15th Iranian Seminar of Analytical Chemistry
Feb, 27 – March, 1, 2007
Chemistry Department
Shiraz University
Discussion on the Complexing Ability of 4'-nitrobenzo-15-Crown-5 with K+Na+ NH4+ Cations in
Acetonitrile- Methanol Binary Media
G. H. Rounaghi*, E. Razavipanah
Department of Chemistry, Faculty of Sciences, Ferdowsi University of Mashhad, Mashhad, Iran
The complexation processes between K+, Na+ and NH4+ cations with macrocyclic ligand, 4'-nitrobenzo15C5, were studied in acetonitrile-methanol (AN-MEOH) binary mixtures at different temperatures
using conductometric method, the conductance data show that the stoichiometry of the complexes
formed between the ligand and K+, Na+ and NH4+ cations is 1:1(M:L) for the case of K+, Na+ cations,
addition of 4'-nitrobenzo-15C5 to these cations solution, causes a continuous increase in the molar
conductivities which indicates the mobility of the complexed cations is more than the uncomplexed
ones.
The values of stability constants of the complexes were determined from conductometric data
using GENPLOT computer program. The obtained results show that the formation constants of
complexes changes with the nature and composition of the binary mixed solvent. The values of
thermodynamic parameters (DH 0C, DS 0C) for formation of the complexes were obtained from
temperature dependence of the formation constants and using the vant’Hoff plot. The results show that
the complexes are entropy stabilized and in some cases the complexation reaction are endothermic, but
in certain cases are exothermic.
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