Structures and electronic spectra of [Pt₂(P₂O₅H₂)₄X₂]^4- (X = Cl, Br and I): A comparative study of ab initio and density functional theory

The structures of [Pt₂(P₂O₅H₂)₄X₂]^4- (X = Cl (1), Br (2) and I (3)) were optimized using the ab initio and density functional theory methods. It is shown that the geometry parameters estimated by MP2 and XαVWN are closer to experimental values. We performed the time-dependent density functional theory (TD-DFT) calculations to explore the influence of different density functionals and structures on electronic absorption spectra in solution. The experimental absorptions with the featured σ (d_z2) → σ^* (d_z2) and π (d_xz, d_yz) → σ^* (d_z2) transitions are well reproduced by the theoretical calculations.