Potential Energy Curves and Geometrical Structure Variations for ([MX₄]^2- : M=Ni(II), Pd(II), Pt(II): X=Cl^-, Br^-) Dissociating into ([MX₃]^- + X^-) : Ab Initio Study

Potential energy curves and internuclear (M-X) distance variations for dissociation reactions of [MX₄]^2- into ([MX₃]^- + X^-) have been calculated using ab initio Hartree-Fock (HF), second order Moller-Plesset perturbation (MP2), and Density Functional Theory (DFT) methods with a triple zeta plus polarization (TZP) basis set. The equilibrium geometrical structures of [MX₄]^2- are optimized to tetrahedral geometry for [NiX₄]^2- and square planar geometry for ([PdX₄]^2- and [PtX₄]^2-). The bond (M-X) distances of [NiCl₄]^2-, [NiBr₄]^2-, [PdCl₄]^2-, [PdBr₄]^2-, [PtCl₄]^2-, and [PtBr⁴]^2- at the DFT level are 2.258, 2.332, 2.351, 2.476, 2.367, and 2.493 A, respectively. The dissociation energies for the bond dissociation of ([MX₃]^-···X^-) at the DFT level are found to be 4.73 eV for [NiCl₄]^2-, 4.89 eV for [NiBr₄]^2-, 4.93 eV for [PdCl₄]^2-, 5.57 eV for [PdBr₄]^2-, 5.44 eV for [PtCl₄]^2-, and 5.87 eV for [PtBr₄]^2-. As the (M···X) distance of ([MX₃]^-···X^-) increases, the distance variation (Rt) of trans (M-X) bond at the trans-position is shorter than those (Rc) of two cis (M-X) bonds at the cisposition. Simultaneously the atomic charge variation of trans-X atom is more positive than those of equilibrium [MX₄]^2- structures, while the variation of leaving X group is more positive