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Relativistic effects on a metal-metal bond: Osmium corrole dimers

Relativistic effects on a metal-metal bond: Osmium corrole dimers
Relativistic effects on a metal-metal bond: Osmium corrole dimers

A series of metal-metal bonded osmium corrole dimers, {Os[TpXPC]} 2 , were synthesized in reasonably good yields (35-46%) via the interaction of the corresponding free-base meso-tris(p-X-phenyl)corroles (H 3 [TpXPC], X = CF 3 , H, CH 3 , and OCH 3 ), Os 3 (CO) 12 , and potassium carbonate in 1,2,4-trichlorobenzene under an inert atmosphere at 180 °C over several hours. The complexes are only the second class of Os corroles reported to date (the first being Os VI N corroles) and also the second class of metal-metal bonded metallocorrole dimers (the other being Ru corrole dimers). Comparison of the X-ray structures, redox potentials, and optical spectra of analogous Ru and Os corrole dimers, along with scalar-relativistic DFT calculations, has provided an experimentally calibrated account of relativistic effects in these complexes. Three of the Os corrole dimers (X = CF 3 , H, and OCH 3 ) were analyzed with single-crystal X-ray diffraction analysis, revealing inversion-related corrole rings with eclipsed Os-N bonds and Os-Os distances of â2.24 Å that are â.06 Å longer than the Ru-Ru distances in the analogous Ru corrole dimers. Interestingly, a comparison of scalar-relativistic and nonrelativistic DFT calculations indicates that this difference in metal-metal bond distance does not, in fact, reflect a differential relativistic effect. For a given corrole ligand, the Ru and Os corrole dimers exhibit nearly identical oxidation potentials but dramatically different reduction potentials, with the Os values â0.5 V lower relative to Ru, suggesting that whereas oxidation occurs in a ligand-centered manner, reduction is substantially metal-centered, which indeed was confirmed by scalar-relativistic calculations. The calculations further indicate that approximately a third of the â0.5 V difference in reduction potentials can be ascribed to relativity. The somewhat muted value of this relativistic effect appears to be related to the finding that reduction of an Os corrole dimer is not exclusively metal-based but that a significant amount of spin density is delocalized over to the corrole ligand; in contrast, reduction of an Ru corrole dimer occurs exclusively on the Ru-Ru linkage. For isoelectronic complexes, the Ru and Os corrole dimers exhibit substantially different UV-vis spectra. A key difference is a strong near-UV feature of the Os series, which in energy terms is blue-shifted by â0.55 V relative to the analogous feature of the Ru series. TDDFT calculations suggest that this difference may be related to higher-energy Os(5d)-based LUMOs in the Os case relative to analogous MOs for Ru.

0020-1669
2798-2806
Alemayehu, Abraham B.
87f64bd7-bb09-4f76-a631-b0991665ad3e
McCormick, Laura J.
f1c2f8cd-adcc-4bbf-9289-0b33a006d2bb
Vazquez-Lima, Hugo
e33ec9ee-1df4-4633-a970-eb464b54aa2f
Ghosh, Abhik
01a311da-a139-43f0-ae29-0efa0e8788f7
Alemayehu, Abraham B.
87f64bd7-bb09-4f76-a631-b0991665ad3e
McCormick, Laura J.
f1c2f8cd-adcc-4bbf-9289-0b33a006d2bb
Vazquez-Lima, Hugo
e33ec9ee-1df4-4633-a970-eb464b54aa2f
Ghosh, Abhik
01a311da-a139-43f0-ae29-0efa0e8788f7

Alemayehu, Abraham B., McCormick, Laura J., Vazquez-Lima, Hugo and Ghosh, Abhik (2019) Relativistic effects on a metal-metal bond: Osmium corrole dimers. Inorganic Chemistry, 58 (4), 2798-2806. (doi:10.1021/acs.inorgchem.8b03391).

Record type: Article

Abstract

A series of metal-metal bonded osmium corrole dimers, {Os[TpXPC]} 2 , were synthesized in reasonably good yields (35-46%) via the interaction of the corresponding free-base meso-tris(p-X-phenyl)corroles (H 3 [TpXPC], X = CF 3 , H, CH 3 , and OCH 3 ), Os 3 (CO) 12 , and potassium carbonate in 1,2,4-trichlorobenzene under an inert atmosphere at 180 °C over several hours. The complexes are only the second class of Os corroles reported to date (the first being Os VI N corroles) and also the second class of metal-metal bonded metallocorrole dimers (the other being Ru corrole dimers). Comparison of the X-ray structures, redox potentials, and optical spectra of analogous Ru and Os corrole dimers, along with scalar-relativistic DFT calculations, has provided an experimentally calibrated account of relativistic effects in these complexes. Three of the Os corrole dimers (X = CF 3 , H, and OCH 3 ) were analyzed with single-crystal X-ray diffraction analysis, revealing inversion-related corrole rings with eclipsed Os-N bonds and Os-Os distances of â2.24 Å that are â.06 Å longer than the Ru-Ru distances in the analogous Ru corrole dimers. Interestingly, a comparison of scalar-relativistic and nonrelativistic DFT calculations indicates that this difference in metal-metal bond distance does not, in fact, reflect a differential relativistic effect. For a given corrole ligand, the Ru and Os corrole dimers exhibit nearly identical oxidation potentials but dramatically different reduction potentials, with the Os values â0.5 V lower relative to Ru, suggesting that whereas oxidation occurs in a ligand-centered manner, reduction is substantially metal-centered, which indeed was confirmed by scalar-relativistic calculations. The calculations further indicate that approximately a third of the â0.5 V difference in reduction potentials can be ascribed to relativity. The somewhat muted value of this relativistic effect appears to be related to the finding that reduction of an Os corrole dimer is not exclusively metal-based but that a significant amount of spin density is delocalized over to the corrole ligand; in contrast, reduction of an Ru corrole dimer occurs exclusively on the Ru-Ru linkage. For isoelectronic complexes, the Ru and Os corrole dimers exhibit substantially different UV-vis spectra. A key difference is a strong near-UV feature of the Os series, which in energy terms is blue-shifted by â0.55 V relative to the analogous feature of the Ru series. TDDFT calculations suggest that this difference may be related to higher-energy Os(5d)-based LUMOs in the Os case relative to analogous MOs for Ru.

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e-pub ahead of print date: 7 February 2019
Published date: 18 February 2019

Identifiers

Local EPrints ID: 438796
URI: http://eprints.soton.ac.uk/id/eprint/438796
ISSN: 0020-1669
PURE UUID: 2e6ae240-688c-4200-8adc-2c0ac873f8ee
ORCID for Laura J. McCormick: ORCID iD orcid.org/0000-0002-6634-4717

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Date deposited: 24 Mar 2020 17:52
Last modified: 26 Nov 2021 03:21

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Contributors

Author: Abraham B. Alemayehu
Author: Hugo Vazquez-Lima
Author: Abhik Ghosh

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