Potential energy surfaces for ligand exchange reactions of square planar diamagnetic PtY2L2 complexes: Hydrogen bond (PtY 2L2⋯L′) versus apical (Y2L 2Pt⋯L′) interaction

The geometrical structures, potential energy surfaces, and energetics for the ligand exchange reactions of tetracoordinated platinum (PtY 2L2 : 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 [PtCl 3(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 ([PtY2L 2⋯L′]‡) correspond to complexes such as (PtCl4⋯H2O)‡ and [Pt(NH 3)2Cl2⋯H2O] ‡, respectively. In the transition state, ([PtCl 4⋯H2O]‡ and [Pt(NH 3)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 H 2O. Simultaneously, the entering H2O interacts with a leaving Cl-. No vertical one metal-ligand interactions ([PtY 2L2⋯L′]‡) are found at the axial positions of the square planar (PtY2L2) complexes, which were formed via a vertically associative mechanism leading to D 3h 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(H 2O)n(n = 2,4)} into {PtCl3(H2O) (n-2) + Cl-(H2O)2} and the binding energies {PtCl4(H2O)n(n = 1-5)} of PtCl 4 with water molecules are drawn.