Issue 8, 2017

Structure and spin state of nonheme FeIVO complexes depending on temperature: predictive insights from DFT calculations and experiments

Abstract

The spin states (S = 1 and S = 2) of nonheme FeIVO intermediates are believed to play an important role in determining their chemical properties in enzymatic and biomimetic reactions. However, it is almost impossible to investigate the spin state effect of nonheme FeIVO species experimentally, since FeIVO models having the S = 1 and S = 2 spin states at the same time neither exist nor can be synthesized. However, recent synthesis of an FeIVO complex with an S = 1 spin state (triplet), [(Me3NTB)FeIVO]2+ (1), and a structurally similar FeIVO complex but with an S = 2 spin state (quintet), [(TQA)FeIVO]2+ (2), has allowed us to compare their reactivities at 233 K. In the present study, we show that structural variants control the spin-state selectivity and reactivity of nonheme FeIVO complexes. While 1 and 2 were proposed to be in an octahedral geometry based on DFT calculations and spectroscopic characterization done at 4 K, further DFT calculations show that these species may well assume a trigonal bipyramidal structure by losing one coordinated solvent ligand at 233 K. Thus, the present study demonstrates that the structure and spin state of nonheme FeIVO complexes can be different at different temperatures; therefore, the structural and/or spin state information obtained at 4 K should be carefully used at a higher temperature (e.g., 233 K). In addition to 1 and 2, [(TPA)FeIVO]2+ (3) with an S = 1 spin state, whose spin state was determined spectroscopically and theoretically at 233 K, is included in this study to compare the chemical properties of S = 1 and S = 2 FeIVO complexes. The present results add another dimension to the discussion of the reactivites of nonheme FeIVO species, in which the structural preference and spin state of nonheme FeIVO species can vary depending on temperature.

Graphical abstract: Structure and spin state of nonheme FeIVO complexes depending on temperature: predictive insights from DFT calculations and experiments

Supplementary files

Article information

Article type
Edge Article
Submitted
19 Apr 2017
Accepted
27 May 2017
First published
30 May 2017
This article is Open Access

All publication charges for this article have been paid for by the Royal Society of Chemistry
Creative Commons BY-NC license

Chem. Sci., 2017,8, 5460-5467

Structure and spin state of nonheme FeIVO complexes depending on temperature: predictive insights from DFT calculations and experiments

N. Y. Lee, D. Mandal, S. H. Bae, M. S. Seo, Y. Lee, S. Shaik, K. Cho and W. Nam, Chem. Sci., 2017, 8, 5460 DOI: 10.1039/C7SC01738C

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