A Theoretical Study on Non‐Bridging Dimer Formation of a Cationic Platinum Complex with a Redox‐Active Ligand

Abstract

The electronic structure of [PtL2]2Cl2· 6H2O crystal is studied focusing on the bonding origin of the dimer formation, using theoretical calculations, where ligand L is a redox‐active ligand and refers either o‐phenylenediamido (L2−), o‐semibenzoquinonediimine(L1−), or o‐benzoquinonediimine(L0). It is a non‐bridging dimer with 3.01 Å of the inter‐molecular Pt⋯ Pt distance. Considering the stoichiometry, the monomer should have +1 charge and 1/2 spin. For the dimer, there are two possibilities of the electronic structure; singlet or triplet state. On the other hand, the observed bond length is shorter than usual PtII⋯ PtII (d8‐d8) interaction, while longer than usual PtIII⋯ PtIII (d7‐d7) interaction. According to the structures and potential energy profiles on these possible spin states, we concluded that the dimer prefers the singlet state, formed by face‐to‐face bonding between the ligands of the two cationic monomers in the non‐bridging Pt dimer. The analysis of molecular orbitals revealed that the Pt⋯ Pt interaction is explained by the d8‐d8 interaction and partial oxidation by the redox‐active ligands. This study highlights the nature of the electronic structure of stacked radical monocations of Pt complex dimer.