COMPLEX FORMATION OF SILVER(I) WITH 18-CROWN-6
2593
solvate state of Ag+ ion. The proportionality coef-
ficient calculated from the equation varies in the range
0.4±0.2.
range 1.5×10–3–7.8×10–2 mol l–1 for each composition
of the mixed solvent. The choice of concentration
conditions for potentiometric measurements and
calculation of the stability constants for [Ag18C6]+
from the experimental data were carried out by means
of the PHMETR program. The average from the
obtained values of the stability constants of silver(I)
crown ether complex at the ion force ~5×10–3–1.0×10–2
created by silver perchlorate and complex ion was
accepted as the standard meaning of this value. The
largest log K0 error was no more than 0.1 logarithmic
unit. It was determined as the standard mean square
deflection with the consideration of Student criterion at
the confidence probability 0.95 for the series of
experiments (3) and (4) for each composition of each
solvent.
k = [ΔtrG0([Ag18C6]+) – ΔtrG0(18C6)]/[ΔtrG0(Ag+)].
Using the relationship obtained on the basis of
Eq. (1) values of variation in Gibbs energies of complex
formation of Ag+ ion with 18-crown-6 taking place at
the varying the solvent composition (MeOH→DMF)
were calculated.
ΔtrG0r = (k – 1)·[ΔtrG0(Ag+)].
As seen from the figure, the results of ΔtrG0r
calculations give quite satisfactory description of the
experimental data. Thus on the basis of variation in the
solvate state of the starting reagents it is possible to
predict the variation in thermodynamic functions of
complex formation proceeding in binary mixtures of
nonaqueous solvents. But for the establishing of
general principles of the effect of nature and the
composition of solvent on the processes of complex
formation in solutions further studies of this problem
must be performed.
REFERENCES
1. Shormanov, V.A. and Sharnin, V.A., Dostizheniya i
problemy teorii solvatatsii: Strukturno-termodina-
micheskie aspekty (Achievements and Problems of the
Solvation Theory: Structural and Thermodynamic
Aspects), Moscow: Nauka, 1998, p. 172.
2. Sharnin, V.A., Zh. Obshch. Khim., 1999, vol. 69, no. 9,
EXPERIMENTAL
p. 1421.
18-Crown-6 (Merck, chemically pure grade) was
dried in a vacuum at room temperature for seven days.
Silver perchlorate was prepared according to [12]. The
substance obtained was dried in a vacuum at 60–70°C
for 10 days. K[Ag(CN)2] was prepared according to
[13]. Methanol of the superfine grade and DMF of the
chemically pure grade were dried according to the
procedures described in [14]. Water content in solvents
was evaluated by Fischer method: methanol contained
0.009 wt %, and DMF, 0.01 wt % of water.
3. Sharnin, V.A., Zh. Obshch. Khim., 2001, vol. 71, no. 9,
p. 1452.
4. Sharnin, V.A., Koord. Khim., 1996, vol. 22, no. 5, p. 418.
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Obshch. Khim., 2001, vol. 71, no. 5, p. 754.
8. Ignaczak, M. and Grzejdziak, A., Monatsh. Chem.,
1984, vol. 115, p. 943.
The evaluation of the stability constants of silver(I)
crown ether complexes in the mixed nonaqueous
MeOH–DMF solvents was carried out potentiometri-
cally without the salt background using the following
the electrochemical circuit consisting of two silver
electrodes. Their electrochemical potential was repro-
duced in nonaqueous media with the accuracy ±0.1 mV.
9. Brown, A.S., J. Am. Chem. Soc., 1934, vol. 56, p. 646.
10. Golikov, A.N., Kuz’mina, I.A., and Sharnin, V.A., Izv.
Vysshikh Uchebnykh Zavedenii, Ser. Khim., Khim.
Technol., 2007, vol. 50, no. 12, p. 18.
11. Krestov, G.A., Termodinamika ionnykh protsessov
(Thermodynamics of Ionic Processes), Leningrad:
Khimiya, 1984.
Ag MeOH−DMF,
MeOH−DMF, Ag
AgClO4
AgClO4, 18C6
12. Moshorin, G.V., Repkin, G.I., and Sharnin, V.A., Zh.
Fiz. Khim., 2006, vol. 80, no. 2, p. 215.
Silver electrodes were prepared by coating the
platimun net with silver by its electrochemical
precipitation from the K[Ag(CN)2] solution. Working
capacity of the electrode system was checked by its
calibration with AgClO4 solutions in the concentration
13. Golikov, A.N., Kuz’mina I,.A., and Sharnin, V.A., Izv.
Vysshikh Uchebnykh Zavedenii, Ser. Khim., Khim.
Tekhnol., 2007, vol. 50, no. 9, p. 38.
14. Stroka, J. and Schneider, H., Polish J. Chem., 1980,
vol. 54, p. 1805.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 79 No. 12 2009