1), antisymmetric and symmetric vibraꢀ
tions of W—O—O (591 and 526 cm–1), and absorption
tively. Apparently, the redox reactions W2O5 + 2 Br–
+
2 H+ → Br2 + 2 WO2 + H2O resulting in decomposition
of tungsten peroxo complexes can occur in solution upon
the addition of QAB.
bands at 722, 650, 571, and 548 cm–1
.
This assumption is also supported by the characteristic
features encountered by mixing with KBr and compacting
into wafers for measurements of IR spectra. As can be
seen from Fig. 3, the spectra of catalysts 2Aa and 2Bb,
which were synthesized with the use of QAF (1Aa) and
QAC (1Bb), respectively, recorded in KBr pellets (a, c)
differ from the spectra measured as Nujol mulls (b, d).
The spectra b and d correspond to the structures of the
complexes synthesized, whereas the absorption bands in
the spectra a and c are inconsistent with these structures,
which can be associated with decomposition of the comꢀ
plexes due to interaction of the Br– ions with the peroxide
groups. The longer the time from the preparation of the
sample to the onset of exposure, the larger discrepanꢀ
cies observed in the spectra. An analogous situation is
also characteristic of the tungsten peroxo complexes
[W2O3(O2)4(H2O)2]2–. The IR spectra of the potassium
salt of this complex are shown in Fig. 4.
The Raman spectra (Fig. 2) were recorded for catalyst
2Aa and the complex salt, which was prepared from the
filtrate after isolation of 2Aa according to the procedure
described earlier.11 The spectra a and b (see Fig. 2) correꢀ
a
1200
800
400
ν/cm–1
b
Attempts to change the conditions of the synthesis in
the step of addition of QAH (variations in the temperaꢀ
ture (5—30 °C) and pH, the addition of either dry QAH
or QAH predissolved in water) were unsuccessful. Thereꢀ
fore, regardless of the nature of the quaternary cation,
QAB do not allow one to perform the synthesis of cataꢀ
lytic systems of the desired composition including tungꢀ
sten peroxo complexes.
1200
800
400
ν/cm–1
Fig. 2. Raman spectra of the catalysts based on
peroxopolyoxometallates: К2[W2O3(O2)4(H2O)2] (a) and
[Bun4N]3{PO4[WO(O2)2]4} (b).
Of all the complexes synthesized (see Table 2), tetraꢀ
nꢀbutylammonium tetra(diperoxotungsto)phosphate (2Aa