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Electronic Structure Description of a Doubly Oxidized Bimetallic Cobalt Complex with Pro-Radical Ligands

Resource type
Date created
2016
Authors/Contributors
Abstract
The geometric and electronic structure of a doubly oxidized bimetallic Co complex containing two redox-active salen moieties connected via a 1,2-phenylene linker has been investigated and compared to an oxidized monomeric analogue. Both complexes, CoL1 and Co2L2 are oxidized to the mono- and di-cations respectively with AgSbF6 and characterized by X-ray crystallography for the monomer, and Vis-NIR spectroscopy, electron paramagnetic (EPR) spectroscopy, SQUID magnetometry and density functional theory (DFT) calculations for both the monomer and dimer. Both complexes exhibit a water molecule coordinated in the apical position upon oxidation. [CoL1-H2O]+ displays a broad NIR band at 8500 cm-1 (8400 M-1cm-1) which is consistent with recent reports on oxidized Co salen complexes (Kochem, A. et. al., Inorg Chem., 2012, 51, 10557-10571, Kurahashi, T. et. al., Inorg. Chem., 2013, 52, 3908-3919). DFT calculations predict a triplet ground state with significant ligand and metal contributions to the singularly occupied molecular orbital (SOMO). The majority (~75%) of the total spin density is localized on the metal, highlighting both high spin Co(III) and Co(II)L• character in the electronic ground state. Further oxidation of CoL1 to the dication affords a low spin Co(III) phenoxyl radical species. The NIR features for [Co2L2-2H2O]2+ at 8600 cm-1 (17800 M-1cm-1) are doubly intense in comparison to [CoL1-H2O]+ owing to the description of [Co2L2-2H2O]2+ as two non-interacting oxidized Co salen complexes bound via the central phenylene linker. Interestingly, TD-DFT calculations predict two electronic transitions that are 353 cm-1 apart. The NIR spectrum of the analogous Ni complex, [Ni2L2]2+, exhibits two intense transitions (4890 cm-1/26500 M-1cm-1 and 4200 cm-1/21200 M-1cm-1) due to exciton coupling in the excited state. Only one broad band is observed in the NIR spectrum for [Co2L2-2H2O]2+ as a result of the contracted donor and acceptor orbitals and overall CT character.
Document
Published as
Clarke, R.M., Hazin, K., Thompson, J.R., Savard, D., Prosser, K.E., and Storr, T. Electronic Structure Description of a Doubly Oxidized Bimetallic Cobalt Complex with Pro-Radical Ligands. Inorg. Chem., 2016, 55, 762-774. doi:10.1021/acs.inorgchem.5b02231
Publication title
Inorg. Chem
Document title
Electronic Structure Description of a Doubly Oxidized Bimetallic Cobalt Complex with Pro-Radical Ligands
Date
2016
Volume
55
First page
762
Last page
774
Publisher DOI
10.1021/acs.inorgchem.5b02231
Copyright statement
Copyright is held by the author(s).
Scholarly level
Peer reviewed?
Yes
Language
English
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Download file Size
Storr-InorgChem-Manuscript-2016.pdf 1.18 MB

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