2013. 54, 2 – UDC 541.6:547.13:546.65 COMPUTATIONAL STUDY ON THE STRUCTURE AND PROPERTIES OF TERNARY COMPLEXES OF Ln3+ (Ln = La, Ce, Nd AND Sm) WITH 5,7-DICHLOROQUINOLINE-8-OL AND 4-VINYL PYRIDINE T. Hosseinnejad1, S.J. Ahmadi2, M.H. Karimi-Jafari3 1Department of Chemistry, Faculty of Science, Alzahra University, Vanak, Tehran, Iran E-mail: tayebeh.hosseinnejad@gmail.com 2Nuclear Science and Technology Research Institute (NSTRI), Tehran, Iran 3Institute of Biochemistry and Biophysics, University of Tehran, Tehran, Iran Received November, 13, 2011 Revised — January, 14, 2012 In the present research, we have mainly concentrated on the survey of interactions in Ln3+ (Ln = La, Ce, Nd and Sm) ternary complexes of 5,7-dichloroquinoline-8-ol (DCQ) and 4-vinyl pyridine (VP), [Ln(VP)2(DCQ)3]3+ by means of density functional theory, Hartree-Fock and Sparkle/PM3 semi-empirical computational methods. <...> For VP and DCQ ligands, the cation binding energy sequence follows the order La3+ > Ce3+ > Nd3+ > Sm3+ as expected based on increasing in the hardness and decreasing in the ionic radius of this lanthanide cation series. <...> A similar trend was observed in the calculated binding energy of the aforesaid ligands with the hydrated lanthanide cation series [Ln(H2O)9]3+, while the computed values of deformation energy of ligands upon complexation demonstrated an opposite order in the lanthanide cation series. <...> Moreover, the solvent effects are considered via a polarized continuum model and provided a significant increase in the binding strength while the relative magnitude of binding energies is the same as that in the gas phase. <...> Combining quantum and statistical mechanical calculations, we have also determined quantitatively a reliable estimate of the conformational distribution of the [Sm(VP)2(DCQ)3]3+ complex at various temperatures in the gas phase by computing the molecular partition functions and consequently the analysis of the conformational equilibrium constants. <...> Keywords: ion imprinting, lanthanide complexes, density functional theory, polarized continuum model, conformational distribution. <...> In the present work, we have provided a computational study on Ln3+ (Ln = La, Ce, Nd and Sm) ternary complexes of 5,7-dichloroquinoline-8-ol and 4-vinyl pyridine (hereafter denoted by DCQ and VP respectively; Fig. 1) to assess the intrinsic interaction energies and structural features of the complexes. <...> The main <...>