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1. Magnetic moments and spin structure in single-phase B20 Co _1+x Si _1−x (x = 0.043)

   https://doi.org/10.1063/5.0090545  

   Wang, Haohan; Balasubramanian, Balamurugan; Liu, Yaohua; Streubel, Robert; Pahari, Rabindra; Ekanayaka, Thilini Kumari; Mishra, Esha; Klewe, Christoph; Shafer, Padraic; Dhall, Rohan; et al (May 2022, Journal of Applied Physics)

   Neutron powder diffraction (NPD) and x-ray magnetic circular dichroism (XMCD) spectroscopy are employed to investigate the magnetism and spin structure in single-phase B20 Co_1.043Si_0.957. The magnetic contributions to the NPD data measured in zero fields are consistent with the helical order among the allowed spin structures derived from group theory. The magnitude of the magnetic moment is (0.3 ± 0.1) μ_B/Co according to NPD, while the surface magnetization probed by XMCD at 3 kOe is (0.18–0.31) μ_B/Co. Both values are substantially larger than the bulk magnetization of 0.11 μ_B/Co determined from magnetometry at 70 kOe and 2 K. These experimental data indicate the formation of a helical spin phase and the associated conical states in high magnetic fields. 

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2. DFT Analysis of Methane C−H Activation and Over‐Oxidation by [Cu ₂ O] ²⁺ and [Cu ₂ O ₂ ] ²⁺ Sites in Zeolite Mordenite: Intra‐ versus Inter‐site Over‐Oxidation

   https://doi.org/10.1002/cphc.202100580  

   Panthi, Dipak; Adeyiga, Olajumoke; Odoh, Samuel_O (October 2021, ChemPhysChem)

   Abstract Methane over‐oxidation by copper‐exchanged zeolites prevents realization of high‐yield catalytic conversion. However, there has been little description of the mechanism for methane over‐oxidation at the copper active sites of these zeolites. Using density functional theory (DFT) computations, we reported that tricopper [Cu₃O₃]²⁺active sites can over‐oxidize methane. However, the role of [Cu₃O₃]²⁺sites in methane‐to‐methanol conversion remains under debate. Here, we examine methane over‐oxidation by dicopper [Cu₂O]²⁺and [Cu₂O₂]²⁺sites using DFT in zeolite mordenite (MOR). For [Cu₂O₂]²⁺, we considered the μ‐(η²:η²) peroxo‐, and bis(μ‐oxo) motifs. These sites were considered in the eight‐membered (8MR) ring of MOR. μ‐(η²:η²) peroxo sites are unstable relative to the bis(μ‐oxo) motif with a small interconversion barrier. Unlike [Cu₂O]²⁺which is active for methane C−H activation, [Cu₂O₂]²⁺has a very large methane C−H activation barrier in the 8MR. Stabilization of methanol and methyl at unreacted dicopper sites however leads to over‐oxidation via sequential hydrogen atom abstraction steps. For methanol, these are initiated by abstraction of the CH₃group, followed by OH and can proceed near 200 °C. Thus, for [Cu₂O]²⁺and [Cu₂O₂]²⁺species, over‐oxidation is an inter‐site process. We discuss the implications of these findings for methanol selectivity, especially in comparison to the intra‐site process for [Cu₃O₃]²⁺sites and the role of Brønsted acid sites. 

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3. Dimetalloylene (M‐E‐M) Complexes of Heavier Main Group Elements Ge, Sn, Pb, Bi via Cleavage of E‐X Bonds (X=N(SiMe ₃ ) ₂ , O t Bu) with an Iridium Hydride

   https://doi.org/10.1002/chem.202301863  

   Saint‐Denis, Tyler_G; Zhang, Bowen; Settineri, Nicholas_S; Handford, Rex_C; Hall, Michael_B; Tilley, T_Don (July 2023, Chemistry – A European Journal)

   Abstract Reactions of the Ir^Vhydride [^MeBDI^Dipp]IrH₄{BDI=(Dipp)NC(Me)CH(Me)CN(Dipp); Dipp=2,6‐iPr₂C₆H₃} with E[N(SiMe₃)₂]₂(E=Sn, Pb) afforded the unusual dimeric dimetallotetrylenes ([^MeBDI^Dipp]IrH)₂(μ₂‐E)₂in good yields. Moreover, ([^MeBDI^Dipp]IrH)₂(μ₂‐Ge)₂was formed in situ from thermal decomposition of [^MeBDI^Dipp]Ir(H)₂Ge[N(SiMe₃)₂]₂. These reactions are accompanied by liberation of HN(SiMe₃)₂and H₂through the apparent cleavage of an E−N(SiMe₃)₂bond by Ir−H. In a reversal of this process, ([^MeBDI^Dipp]IrH)₂(μ₂‐E)₂reacted with excess H₂to regenerate [^MeBDI^Dipp]IrH₄. Varying the concentrations of reactants led to formation of the trimeric ([^MeBDI^Dipp]IrH₂)₃(μ₂‐E)₃. The further scope of this synthetic route was investigated with group 15 amides, and ([^MeBDI^Dipp]IrH)₂(μ₂‐Bi)₂was prepared by the reaction of [^MeBDI^Dipp]IrH₄with Bi(NMe₂)₃or Bi(OtBu)₃to afford the first example of a “naked” two‐coordinate Bi atom bound exclusively to transition metals. A viable mechanism that accounts for the formation of these products is proposed. Computational investigations of the Ir₂E₂(E=Sn, Pb) compounds characterized them as open‐shell singlets with confined nonbonding lone pairs at the E centers. In contrast, Ir₂Bi₂is characterized as having a closed‐shell singlet ground state. 

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4. Understanding the Early Stages of Nickel Sulfide Nanocluster Growth: Isolation of Ni ₃ , Ni ₄ , Ni ₅ , and Ni ₈ Intermediates

   https://doi.org/10.1002/smll.202003133  

   Touchton, Alexander J.; Wu, Guang; Hayton, Trevor W. (September 2020, Small)

   Abstract Addition of sub‐stoichiometric quantities of PEt₃and diphenyl disulfide to a solution of [Ni(1,5‐cod)₂] generates a mixture of [Ni₃(SPh)₄(PEt₃)₃] (1), unreacted [Ni(1,5‐cod)₂], and [(1,5‐cod)Ni(PEt₃)₂], according to¹H and³¹P{¹H} NMR spectroscopic monitoring of the in situ reaction mixture. On standing, complex1converts into [Ni₄(S)(Ph)(SPh)₃(PEt₃)₃] (2), via formal addition of a “Ni(0)” equivalent, coupled with a CS oxidative addition step, which simultaneously generates the Ni‐bound phenyl ligand and the μ₃‐sulfide ligand. Upon gentle heating, complex2converts into a mixture of [Ni₅(S)₂(SPh)₂(PEt₃)₅] (3) and [Ni₈(S)₅(PEt₃)₇] (4), via further addition of “Ni(0)” equivalents, in combination with a series of C–S oxidative addition and CC reductive elimination steps, which serve to convert thiophenolate ligands into sulfide ligands and biphenyl. The presence of1–4in the reaction mixture is confirmed by their independent syntheses and subsequent spectroscopic characterization. Overall, this work provides an unprecedented level of detail of the early stages of Ni nanocluster growth and highlights the fundamental reaction steps (i.e., metal atom addition, CS oxidative addition, and CC reductive elimination) that are required to grow an individual cluster. 

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5. Evaluating Diazene to N ₂ Interconversion at Iron‐Sulfur Complexes

   https://doi.org/10.1002/chem.202304072  

   Hooper, Reagan_X; Wertz, Ashlee_E; Shafaat, Hannah_S; Holland, Patrick_L (March 2024, Chemistry – A European Journal)

   Abstract Biological N₂reduction occurs at sulfur‐rich multiiron sites, and an interesting potential pathway is concerted double reduction/ protonation of bridging N₂through PCET. Here, we test the feasibility of using synthetic sulfur‐supported diiron complexes to mimic this pathway. Oxidative proton transfer from μ‐η¹ : η¹‐diazene (HN=NH) is the microscopic reverse of the proposed N₂fixation pathway, revealing the energetics of the process. Previously, Sellmann assigned the purple metastable product from two‐electron oxidation of [{Fe²⁺(PPr₃)L¹}₂(μ‐η¹ : η¹‐N₂H₂)] (L¹=tetradentate SSSS ligand) at −78 °C as [{Fe²⁺(PPr₃)L¹}₂(μ‐η¹ : η¹‐N₂)]²⁺, which would come from double PCET from diazene to sulfur atoms of the supporting ligands. Using resonance Raman, Mössbauer, NMR, and EPR spectroscopies in conjunction with DFT calculations, we show that the product is not an N₂complex. Instead, the data are most consistent with the spectroscopically observed species being the mononuclear iron(III) diazene complex [{Fe(PPr₃)L¹}(η²‐N₂H₂)]⁺. Calculations indicate that the proposed double PCET has a barrier that is too high for proton transfer at the reaction temperature. Also, PCET from the bridging diazene is highly exergonic as a result of the high Fe^3+/2+redox potential, indicating that the reverse N₂protonation would be too endergonic to proceed. This system establishes the “ground rules” for designing reversible N₂/N₂H₂interconversion through PCET, such as tuning the redox potentials of the metal sites. 

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