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

Na Young Lee, Debasish Mandal, Seong Hee Bae, Mi Sook Seo, Yong Min Lee, Sason Shaik, Kyung Bin Cho, Wonwoo Nam

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21 Scopus citations

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.

Original languageEnglish
Pages (from-to)5460-5467
Number of pages8
JournalChemical Science
Volume8
Issue number8
DOIs
StatePublished - 2017

Bibliographical note

Funding Information:
The authors acknowledge financial support from the NRF of Korea through the CRI (NRF-2012R1A3A2048842 to W. N.), GRL (NRF-2010-00353 to W. N.) and MSIP (NRF-2013R1A1A2062737 to K.-B. C.). The Israel Science Foundation (ISF) is acknowledged by S. S. (ISF grant 1183/13).

Publisher Copyright:
© 2017 The Royal Society of Chemistry.

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