Theoretical studies on spectroscopic properties of binuclear palladium(II) halide with phosphine ligands

The structures of trans-[Pd2X4(PH2CH2PH2)2] (X = Cl (1), Br (2) and I (4)) and [Pd2(μ-I)2I2(PH2CH2PH2)2] (3) in the ground and excited states were optimized by the MP2 and unrestricted MP2 methods. It is shown that upon excitation the Pd–Pd distances shorten ca. 0.40 Å for 1, 2 and 4 but lengthen ca. 0.10 Å for 3. This is rationalized by their electronic structures in the excited states and spectroscopic calculations. On the basis of such structures, we predict the absorption and emission spectra of 1–3 in the CHCl3 solution at the time-dependent density functional theory (TD-DFT) level. Experimental absorption spectra are well reproduced by theoretically simulated spectra.