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

Abstract

Potential energy curves and intemuclear (M-X) distance variations for dissociation reactions of [MX 4 ] 2 - into ([MX 3 ] - + 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 [MX 4 ] 2 - are optimized to tetrahedral geometry for [NiX 4 ] 2 - and square planar geometry for ([PdX 4 ] 2 - and [PtX 4 ] 2 - ). The bond (M-X) distances of [NiCl 4 ] 2 - , [NiBr 4 ] 2 - , [PdCl 4 ] 2 - , [PdBr 4 ] 2 - , [PtCl 4 ] 2 - , and [PtBr 4 ] 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 ([MX 3 ] - ...X - ) at the DFT level are found to be 4.73 eV for [NiCl 4 ] 2 - , 4.89 eV for [NiBr 4 ] 2 - , 4.93 eV for [PdCl 4 ] 2 - , 5.57 eV for [PdBr 4 ] 2 - , 5.44 eV for [PtCl 4 ] 2 - , and 5.87 eV for [PtBr 4 ] 2 - . As the (M...X) distance of ([MX 3 ]...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 exposition. Simultaneously the atomic charge variation of trans-X atom is more positive than those of equilibrium [MX 4 ] 2 - structures, while the variation of leaving X group is more positive.