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Title: X-ray Absorption Spectroscopy as a Probe of Ligand Noninnocence in Metallocorroles: The Case of Copper Corroles

Abstract

The question of ligand noninnocence in Cu corroles has long been a topic of discussion. This work introduces a Cu K-edge X-ray absorption spectroscopy (XAS) study, which allows a direct probe of the metal oxidation state, of three Cu corroles, Cu[TPC], Cu[Br 8TPC], and Cu[(CF 3) 8TPC] (TPC = meso-triphenylcorrole), and the analogous Cu(II) porphyrins, Cu[TPP], Cu[Br 8TPP], and Cu[(CF 3) 8TPP] (TPP = meso-tetraphenylporphyrin). The Cu K rising-edges of the Cu corroles were found to be about 0–1 eV upshifted relative to the analogous porphyrins, which is substantially lower than the 1–2 eV shifts typically exhibited by authentic Cu(II)/Cu(III) model complex pairs. In an unusual twist, the Cu K pre-edge regions of both the Cu corroles and the Cu porphyrins exhibit two peaks split by 0.8–1.3 eV. Based on time-dependent density functional theory calculations, the lower- and higher-energy peaks were assigned to a Cu 1s → 3d$$_{x^{2}–y^{2}}$$ transition and a Cu 1s → corrole/porphyrin π* transition, respectively. From the Cu(II) porphyrins to the corresponding Cu corroles, the energy of the Cu 1s → 3d$$_{x^{2}–y^{2}}$$ transition peak was found to upshift by 0.6–0.8 eV. This shift is approximately half that observed between Cu(II) to Cu(III) states for well-defined complexes. The Cu K-edge XAS spectra thus show that although the metal sites in the Cu corroles are more oxidized relative to those in their Cu(II) porphyrin analogues, they are not oxidized to the Cu(III) level, consistent with the notion of a noninnocent corrole. The relative importance of σ-donation versus corrole π-radical character is discussed.

Authors:
 [1];  [2];  [3];  [3]; ORCiD logo [2]; ORCiD logo [3]
  1. Stanford Univ., CA (United States)
  2. Arctic Univ. of Norway, Tromsø (Norway)
  3. SLAC National Accelerator Lab., Menlo Park, CA (United States); Stanford Univ., CA (United States)
Publication Date:
Research Org.:
SLAC National Accelerator Lab., Menlo Park, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); National Institutes of Health (NIH)
OSTI Identifier:
1532490
Grant/Contract Number:  
AC02-76SF00515; 231086; 262229; R01DK031450
Resource Type:
Accepted Manuscript
Journal Name:
Inorganic Chemistry
Additional Journal Information:
Journal Volume: 58; Journal Issue: 10; Journal ID: ISSN 0020-1669
Publisher:
American Chemical Society (ACS)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY

Citation Formats

Lim, Hyeongtaek, Thomas, Kolle E., Hedman, Britt, Hodgson, Keith O., Ghosh, Abhik, and Solomon, Edward I. X-ray Absorption Spectroscopy as a Probe of Ligand Noninnocence in Metallocorroles: The Case of Copper Corroles. United States: N. p., 2019. Web. doi:10.1021/acs.inorgchem.9b00128.
Lim, Hyeongtaek, Thomas, Kolle E., Hedman, Britt, Hodgson, Keith O., Ghosh, Abhik, & Solomon, Edward I. X-ray Absorption Spectroscopy as a Probe of Ligand Noninnocence in Metallocorroles: The Case of Copper Corroles. United States. doi:10.1021/acs.inorgchem.9b00128.
Lim, Hyeongtaek, Thomas, Kolle E., Hedman, Britt, Hodgson, Keith O., Ghosh, Abhik, and Solomon, Edward I. Thu . "X-ray Absorption Spectroscopy as a Probe of Ligand Noninnocence in Metallocorroles: The Case of Copper Corroles". United States. doi:10.1021/acs.inorgchem.9b00128.
@article{osti_1532490,
title = {X-ray Absorption Spectroscopy as a Probe of Ligand Noninnocence in Metallocorroles: The Case of Copper Corroles},
author = {Lim, Hyeongtaek and Thomas, Kolle E. and Hedman, Britt and Hodgson, Keith O. and Ghosh, Abhik and Solomon, Edward I.},
abstractNote = {The question of ligand noninnocence in Cu corroles has long been a topic of discussion. This work introduces a Cu K-edge X-ray absorption spectroscopy (XAS) study, which allows a direct probe of the metal oxidation state, of three Cu corroles, Cu[TPC], Cu[Br8TPC], and Cu[(CF3)8TPC] (TPC = meso-triphenylcorrole), and the analogous Cu(II) porphyrins, Cu[TPP], Cu[Br8TPP], and Cu[(CF3)8TPP] (TPP = meso-tetraphenylporphyrin). The Cu K rising-edges of the Cu corroles were found to be about 0–1 eV upshifted relative to the analogous porphyrins, which is substantially lower than the 1–2 eV shifts typically exhibited by authentic Cu(II)/Cu(III) model complex pairs. In an unusual twist, the Cu K pre-edge regions of both the Cu corroles and the Cu porphyrins exhibit two peaks split by 0.8–1.3 eV. Based on time-dependent density functional theory calculations, the lower- and higher-energy peaks were assigned to a Cu 1s → 3d$_{x^{2}–y^{2}}$ transition and a Cu 1s → corrole/porphyrin π* transition, respectively. From the Cu(II) porphyrins to the corresponding Cu corroles, the energy of the Cu 1s → 3d$_{x^{2}–y^{2}}$ transition peak was found to upshift by 0.6–0.8 eV. This shift is approximately half that observed between Cu(II) to Cu(III) states for well-defined complexes. The Cu K-edge XAS spectra thus show that although the metal sites in the Cu corroles are more oxidized relative to those in their Cu(II) porphyrin analogues, they are not oxidized to the Cu(III) level, consistent with the notion of a noninnocent corrole. The relative importance of σ-donation versus corrole π-radical character is discussed.},
doi = {10.1021/acs.inorgchem.9b00128},
journal = {Inorganic Chemistry},
number = 10,
volume = 58,
place = {United States},
year = {2019},
month = {5}
}

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This content will become publicly available on May 2, 2020
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