Conductometric study of complexation reaction of Dibenzo-24-crown-8 withCe3+ cation in some non-aqueous solvents and their binary mixture

Pedersen first discovered the complexation of crown ethers with alkali metal ions [1]. Crownethers are one of the most widely studied family of host compounds in the field of supramolecularchemistry, involving non-covalent interactions [2]. The main characteristic of these compounds isthe complexation of their ether oxygens with various ionic species. Formation of a complexbetween a macrocyclic ligand and a cation, depends on many factors including: the relative sizeof the cation and the crown cavity, cation charge and type, nature of counter anion, number andtype of donor atoms, substituents at the crown molecule, electron density of the crown cavity,the crown ether ring flexibility, and also the effect of solvent [3,4]. One of the techniques whichis used for study of complexation process is conductometry [5]. This technique is a sensitive andinexpensive method with a simple experimental arrangement for such investigations [6]. In thepresent work, the complex formation between of dibenzo-24-crown-8 (DB24C8) with Ce3+ cationin acetonitrile (AN), methanol (MeOH), tetrahydrofuran (THF) and also in the binary mixtures ofacetonitrile-methanol (AN-MeOH), acetonitrile-tetrahydrofuran (AN-THF) and tetrahydrofuranmethanol(THF-MeOH) was studied at various temperatures using conductometric method. Theconductance-mole ratio data show that the stoichiometry of the complex which is formedbetween the macrocyclic ligand and the rare earth metal cation is 1:1 [M:L]. The stabilityconstant of the (DB24C8.Ce)3+ complex at each temperature, was determind using a computerprogram, GENPLOT. The obtained results show that the stability order of the complex at 15°Cand 35°C in pure non-aqueous solvents is: THF > AN > MeOH and in the case of the mixedsolvent solutions, the stability constant of the complex, changes with the nature and alsocomposition of solvent systems. The standard thermodynamic quantities (ΔHc° and ΔSc°) of thecomplexation reaction were evaluated by the temperature dependence of formation constant, using the van’t Hoff plots. The results obtained in this study, show that the values ofthermodynamic of the complexation reaction is influenced by the nature and composition of thebinary mixed solvent solutions.

کلیدواژه ها:

Dibenzo-24-crown-8 ، Ce3+ cation ، Non-aqueous solvents ، Conductometry