The structures of trans-[M₂(CN)₄(PH₂CH₂PH₂)₂] [M＝Pt (1), Pd (2) and Ni (3)] and trans- [M(CN)₂(PH₃)₂] [M＝Pt (4), Pd (5) and Ni (6)] in the ground and ^1,3[(d_z2)(p_z)] excited states were optimized by the MP2 and CIS methods, respectively. The CIS calculations revealed that upon excitation the Pt-Pt distance of 1 shortens but those of 2 and 3 lengthened. Ex-perimental emissions were well reproduced by the TD-DFT calculations. For example, the fluores-cent/phosphorescent emissions of 1 were predicted to take place at 356/417 nm in the solid state and at 348/404 nm in the CH₂Cl₂ solution, agreeing with experimental 388/450 and 386/448 nm, respectively. It is shown that the metal-metal interaction decreases on going from 1 to 3 in their excited states, leading to the increase of the σ(p_z)→σ* (d_z2) emission energy along the series complexes. With respect to analogous mononu-clear d⁸ complexes (4～6), the d⁸-d⁸ interaction results in a large red shift of emission wavelength for the binuclear Pt(II) complex but slightly affects those of the binuclear Pd(II) and Ni(II) complexes.

Key words: d⁸ complex, metal-metal interaction, excited state, TD-DFT