ORIGINAL ARTICLE Study of complex formation between C 18 H 36 N 2 O 6 and UO 2þ 2 cation in some binary mixed non-aqueous solutions G.H. Rounaghi * , Z. Eshaghi, L. Zare Department of Chemistry, Faculty of Sciences, Payame Noure University of Mashhad, Mashhad, Iran Received 25 June 2012; accepted 23 October 2012 KEYWORDS C 18 H 36 N 2 O 6 (kryptofix 222); UO 2þ 2 cation; Binary mixed organic sol- vents; Conductometry Abstract The complexation reaction between UO 2þ 2 cation and the macrobicyclic ligand C 18 H 36 N 2 O 6 was studied in acetonitrile–dimethylformamide (AN–DMF), acetonitrile–tetrahydro- furan (AN–THF), acetonitrile–dichloromethane (AN–DCM) binary solvent solutions at different temperatures using the coductometric method. In most cases, C 18 H 36 N 2 O 6 forms a 1:1 [M:L] com- plex with the UO 2þ 2 cation. But in some of the studied solvent systems, in addition to formation of a 1:1 complex, a 1:2 [M:L 2 ] complex is formed in solution. A non-linear behavior was observed for changes of log K f of the (C 18 H 36 N 2 O 6 ÆUO 2 ) 2+ complex versus the composition of the binary mixed solvents. The sequence of the stability of the (C 18 H 36 N 2 O 6 ÆUO 2 ) 2+ complex in pure solvent systems at 25 °C decreases in the order: AN > THF > DMF. In the case of binary solvent solutions, the stability constant of the complex at 25 °C was found to be: AN–DCM > AN–THF > AN– DMF. The values of thermodynamic quantities (DS  c ; DH  c Þ, for the formation of the complex were obtained from temperature dependence of the stability constant of the complex using the van’t Hoff plots. The results show that in all cases, the complex is both entropy and enthalpy stabilized and both of these parameters are affected by the nature and composition of the mixed solvent systems. ª 2012 King Saud University. Production and hosting by Elsevier B.V. All rights reserved. 1. Introduction Uranium is a radioactive metal that exists ubiquitously in the environment (Gongalsky Konstantin, 2003). Since uranium is one of the main sources in nuclear energy generation and enriched uranium is a major component in nuclear weapons, human beings have a high chance of being exposed to uranium, which can cause severe effects on human health (Craft et al., 2004; Zhou and Gu, 2005). A large amount of uranium in drinking water may lead to harmful biological ef- fects in humans. Chemical toxicity caused by natural uranium poses a major risk to the kidneys. Also it is important to mon- itor the concentration of uranium at various stages of prepara- tion of uranium dioxide fuel pellets (Murty et al., 1997) and also in the environment safety assessment related to the nucle- ar industry (Miller et al., 1994). For these reasons, detection of uranium is very important. In nature, hexavalent uranium is commonly associated with oxygen as the uranyl ion, UO 2þ 2 . Thermodynamic studies on the complexation of C 18 H 36 N 2 O 6 with the UO 2þ 2 cation have been performed in or- der to elucidate the nature of the cation-binding behavior from the thermodynamic point of view and also to gain insights into * Corresponding author. E-mail address: ghrounaghi@yahoo.com (G.H. Rounaghi). q Peer review under responsibility of King Saud University. Production and hosting by Elsevier Arabian Journal of Chemistry (2012) xxx, xxx–xxx King Saud University Arabian Journal of Chemistry www.ksu.edu.sa www.sciencedirect.com 1878-5352 ª 2012 King Saud University. Production and hosting by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.arabjc.2012.10.019 Please cite this article in press as: Rounaghi, G.H. et al., Study of complex formation between C 18 H 36 N 2 O 6 and UO 2þ 2 cation in some binary mixed non-aqueous solutions. Arabian Journal of Chemistry (2012), http://dx.doi.org/10.1016/j.arabjc.2012.10.019