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Title: Ligand Field Strength Mediates Electron Delocalization in Octahedral [( H L) 2 Fe 6 (L') m] n+ Clusters

Abstract

To assess the impact of terminal ligand binding on a variety of cluster properties (redox delocalization, ground-state stabilization, and breadth of redox state accessibility), we prepared three electron-transfer series based on the hexanuclear iron cluster [( HL) 2Fe 6(L') m] n+ in which the terminal ligand field strength was modulated from weak to strong (L' = DMF, MeCN, CN). The extent of intracore M–M interactions is gauged by M–M distances, spin ground state persistence, and preference for mixed-valence states as determined by electrochemical comproportionation constants. Coordination of DMF to the [( HL) 2Fe 6] core leads to weaker Fe–Fe interactions, as manifested by the observation of ground states populated only at lower temperatures (<100 K) and by the greater evidence of valence trapping within the mixed-valence states. Comproportionation constants determined electrochemically (K c = 10 4–10 8) indicate that the redox series exhibits electronic delocalization (class II–III), yet no intervalence charge transfer (IVCT) bands are observable in the near-IR spectra. Ligation of the stronger σ donor acetonitrile results in stabilization of spin ground states to higher temperatures (~300 K) and a high degree of valence delocalization (K c = 10 2–10 8) with observable IVCT bands. Finally, the anionic cyanide-boundmore » series reveals the highest degree of valence delocalization with the most intense IVCT bands (K c = 10 12–10 20) and spin ground state population beyond room temperature. Lastly, across the series, at a given formal oxidation level, the capping ligand on the hexairon cluster dictates the overall properties of the aggregate, modulating the redox delocalization and the persistence of the intracore coupling of the metal sites.« less

Authors:
 [1];  [1];  [1]
  1. Harvard Univ., Cambridge, MA (United States). Dept. of Chemistry and Chemical Biology
Publication Date:
Research Org.:
Harvard Univ., Cambridge, MA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1441143
Grant/Contract Number:  
SC0008313; GM 098395
Resource Type:
Accepted Manuscript
Journal Name:
Journal of the American Chemical Society
Additional Journal Information:
Journal Volume: 137; Journal Issue: 34; Journal ID: ISSN 0002-7863
Publisher:
American Chemical Society (ACS)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; 36 MATERIALS SCIENCE

Citation Formats

Hernandez Sanchez, Raul, Zheng, Shao-Liang, and Betley, Theodore A. Ligand Field Strength Mediates Electron Delocalization in Octahedral [(H L)2 Fe 6 (L')m]n+ Clusters. United States: N. p., 2015. Web. doi:10.1021/jacs.5b06453.
Hernandez Sanchez, Raul, Zheng, Shao-Liang, & Betley, Theodore A. Ligand Field Strength Mediates Electron Delocalization in Octahedral [(H L)2 Fe 6 (L')m]n+ Clusters. United States. doi:10.1021/jacs.5b06453.
Hernandez Sanchez, Raul, Zheng, Shao-Liang, and Betley, Theodore A. Fri . "Ligand Field Strength Mediates Electron Delocalization in Octahedral [(H L)2 Fe 6 (L')m]n+ Clusters". United States. doi:10.1021/jacs.5b06453. https://www.osti.gov/servlets/purl/1441143.
@article{osti_1441143,
title = {Ligand Field Strength Mediates Electron Delocalization in Octahedral [(H L)2 Fe 6 (L')m]n+ Clusters},
author = {Hernandez Sanchez, Raul and Zheng, Shao-Liang and Betley, Theodore A.},
abstractNote = {To assess the impact of terminal ligand binding on a variety of cluster properties (redox delocalization, ground-state stabilization, and breadth of redox state accessibility), we prepared three electron-transfer series based on the hexanuclear iron cluster [(HL)2Fe6(L')m]n+ in which the terminal ligand field strength was modulated from weak to strong (L' = DMF, MeCN, CN). The extent of intracore M–M interactions is gauged by M–M distances, spin ground state persistence, and preference for mixed-valence states as determined by electrochemical comproportionation constants. Coordination of DMF to the [(HL)2Fe6] core leads to weaker Fe–Fe interactions, as manifested by the observation of ground states populated only at lower temperatures (<100 K) and by the greater evidence of valence trapping within the mixed-valence states. Comproportionation constants determined electrochemically (Kc = 104–108) indicate that the redox series exhibits electronic delocalization (class II–III), yet no intervalence charge transfer (IVCT) bands are observable in the near-IR spectra. Ligation of the stronger σ donor acetonitrile results in stabilization of spin ground states to higher temperatures (~300 K) and a high degree of valence delocalization (Kc = 102–108) with observable IVCT bands. Finally, the anionic cyanide-bound series reveals the highest degree of valence delocalization with the most intense IVCT bands (Kc = 1012–1020) and spin ground state population beyond room temperature. Lastly, across the series, at a given formal oxidation level, the capping ligand on the hexairon cluster dictates the overall properties of the aggregate, modulating the redox delocalization and the persistence of the intracore coupling of the metal sites.},
doi = {10.1021/jacs.5b06453},
journal = {Journal of the American Chemical Society},
number = 34,
volume = 137,
place = {United States},
year = {2015},
month = {7}
}

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