Synthesis and properties of Na6[Pb(S2O 3)4] · 6H2O

Article abstract of DOI:10.1134/S0036023610020075

Conditions for the synthesis of the water-soluble lead thiosulfate complex Na₆[Pb(S₂O₃)₄] · 6H2O were determined. The complex synthesized was characterized by UV and IR spectroscopy and X-ray phase and thermal a

Full text of DOI:10.1134/S0036023610020075

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ISSN 0036ꢀ0236, Russian Journal of Inorganic Chemistry, 2010, Vol. 55, No. 2, pp. 179–185. © Pleiades Publishing, Ltd., 2010.
Original Russian Text © N.B. Egorov, 2010, published in Zhurnal Neorganicheskoi Khimii, 2010, Vol. 55, No. 2, pp. 185–190.
SYNTHESIS AND PROPERTIES
OF INORGANIC COMPOUNDS
Synthesis and Properties of Na6[Pb(S2O3)4] · 6H2O
N. B. Egorov
Tomsk Polytechnic University, pr. Lenina 30, Tomsk, 634050 Russia
Received September 19, 2008
Abstract—Conditions for the synthesis of the waterꢀsoluble lead thiosulfate complex Na6[Pb(S2O3)4] · 6H2O
were determined. The complex synthesized was characterized by UV and IR spectroscopy and Xꢀray phase
and thermal analyses. Thermolysis schemes were proposed on the basis of the IR and mass spectra of the therꢀ
mal decomposition products.
DOI: 10.1134/S0036023610020075
The interaction of equivalent amounts of Pb(NO3)2 higher. At other ratios insoluble PbS2O3 remains in the
or Pb(CH3COO)2 with Na2S2O3 in aqueous solutions
yields poorly soluble compounds PbS2O3 [1] and
Pb3(S2O3)2(CH3COO)2 [2]. These compounds are disꢀ
solved in an Na2S2O3 excess to form lead thiosulfate
complex ions [Pb(S2O3)2]2–, [Pb(S2O3)3]4–, and
[Pb(S2O3)4]6– [3].
The purpose of this work is to recover waterꢀsoluble
lead thiosulfate complexes in the solid phase and charꢀ
acterize them.
solution.
Thus, the lead thiosulfate complexes were recoꢀ
vered to the solid phase from solutions with the molar
ratio Pb2+ :
2− = 1 : 4.
On heating and storage solutions of the lead thioꢀ
sulfate complexes decompose to form PbS, which
makes impossible their isolation by the evaporation of
the solvent.
S2O3
The lead thiosulfate complexes can be isolated
from solutions using alcohol. When ethanol is used,
the lead thiosulfate complexes are isolated as an oily
liquid, which is separated and treated with absolute
ethanol (without additional treatment, the liquid
decomposes with time to form PbS). The oily liquid
gradually transforms into a powder, which is filtered
off, washed, and dried in air.
A drawback of method (1) is the necessity to repreꢀ
cipitate the product because of its contamination with
NaNO3, which enchances the decomposition of the
lead thiosulfate complexes. In this case, the yield of
the product decreases.
EXPERIMENTAL
The following reagents were used: Na2S2O3 5H2O
⋅
(pure for analysis grade), Pb(NO3)2 (pure for analysis
grade), and PbS2O3 prepared by reacting solutions of
Pb(NO3)2 and Na2S2O3 [1].
Lead thiosulfate complexes were synthesized using
two methods. In method (1), exact weighed portions
5H2O and Pb(NO3)2 were dissolved in a
minimum volume of water and combined by pouring a
solution of Pb(NO3)2 solution to a solution of Na2S2O3
the relevant reaction is
of Na2S2O3
⋅
;
The product is isolated as a nonhygroscopic white
powder. The yield of the lead thiosulfate complexes in
method (2) is 75%.
The compositions and structures of the compounds
synthesized were determined by elemental and therꢀ
mal analyses and IR spectroscopy.
The complexes were analyzed for lead [4] and sulꢀ
fur [5]. The amount of water was determined from
thermal analysis data.
Pb(NO3)2 + xNa2S2O3
(1)
Na(2x − 2)[Pb(S2O3)x] + 2NaNO3,
= 2–4.
Reaction (1) proceeded in two stages: poorly soluꢀ
where
x
ble PbS2O3 was first formed in the solution (the soluꢀ
bility product was
4
×
10–7) and then dissolved in an
Na2S2O3 excess.
In method (2), a PbS2O3 powder was dissolved in a
saturated solution of Na2S2O3; the relevant reaction is
For Na6[Pb(S2O3)4] 6H2O anal. calcd. (%): Pb,
⋅
22.98; S, 28.45; H2O, 11.98.
PbS2O3 + yNa2S2O3
Na2y[Pb(S2O3) y + 1 ],
(2)
(
)
Found (%): Pb, 23.1; 23.02; S, 28.40; 28.35; H2O,
11.81.
Thus, according to the elemental and thermal
analyses, the synthesized compound is formulated as
where y = 1–3.
Lead thiosulfate PbS2O3 formed then the solutions
were combined according to method (1) and the
PbS2O3 powder used in method (2) are completely disꢀ
solved only when the molar ratio Pb2+ :
Na6[Pb(S2O3)4]
⋅
6H2O (sodium tetrathiosulfatoplumꢀ
2− = 1 : 4 or bate hexahydrate).
S2O3
179

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180
EGOROV
Xꢀray diffraction patterns were measured on a Shiꢀ
madzu XRD 6000 diffractometer (Cu radiation).
IR spectra as KBr pellets were recorded on a Nicoꢀ
let 6700 IR spectrometer in the range 400–4000 cm–1
at room temperature.
The electronic absorption spectra of solutions were
recorded on an Evolution 600 spectrophotometer
using 1ꢀcm quartz cells.
Thermogravimetric studies were carried out on an
SDT Q600 analyzer in the temperature range from 20
to 800°C under a nitrogen or air atmosphere. Thermal
decomposition products were identified using IR
absorption spectra recorded for samples stored before
At a solution concentration of 0.1 mol/L, platy
pearly roundꢀshaped crystals precipitate from the
solutions after 8–10 h. The IR spectrum of the comꢀ
pound isolated from the solution is identical to that of
PbS2O3 (Table 2). This indicates that in an aqueous
solution the complex undergoes hydrolysis and
decomposes.
It should be noted that PbS2O3 prepared by reacting
solutions of Pb(NO3)2 and Na2S2O3 has no proꢀ
nounced crystal structure, unlike PbS2O3 formed by
the hydrolysis of sodium tetrathiosulfatoplumbate
hexahydrate.
K
α
The electronic absorption spectra of PbS2O3,
and after the corresponding endoꢀ or exotherms in a Na2S2O3
vacuum or in air.
Gases evolved upon the thermal decomposition
were analyzed using a TRACE DSQ chromatograph/
mass spectrometer.
,
and sodium tetrathiosulfatoplumbate
hexahydrate are shown in Fig. 1. The spectrum of
sodium tetrathiosulfatoplumbate hexahydrate, as well
as that of PbS2O3, is characterized by the presence of
two absorption bands in the UV region: one is the
chargeꢀtransfer band from thiosulfate ions to solvent
molecules with a maximum at 215 nm, which is also
observed in the spectrum of Na2S2O3, and the other is
the chargeꢀtransfer band from thiosulfate ions to lead
ions with a maximum at 256 nm. The electronic
absorption spectrum of sodium tetrathiosulfatoplumꢀ
bate hexahydrate differs from that of PbS2O3 by the
bathochromic shift of the adsorption edge at 215 nm,
which is related to an increase in the amount of the
thiosulfate ions surrounding the lead ion.
The study of the thermolysis of the compound in
air and in a nitrogen atmosphere showed that the therꢀ
mal decomposition of sodium tetrathiosulfatoplumꢀ
bate hexahydrate proceeded in three stages (Figs. 2, 3).
Heating first results in removal of water of crystallizaꢀ
tion. Second, the dehydrated complex decomposes at
the second stage. At the third stage, the decomposition
products are oxidized (in air) or removed (in nitroꢀ
gen).
RESULTS AND DISCUSSION
The Xꢀray phase study showed that the compounds
synthesized by methods (1) and (2) were alike, being
one individual substance that possessed a characterisꢀ
tic Xꢀray pattern containing no lines of the starting
components (Table 1).
The individual character of the compound was also
proved by IR spectra. The frequencies observed in the
IR spectra of the compound and their assignments to
the vibrations of atomic groups are given in Table 2.
According to [1], the vibration νas(SO) is the most
fruitful for the determination of the structure of thioꢀ
sulfate compounds: >1175 cm–1 (S bridging), 1175–
1130 cm–1 (S coordinated), ~1130 cm–1 (ionic
2−),
S2O3
and <1130 cm–1 (O coordinated). The shift of the
νs(SO) vibration to higher frequencies than 1000 cm–1
indicates the coordination through the sulfur atom,
and the shift to below 1000 cm–1 indicates the coordiꢀ
nation through the oxygen atom. As can be seen from
the data in Table 2, the thiosulfate group is coordiꢀ
nated to the lead atom through the sulfur and oxygen
atoms and acts as a bidentate ligand.
The thermolysis is accompanied by the formation
of volatiles. According to the massꢀspectrometric
data, the thermolysis products contains ions with the
following mass numbers: 48, 64, 80, 96, 128, 160, 192,
224, and 256. The peaks in the mass spectrum correꢀ
sponding to the masses 48 and 64 amu are attributed to
the fragmentation radical ion SO+ and sulfur dioxide
The 3300–3600 cm–1 range of the IR spectrum
+
contains two peaks with maxima at 3395 and 3517 cm–1
. The presence in the mass spectra of the molecuꢀ
+
SO2
associated with
ν
(OH) of water molecules. The presꢀ
lar ion with the mass number 256 and its fragmenꢀ
S8
ence of two maxima may arise from the nonequivaꢀ
lence of water molecules in the structure of sodium
tetrathiosulfatoplumbate hexahydrate as to the disꢀ
tance from the metal atom and involvement in hydroꢀ
gen bonding.
The compound synthesized is highly soluble in
water. At concentrations of 0.5 mol/L and higher,
sodium tetrathiosulfatoplumbate hexahydrate is disꢀ
tation from S8 to S2 (
m/z = 224, 192, 160, 128, 96,
and 64) indicate the formation of sulfur upon the therꢀ
molysis of sodium tetrathiosulfatoplumbate hexahyꢀ
drate. The mass spectrum also contains a lowꢀintenꢀ
sity peak with the mass number 80, which may be
+
assigned to sulfur trioxide
.
SO3
The DTA curves in the range 20–90°С contain two
solved with the formation of a minor amount of PbS, endotherms with maxima at 52 and 88°С correspondꢀ
and the solution turns brown. On storage, the highly ing to the stepped dehydration of sodium tetrathioꢀ
concentrated solutions decompose with time to form sulfatoplumbate hexahydrate. The weight loss in air is
PbS.
11.5% under a nitrogen atmosphere 11.81%, which
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SYNTHESIS AND PROPERTIES
Table 1. Interplanar spacings and line intensities for Na6[Pb(S2O3)4] 6H2O
181
⋅
d, Å
I
, %
d
, Å
I, %
d
, Å
I
, %
12.133
11.841
11.539
10.961
10.644
10.132
9.709
7.622
7.459
6.736
6.532
6.412
6.329
6.233
5.756
5.668
5.619
5.514
5.460
5.387
5.102
4.995
4.944
4.715
4.643
4.575
4.458
4.431
4.334
4.262
4.163
4.099
4.048
3.981
3.948
3.831
3.778
3.719
3.664
5
9
3.605
3.537
3.503
3.474
3.442
3.378
3.356
3.290
3.275
3.222
3.202
3.114
3.091
3.021
2.993
2.978
2.958
2.926
2.888
2.864
2.833
2.799
2.762
2.739
2.714
2.680
2.648
2.579
2.558
2.537
2.486
2.453
2.416
2.406
2.361
2.350
2.323
2.311
2.257
5
2.247
2.236
2.227
2.202
2.193
2.167
2.122
2.095
2.085
2.072
2.063
2.053
2.045
2.034
2.018
2.010
1.986
1.978
1.970
1.942
1.922
1.914
1.887
1.878
1.868
1.861
1.852
1.836
1.822
1.812
1.803
1.790
1.775
1.742
1.736
1.705
1.697
1.691
1.679
8
5
9
24
32
18
16
28
5
29
33
26
89
13
100
66
5
11
6
7
9
15
10
7
13
10
15
5
38
25
28
19
17
21
24
12
54
24
39
63
29
7
7
13
16
5
6
5
14
48
59
47
52
6
10
5
14
12
10
5
25
5
14
10
12
15
16
13
6
14
10
5
14
50
19
21
6
20
8
10
100
25
14
10
29
14
5
6
5
7
21
10
12
10
19
7
7
6
7
6
10
9
5
22
5
5
48
28
7
11
9
10
6
7
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182
EGOROV
Table 2. Maxima of the vibration frequencies (cm–1) and their assignment in the IR spectra of Na6[Pb(S2O3)4]
⋅
6H2O,
Na2S2O3, PbS2O3, and the compound formed by the hydrolysis of Na6[Pb(S2O3)4]
⋅
6H2O
Na6[Pb(S2O3)4]
⋅
6H2O Na2S2O3 [1] PbS2O3 [1] Compound formed by Na6[Pb(S2O3)4] 6H2O hydrolysis Band assignment
⋅
3526
3396
1631
1594
1151
1126
1027
1011
694
ν
(OH)
(OH)
δ
1160
1130
1002
1140
1116
988
1141
1119
988
ν
as(SO)
ν
s(SO)
680
668
645
624
645
625
δ
s(SO)
680
643
551
542
439
555
535
338
541
516
434
542
517
435
δ
as(SO)
ν
(SS)
corresponds to the removal of six water molecules per groups of sodium tetrathiosulfatoplumbate hexahyꢀ
molecule of the compound and the formation of anhyꢀ drate appear at 90 (Fig. 4, curve ). These changes
drous sodium tetrathiosulfatoplumbate (the calcuꢀ are due to the splitting of the absorption bands in the
°
С
1
lated loss is 11.98%).
frequency regions of νas(SO) and νs(SO). Visually
sodium tetrathiosulfatoplumbate retains its original
The dehydration of sodium tetrathiosulfatoplumꢀ
bate hexahydrate in both nitrogen and air is accompaꢀ
nied by partial decomposition and removal of the
white color up to 120°С
.
The heating in the range 115–180°С is accompaꢀ
decomposition products, as observed in the TG curves. nied by the distortion of the sodium tetrathiosulfꢀ
The nonequivalence of the water molecules in sodium atoplumbate structure, which is seen from the changes
tetrathiosulfatoplumbate hexahydrate in the IR specꢀ in the IR spectra. The compound becomes brown.
tra of the residues becomes more pronounced as temꢀ
perature increase (Fig. 4, curve ). According to the IR
spectra, the complete dehydration of sodium
tetrathiosulfatoplumbate hexahydrate occurs at 115°С
in both cases.
In both cases, the complete decomposition of
sodium tetrathiosulfatoplumbate occurs in the range
180–350°С. The absorption bands characteristic of
the thiosulfate groups gradually disappear from the IR
spectra, the absorption band at 1120–1150 cm–1
1
The first changes in the IR spectra of the residues becomes broader, and the absorption band with the
arising from the decomposition of the thiosulfate maximum at 625 cm–1 assigned to the bending vibraꢀ
D
6
4
3
2
2
1
0
210
230
250
270
290
310
330
350
, nm
λ
–4
–4
Fig. 1. Electronic absorption spectra of (1) Na S O (5 × 10 mol/L), (2) PbS O (5 × 10 mol/L), and (3) Na [Pb(S O ) ] ·
2 2 3 2 3 6 2 3 4
–4
6H O (5 × 10 mol/L).
2
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