Some square-planar metal benzene derivative [XM(PEt₃)₂-C₆H₄-A] (M＝Pd, Pt; X＝Br, I; A＝NO₂, CHO) were reported to possess rather large second hyperpolarizabilities. The series of compounds have been studied by using ab initio method. An extending Lanl2DZ basis set was used in calculations. According to our RHF/extending-Lanl2DZ calculations, the trans influence of X is evident with the iodo ligand better than bromo ligand for γ. The importance of benzene acceptor (A) is also evident, γ values were found to be increased with increase of acceptor strength, giving the higher values for the nitro derivatives.

Key words: metal complex, second hyperpolarizability, basis set, ab initio