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

Journal Article · · European Journal of Inorganic Chemistry
 [1];  [2];  [3];  [1]; ORCiD logo [4]
  1. Univ. of Kansas, Lawrence, KS (United States). Dept. of Chemistry
  2. New Mexico State Univ., Las Cruces, NM (United States). Dept. of Chemistry and Biochemistry
  3. New Mexico State Univ., Las Cruces, NM (United States). Dept. of Chemistry and Biochemistry; Indiana Univ., Bloomington, IN (United States). Dept. of Chemistry
  4. Roosevelt Univ., Chicago, IL (United States). Dept. of Biological, Chemical and Physical Sciences
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Six‐coordinate Mn III 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) 3 B] – , (MeIm = 3‐methylimidazole) lead to formation of bis(scorpionate) complexes of Mn III with spin triplet ground states; three of which were investigated herein: [Tp 2 Mn]SbF 6 ( 1 SbF 6 ), [Tp* 2 Mn]SbF 6 ( 2 SbF 6 ), and [{Ph(MeIm) 3 B} 2 Mn]CF 3 SO 3 ( 3 CF 3 SO 3 ). These trigonally symmetric complexes were studied experimentally by magnetic circular dichroism (MCD) spectroscopy (the propensity of 3 to oxidize to Mn IV 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 3 A 2g electronic ground state for the three complexes, and provide information on the energy of the “conventional” high‐spin excited state ( 5 E g ) 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, 3 E g , 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) Mn III complexes provides quantitative insight into the role played by the scorpionate ligand in stabilizing unusual electronic structures.

Research Organization:
New Mexico State Univ., Las Cruces, NM (United States)
Sponsoring Organization:
USDOE Office of Science (SC), Basic Energy Sciences (BES); National Science Foundation (NSF); National Institutes of Health (NIH)
Contributing Organization:
Univ. of California, Berkeley, CA (United States)
Grant/Contract Number:
FG02-08ER15996; CHE‐1056470; T32 GM08545; DE‐FG02‐08ER15996
OSTI ID:
1467007
Alternate ID(s):
OSTI ID: 1786417
Journal Information:
European Journal of Inorganic Chemistry, Vol. 2016, Issue 15-16; ISSN 1434-1948
Publisher:
ChemPubSoc EuropeCopyright Statement
Country of Publication:
United States
Language:
English
Citation Metrics:
Cited by: 12 works
Citation information provided by
Web of Science

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Cited By (2)

Near-infrared 2 E g → 4 A 2g and visible LMCT luminescence from a molecular bis -(tris(carbene)borate) manganese(IV) complex journal May 2017
Rational Design of Tetranuclear Complexes Employing N -Imidoylamidine Based Ligands : Rational Design of Tetranuclear Complexes Employing journal January 2019

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Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
scorpionate ligands
magnetic circular dichroism
electronic structure
zero-field splitting
ab initio calculations