ISSN 1070-4272, Russian Journal of Applied Chemistry, 2015, Vol. 88, No. 6, pp. 977−984. © Pleiades Publishing, Ltd., 2015.
Solvent Inﬂ uence upon Complex Formation between
with Samarium(III) Metal Cation
in Binary Mixed Non-aqueous Solvents
, Haman Tavakkoli, and Negar Rajabi
Department of Chemistry, College of Science, Ahvaz Branch, Islamic Azad University, Ahvaz, Iran
Received June 4, 2015
Abstract—The complexation reaction of macrocyclic ligand, 4,13-didecyl-1,7,10,16-tetraoxa-4,13-diazacy-
clooctadecane (kryptoﬁ x 22 DD) with Sm
cation was studied in acetonitrile-1,2-dichloroethane (AN–1,2-DCE),
acetonitrile–methylacetate (AN–MeOAc), acetonitrile–ethylacetate (AN–EtOAc) and acetonitrile–methanol
(AN–MeOH) binary mixtures at different temperatures using conductometric method. The conductance data show
that in most of the solvent systems, the stoichiometry of the complex formed between kryptoﬁ x 22 DD and Sm
cation is 1 : 1 [M : L]. But, in some cases a 2 : 2 [M
] complex is formed in solution. The stability constant of
the resulting complex in binary mixed non-aqueous solvents decreases in the order AN–EtOAc > AN–MeOAc >
AN–1,2-DCE > AN–MeOH. A non-linear behavior was observed for changes of log K
of (kryptoﬁ x 22 DD
complex vs. the composition of the binary mixed solvents. The obtained results show that the stability of the
complex is quite sensitive to the composition of the mixed solvents. The values of thermodynamic quantities (∆H
) for formation of (kryptoﬁ x 22 DD·Sm)
complex were obtained from temperature dependence of the
stability constant using the van’t Hoff plots. The results show that in most cases the complex is entropy stabilized
and both parameters are affected by the nature and composition of the mixed solvents.
Samarium (Sm) is a rare earth element that, indirectly,
has the distinction of being the ﬁ rst naturally occurring
chemical element to be named after a living person.
Samarium has a long history in the nuclear industry.
Soon after the Second World War the Indianapolis-
based chemical giant Eli Lilley developed a fractional
crystallisation technique for separating neodymium from
ore. The synthesis of samarium and gadolinium was a by-
product of the process and since
Sm is a strong neutron
absorber the product, called “‘Lindsay Mix,” was sold
as an early form of neutron damper for nuclear control
rods. Even today samarium is still used as a neutron
absorber in reactor control rods; particularly, when mixed
with europium and gadolinium forming the so-called
samarium–europium–gadolinium (SEG) concentrate.
Samarium can easily form complexes with various
types of ligands, e.g., inorganic ligands, small organic
ligands or macrocyclic ligands [1, 2]. Several studies
have been carried out to enhance the selectivity in the
separation of lanthanides and actinides elements in the
extraction systems [3–5].
The metal-ion chemistry of macrocyclic ligands has
been the subject of great interest since Pedersen ﬁ rst
reported the synthesis of crown ether in 1967 . Crown
ethers are macrocyclic polyethers whose structure exhibits
a conformation with a so-called hole capable of trapping
cations by coordination with lone pair of electrons on the
oxygen atoms. The ability of these compounds to form
stable complexes with cations has spurred interest in these
The text was submitted by the authors in English.