Leila Vatannavaz - Farhangian University,Tehran, Iran
Mohammad Hassan Zebarjadian - Faculty of Chemistry, Bu-Ali Sina University, Hamedan,۶۵۱۷۴, Iran
Seyyed Javad Sabounchei - Faculty of Chemistry, Bu-Ali Sina University, Hamedan,۶۵۱۷۴, Iran

The unsymmetrical phosphorus ylide, (p-tolyl)3P=CHCOC6H4(p-CN) (L) is shown to react with Hg(II) halides to form binuclear products Fig. 1 with the composition {HgX2[(p-tolyl)3P=CHCOC6H4(p-CN)]}2, where X = Cl, Br and I. 31P NMR measurements were employed to monitor the stoichiometry and stability of HgX2 complexes with phosphorus ylide in binary Tetrahydrofuran – Dimethylsulfoxide mixtures of varying composition. In all cases studied, the variation of 31P chemical shift with the [HgX2]/[ylide] mole ratio indicated the formation of 1:1 complexes. The formation constants of the resulting complexes were evaluated from computer fitting of the mole ratio data to an equation that relates the observed chemical shifts to the formation constant. In all solvent mixtures used, the stabilities of the resulting 1:1 complexes varied in the order HgCl2 > HgBr2 > HgI2. It was found that, in the case of all complexes, an increase in the percentage of Tetrahydrofuran in the solvent mixtures, significantly increased the stability of the complexes. The temperature dependence formation constant were used for the evaluation of the enthalpy and entropy values for the complexation reaction. It was concluded that in all complexes, except for Hg(II) halides, the resulting complex enthalpy is stabilized and the ΔH compensates the TΔS contribution