ISSN 1070-3284, Russian Journal of Coordination Chemistry, 2009, Vol. 35, No. 9, pp. 633–639. © Pleiades Publishing, Ltd., 2009.
Original Russian Text © A.K. Lyashchenko, D.V. Loginova, A.S. Lileev, N.A. Ivanova, I.A. Efimenko, 2009, published in Koordinatsionnaya Khimiya, 2009, Vol. 35, No. 9,
pp. 643–649.
Dielectric Constant and Dielectric Relaxation in Aqueous
Solutions of K2[PdCl4] and K2[PtCl4]
A. K. Lyashchenko*, D. V. Loginova, A. S. Lileev, N. A. Ivanova, and I. A. Efimenko
Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences,
Leninskii pr. 31, Moscow, 119991 Russia
*E-mail: aklyas@mail.ru
Received September 8, 2008
Abstract—The MW-dielectric properties of aqueous solutions of K2[PtCl4] (I) and K2[PdCl4] (II) were studied
at 298 and 313 K in the frequency range (12–25 GHz) corresponding to the maximum dielectric constant dis-
persion for water and aqueous solutions of these salts. The low-frequency conductivities were measured. The
static dielectric constant, the dielectric relaxation time, and the enthalpy of activation of the dielectric relaxation
of the solutions were determined. Compared to pure water, in solutions of salts I and II, the orientational mobil-
ity of water molecules is increased and the network of H-bonds is violated more strongly than that of most other
ions with hydrophilic hydration. It was demonstrated for the first time that dielectric spectroscopy can be used
for analyzing complexation processes in systems containing aqua and hydroxo chloride complexes of metals.
DOI: 10.1134/S1070328409090012
Aqueous solutions of K2[PdCl4] and K2[PtCl4] are
typical examples of systems with complex anions in
solution. The ions [PtCl4]2– and [PdCl4]2– are similar in
structure and size. In binary and ternary aqueous elec-
trolytes with a relatively small excess of chloride ions,
the solutions contain aqua and hydroxo chloride com-
plexes of Pt(II) and Pd(II). The compositions of these
complexes depend on the concentrations of Cl– and ç+
ions and the temperature [1]. Compared to chloro com-
plexes of Pt(II), analogous Pd(II) complexes are ther-
modynamically less stable, much more labile [1, 2],
and easily hydrolyzable in aqueous solution.
The description of processes in biological systems is
impossible without knowing the character of complex-
ation; in addition, phenomena occurring in interactions
of complexes with water should be understood. On the
one hand, water molecules are “normal” ligands in the
coordination sphere of the central atom. On the other
hand, the molecular kinetic properties of water change
upon hydration of metal complexes. In the case of Pt(II)
and Pd(II) complexes, the hydration is more compli-
cated than common aqueous electrolytes containing
simple cations and anions.
To analyze hydration effects, we used MW-dielec-
tric spectroscopy in the frequency range corresponding
to the maximum dispersion of the dielectric constants
of water and aqueous solutions (7–30 GHz). This tech-
nique detects changes in the kinetic mobility of water
molecules in the hydration shells of ions. This is one of
few direct techniques that allows the characterization of
water molecule dynamics over times of ~10–11 s from
experimental data on the dielectric relaxation time τ.
The temperature dependence of τ is used to calculate
the activation parameters of dielectric relaxation
A comparative study of Pt(II) and Pd(II) complexes
are of great interest because of their biological activity.
The discovery of a new class of promising antitumor
platinum-based drugs [3] prompted a search for sub-
stances with cytostatic activity among complexes of
other platinum metals, first of all among palladium
complexes. However, most Pd complexes (including an
analog of cis-[Pt(NH3)2Cl2] widely used in oncology)
were ineffective [4, 5]. Presumably, this is associated
with the higher lability of palladium salts compared to (∆H+ε+, ∆Gε++, T∆Sε++ ), which reflect changes in the
platinum ones. At the same time, a comparative study
of the primary effects of Pt and Pd complexes on bio-
degrees of binding and structuration of the network of
H-bonds in solution.
logical systems revealed that the PdCl24– ion is more
active than PtCl24– [6]. Complexes containing the
PdCl24– ion were found to exhibit not only antitumor
activity but also radioprotective [7, 8] and immuno-
modulating effects [9].
Another important hydration characteristic of aque-
ous electrolytes is static dielectric constant es. This
quantity cannot be determined directly because of the
high conduction of electrolyte systems. Yet it can be
calculated from high-frequency data on dielectric con-
"
stant e' and dipole-associated losses ed by extrapola-
633