Effect of the composition of an acetonitrile-dimethyl sulfoxide solvent on stability of the silver(I) complexes with 18-crown-6 ether

Article abstract of DOI:10.1134/S0036023607110174

The effect of the composition of an acetonitrile-dimethyl sulfoxide (AN-DMSO) mixed solvent on the stability of silver(I) complexes with 18-crown-6 ether (18C6) is studied by potentiometry. An insignificant increase in the stability of [Ag18C6]⁺

Full text of DOI:10.1134/S0036023607110174

ISSN 0036-0236, Russian Journal of Inorganic Chemistry, 2007, Vol. 52, No. 11, pp. 1739–1740. © Pleiades Publishing, Inc., 2007.
Original Russian Text © A.N. Golikov, I.A. Kuz’mina, V.A. Sharnin, 2007, published in Zhurnal Neorganicheskoi Khimii, 2007, Vol. 52, No. 11, pp. 1849–1851.
COORDINATION
COMPOUNDS
Effect of the Composition of an Acetonitrile–Dimethyl Sulfoxide
Solvent on Stability of the Silver(I) Complexes
with 18-Crown-6 Ether
A. N. Golikov, I. A. Kuz’mina, and V. A. Sharnin
Ivanovo State University of Chemical Technology, Ivanovo, Russia
E-mail: oxt703@isuct.ru
Received June 6, 2006
Abstract—The effect of the composition of an acetonitrile–dimethyl sulfoxide (AN–DMSO) mixed solvent on
the stability of silver(I) complexes with 18-crown-6 ether (18C6) is studied by potentiometry. An insignificant
increase in the stability of [Ag18C6]+ (0.34 log units) is observed on going from acetonitrile to dimethyl sul-
foxide. The effect of solvation on the shift of complex formation equilibrium is considered.
DOI: 10.1134/S0036023607110174
Interest in crown ethers as ligands is due to their adding dilute perchloric acid to silver carbonate, which
unique property to bind metal ions with high selectivity, was synthesized by mixing aqueous solutions of silver
incorporating them into the inner cavity of their ring- nitrate and sodium carbonate [1]. A solution of
shaped molecule. A large amount of study has been car- K[Ag(CN)2], necessary for electrode coating, was pre-
ried out to elucidate the effect of aqueous–organic and
individual solvents on the stability of complexes of
d-metal ions with macrocyclic ligands. However, there
is no data on the effect of binary mixtures of nonaque-
ous solvents on the thermodynamics of complexforma-
tion reactions. Therefore, in this work we studied
potentiometrically the effect of AN–DMSO solvent
composition on the stability of 18-crown-6 ether
(18C6) complexes with Ag+ ions.
pared using a method proposed by us [2]. Dimethyl sul-
foxide (reagent grade) and acetonitrile (high purity
grade) were purified and dehydrated according to pro-
cedures described in work [3] and [4], respectively.
Water in the solvents was determined according to the
Fischer method. In the final products, water was
0.045 wt % for DMSO and 0.023 wt % for AN.
18-Crown-6 ether, NaClO4, and AgClO4 were stored
in weighed bottles closed with well-ground plugs and
stored in a desiccator over P2O5. The bottle with
AgClO4 was darkened.
EXPERIMENTAL
Silver electrodes were produced by electrodeposi-
tion of silver on a platinum gauze from cyanide solu-
tions according to work [2].
18-Crown-6 ether (reagent grade) was dried at room
temperature in vacuo for several days. Sodium perchlo-
rate (pure grade) was purified by triple recrystallization
The stability constants of silver(I) complexes with
from distilled water and dried in vacuo at 70°C to con- 18C6 were determined potentiometrically using the
stant weight. Silver perchlorate was synthesized by galvanic cell
Ag AN–DMSO, NaClO4, AN–DMSO, NaClO4, Ag
AgClO4, 18C6
AgClO4
°
Two solutions were brought in contact through an
unlubricated ground joint [5].
voir of the reference electrode was the same as cAg+ in the
working cell. The standard solution was identical to the
test solution in both the solvent composition and the con-
tent of the supporting salt. The solution ionic strength was
adjusted by a 0.1 M solution of sodium perchlorate. The
During an experiment, 20 mL of a solution of
AgClO4 (the initial Ag+ concentration was ~1 ×
10−2 mol/L) were titrated with a solution of 18C6
( c18C6 ~ 0.25 mol/L). The Ag+ concentration in a reser- temperature in the reaction volume was 298.15 K.
°
1739

1740
GOLIKOV et al.
Stability constants of silver(I) with 18C6 in AN–DMSO sol-
stable solvates between the solvent and ligand mole-
cules, which is favored by the linear conformation of
strongly polar AN molecules and the optimal distances
between the donor atoms of the crown ether [8–10].
Addition of dimethyl sulfoxide destabilizes the solva-
tion shell of the ligand, favoring an increase in the sta-
bility of [Ag18C6]+. However, the Ag+ ion is stabilized
with increasing DMSO content in the binary solvent,
which is due to the formation of rather stable solvates
of silver(I) with DMSO [11, 12]. Therefore, the overall
increase in the stability of the complex ions is not so
significant as expected from the change in the solvate
state of the ligand.
vents at 298.15 K and I = 0.1 mol/L (NaClO4)
xDMSO, mole fraction
logK°
0
0.42 0.05
0.54 0.10
0.63 0.08
0.66 0.08
0.67 0.08
0.74 0.02
0.76 0.02
0.1
0.2
0.4
0.6
0.8
1.0
The performance ability of the electrode system was
verified by calibrating it in each composition of the
AN–DMSO mixed solvent.
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RESULTS AND DISCUSSION
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where t is the Student coefficient, n is the mean value,
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Presumably, a decrease in the stability of the com-
plex in AN is predominantly due to the formation of
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 52 No. 11 2007