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1. Thickness and temperature dependence of the atomic-scale structure of SrRuO3 thin films

   https://doi.org/10.1063/5.0087791  

   Zhang, Xuanyi; Penn, Aubrey_N; Wysocki, Lena; Zhang, Zhan; van_Loosdrecht, Paul_H_M; Kornblum, Lior; LeBeau, James_M; Lindfors-Vrejoiu, Ionela; Kumah, Divine_P (May 2022, APL Materials)

   The temperature-dependent layer-resolved structure of 3 to 44 unit cell thick SrRuO3 (SRO) films grown on Nb-doped SrTiO3 substrates is investigated using a combination of high-resolution synchrotron x-ray diffraction and high-resolution electron microscopy to understand the role that structural distortions play in suppressing ferromagnetism in ultra-thin SRO films. The oxygen octahedral tilts and rotations and Sr displacements characteristic of the bulk orthorhombic phase are found to be strongly dependent on temperature, the film thickness, and the distance away from the film–substrate interface. For thicknesses, t, above the critical thickness for ferromagnetism (t > 3 uc), the orthorhombic distortions decrease with increasing temperature above TC. Below TC, the structure of the films remains constant due to the magneto-structural coupling observed in bulk SRO. The orthorhombic distortions are found to be suppressed in the 2–3 interfacial layers due to structural coupling with the SrTiO3 substrate and correlate with the critical thickness for ferromagnetism in uncapped SRO films. 

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2. The novel oxy-sulfide glassy ionic conductors Na4P2S7-xOx 0 ≤ x ≤ 7: Understanding the features of static and dynamic cations

   https://doi.org/10.1016/j.ssi.2023.116363  

   Shastri, Ananda; Rons, Nathan; Ding, Qing-Ping; Kmiec, Steven J.; Olson, Madison; Furukawa, Yuji; Martin, Steve W. (December 2023, Solid State Ionics)

   We present a 23Na nuclear spin dynamics model for interpreting nuclear magnetic resonance (NMR) spin-lattice relaxation and central linewidth data in the invert glass system Na4P2S7-xOx, 0 ≤ x ≤ 7. The glassy nature of this material results in variations in local Na+ cation environments that may be described by a Gaussian distribution of activation energies. A consistent difference between the mean activation energies determined by NMR and DC conductivity measurements was observed, and interpreted using a percolation theory model. From this, the Nasingle bondNa coordination number in the sodium cation sublattice was obtained. These values were consistent with jumps through tetrahedral faces of the sodium cages for the sulfur rich glasses, x < 5, consistent with proposed models of their short range order (SRO) structures. From NMR spin-echo measurements, we determined the Nasingle bondNa second moment M2 resulting from the Nasingle bondNa magnetic dipole interaction of nearest neighbors. Values of M2 obtained as a function of sodium number density N were in agreement with models for uniform sodium distribution, indicating that these invert glass systems form so as to maximize the average Nasingle bondNa distance. A simple Coulombic attraction model between Na+ cation and X (=S−, O−) anion was applied to calculate the activation energy. In the range 1.5 ≤ x ≤ 7, an increase in activation energy with increasing oxygen content x occurred, and was consistent with the decrease in average anionic radius, and the increase in Coulombic attraction. For small oxygen additions, 0 ≤ x ≤ 1.5, the suggested minimum at low oxygen concentration seen in the activation energies obtained from DC conductivity data is not evident in the model. 

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3. Surface Interrogation of Electrodeposited MnO _x and CaMnO ₃ Perovskites by Scanning Electrochemical Microscopy: Probing Active Sites and Kinetics for the Oxygen Evolution Reaction

   https://doi.org/10.1002/anie.202008052  

   Jin, Zhaoyu; Bard, Allen J. (November 2020, Angewandte Chemie International Edition)

   Abstract Surface interrogation scanning electrochemical microscopy (SI‐SECM) of two electrodeposited manganese‐based electrocatalysts, amorphous MnO_xand perovskite CaMnO₃, was used to investigate the manganese oxidation state relating to the oxygen evolution reaction (OER) under neutral conditions. The results indicate the amounts of Mn^IIIand Mn^IVspecies in MnO_xand CaMnO₃depend on potential. A Mn^Vspecies was identified in both structures during the OER. Time‐delay titration of Mn^Vfurther revealed that MnO_xproduced two types of active sites with different OER reaction rates:k′_fast(MnO_x)=1.21 s⁻¹andk’_slow(MnO_x)=0.24 s⁻¹. In contrast, CaMnO₃perovskites in which the Mn^Vspecies formed at a less positive potential than that in MnO_x, displayed only one kinetic behavior with a faster reaction rate of 1.72 s⁻¹. 

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4. Metal‐Templated, Tight Loop Conformation of a Cys‐X‐Cys Biomimetic Assembles a Dimanganese Complex

   https://doi.org/10.1002/anie.201913259  

   Le, Trung; Nguyen, Hao; Perez, Lisa M.; Darensbourg, Donald J.; Darensbourg, Marcetta Y. (January 2020, Angewandte Chemie International Edition)

   Abstract With the goal of generating anionic analogues to MN₂S₂⋅Mn(CO)₃Br we introduced metallodithiolate ligands, MN₂S₂²⁻prepared from the Cys‐X‐Cys biomimetic, ema⁴⁻ligand (ema=N,N′‐ethylenebis(mercaptoacetamide); M=Ni^II, [V^IV≡O]²⁺and Fe^III) to Mn(CO)₅Br. An unexpected, remarkably stable dimanganese product, (H₂N₂(CH₂C=O(μ‐S))₂)[Mn(CO)₃]₂resulted from loss of M originally residing in the N₂S₂⁴⁻pocket, replaced by protonation at the amido nitrogens, generating H₂ema²⁻. Accordingly, the ema ligand has switched its coordination mode from an N₂S₂⁴⁻cavity holding a single metal, to a binucleating H₂ema²⁻with bridging sulfurs and carboxamide oxygens within Mn‐μ‐S‐CH₂‐C‐O, 5‐membered rings. In situ metal‐templating by zinc ions gives quantitative yields of the Mn₂product. By computational studies we compared the conformations of “linear” ema⁴⁻to ema⁴⁻frozen in the “tight‐loop” around single metals, and to the “looser” fold possible for H₂ema²⁻that is the optimal arrangement for binucleation. XRD molecular structures show extensive H‐bonding at the amido‐nitrogen protons in the solid state. 

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5. Origin of the ²⁹ Si NMR chemical shift in R ₃ Si–X and relationship to the formation of silylium (R ₃ Si ⁺ ) ions

   https://doi.org/10.1039/D0DT02099K  

   Huynh, Winn; Conley, Matthew P. (November 2020, Dalton Transactions)

   null (Ed.)

   The origin in deshielding of 29 Si NMR chemical shifts in R 3 Si–X, where X = H, OMe, Cl, OTf, [CH 6 B 11 X 6 ], toluene, and O X (O X = surface oxygen), as well as i Pr 3 Si + and Mes 3 Si + were studied using DFT methods. At the M06-L/6-31G(d,p) level of theory the geometry optimized structures agree well with those obtained experimentally. The trends in 29 Si NMR chemical shift also reproduce experimental trends; i Pr 3 Si–H has the most shielded 29 Si NMR chemical shift and free i Pr 3 Si + or isolable Mes 3 Si + have the most deshielded 29 Si NMR chemical shift. Natural localized molecular orbital (NLMO) analysis of the contributions to paramagnetic shielding ( σ p ) in these compounds shows that Si–R (R = alkyl, H) bonding orbitals are the major contributors to deshielding in this series. The Si–R bonding orbitals are coupled to the empty p-orbital in i Pr 3 Si + or Mes 3 Si + , or to the orbital in R 3 Si–X. This trend also applies to surface bound R 3 Si–O X . This model also explains chemical shift trends in recently isolated t Bu 2 SiH 2 + , t BuSiH 2 + , and SiH 3 + that show more shielded 29 Si NMR signals than R 3 Si + species. There is no correlation between isotropic 29 Si NMR chemical shift and charge at silicon. 

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