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A. Szymanska et al. / Polyhedron 60 (2013) 39–46
Ammonium
bis(pyridine-3-carboxylicacid
N-
oxide)bis{oxodiperoxomolybdate(VI)} compound 1. HMA
(1.43 mmol) was dissolved in cold H2O2 (30 ml, 30%, temp.
ꢀ0 °C). 1 ml of NH3aq was added to the resulting solution. Next
the blood-red solution was acidified with concentrated HCl until
it turned yellow. During constant stirring of the solution 0.01 mol
of nicotinic acid was added. After about 5–7 h the precipitate A
was filtered off. The resulting solution was allowed to crystallize
and after 3–4 days crystals of 1 were obtained. When nicotinic acid
was replaced by nicotinic acid N-oxide, precipitate 1 was obtained
after about 24 h. Yield 90%, C 21.43 (calc. 21.70), H 2.535 (calc.
2.43), N 8.61 (calc. 8.44).
Pyridinium-3-carboxylicacid bis(pyridine-3-carboxylicacid
N-oxide)bis{oxodiperoxomolybdate(VI)} dihydrate, compound
2. Na2MoO4ÁH2O (0.01 mol) was dissolved in 30 ml (30%) cold
H2O2. The resulting red solution was acidified by drops of HCl until
it turned yellow. Next 0.02 mol of nicotinic acid was added to the
solution. After 5–7 h the precipitate B was filtered off and the solu-
tion was left to crystallize at room temperature. After 5–7 days yel-
low crystals of 2 were obtained. Using a mixture of nicotinic acid
N-oxide and nicotinic acid (1:1) the synthesis time is reduced to
1–2 days and the yield is increased. Yield 82%, C 29.69 (calc.
31.60), H 2.532 (calc. 2.65), N 5.70 (calc. 6.14).
Aquaoxodiperoxo(pyridinium-3-carboxylato)molybde-
num(VI), compound 3. HMA (1.23 g) was dissolved in hydrogen
peroxide (20 ml). Next 0.01 mol of nicotinic acid was added
(0.12 g) and the solution was left to crystallize. Small white crys-
tals appeared after about one hour and the next day they were fil-
tered off. Yield 80%, C 22.76 (calc. 22.73), H 22.50 (calc. 2.23), N
4.41 (calc. 4.42).
Scheme 1. Molecular structures of known peroxomolybdates with pyridine (1st
row), pyridine N-oxides (2nd row), pyridine carboxylic acids (3rd row). Cations, if
present, were omitted for clarity (N+–OÀ represent N-oxide fragment). In the
bottom row reaction of the hypothetical reagent ‘oxodiperoxomolybdenum’ moiety
with nicotinic acid is presented. X represents an unknown product.
OXPCXM). There are compounds containing ‘‘purely inorganic per-
oxomolybdate’’ anions (PYPOMO10, MOHFUL) and compounds
composed of: pyridine N-oxides (LEHZIN, ICIVUL), pyridine-car-
boxylic acid (PXCPYM, OXPCXM) or pyridine carboxylic acid N-
oxide molecules (FOXZOH). Picolinic acid (pyridine-2-carboxylic),
an isomer of nicotinic acid, can act as a co-creator of ‘‘picolinic acid
peroxomolybdate complex’’ and its molecules can undergo proton-
ation acting as cations (PXCPYM).
Crystals of 3 turned out to be the same compound as precipitate
B obtained in previous procedure, whereas precipitate A is slightly
different despite almost the same composition.
2.3. X-ray crystallographic study
Study of peroxomolybdenum nicotinic acid compounds can
supplement the existing knowledge of peroxomolybdates with
pyridine-carboxylic acids. Due to the different position of the car-
boxyl group (3-carboxopyridine acid), we can expect a new type of
compounds, including multimeric (dimers, trimers, etc.) or poly-
meric anions (see Scheme 1). Review of the structures indicate that
the results of syntheses with the use of nicotinic acid are difficult
to predict and they are also interesting from the crystal engineer-
ing point of view.
Single-crystal X-ray diffraction studies were performed for all
1–3 compounds. Single crystals were picked up from mother solu-
tions and mounted on the goniometer head. The temperature of
the crystals during the measurement was 293 K. X-ray data were
collected on
a Bruker-Nonius Kappa-CCD diffractometer. For
absorption correction the multiscan procedure was performed by
diffractometer software [7]. Structure solution and refinement
were carried out using the SHELXS and SHELXL-97 programs [8]. All
non-hydrogen atoms were refined anisotropically. Hydrogen
atoms were located from difference Fourier maps. Crystal data
for all obtained oxodiperoxo complexes are presented in Table 1.
2. Experimental
2.1. Materials
2.4. Measurements
All chemicals were purchased from POCH Gliwice and Aldrich,
were used as received.
For IR measurements the samples were pressed into pellets
with KBr and investigated at room temperature with the use of
Fourier and the vacuum spectrometer Bruker VERTEX 70 V. All
spectral lines expected for oxodiperoxo compounds were found
in the recorded spectra.
2.2. Syntheses
Yellow crystals of 1, 2 were obtained initially from aqueous
solutions of HMA (amonium heptamolybdate tetrahydrate
[(NH4)6Mo7O24Á4H2O]) with the addition of H2O2 and nicotinic
acid. Since the synthesis was slow (several weeks) and not
reproducible, we conducted extensive research to find fast and reli-
able methods of synthesis. Compounds 1, 2 were found to contain
N-oxide groups (formed by oxidation of nicotinic acid); therefore,
the use of nicotinic acid N-oxide in the synthesis process was at-
tempted. In the course of preparatory work, reliable methods of
synthesis of both compounds were elaborated. In addition, the
compound 3 was isolated and examined.
X-ray thermal decomposition studies were carried out using a
powder diffractometer Philips X’Pert Pro MPD, equipped with an
Anton Paar high-temperature chamber. X-ray data were collected
at the following temperatures: 25, 50, 75, 100, 125, 150, 175,
200, 225, 250, 275, 300, 350, 400, 500, 600 and 25 °C again. The
heating rate was 5 °C/min, the time of each measurement
15 min. Prior to measurement the temperature was stabilized for
5 min. The 2h range was from 5 to 65°.
SEM images were performed for each sample after thermal
decomposition (600 °C) with the use of an ultrahigh-resolution
Field Emission Scanning Electron Microscope JEOL JSM-7500F