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1. Unprecedented Five‐Coordinate Iron(IV) Imides Generate Divergent Spin States Based on the Imide R‐Groups

   https://doi.org/10.1002/anie.201903132  

   Anneser, Markus R. ; Elpitiya, Gaya R. ; Townsend, Jacob ; Johnson, Elizabeth J. ; Powers, Xian B. ; DeJesus, Joseph F. ; Vogiatzis, Konstantinos D. ; Jenkins, David M. ( May 2019 , Angewandte Chemie International Edition)

   Three five‐coordinate iron(IV) imide complexes have been synthesized and characterized. These novel structures have disparate spin states on the iron as a function of the R‐group attached to the imide, with alkyl groups leading to low‐spin diamagnetic (S=0) complexes and an aryl group leading to an intermediate‐spin (S=1) complex. The different spin states lead to significant differences in the bonding about the iron center as well as the spectroscopic properties of these complexes. Mössbauer spectroscopy confirmed that all three imide complexes are in the iron(IV) oxidation state. The combination of diamagnetism and¹⁵N labeling allowed for the first¹⁵N NMR resonance recorded on an iron imide. Multi‐reference calculations corroborate the experimental structural findings and suggest how the bonding is distinctly different on the imide ligand between the two spin states.

    

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2. Probing Redox Non‐Innocence in Iron–Carbene Complexes {Fe=C(H)Ar} 10–11 by 1,2 H and 13 C Pulse Electron Paramagnetic Resonance

   https://doi.org/10.1002/ange.202110704  

   Arnett, Charles H. ; Oyala, Paul H. ; Agapie, Theodor ( November 2021 , Angewandte Chemie)

   We report the synthesis and spectroscopic characterization of a series of iron‐carbene complexes in redox states {Fe=C(H)Ar}^10–11. Pulse EPR studies of the^1,2H and¹³C isotopologues of {Fe=C(H)Ar}¹¹reveal the high covalency of the Fe–carbene bonding, leading to a more even spin distribution than commonly observed for reduced Fischer carbenes.

    

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3. Probing Redox Non‐Innocence in Iron–Carbene Complexes {Fe=C(H)Ar} 10–11 by 1,2 H and 13 C Pulse Electron Paramagnetic Resonance

   https://doi.org/10.1002/anie.202110704  

   Arnett, Charles H. ; Oyala, Paul H. ; Agapie, Theodor ( November 2021 , Angewandte Chemie International Edition)

   We report the synthesis and spectroscopic characterization of a series of iron‐carbene complexes in redox states {Fe=C(H)Ar}^10–11. Pulse EPR studies of the^1,2H and¹³C isotopologues of {Fe=C(H)Ar}¹¹reveal the high covalency of the Fe–carbene bonding, leading to a more even spin distribution than commonly observed for reduced Fischer carbenes.

    

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4. CaMn 3 IV O 4 Cubane Models of the Oxygen‐Evolving Complex: Spin Ground States S <9/2 and the Effect of Oxo Protonation

   https://doi.org/10.1002/ange.202105303  

   Lee, Heui Beom ; Shiau, Angela A. ; Marchiori, David A. ; Oyala, Paul H. ; Yoo, Byung‐Kuk ; Kaiser, Jens T. ; Rees, Douglas C. ; Britt, R. David ; Agapie, Theodor ( August 2021 , Angewandte Chemie)

   We report the single crystal XRD and MicroED structure, magnetic susceptibility, and EPR data of a series of CaMn₃^IVO₄and YMn₃^IVO₄complexes as structural and spectroscopic models of the cuboidal subunit of the oxygen‐evolving complex (OEC). The effect of changes in heterometal identity, cluster geometry, and bridging oxo protonation on the spin‐state structure was investigated. In contrast to previous computational models, we show that the spin ground state of CaMn₃^IVO₄complexes and variants with protonated oxo moieties need not beS=9/2. Desymmetrization of thepseudo‐C₃‐symmetric Ca(Y)Mn₃^IVO₄core leads to a lowerS=5/2 spin ground state. The magnitude of the magnetic exchange coupling is attenuated upon oxo protonation, and anS=3/2 spin ground state is observed in CaMn₃^IVO₃(OH). Our studies complement the observation that the interconversion between the low‐spin and high‐spin forms of the S₂state is pH‐dependent, suggesting that the (de)protonation of bridging or terminal oxygen atoms in the OEC may be connected to spin‐state changes.

    

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5. CaMn 3 IV O 4 Cubane Models of the Oxygen‐Evolving Complex: Spin Ground States S <9/2 and the Effect of Oxo Protonation

   https://doi.org/10.1002/anie.202105303  

   Lee, Heui Beom ; Shiau, Angela A. ; Marchiori, David A. ; Oyala, Paul H. ; Yoo, Byung‐Kuk ; Kaiser, Jens T. ; Rees, Douglas C. ; Britt, R. David ; Agapie, Theodor ( August 2021 , Angewandte Chemie International Edition)

   We report the single crystal XRD and MicroED structure, magnetic susceptibility, and EPR data of a series of CaMn₃^IVO₄and YMn₃^IVO₄complexes as structural and spectroscopic models of the cuboidal subunit of the oxygen‐evolving complex (OEC). The effect of changes in heterometal identity, cluster geometry, and bridging oxo protonation on the spin‐state structure was investigated. In contrast to previous computational models, we show that the spin ground state of CaMn₃^IVO₄complexes and variants with protonated oxo moieties need not beS=9/2. Desymmetrization of thepseudo‐C₃‐symmetric Ca(Y)Mn₃^IVO₄core leads to a lowerS=5/2 spin ground state. The magnitude of the magnetic exchange coupling is attenuated upon oxo protonation, and anS=3/2 spin ground state is observed in CaMn₃^IVO₃(OH). Our studies complement the observation that the interconversion between the low‐spin and high‐spin forms of the S₂state is pH‐dependent, suggesting that the (de)protonation of bridging or terminal oxygen atoms in the OEC may be connected to spin‐state changes.

    

   more » « less