On preparation of platinum(iV) nitrate solutions from hexahydroxoplatinates(iV)

Article abstract of DOI:10.1134/S1070427212070014

The parameters of the processes underlying the current technology of preparation of a Pt(NO₃)₄ solution were studied and optimized. The basic problems of the process scheme were determined, including limited storage time of solid hexahydroxoplatinum (iV) acid. Approaches were suggested for increasing the yield and the storage time of intermediate products and for simplifying the conditioning scheme of platinum (iV) nitrate with a signifi cant reduction of time and energy costs.

Full text of DOI:10.1134/S1070427212070014

ISSN 1070-4272, Russian Journal of Applied Chemistry, 2012, Vol. 85, No. 7, pp. 995−1002. © Pleiades Publishing, Ltd., 2012.
Original Russian Text © A.B. Venediktov, S.V. Korenev, D.B. Vasil’chenko, A.V. Zadesenets, E.Yu. Filatov, S.N. Mamonov, L.V. Ivanova,
N.G. Prudnikova, E.Yu. Semitut, 2012, published in Zhurnal Prikladnoi Khimii, 2012, Vol. 85, No. 7, pp. 1025−1032.
INORGANIC SYNTHESIS
AND INDUSTRIAL INORGANIC CHEMISTRY
On Preparation of Platinum(IV) Nitrate Solutions
from Hexahydroxoplatinates(IV)
A. B. Venediktov, S. V. Korenev, D. B. Vasil’chenko, A. V. Zadesenets, E. Yu. Filatov,
S. N. Mamonov, L. V. Ivanova, N. G. Prudnikova, and E. Yu. Semitut
Nikolaev Institute of Inorganic Chemistry, Siberian Branch, Russian Academy of Sciences, Novosibirsk, Russia
e-mail: venedik@niic.nsc.ru
Krastsvetmet Open Joint-Stock Company, Krasnoyarsk, Russia
Received February 28, 2011
Abstract—The parameters of the processes underlying the current technology of preparation of a Pt(NO3)4
solution were studied and optimized. The basic problems of the process scheme were determined, including limited
storage time of solid hexahydroxoplatinum (IV) acid. Approaches were suggested for increasing the yield and the
storage time of intermediate products and for simplifying the conditioning scheme of platinum (IV) nitrate with
a significant reduction of time and energy costs.
DOI: 10.1134/S1070427212070014
To date, platinum (IV) nitrate (PN) may be considered
as the most promising precursor for the preparation of
supported platinum catalysts, used for post-combustion
of exhaust gases, in particular. This is primarily due to
the fact that a conditioned nitric acid solution of PN is
virtually free from catalyst poisons, especially alkali
metal and Cl- ions, and is therefore superior to precursors
with another ligand environment of platinum (IV). In
addition, PN has a low thermal stability.
the above studies have used the most up-to-date methods
(EXAFS, TEM, NMR), their conclusions are too general
and contain no experimental data on the specific platinum
forms in the solutions.
Available in Russia technology of the preparation of
PN solutions is to a certain extent similar to that proposed
in a patent [3], but is much simpler and improved. The
essence of both methods is expressed by the scheme:
Studies of the acid solutions of NP by the 195Pt NMR
method showed that the solution composition substantial-
ly changes with time. The same conclusion was made in
[1]. The chemistry of these processes remains unknown.
Practically no data are available in the literature on the
forms of platinum in solutions with a high concentration
of metal (cPt ~ 2 M) and nitric acid (up to ~ 10 M),
including existence, nuclearity, and time transformations
of forms, and features of the transformation processes.
Only two studies [1, 2] are published that have a catalytic
orientation and are devoted to commercial PN solutions at
deep alkalization ([OH-]: [Pt] ~ 10). Despite a number of
discrepancies, the above studies confirmed polynuclearity
of the Pt (IV) forms and presence of bridging hydroxo-and
(or) oxo groups between mononuclear fragments. Though
MOH
HNO3
H PtCl —— M Pt(OH) —— H Pt(OH)
→
→
2
6
2
6
2
6
HNO3(conc)
——— PN solution,
→
where М is K+ [3] or Na+ (in a current process), with the
Na+ and Cl– concentrations in the final product must be
strictly controlled in the latter process.
The principal problem in terms of technology is small
storage time of solid H2Pt(OH)6 prior to preparing PN
solutions: 2 or no more than 3 months at best.After expir-
ing these periods, the properties of the reagent change.As
a result, the resulting final product, a nitric acid solution
of PN, does not pass control tests.
995

996
VENEDIKTOV et al.
H2PtCl6·nH2O. According to current regulations, depo-
The study is aimed at increasing the yield of targed
sition of a compound I includes several operations with
a total time of at least 48 hours, ensuring a product yield
of about 72%. Therefore, first, we studied the possibility
of shortening the process time and reducing the number
of operations at the given stage. Moreover, we aimed at
separating a compound I with a content of the residual
Cl- ions not exceeding 0.5%, which corresponds to the
existing requirements for platinum(IV) nitrate solution
and makes preparation of the solution simpler.
products or simplifying the operations in the existing
scheme of the preparation of platinum(IV) nitrate solu-
tions.
EXPERIMENTAL
Chloroplatinic acid produced at a Krastsvetmet Open
Joint-Stock Company plant with a platinum content of
39.1% was starting reagent in all experiments. We used
in the experiments solid H2Pt(OH)6 (65.0% Pt) and a PN
solution (16.6% Pt, d = 1.68 g·cm–3, сPt = 1.43 M, [HNO3]
≈ 13 M), prepared at the above plant. All other reagents
used were no lower than chemical purity grade.
The technique of the experiments was as follows.
A sample of solid H2PtCl6·nH2O (2.44–2.58 g) was
transferred into a narrow and high quartz vessel (capacity
about 25 ml), to which necessary amount of a carbonate-
free solution of NaOH (d = 1.42 g cm–3) was introduced
by weighing (to within ± 0.01 g) to the OH– : Pt molar
ratio about 12. Then, deionized water was added to the
mixture to a total volume of 10–12 ml, the vessel was
covered with a watch glass and heated to a boiling point
without emissions and pushes of the fluid. The boiling
point of the mixtures was 102 ± 1 °C. Boiling began after
12–15 min of switching on heating. After about 30 min
elapsed, crystals of different sizes began to form in the
systems and solutions changed color from a red-orange
to yellow. The time of the reaction was fixed in each
experiment. In some experiments, the reaction mixture
was irradiated by the UV light (a DRSh mercury lamp).
The X-ray phase analysis (XRA) of polycrystalline
samples was carried out on a DRON-RM4 diffractometer
(CuKα radiation, graphite monochromator in the reflected
beam, scintillation detector with amplitude discrimina-
tion). The samples were prepared by applying a suspen-
sion in hexane on the polished side of the cell made of
fused quartz. As an external standard was used a sample
of polycrystalline silicon (a = 5.4309 Å), prepared
similarly. The thermal analysis (DTA) was performed
on a TG 209 F1 Iris Thermo Microbalance instrument
(NETZSCH) in Al2O3 crucibles in a helium or hydrogen
atmosphere at a heating rate of 10° min–1. Experimental
data were processed with a standard Proteus Analysis
software package. In addition, a modified derivatograph
Q-1000 was used for thermal analysis in different gaseous
environments. IR spectra of samples (KBr pellets) were
recorded on a Scimitar FTS 2000 spectrophotometer in
the region 400–4000 cm–1. The content of Cl– ions in
solid samples was determined by capillary electrophoresis
(Capel-103R instrument). Prior to the analysis, complexes
were reduced to metallic platinum with hydrazine hydrate.
The content of Na+ was determined by the atomic absorp-
tion spectroscopy (AAS) on a Z 8000 spectrophotometer
(Hitachi) equipped with Zeeman background correction.
The pH values were measured with an Anion-4100 pH
meter (Infraspak-Analit). The electron absorption spectra
(EAS) were recorded on a MPC-310 spectrophotometer
(Shimadzu) and 195Pt NMR spectra, on anAvance III 500
Bruker spectrometer (frequency 107.5 MHz). Chemical
shifts, positive in a weak field, were counted from the
position of the 21.04-MHz line.
After completing the reaction, solutions with the
precipitates were cooled with an ice-water mixture,
transferred onto a finely porous glass filter, and dried to
constant weight. All the precipitate was quantitatively
transferred from the reaction vessel onto the filter. For
this purpose, we used only mother liquor, which was also
cooled to about 0 °C in most experiments. The separated
precipitates were washed with a minimal volume of ice-
cold water and then with methanol to negative reaction
for Cl- ions (the AgNO3 tests). The maximum volume of
methanol in the experiments was about 30 ml. The use
of acetone instead of СН3ОН for washing precipitate I
did not virtually allow removal of NaCl, whose presence
was clearly seen on diffraction patterns. Evidently, this
is because the solubility of the salt in methanol sharply
increases compared to acetone (1.41 wt% in the first case
[4]). The results of this series of experiments are shown
in Fig. 1.
Analyzing the data in Fig. 1, we note the following.
First, a simple cooling of the reaction mixtures to T ≈ 0 C
before separating precipitates I can significantly increase
Sodium hexahydroxoplatinate(IV). A complex
Na2Pt(OH)6 (I) is the starting product in a processing
chain used for the preparation of PN solutions from
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ON PREPARATION OF PLATINUM(IV) NITRATE SOLUTIONS
997
the product yield. At the reaction time τ = 180 min the
yield was 83.3–90.1%. The experiment at cooling to
room temperature, with reaction time the same (lower
point in Fig. 1), gives a 67% yield. Second, the reaction
time can be reduced to at least 180 minutes, which will
significantly reduce energy consumption. At first glance,
it might seem that the results of some experiments have
poor reproducibility. However, the spread does no exceed
10 rel% and is most likely explained by the fact that on
cooling mother liquors used for transferring precipitates
I from the reaction vessel the temperature was not con-
trolled. A very large scatter of data at τ = 30 min is hard
to explain, and we can only conclude that this time of the
reaction is unacceptable.
Fig. 1. Yield of Na2Pt(OH)6 Q (%) vs. the reaction time τ (min).
The experiments with UV irradiation are based
on the well-known phenomenon, photoactivation of
[PtCl6]2– complexes, which could facilitate formation
of a compound I. At the same time, the effect of light is
ambiguous (Fig. 1).
Sample preparation: (1) cooling to Т ~ 0°C, without UV irradia-
tion, (2) cooling and UV irradiation, and (3) cooling, without
UV irradiation.
coincide with the published data for М2Pt(OH)6 (M+ is
Li, Na, or K) [6–8]. The broad intense band in the region
3400–3500 cm–1 belongs to the stretching vibrations of
OH groups. In the literature, assignment of two bands,
at 1040 and 1110 cm–1, is ambiguous. Most likely, these
bands correspond to deformation vibrations of a PtOH
fragment. The bands at 517 and 656 cm–1 may be due
to the stretching vibrations of Pt–O bond and Pt–OH
deformation vibrations [7].
The obtained samples I were studied by XPA.All sam-
ples, except for those washed with acetone, were single-
phase and their diffraction patterns clearly matched the
available X-ray diffraction database for Na2Pt(OH)6 [5].
The above analysis cannot be applied for the determina-
tion of microcomponents, NaCl inclusions, in particular.
The content of Cl- ions was determined by the method
of capillary electrophoresis. To eliminate influence of
dominating Pt(OH)62– complexes, the starting sodium
salt was reduced by hydrazine hydrate to platinum black,
which was then filtered, and the filtrate was analyzed. In
five samples of compound I from different experiments
the content of chloride ions obtained in the three parallel
determinations at Rconf = 0.95 was 0.21–0.44% at Sr ≤
0.1. Thus, the product of the first chain of the synthesis
of a PN solution was quite conditioning in terms of the
content of impurity chloride ion.
A 0.117 M solution of compound I (pH 11.17) was
titrated with a 0.100 N sulfuric acid. It was found that
H2Pt(OH)6 is precipitated with a nearly quantitative
yield at pH ≈ 2. Upon precipitation in acidic medium,
the acid dissociation constants of the compound cannot
be evaluated.
The thermolysis of a compound I in inert atmosphere
(He) has no separated stages. Only products formed by
thermal decomposition at T = 800–850°C, a mixture of
metallic Pt with α-and β-Na2PtO3, were identified by XPA.
The mass ratio of Pt0 to the oxide phases is approximately
1 : 1. Most likely, the thermolysis process under the given
conditions can be described by the equation
The attained easiness and simplicity of such purifica-
tion of a compound I is associated with the use of metha-
nol at the stage of washing of the separated precipitates. It
is clear that this technique is solely for the laboratory use.
In addition to XPA, the obtained sodium
hexahydroxoplatinates (IV) were studied by other
methods. Determination of Na in a compound I gives a
value of 13.1%, which within the error of the AAS (±0.4
abs %) coincides with the calculated value (13.40%).
The EAS of aqueous solution of a compound I is an
increasing exponent at λ ≤ 500 nm not containing clearly
resolved lines. IR spectra of a compound I completely
2Na2Pt(OH)6 → Pt + α-, β-Na2PtO3 + O2 + Na2O
+ 6H2O.
(1)
Interestingly, the thermolysis of lithium salt up to Т ≈
1000°С in nitrogen proceeds by the total equation
Li2Pt(OH)6 > Li2PtO3 + 3H2O
(2)
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 85 No. 7 2012

998
VENEDIKTOV et al.
several days to several months under normal conditions.
The color of some samples remained unchanged after one
year of receiving them.
Similar phenomenon was also observed in mother
liquors after separating precipitates I: colloidal particles
of black color were formed during storage of light yellow
liquids in polypropylene terephthalate containers.Accord-
ing to XPA, they are a metallic platinum. Interestingly,
mother liquors stored in a glass or plastic vessel with
the addition of finely divided glass retain the initial state
during the year, with metallic platinum not separated in
these cases.
DTA
TG
Fig. 2. Thermogram for salt (I) in hydrogen. (m) Sample mass
(% of initial) and (T) temperature (°C); the same for Fig. 3
Probably, the above facts may indicate that the com-
pound I is thermodynamically unstable. The thermal
decomposition in an inert atmosphere is incomplete,
proceeds in a very wide temperature range, and the re-
action products themselves can not be characterized by
reliable values of thermodynamic functions. However, the
compound H2[Pt(OH)6] related to the compound I is ther-
modynamically stable [10]. The standard Gibbs energy of
formation of this compound is –989 kJ mol–1. Therefore,
the described changes in the state of the compound I on
storage are most likely associated with another reasons
than thermodynamic stability.
and is not accompanied by the formation of Pt0 [6]. In
[6], products of reaction (2) were identified solely by the
mass loss, and no XPA was carried out.
Figure 2 shows the DTA curves of the salt I in hydro-
gen atmosphere. Replacement of the inert atmosphere
for the reducing one substantially changes thermolysis
process. In the comparable gaseous environments, the
temperature of the end of the decomposition in Н2 is
reduced by about 400°C, with the reaction proceeding
by the equation
In conclusion, we note that the transformations of
a compound I on storage (yellowish color changes to
black color) at Т = –(12–14)°С do not proceed.
Na2Pt(OH)6 > Pt + 2NaOH + 4 H2O.
(3)
Hexahydroxoplatrinum (IV) acid, Н2[Pt(OH)6].
The crystal structure of Н2[Pt(OH)6] (compound II) and
its salts with alkali metals is known [11, 12]. Solid prepa-
rations of II were characterized by means of DTA, XPA,
and IR spectroscopy. Figure 3 shows the DTA curves for
the acid (II).
The validity of equation (3) is confirmed by the XPA
(only reflections of metallic platinum are present and
reflections of Na2PtO3 are absent in the final products)
and by the coincidence of the experimental mass loss
(21.0%) with its calculated value (20.98%).
The 195Pt NMR spectrum of an aqueous solution I
has a single line with a chemical shift of 7830 ppm,
which agrees well with a value of 7823 ppm from [9].
The spectrum does not change for at least 2 months of
storage of the solution.
A part of the TG curve within 440 ± 20 °C showing
a mass loss of about 24% is due to the formation of PtO2.
The next step above 550°C corresponds to the mass loss
Δm = const = 35.0%.According to the XPA, the product is
a metallic platinum. The theoreticalΔm value is 34.79%.
Consequently, the thermolysis of the studied sample in
inert atmosphere is well described by the scheme:
On storage, the color of the solid samples of
Na2Pt(OH)6 varied from yellowish to gray and then to
black. Only reflections of the original salt, regardless
of the degree of blackening, were recorded on the dif-
fraction patterns of these products. This phenomenon
is explained only by the fact that “black” components,
which may in principle be Pt0 and (or) platinum oxide,
are in the amorphous or very fine state. The observed
phenomenon is spontaneous and random. Blackening
of the solid samples I was observed during storage from
Н2[Pt(OH)6] > PtO2 + 4Н2О > Pt0.
(4)
Figure 4 demonstrates diffraction patterns of a com-
pound II obtained from different batches in comparison
with the data of [13].As seen, the KZTsM sample contains
a highly crystalline phase (II) and no amorphous phase.
At the same time, peaks corresponding to the insignificant
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ON PREPARATION OF PLATINUM(IV) NITRATE SOLUTIONS
999
a
DTA
b
c
TG
Fig. 4. Diffraction patterns of H2[Pt(OH)6]. Sample: (a)
produced at a Krastsvetmed Open Joint-Stock Company, (b)
synthesized in the study, and (c) data of [14]. (I) Intensity
(rel. units), (2θ) scan angle (deg), and (I) reflections of impurity
crystalline phases.
Fig. 3. Thermogram for Н2[Pt(OH)6] in helium.
amount (less than 5 wt %) of crystalline phase of unknown
composition are also present. The freshly synthesized
sample of the acid is highly crystalline (Fig. 4b), with
minority of the impurity crystalline phase, apparently
a polymeric compound, also present. A certain basis
for this assumption is the IR spectrum of the product
(II). In contrast to the spectrum of the sodium salt, it is
poorly resolved, contains a broad intense band centered
at 3140 cm–1 and the low-intensity bands at 1620 and
530 cm–1. The first two bands belong, respectively, to
stretching and deformation vibrations of water molecules,
which are present owing to polycondensation reactions
proceeding with the formation of dimers or oligomers
containing bridging OH groups [14].
steps: (a) the separated deposit was stirred in a 0.001 M
HNO3 (volume 30 ml) for 0.5–1 h with a magnetic stirrer,
(b) the pulp was settled for the same time in a water-ice
mixture, (c) 3–5 ml of the transparent colorless solution
were taken for the determination of Na+ ions and then
the solution was separated by decantation at T ≈ 0°C to
minimum volume, with no solid phase entering into the
decantate.
The above cycle was repeated ten times. The ex-
perimental results are presented in Table. 1. The total
time of all the described procedures was about 12 h.
As seen from Table 1, the proposed method can yield
a product of necessary quality (containing no more than
0.5% Na+) after the sixth cycle, which is lower by an
order of magnitude than the time spent in the current
plant regulation. Moreover, with use of ice nitric acid
solution (0.001 M HNO3) as a washing fluid the appear-
ance of a white suspension after the sixth cycle may be
a distinct sign of the completion of the process, and no
additional control is necessary. At the end of the series,
the remaining product (see diffraction pattern in Fig. 4b)
was separated, dried, and weighed. Its mass was 1.064 g.
With respect to a weighed portion (I), the yield of the
acid (I) was 88.4%, with account taken for the weight of
insoluble residue (98.2% by platinum). These values are
significantly higher than those available in technology
(up to 60% recovery for platinum).
In further experiments, we set two main goals: (1)
simplification of the acid treatment to remove Na+ and
(2) determination of the conditions, at which the storage
time of the acid (II) is the maximum admissible value.
The first problem was solved by the procedure including
preparation of a salt Na2[Pt(OH)6] by the above method
and washing it to a Cl– content of 0.34 ± 0.03%. Sample
(1.380 g) of the freshly prepared salt I was dissolved in
30 ml of deionized water (s : l = 1 : 22) for 25 min and the
insoluble residue was separated by filtration in the form
of a fine black powder (weight 0.138 g). The residue,
while processed with HCl at low temperature, undergoes
fast and qualitative passage into yellow solution, which,
while heated on a water bath for a short time, very quickly
turns to a clearly heterogeneous mixture of black-brown
color. Consequently, it is another form than Pt0. Then,
Н2[Pt(OH)6] was precipitated from the resulting transpar-
ent colorless filtrate (initial pH 12.04) with HNO3(conc.) to
pH 3.22. We carried out the following series of successive
Asmentionedabove,Н2[Pt(OH)6]isthermodynamically
stable [12]. Therefore, we can assume that the sodium salt
is stable. In this case, the reasons for the limited storage
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 85 No. 7 2012

1000
VENEDIKTOV et al.
about 5 h prior to the measurements.
Table 1. Results of experiments on Н2[Pt(OH)6] treatment by
the proposed method to remove sodium ions
As seen from Table. 2, the 195Pt NMR spectra of the PN
solutions kept for about 5 h have a plenty of signals, which
can hardly be attributed to the coexistence of mononuclear
platinum forms in aqueous PN solutions with high HNO3
concentrations. There are two reasons for this conclusion.
First, the system Pt(OH)62––(H)NO3–Н2O looks like
a very dynamic system, which is very unusual for such
extremely inert central atom as platinum (IV). Second,
the difference in chemical shifts of some nearby signals is
on the order n × 101 ppm, which is extremely small value
for the ligand substitution in platinum (IV) complexes [9].
Unfortunately, the nitric acid ate solutions of PN have
no reliably identified reference compounds, which are
formed in the course of the transformations in the system.
Therefore, any interpretation of the data from Table 2
is ambiguous. Apparently, only one conclusion can be
made: the signals in a weak field and their diversity in
the 195Pt NMR spectra are due to oligomeric compounds
with minor changes in the coordination spheres. For the
sulfate complexes of Rh (III) this result was established
in [15]. Therefore, for Pt (IV) compounds, the similar
interpretation seems reasonable. It may be assumed that
the above oligomeric compounds are also formed in PN
solutions, with some signals from monomeric compounds
and their relative intensities in the strong field retained.
Na content
сNa,
μg·ml–1
mNa in sample,
Cycle no.
in Н2[Pt(OH)6],
mg
%
1
2
3
4
5
6
7
8
9
4700
2030
1010
365
141
11.4
4.90
2.44
0.88
0.73
0.22
0.1
60.9
30.3
10.95
9.06
2.76
1.29
0.66
0.645
302
92.0
43.0
22.0
21.5
0.053
0.052
10
7.0
0.21
0.017
time of a compound II should be sought in another
direction. Note, on diffraction patterns of Н2[Pt(OH)6]
an unknown phase (or phases) is (are) clearly resolved
(Fig. 4). The increase in the storage time of a compound
II is achieved by maintaining the solid samples II in
a freezing chamber [T = –(13 ± 1)°C]. It turned out that in
this case, the PN solutions obtained from the salt II sustain
control plant tests, even after 10 months of preparation.
At the same time, spectra of the PN solutions kept
during the year, irrespective of storage conditions, have
no signals in the whole range of the currently available
195Pt (IV, II) NMR signals, from –500 to 12200 ppm. In
[1], similar result was explained by nucleation of initial
monomeric Pt (IV) hydroxoforms to form oligomers
with bridging OH groups. This can lead to splitting, shift
(in weak field), and broadening of the signals until their
complete disappearance in the spectrum.
Solutions of Pt(IV) nitrate. An one-year monitor-
ing of the platinum(IV) nitrate solutions prepared from
frozen samples of Н2[Pt(OH)6] showed that the control
properties of these solutions remain unchanged regard-
less of the storage temperature. The X-ray analysis of
the PN solution at about –180 °C showed that under
these conditions the substance is in a glassy, rather than
in crystalline phase (no clear reflections are present on
diffraction pattern).
CONCLUSIONS
The 195Pt NMR spectra of the PN solutions prepared
in accordance with the above recommendations were re-
corded. To do this, samples (0.70–0.73 g) of a freshly pre-
(1) All stages of the preparation of platinum(IV) solu-
tions from hexachloroplatinic acid were studied. The main
features of the process chain were determined, which
enabled a considerable reduction of time and energy
expenditure along with simplification of the process and
improvement of its performance.
pared acid (II) were inserted into a 3.0 ml of HNO3(conc)
.
Preliminarily, aliquots of HNO3 were heated to different
temperatures in the range 0–65°C. The results of the NMR
analysis are given in Table 2. Experiments nos. 1a, 1b, and
1c correspond to a solution of freshly precipitated prod-
uct II, which was dissolved in HNO3(conc) for 30 s, with
NMR signals successfully accumulated for 10 minutes.
For experiments nos. 2–4, the PN solutions were kept for
(2) Simple and efficient method was suggested for
prolonged storage of a target product, H2Pt(OH)6, and
its treatment to remove sodium ions.
(3) It was found that “aging” of platinum(IV) solutions
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 85 No. 7 2012

ON PREPARATION OF PLATINUM(IV) NITRATE SOLUTIONS
Table 2. Chemical shifts in 195Pt NMR spectra of Pt(IV) nitrate solutions
1001
Chemical shift, ppm, in experiment no.
Line
1a
(room)b
2
1c (room)
3
1b (room)
4a (room)
(0°С)
(65°С)
1
2
7863
7860
7858
–
–
–
7953
7953
7950
–
–
–
3
8056
8056
8056
–
–
–
4
8119
–
–
–
–
–
5
8166
8167
8167
8170
8178
8272
8290
8393
8398
8431
8434
–
8170
8178
8273
8290
8394
8398
8431
8434
8450
8465
8473
8526
8545
8579
8607
8734
8740
8748
8761
8767
8856
9120
8169
8177
8272
8289
8393
8398
8431
8434
8450
8465
8473
8527
8546
8579
8607
8734
8740
8748
8762
8767
8856
9120
6
8174
8174
8174
7
–
–
8271
8
8286
8286
8286
9
8389
–
8390
–
8390
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
–
–
–
8430
–
–
8432
–
–
–
–
–
–
8465
8473
8526
8546
8579
8607
8734
8740
8748
8762
8767
8856
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
a Н2[Pt(OH)6] sample was stored for 6 months at room temperature prior to dissolution in HNO3.
b
Temperature, at which a compound (II) was dissolved in nitric acid, is given in the brackets.
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1002
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The authors are thankful to N.I.Alferova, S.V. Tkachev,
O.V. Shuvaeva, and E.V. Polyakova (Nikolaev Instritute
of Inorganic Chemistry, Siberian Branch of the Russian
Academy of Sciences) and I.V. El’tsov (Novosibirsk
State University).
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