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Ab initio and density functional theory study of the electronic structure of rhenium complexes with noninnocent dioxolene ligands: Localized vs delocalized valence states
Author(s) -
Dmitriev Alexey A.,
Gritsan Nina P.
Publication year - 2019
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/qua.26018
Subject(s) - delocalized electron , chemistry , antibonding molecular orbital , density functional theory , rhenium , electronic structure , valence (chemistry) , ground state , computational chemistry , ab initio , singlet state , valence electron , crystallography , main group element , atomic orbital , atomic physics , electron , excited state , physics , inorganic chemistry , transition metal , quantum mechanics , organic chemistry , biochemistry , catalysis
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) 2 PPh 3 ] − ( 2 ) and [ReCl 3 (Diox)PPh 3 ] ( 3 ) complexes, the Re V ‐ Cat 2 and Re IV ‐ 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 Re V ‐ Cat 2 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 Re IV ‐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 .