Spectroscopic and Computational Investigation of Low-Spin MnIII Bis(scorpionate) Complexes

View/ Open
Issue Date
2016-06Author
Colmer, Hannah Elizabeth
Margarit, Charles G.
Smith, Jeremy M.
Jackson, Timothy A.
Telser, Joshua
Publisher
Wiley
Type
Article
Article Version
Scholarly/refereed, author accepted manuscript
Rights
This is the peer reviewed version of the following article: Colmer, H. E., Margarit, C. G., Smith, J. M., Jackson, T. A., & Telser, J. (2016). Spectroscopic and Computational Investigation of Low-Spin Mn(III) Bis(scorpionate) Complexes. European Journal of Inorganic Chemistry, 2016(15-16), 2413–2423. http://doi.org/10.1002/ejic.201501250, which has been published in final form at 10.1002/ejic.201501250. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.
Metadata
Show full item recordAbstract
Six-coordinate MnIII complexes are typically high-spin (S = 2), however, the scorpionate ligand, both in its traditional, hydridotris(pyrazolyl)borate form, Tp– and Tp*– (the latter with 3,5-dimethylpyrazole substituents) and in an aryltris(carbene)borate (i.e., N-heterocyclic carbene, NHC) form, [Ph(MeIm)3B]–, (MeIm = 3-methylimidazole) lead to formation of bis(scorpionate) complexes of MnIII with spin triplet ground states; three of which were investigated herein: [Tp2Mn]SbF6 (1SbF6), [Tp*2Mn]SbF6 (2SbF6), and [{Ph(MeIm)3B}2Mn]CF3SO3 (3CF3SO3). These trigonally symmetric complexes were studied experimentally by magnetic circular dichroism (MCD) spectroscopy (the propensity of 3 to oxidize to MnIV precluded collection of useful MCD data) including variable temperatures and fields (VTVH-MCD) and computationally by ab initio CASSCF/NEVPT2 methods. These combined experimental and theoretical techniques establish the 3A2g electronic ground state for the three complexes, and provide information on the energy of the “conventional” high-spin excited state (5Eg) and other, triplet excited states. These results show the electronic effect of pyrazole ring substituents in comparing 1 and 2. The tunability of the scorpionate ligand, even by perhaps the simplest change (from pyrazole in 1 to 3,5-dimethylpyrazole in 2) is quantitatively manifested through perturbations in ligand-field excited-state energies that impact ground-state zero-field splittings. The comparison with the NHC donor is much more dramatic. In 3, the stronger σ-donor properties of the NHC lead to a quantitatively different electronic structure, so that the lowest lying spin triplet excited state, 3Eg, is much closer in energy to the ground state than in 1 or 2. The zero-field splitting (zfs) parameters of the three complexes were calculated and in the case of 1 and 2 compare closely to experiment (lower by < 10 %, < 2 cm–1 in absolute terms); for 3 the large magnitude zfs is reproduced, although there is ambiguity about its sign. The comprehensive picture obtained for these bis(scorpionate) MnIII complexes provides quantitative insight into the role played by the scorpionate ligand in stabilizing unusual electronic structures.
Collections
Citation
Colmer, H. E., Margarit, C. G., Smith, J. M., Jackson, T. A., & Telser, J. (2016). Spectroscopic and Computational Investigation of Low-Spin Mn(III) Bis(scorpionate) Complexes. European Journal of Inorganic Chemistry, 2016(15-16), 2413–2423. http://doi.org/10.1002/ejic.201501250
Items in KU ScholarWorks are protected by copyright, with all rights reserved, unless otherwise indicated.
We want to hear from you! Please share your stories about how Open Access to this item benefits YOU.