Ab initio and density functional theory study of the electronic structure of rhenium complexes with noninnocent dioxolene ligands: Localized vs delocalized valence states

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Abstract

The dioxolene type ligands (Diox) derived from ortho-quinones are the most widely studied redox noninnocent ligands existing in the dianionic (Cat), anion radical (SQ) or neutral (Q) forms although a highly delocalized electronic structure is also possible. For [ReO(Diox)2PPh3] (2) and [ReCl3(Diox)PPh3] (3) complexes, the ReV-Cat2 and ReIV-SQ localized valence states were proposed on the basis of their XRD structures. To understand in detail the electronic structure of these complexes, we performed a series of the all-electron calculations at the DKH2-CASSCF/CASPT2 and DKH2-CASSCF/NEVPT2 levels taking into account scalar relativistic and spin-orbit effects. All calculations predicted that 2 has a singlet ground state with a predominant contribution of a single electronic configuration with doubly occupied molecular orbitals being pure o-quinone LUMOs of both Diox ligands that corresponds to the ReV-Cat2 valence state. Complex 3 has a triplet ground state with four electronic configurations contributing mainly into its wavefunction and differing by the occupation of bonding and antibonding combinations of the o-quinone LUMO and rhenium d-AO with nearly equal contributions. This leads to the empirical “metrical oxidation state” of dioxolene ligand being −1 that is usually referred to the ReIV-SQ oxidation state. However, in fact, the negative charge on the Diox ligand is mainly provided by a pair of electrons on the bonding MO. The standard DFT calculations entirely fail to correctly predict the ground state multiplicity for 3.

Original languageEnglish
Article number26018
Number of pages10
JournalInternational Journal of Quantum Chemistry
Volume119
Issue number23
DOIs
Publication statusPublished - 5 Dec 2019

Keywords

  • DFT and CASSCF
  • dioxolene ligands
  • electronic structure
  • metrical oxidation state
  • rhenium complexes
  • CATECHOLATE
  • TRANSITION-METAL-COMPLEXES
  • APPROXIMATION
  • SEMIQUINONE
  • CRYSTAL-STRUCTURE
  • CORRELATION-ENERGY
  • IMPLEMENTATION
  • 2ND-ORDER PERTURBATION-THEORY
  • BASIS-SETS
  • TAUTOMERISM

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