A conductometric study on the effect of Solvent upon complex formation between kryptofix22DD with Ho3+ metal cation in organic solvents

Lanthanide complexes are of interest due to their importance in optical imaging of cells, as luminescent chemosensors for medical diagnostics, contrast reagents for medical magnetic resonance imaging, shift reagents for NMR spectrometry [1, 2], as well as, their potential applications in fundamental and applied science [3–5] such as organic synthesis, bioorganic chemistry and homogeneous catalysis.The complexation reaction between Ho3+cation with macrocyclic ligand kryptofix22DD, was studied in ethylacetate (EtOAC), methanol (MeOH), propylencharbonate(PC),tetrahydrofuran(THF) at different temperatures using coductometric method. Kryptofix22DD forms a 1:1 complex with Ho+ cation. The stability order of (kryptofix22DD.Ho)3+ complex changes with the type of the organic solvents and also with temperature. The stability constant of the complex in the non aqueuse solutions varies in order: EtOAC THF PC MeOH. The values of standard thermodynamic parameters (∆S°c, ∆H°c)for formation of (kryptofix22DD.Ho)3+ complex were obtained from temperature dependence of the formation constant of the complex using the van,t Hoff plots. The obtained results show that the entropy and enthalpy complexation reaction between kryptofix22DD with this metal cation depend on the nature of the solvents.