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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 27, Number 9
BKCSDE 27(9)
September 20, 2006 

Potential Energy Surfaces for Ligand Exchange Reactions of Square Planar Diamagnetic PtY2L2 Complexes:Hydrogen Bond (PtY2L2…L') versus Apical (Y2L2Pt…L') Interaction
Jong Keun Park*, Bong Gon Kim
Geometrical structures, Potential energy surfaces, Ligand exchange reactions, Atomic charge, Density functional theory
The geometrical structures, potential energy surfaces, and energetics for the ligand exchange reactions of tetracoordinated platinum (PtY2L2 : Y, L=Cl-, OH-, OH2, NH3) complexes in the ligand-solvent interaction systems were investigated using the ab initio Hartree-Fock (HF) and Density Functional Theory (DFT) methods. The potential energy surfaces for the ligand exchange reactions used for the conversions of (PtCl4 + H2O) to [PtCl3(H2O) + Cl-] and [Pt(NH3)2Cl2 + H2O] to [Pt(NH3)2Cl(H2O) + Cl-] were investigated in detail. For these two exchange reactions, the transition states ([PtY2L2…L']‡) correspond to complexes such as (PtCl4…H2O)‡ and [Pt(NH3)2Cl2…H2O]‡, respectively. In the transition state, ([PtCl4…H2O]‡ and [Pt(NH3)2Cl2…H2O]‡) have a kind of 6-membered (Pt-Cl…HOH…Cl) and (Pt-OH…Cl…HN) interactions, respectively, wherein a central Pt(II) metal directly combines with a leaving Cl- and an entering H2O. Simultaneously, the entering H2O interacts with a leaving Cl-. No vertical one metal-ligand interactions ([PtY2L2 …L']‡) are found at the axial positions of the square planar (PtY2L2) complexes, which were formed via a vertically associative mechanism leading to D3h or C2v-transition state symmetry. The geometrical structure variations, molecular orbital variations (HOMO and LUMO), and relative stabilities for the ligand exchange processes are also examined quantitatively. Schematic diagrams for the dissociation reactions of {PtCl4(H2O)n(n = 2,4)} into {PtCl3(H2O)(n-2) + Cl-(H2O)2} and the binding energies {PtCl4(H2O)n(n = 1-5)} of PtCl4 with water molecules are drawn.
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