ABSTRACT The dioxolene type ligands (Diox) derived from ortho ‐quinones are the most extensively studied redox non‐innocent ligands existing in the dianionic (Cat), anion radical (SQ) or neutral (Q) forms although a highly delocalized electronic structure is also possible. For three manganese complexes with two dioxolene type ligands the Mn IV ‐ Cat 2 ( 1 ), SQ‐Mn III ‐ Cat ( 2 ), and Mn II ‐ SQ 2 ( 3 ) localized valence states were proposed on the basis of their XRD structures. To understand in detail the electronic structure and magnetic properties of these complexes, we performed a series of the ab initio calculations at the SA‐CASSCF/NEVPT2 level taking into account spin‐orbit effects. All calculations predicted the quartet ground state of 1 which wavefunction has an explicit multireference nature with predominant contribution of three electronic configuration differing by the occupation of dioxolene MOs and manganese d‐AO. The result of this is a coexistence of several valence states, namely, one mixed SQ‐Mn III ‐ Cat ↔ Cat‐Mn III ‐ SQ and two localized Mn IV ‐ Cat 2 and Mn II ‐ SQ 2 . Complex 2 has a triplet ground state. Three main electronic configurations contribute to its wavefunction and all of them correspond to the proposed valence state, SQ‐Mn III ‐ Cat . Complex 3 has a quartet ground state. Its wavefunction is strongly multireference as well leading to coexistence of three main valence states: dominant localized Mn II ‐ SQ 2 and two delocalized Mn II‐III ‐( Diox 2 ) 2.5– and Mn I‐II ‐( Diox 2 ) 1.5– . The calculated temperature dependence of magnetic susceptibility shows excellent agreement with the experiment for 1 and 2 . The standard DFT calculations can lead to incorrect prediction of the ground state and order of the excited states for 1 – 3 .
Alexey A. Dmitriev (Wed,) studied this question.