Boronated Cyanometallates
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1.
California Institute of Technology
Abstract
Thirteen boronated cyanometallates [M(CN-BR3)6]3/4/5– [M = Cr, Mn, Fe, Ru, Os; BR3 = BPh3, B(2,4,6,-F3C6H2)3, B(C6F5)3] and one metalloboratonitrile [Cr(NC-BPh3)6]3– have been characterized by X-ray crystallography and spectroscopy [UV–vis–near-IR, NMR, IR, spectroelectrochemistry, and magnetic circular dichroism (MCD)]; CASSCF+NEVPT2 methods were employed in calculations of electronic structures. For (t2g)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 π + B–C borane σ orbitals. CASSCF+NEVPT2 calculations including t1u and t2u orbitals reproduced t1u/t2u → t2g excitation energies. Many [M(CN-BR3)6]3/4– complexes exhibited highly electrochemically reversible redox couples. Notably, the reduction formal potentials of all five [M(CN-B(C6F5)3)6]3– anions scale with the LMCT energies, and Mn(I) and Cr(II) compounds, [K(18-crown-6)]5[Mn(CN-B(C6F5)3)6] and [K(18-crown-6)]4[Cr(CN-B(C6F5)3)6], are surprisingly stable. Continuous-wave and pulsed electron paramagnetic resonance (EPR; hyperfine sublevel correlation) spectra were collected for all Cr(III) complexes; as expected, 14N hyperfine splittings are greater for (Ph4As)3[Cr(NC-BPh3)6] than for (Ph4As)3[Cr(CN-BPh3)6].
Copyright and License (English)
© 2022 American Chemical Society.
Acknowledgement (English)
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., and 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 the NMR data. We thank Wesley W. Kramer and Brian C. Sanders for general discussion and Nathanael P. Kazmierczak for helpful discussions on the absorbance and MCD simulation. 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. We thank Julius J. Oppenheim for assistance with calculations.
Funding (English)
This work was supported by the National Science Foundation (Grant CHE-1763429). Additional funding was provided by two Arthur A. Noyes SURF Fellowships (to C.N. and A.A.) and the Beckman Institute Laser Resource Center supported by the Arnold and Mabel Beckman Foundation.
Contributions (English)
All authors have given approval to the final version of the manuscript.
Data Availability (English)
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Synthetic details, computational calculation parameters, additional UV–vis–NIR, MCD, electrochemistry, and EPR data and parameters (PDF)
CCDC 2145310–2145321, 2145325, and 2145326 contain the supplementary crystallographic data for this paper.
Conflict of Interest (English)
The authors declare no competing financial interest.
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Additional details
- ISSN
- 1520-510X
- National Science Foundation
- CHE-1763429
- California Institute of Technology
- Summer Undergraduate Research Fellowship
- National Institute of Standards and Technology
- Arnold and Mabel Beckman Foundation
- Dow Chemical (United States)
- Dow Next Generation Educator Fund
- Resnick Sustainability Institute
- Caltech groups
- Resnick Sustainability Institute