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Boronated Cyanometallates

McNicholas, Brendon J. and Nie, Cherish and Jose, Anex and Oyala, Paul H. and Takase, Michael K. and Henling, Larry M. and Barth, Alexandra T. and Amaolo, Alessio and Hadt, Ryan G. and Solomon, Edward I. and Winkler, Jay R. and Gray, Harry B. and Despagnet-Ayoub, Emmanuelle (2022) Boronated Cyanometallates. . (Unpublished)

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Fourteen boronated cyanometallates ([M(CN-BR₃)₆]^(3/4/5–) (M = Cr, Mn, Fe, Ru, Os, R = BPh₃, B(2,4,6,-F₃C₆H₂)₃, B(C₆F5)₃) have been characterized by X-ray crystallography and spectroscopy [UV-vis-NIR, NMR, IR, spectroelectrochemistry, and magnetic circular dichroism (MCD)]; CASSCF+NEVPT2 methods were employed in calculations of electronic structures. For (t_(2g))⁵ electronic configurations, the lowest energy ligand-to-metal charge transfer (LMCT) absorptions and MCD C terms in the spectra of boronated species have been assigned to transitions from cyanide σ+π + B-C borane σ orbitals. CASSCF+NEVPT2 calculations including t1u and t2u orbitals reproduced t_(1u)/t_(2u) → t_(2g) excitation energies. All ([M(CN-BR3)6]3/4− complexes exhibited highly electrochemically reversible redox couples. Notably, the formal potentials of all five [M(CN-B(C₆F₅)₃)₆]³⁻ anions scale with LMCT energies; and Mn(I) and Cr(II) compounds, (K(18-crown-6))₅[Mn(CN-B(C6F₅)₃)₆] and (TBA)₄[Cr(CN-B(C₆F₅)₃)₆], are surprisingly stable. Continuous wave and pulsed electron paramagnetic resonance (hyperfine sublevel correlation) spectra were collected for all Cr(III) complexes; as expected, ¹⁴N hyperfine splittings are greater for (TBA)₃[Cr(NC-BPh₃)₆] than for (TBA)₃[Cr(CN-BPh₃)₆]. Using (TBA)₄[Fe(CN-B(C₆F₅)₃)₆] and (TBA)₃[Fe(CN)₆], a model flow battery was constructed and found to have an 80% energy efficiency.

Item Type:Report or Paper (Discussion Paper)
Related URLs:
URLURL TypeDescription Paper
McNicholas, Brendon J.0000-0002-3654-681X
Oyala, Paul H.0000-0002-8761-4667
Takase, Michael K.0000-0001-8365-3645
Barth, Alexandra T.0000-0002-1813-4029
Hadt, Ryan G.0000-0001-6026-1358
Solomon, Edward I.0000-0003-0291-3199
Winkler, Jay R.0000-0002-4453-9716
Gray, Harry B.0000-0002-7937-7876
Despagnet-Ayoub, Emmanuelle0000-0002-9013-7574
Additional Information:The content is available under CC BY NC ND 4.0 License. We dedicate this paper to the memory of Bob Grubbs, a great scientist and dear friend, who urged (ordered!) three of us (H.B.G., B.J.M., E.D.A.) to develop new redox complexes for use in nonaqueous redox flow batteries. After considering various options, we began work on boronated cyanometallates. We acknowledge the X-ray Crystallography Facility in the Beckman Institute at Caltech, and the Dow Next Generation Instrumentation Grant for X-ray structure collection. R.G.H. gratefully acknowledges financial support from Caltech and the Dow Next Generation Educator Fund. EPR spectroscopy was performed in the Caltech EPR facility, which is also supported by the Beckman Institute and the Dow Next Generation Educator Fund. We thank David van der Velde for assistance in interpreting NMR data. We thank Wesley Kramer and Brian Sanders for helpful discussions. The computations presented here were conducted in the Resnick High Performance Computing Center, a facility supported by Resnick Sustainability Institute at the California Institute of Technology. This work was supported by the National Science Foundation (CHE-1763429). Additional funding was provided by two Arthur A. Noyes SURF Fellowships (C. N. and A. A.) and the Beckman Institute Laser Resource Center supported by the Arnold and Mabel Beckman Foundation. Author Contributions. All authors have given approval to the final version of the manuscript.
Group:Resnick Sustainability Institute
Funding AgencyGrant Number
Dow Next Generation Educator FundUNSPECIFIED
Caltech Beckman InstituteUNSPECIFIED
Caltech Summer Undergraduate Research Fellowship (SURF)UNSPECIFIED
Record Number:CaltechAUTHORS:20220726-998148000
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:115868
Deposited By: George Porter
Deposited On:27 Jul 2022 19:28
Last Modified:24 Mar 2023 17:34

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