Title: Exposing the inadequacy of redox formalisms by resolving redox inequivalence within isovalent clusters

Abstract

Here we examine a family of trinuclear iron complexes by multiple-wavelength, anomalous diffraction (MAD) to explore the redox load distribution within cluster materials by the free refinement of atomic scattering factors. Several effects were explored that can impact atomic scattering factors within clusters, including 1) metal atom primary coordination sphere, 2) M–M bonding, and 3) redox delocalization in formally mixed-valent species. Complexes were investigated which vary from highly symmetric to fully asymmetric by ⁵⁷Fe Mössbauer and X-ray diffraction to explore the relationship between MAD-derived data and the data available from these widely used characterization techniques. The compounds examined include the all-ferrous clusters [ⁿBu₄N][(^tbsL)Fe₃(μ³–Cl)] (1) ([^tbsL]^6– = [1,3,5-C₆H₉(NC₆H₄-o-NSi^tBuMe₂)₃]^6–]), (^tbsL)Fe₃(py) (2), [K(C₂₂₂)]₂[(^tbsL)Fe₃(μ³–NPh)] (4) (C₂₂₂ = 2,2,2-cryptand), and the mixed-valent (^tbsL)Fe₃(μ³–NPh) (3). Redox delocalization in mixed-valent 3 was explored with cyclic voltammetry (CV), zero-field ⁵⁷Fe Mössbauer, near-infrared (NIR) spectroscopy, and X-ray crystallography techniques. We find that the MAD results show an excellent correspondence to ⁵⁷Fe Mössbauer data; yet also can distinguish between subtle changes in local coordination geometries where Mössbauer cannot. Differences within aggregate oxidation levels are evident by systematic shifts of scattering factor envelopes to increasingly higher energies. However, distinguishing local oxidation levels in iso- or mixed-valent materials can be dramatically obscuredmore » by the degree of covalent intracore bonding. MAD-derived atomic scattering factor data emphasize in-edge features that are often difficult to analyze by X-ray absorption near edge spectroscopy (XANES). Thus, relative oxidation levels within the cluster were most reliably ascertained from comparing the entire envelope of the atomic scattering factor data.« less

Authors:

Bartholomew, Amymarie K. ^[1]; Teesdale, Justin J. ^[1]; Hernández Sánchez, Raúl  ^[1];

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• Search DOE PAGES for ORCID "0000-0001-6013-2708"

Malbrecht, Brian J. ^[1]; Juda, Cristin E. ^[1]; Ménard, Gabriel ^[1]; Bu, Wei  ^[2];

• Search DOE PAGES for author "Bu, Wei"
• Search DOE PAGES for ORCID "0000-0002-9996-3733"

Iovan, Diana A. ^[1]; Mikhailine, Alexandre A. ^[1]; Zheng, Shao-Liang ^[1]; Sarangi, Ritimukta ^[3]; Wang, SuYin Grass ^[2]; Chen, Yu-Sheng ^[2]; Betley, Theodore A. ^[1]

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+ Show Author Affiliations

1. Harvard Univ., Cambridge, MA (United States)
2. Univ. of Chicago, Argonne, IL (United States)
3. SLAC National Accelerator Lab., Menlo Park, CA (United States). Stanford Synchrotron Radiation Lightsource (SSRL)

Publication Date:

Fri Jul 19 00:00:00 EDT 2019

Research Org.:

Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS)

Sponsoring Org.:

National Institutes of Health (NIH); Consejo Nacional de Ciencia y Tecnología (CONACYT); Fundación México; National Science Foundation (NSF); Natural Sciences and Engineering Research Council of Canada (NSERC); Dreyfus Foundation; USDOE Office of Science (SC), Biological and Environmental Research (BER); National Institute of General Medical Sciences (NIGMS)

OSTI Identifier:

1561318

Grant/Contract Number:  

GM 098395; SC0008313; SC0019144; NSF/CHE-1346572; AC02-06CH11357

Resource Type:

Accepted Manuscript

Journal Name:

Proceedings of the National Academy of Sciences of the United States of America

Additional Journal Information:

Journal Volume: 116; Journal Issue: 32; Journal ID: ISSN 0027-8424

Publisher:

National Academy of Sciences

Country of Publication:

United States

Language:

ENGLISH

Subject:

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; redox distribution; clusters; bioinorganic