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Electronic structure of manganese corroles revisited: X-ray structures, optical and x-ray absorption spectroscopies, and electrochemistry as probes of ligand noninnocence

Electronic structure of manganese corroles revisited: X-ray structures, optical and x-ray absorption spectroscopies, and electrochemistry as probes of ligand noninnocence
Electronic structure of manganese corroles revisited: X-ray structures, optical and x-ray absorption spectroscopies, and electrochemistry as probes of ligand noninnocence

Presented herein is a detailed multitechnique investigation of ligand noninnocence in S = 3/2 manganese corrole derivatives at the formal MnIV oxidation state. The Soret maxima of Mn[TpXPC]Cl (TpXPC = meso-tris(p-X-phenyl)corrole, where X = CF3, H, Me, and OMe) were found to red-shift over a range of 37 nm with increasing electron-donating character of X. For Mn[TpXPC]Ph, in contrast, the complex Soret envelopes were found to be largely independent of X. These observations suggested a noninnocent corrole·2--like ligand for the MnCl complexes and an innocent corrole3- ligand for the MnPh complexes. Single-crystal X-ray structures of three Mn[TpXPC]Cl complexes revealed skeletal bond-length alternations indicative of a noninnocent corrole, while no such alternation was observed for Mn[TpOMePC]Ph. B3LYP density functional theory (DFT) calculations on Mn[TPC]Cl yielded strong spatial separation of the α and β spin densities, consistent with an antiferromagnetically coupled MnIII-corrole·2- description. By comparison, relatively little spatial separation of the α and β spin densities was found for Mn[TPC]Ph, consistent with an essentially MnIV-corrole3- description. X-ray absorption of near-edge spectroscopy (XANES) revealed a moderate blue shift of 0.6 eV for the Mn K-pre-edge of Mn[TpCF3PC]Ph and a striking enhancement of the pre-edge intensity, relative to Mn[TpCF3PC]Cl, consistent with a more oxidized, i.e., MnIV, center in Mn[TpCF3PC]Ph. Time-dependent DFT calculations indicated that the enhanced intensity of the Mn K-pre-edge of Mn[TpCF3PC]Ph results from the extra 3dz2 hole, which mixes strongly with the Mn 4pz orbital. Combined with similar results on Fe[TPC]Cl and Fe[TPC]Ph, the present study underscores the considerable potential of metal K-edge XANES in probing ligand noninnocence in first-row transition-metal corroles. Cyclic voltammetry measurements revealed highly negative first reduction potentials for the Mn[TpXPC]Ph series (∼-0.95 V) as well as large electrochemical HOMO-LUMO gaps of ∼1.7 V. The first reductions, however, are irreversible, suggesting cleavage of the Mn-Ph bond.

0020-1669
9656-9669
Ganguly, Sumit
0e87078e-c576-4b20-a10d-dafd6288f8b2
McCormick, Laura J.
f1c2f8cd-adcc-4bbf-9289-0b33a006d2bb
Conradie, Jeanet
814b9b0c-ae44-4f35-b80b-4d27bd575030
Gagnon, Kevin J.
5535af49-cc12-48b8-b007-28bb1f1b070c
Sarangi, Ritimukta
8be920ed-0149-4f14-871b-78eb0bc4c820
Ghosh, Abhik
01a311da-a139-43f0-ae29-0efa0e8788f7
Ganguly, Sumit
0e87078e-c576-4b20-a10d-dafd6288f8b2
McCormick, Laura J.
f1c2f8cd-adcc-4bbf-9289-0b33a006d2bb
Conradie, Jeanet
814b9b0c-ae44-4f35-b80b-4d27bd575030
Gagnon, Kevin J.
5535af49-cc12-48b8-b007-28bb1f1b070c
Sarangi, Ritimukta
8be920ed-0149-4f14-871b-78eb0bc4c820
Ghosh, Abhik
01a311da-a139-43f0-ae29-0efa0e8788f7

Ganguly, Sumit, McCormick, Laura J., Conradie, Jeanet, Gagnon, Kevin J., Sarangi, Ritimukta and Ghosh, Abhik (2018) Electronic structure of manganese corroles revisited: X-ray structures, optical and x-ray absorption spectroscopies, and electrochemistry as probes of ligand noninnocence. Inorganic Chemistry, 57 (16), 9656-9669. (doi:10.1021/acs.inorgchem.8b00537).

Record type: Review

Abstract

Presented herein is a detailed multitechnique investigation of ligand noninnocence in S = 3/2 manganese corrole derivatives at the formal MnIV oxidation state. The Soret maxima of Mn[TpXPC]Cl (TpXPC = meso-tris(p-X-phenyl)corrole, where X = CF3, H, Me, and OMe) were found to red-shift over a range of 37 nm with increasing electron-donating character of X. For Mn[TpXPC]Ph, in contrast, the complex Soret envelopes were found to be largely independent of X. These observations suggested a noninnocent corrole·2--like ligand for the MnCl complexes and an innocent corrole3- ligand for the MnPh complexes. Single-crystal X-ray structures of three Mn[TpXPC]Cl complexes revealed skeletal bond-length alternations indicative of a noninnocent corrole, while no such alternation was observed for Mn[TpOMePC]Ph. B3LYP density functional theory (DFT) calculations on Mn[TPC]Cl yielded strong spatial separation of the α and β spin densities, consistent with an antiferromagnetically coupled MnIII-corrole·2- description. By comparison, relatively little spatial separation of the α and β spin densities was found for Mn[TPC]Ph, consistent with an essentially MnIV-corrole3- description. X-ray absorption of near-edge spectroscopy (XANES) revealed a moderate blue shift of 0.6 eV for the Mn K-pre-edge of Mn[TpCF3PC]Ph and a striking enhancement of the pre-edge intensity, relative to Mn[TpCF3PC]Cl, consistent with a more oxidized, i.e., MnIV, center in Mn[TpCF3PC]Ph. Time-dependent DFT calculations indicated that the enhanced intensity of the Mn K-pre-edge of Mn[TpCF3PC]Ph results from the extra 3dz2 hole, which mixes strongly with the Mn 4pz orbital. Combined with similar results on Fe[TPC]Cl and Fe[TPC]Ph, the present study underscores the considerable potential of metal K-edge XANES in probing ligand noninnocence in first-row transition-metal corroles. Cyclic voltammetry measurements revealed highly negative first reduction potentials for the Mn[TpXPC]Ph series (∼-0.95 V) as well as large electrochemical HOMO-LUMO gaps of ∼1.7 V. The first reductions, however, are irreversible, suggesting cleavage of the Mn-Ph bond.

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Published date: 20 August 2018

Identifiers

Local EPrints ID: 438919
URI: http://eprints.soton.ac.uk/id/eprint/438919
ISSN: 0020-1669
PURE UUID: fe108db1-fece-4224-9025-faabb59c25ce
ORCID for Laura J. McCormick: ORCID iD orcid.org/0000-0002-6634-4717

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Date deposited: 26 Mar 2020 17:35
Last modified: 26 Nov 2021 03:21

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Contributors

Author: Sumit Ganguly
Author: Jeanet Conradie
Author: Kevin J. Gagnon
Author: Ritimukta Sarangi
Author: Abhik Ghosh

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