Kinetics of reactions between bromoplatinum(II) complexes and silver nitrate

Article abstract of DOI:10.1134/S0036023607120145

The kinetics of the reactions of bromide complexes [[PtenBr₂], [Pt(NH₃)₂Br₂], and [enPtBr₂Pten] (NO₃)₂ with AgNO₃ are studied potentiometrically. The reactions occur i

Full text of DOI:10.1134/S0036023607120145

ISSN 0036-0236, Russian Journal of Inorganic Chemistry, 2007, Vol. 52, No. 12, pp. 1887–1891. © Pleiades Publishing, Inc., 2007.
Original Russian Text © M.I. Gel’fman, O.V. Salishcheva, N.E. Moldagulova, E.V. Seryakova, 2007, published in Zhurnal Neorganicheskoi Khimii, 2007, Vol. 52, No. 12,
pp. 2003–2006.
COORDINATION
COMPOUNDS
Kinetics of Reactions
between Bromoplatinum(II) Complexes and Silver Nitrate
M. I. Gel’fman, O. V. Salishcheva, N. E. Moldagulova, and E. V. Seryakova
Technological Institute of Food Industry, Kemerovo, Russia
Received December 24, 2004
Abstract—The kinetics of the reactions of bromide complexes [[PtenBr2], [Pt(NH3)2Br2], and
[enPtBr2Pten](NO3)2 with AgNO3 are studied potentiometrically. The reactions occur in two stages with dra-
matically different rates. Rate constants are determined for the second stage. The kinetics of the reaction
between the dimeric complex and AgNO3 are studied at 5, 15, 25, and 35°ë. The activation energy is deter-
mined.
DOI: 10.1134/S0036023607120145
In reactions between stoichiometric amounts of amount of the complex to a 0.3 M sodium nitrate solu-
haloplatinum(II) complexes and silver nitrate, halide tion. Silver nitrate was added as an aqueous solution
ions even at ambient temperature are almost completely with Ò = 0.025 mol/L.
eliminated from the inner sphere of the complexes and
precipitated as silver halide, e.g.,
RESULTS AND DISCUSSION
[Pt(NH3)2Br2] + 2AgNO3 + 2H2O
Kinetic experiments consisted of measurements
over time of the emf of galvanic cells built of a silver
ion-selective indicator electrode and an Ag/AgCl refer-
ence electrode.
= [Pt(NH3)2(H2O)](NO3)2 + 2AgBr↓.
This work concerns the kinetics of the reaction
between silver nitrate and platinum(II) complexes,
either monomeric ([PtenBr2] or [Pt(NH3)2Br2]) or
dimeric ([enPtBr2Pten](NO3)2, where en stands for eth-
ylenediamine and m for methylamine), the latter con-
taining two bridging bromine atoms.
The substitution of a water molecule for each inner-
sphere bromide ion Br– adds unity to the charge of the
complex. It was natural to suggest that the reaction of a
complex containing two bromide ions with silver
nitrate would occur in two stages at substantially differ-
ing rates:
EXPERIMENTAL
(1) [PtenBr2] + Ag+ + H2O
= [PtenBrH2O]+ + AgBr↓,
(2) [PtenBrH2O]+ + Ag+ + H2O
[PtenCl2] and trans-[Pt(NH3)2Cl2] were synthesized
according to [1].
The synthesis of the dimeric complex
[enPtBr2Pten](NO3)2 is described in [2].
= [Pten(H2O) ]2+ + AgBr↓;
The Ag+ concentrations in solutions were deter-
mined on an ANION-410 pH meter/conductometer
using a silver ion-selective electrode and an Ag/AgCl
saturated reference electrode. A calibration curve was
plotted as the emf versus Ag+ concentration in standard
solutions (Ò = 1 × 10–2, 1 × 10–3, 1 × 10–4, 1 × 10–5 mol/L).
2
and
(1) [Pt(NH3) Br2] + Ag+ + H2O
2
The temperature of test solutions was adjusted accu-
rate to 0.5°ë with a thermostat.
= [Pt(NH3) BrH2O]+ + AgBr↓,
2
(2) [Pt(NH3) BrH2O]+ + Ag+ + H2O
Kinetic experiments were carried out at the starting
concentration of the complex equal to 1 × 10–3 mol/L.
The solutions were prepared by inserting the calculated
2
= [Pt(NH3) (H2O) ]2+ + AgBr↓.
2
2
1887

1888
GEL’FMAN et al.
Table 1. Kinetics of the reaction between [PtenBrH2O]NO3
and silver nitrate at 25°C
At the first stage of the reaction of silver nitrate with
the dimeric complex, one bromide bridge should be
broken, and at the second, a monomeric aqua complex
should form:
cAgNO , mol/L
Time, s
k
3
(1) [enPtBr2Pten]2+ + Ag+ + 2H2O
0
10
0.0010
= [en(H2O)PtBrPt(H2O)en]3+ + AgBr↓,
(2) [en(H2O)PtBrPt(H2O)en]3+ + Ag+ + 2H2O
0.00089
0.00080
0.00073
0.00068
0.00062
0.00058
0.00054
0.00050
0.00048
0.00046
0.00044
0.00041
0.00039
0.00038
0.00036
0.00034
0.00033
0.00031
0.00029
0.00029
0.00027
0.00027
0.00026
0.00025
0.00025
0.00024
11.48
12.50
12.20
11.34
11.85
11.63
11.93
12.20
11.85
11.37
11.29
11.84
11.98
11.65
11.70
11.76
11.62
11.50
11.83
11.55
11.46
10.98
11.15
11.00
10.94
11.31
11.66 0.36
= 2[Pten(H2O)2]2+ + AgBr↓.
20
The kinetics of the first reaction stage were studied
as follows: an ion-selective electrode was immersed
into the aqueous solution of the complex with NaNO3
background, silver nitrate was added in a proportion of
1 mol per mole of the complex, and the emf of the gal-
vanic cell was measured over time. The silver concen-
tration in the solutions decreased so quickly that it was
impossible to determine rate constants: reactions with
cis-diamine and the dimer came virtually to the end in
70–100 s and those with trans-diamine in 20 s in agree-
ment with the trans-influence laws.
30
40
50
60
70
80
After the first stage ended, a new silver nitrate incre-
ment was added to the solution in a proportion of 1 mol
per mole of the complex, and measurements were con-
tinued. The silver-ion concentrations were used to cal-
culate the rate constant of the second reaction stage
using the rate equation for a second-order reaction,
90
100
110
120
130
140
150
160
170
190
200
210
230
240
250
260
270
280
c0 – c
τc0c
------------
k =
,
where Ò0 is the starting silver(I) ion concentration and Ò
is the silver(I) ion concentration τ seconds after the
reaction onset.
The rate constants calculated from the above equa-
tion remained virtually the same during the experiment.
Tables 1–3 display the experimental data and rate
constants for the test complexes at 25°ë.
Comparison between the rate constants listed in
Tables 1 and 2 shows that the rate of the reaction of sil-
ver nitrate with [PtenBrH2O]NO3 is almost two times
that with trans-[Pt(NH3)2BrH2O]NO3. This seems nat-
ural in view of the fact that the coordinated bromide ion
in the monomeric complex is trans to the amine mole-
cule, which has a stronger trans-influence than a water
molecule [3].
Table 3 shows that the bridging bromide ion reacts
with the silver(I) ion more rapidly than the terminal
bromide ions. We observed this effect previously in
studies of the reaction kinetics of bromide complexes
with potassium iodide.
To estimate the activation energy for the reaction of
the dimeric complex [en(H2O)PtBrPt(H2O)en](NO3)
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 52 No. 12 2007

KINETICS OF REACTIONS BETWEEN BROMOPLATINUM(II) COMPLEXES
of the
1889
Table 2. Kinetics of the reaction between trans- Table 3. Kinetics
reaction between
[en(H2O)PtBrPt(H2O)en](NO3)3 and silver nitrate at 25°C
[Pt(NH3)2BrH2O]NO3 and silver nitrate at 25°C
cAgNO , mol/L
Time, s
k
cAgNO , mol/L
3
Time, s
k
3
0
70
0.0010
0
195
210
240
265
285
305
330
365
400
440
480
505
580
645
0.00050
0.00030
0.00029
0.00028
0.00027
0.00026
0.00025
0.00024
0.00023
0.00022
0.00021
0.00020
0.00019
0.00018
0.00017
0.00028
0.00026
0.00024
0.00022
0.00020
0.00019
0.00017
0.00016
0.00014
0.00013
0.00012
0.00011
0.00010
0.000098
0.000097
0.000090
0.000089
0.000084
0.000083
0.000082
0.000081
0.000080
0.000080
0.000080
36.73
34.67
35.18
35.45
35.04
35.53
36.52
37.50
35.98
35.54
34.64
34.43
36.73
35.40
34.48
36.11
35.92
36.35
35.07
34.45
34.15
33.60
33.33
32.86
35.23 1.12
6.84
6.90
80
90
100
110
120
130
140
160
190
220
235
245
260
270
280
285
300
315
325
330
340
345
350
6.55
6.436
6.488
6.56
6.57
6.43
6.36
6.28
6.25
6.46
6.13
6.02
6.45 0.23
with silver nitrate, we studied the kinetics of this reac-
tion at 5, 15, and 35°ë (Tables 4–6).
The figure demonstrates the lnk = f(1/T) plot for
this reaction. The activation energy found from this plot
is 83.1 kJ/mol. Thus, the reaction of the dimeric com-
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 52 No. 12 2007

1890
GEL’FMAN et al.
Table 4. Kinetics
of
the
reaction between Table 5. Kinetics
of
the
reaction between
[en(H2O)PtBrPt(H2O)en](NO3)3 and silver nitrate at 5°C
[en(H2O)PtBrPt(H2O)en](NO3)3 and silver nitrate at 15°C
cAgNO , mol/L
cAgNO , mol/L
Time, s
k
Time, s
k
3
3
0
162
180
200
210
220
230
250
260
280
290
310
320
340
360
370
390
410
430
450
472
480
500
525
570
0.001
0
70
0.001
0.00055
0.00053
0.00053
0.00052
0.00051
0.0005
4.92
4.85
4.43
4.36
4.37
4.35
4.33
4.34
4.37
4.39
4.45
4.50
4.60
4.53
4.60
4.56
4.59
4.60
4.39
4.50
4.43
4.37
4.38
4.15
4.48 0.16
0.00057
0.00048
0.00044
0.00043
0.00041
0.00039
0.00038
0.00038
0.00036
0.00035
0.00033
0.00032
0.0003
10.69
10.83
10.60
10.20
10.28
10.43
10.20
9.60
100
120
130
140
150
160
170
180
190
210
220
240
260
280
300
350
370
400
470
520
552
600
642
0.00048
0.00047
0.00045
0.00044
0.00042
0.00041
0.00039
0.00038
0.00037
0.00036
0.000347
0.000336
0.000336
0.00032
0.00032
0.000314
0.000303
0.000297
9.88
9.78
9.67
9.66
9.72
0.00028
0.00026
0.00024
0.00021
0.00020
0.00019
0.00018
0.00016
0.00015
0.00014
0.00013
9.90
10.16
10.56
10.37
10.55
10.52
9.31
10.10
9.80
9.91
9.73
10.10 0.39
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 52 No. 12 2007

KINETICS OF REACTIONS BETWEEN BROMOPLATINUM(II) COMPLEXES
1891
Table 6. Kinetics
of
the
reaction between
lnk
6
[en(H2O)PtBrPt(H2O)en](NO3)3 and silver nitrate at 35°C
c
, mol/L
Time, s
k
AgNO3
5
4
3
2
1
0
30
50
70
85
0.001000
0.000180
0.000120
0.000086
0.000072
0.000069
0.000063
0.000058
0.000053
0.000049
0.000046
0.000043
0.000040
0.000038
0.000036
0.000034
0.000032
0.000031
0.000029
0.000026
0.000023
–
151.85
152.41
151.83
151.63
149.92
148.73
147.65
148.90
149.30
148.14
148.37
150.00
148.91
148.77
149.54
151.25
148.85
152.19
149.85
151.70
150.00 1.52
90
100
110
120
130
140
150
160
170
180
190
200
210
220
250
280
0
3.2
3.3
3.4
3.5
3.6
3.7
–1
l/T × 103, K
Plot
lnk
vs.
1/T
for
the
reaction
of
[en(H O)PtBrPt(H O)en](NO ) with silver nitrate.
2
2
3 3
with potassium iodide [4].
REFERENCES
1. I. I. Chernyaev, Synthesis of Complexes of the Platinum-
Family Metals. Handbook (Nauka, Moscow, 1964) [in
Russian].
2. O. V. Salishcheva, N. E. Moldagulova, and M. I. Gel’fman,
Zh. Neorg. Khim. 49 (1), 54 (2004) [Russ. J. Inorg.
Chem. 49 (1),54 (2004)].
3. A. A. Grinberg, Introduction to the Chemistry of Com-
plexes (Khimiya, Leningrad, 1971) [in Russian].
4. M. I. Gel’fman, O. V. Salishcheva, and N. E. Moldagu-
lova, Zh. Neorg. Khim. 49 (9), 1454 (2004) [Russ. J.
Inorg. Chem. 49 (9), 1342 (2004)].
plex with silver nitrate has a higher rate and a lower
activation energy than the reaction of the same complex
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 52 No. 12 2007