Bond dissociation energies of ligands in square planar Pd(II) and Pt(II) complexes: An assessment using trans influence

DFT calculations using MPWB1K method with COSMO continuum solvation model have been carried out to quantify the trans influence of various X ligands (EX) in [PtIICl3X]n− complexes as well as the mutual trans influence of two X and Y ligands (EXY) in [PtIICl2XY]n− complexes. A quantitative structure energy relationship (QSER) is derived for predicting the EXY using EX and EY and this relationship showed a strong similarity to a QSER derived for predicting EXY of [PdIICl2XY]n− complexes. Quantification of the contributions of EX and EXY to the bond dissociation energy of the ligand X (BDEX) in complexes of the type [MIIX(Y)X′(Y′)] (M = Pd, Pt) is also achieved. The BDEX of any ligand X in these complexes can be predicted using the equations, viz. BDEX(Pd) = 1.196EX − 0.603EXY − 0.118EX’Y’ + 0.442DX + 15.169 for Pd(II) complexes and BDEX(Pt) = 1.420EX − 0.741EXY − 0.125EX’Y’ + 0.498DX + 13.852 for Pt(II) complexes, where DX corresponds to the bond dissociation energy of X in [MIICl3X]n− complexes. These expressions suggest that the mutual trans influence from X and Y is more dominant than the mutual trans influence from X′ and Y′ and both factors contribute significantly to the weakening of M–X bond. We also obtained a strong linear relationship between EX and the electron density ρ(r) at the bond critical point of M–Cl bond trans to the X in [MIICl3X]n− and this allows us to express the BDEX(Pd) and BDEX(Pt) in terms of only the ρ(r) and DX. We have demonstrated that using a database comprising of DX and the ρ(r), the bond dissociation energy of X in complexes of the type [MIIX(Y)X′(Y′)] can be predicted.