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1. Formation of monomeric Sn( ii ) and Sn( iv ) perfluoropinacolate complexes and their characterization by 119 Sn Mössbauer and 119 Sn NMR spectroscopies

   https://doi.org/10.1039/d0dt02837a  

   Elinburg, Jessica K. ; Hyre, Ariel S. ; McNeely, James ; Alam, Todd M. ; Klenner, Steffen ; Pöttgen, Rainer ; Rheingold, Arnold L. ; Doerrer, Linda H. ( October 2020 , Dalton Transactions)

   null (Ed.)

   The synthesis and characterization of a series of Sn( ii ) and Sn( iv ) complexes supported by the highly electron-withdrawing dianionic perfluoropinacolate (pin F ) ligand are reported herein. Three analogs of [Sn IV (pin F ) 3 ] 2− with NEt 3 H + ( 1 ), K + ( 2 ), and {K(18C6)} + ( 3 ) counter cations and two analogs of [Sn II (pin F ) 2 ] 2− with K + ( 4 ) and {K(15C5) 2 } + ( 5 ) counter cations were prepared and characterized by standard analytical methods, single-crystal X-ray diffraction, and 119 Sn Mössbauer and NMR spectroscopies. The six-coordinate Sn IV (pin F ) complexes display 119 Sn NMR resonances and 119 Sn Mössbauer spectra similar to SnO 2 (cassiterite). In contrast, the four-coordinate Sn II (pin F ) complexes, featuring a stereochemically-active lone pair, possess low 119 Sn NMR chemical shifts and relatively high quadrupolar splitting. Furthermore, the Sn( ii ) complexes are unreactive towards both Lewis bases (pyridine, NEt 3 ) and acids (BX 3 , Et 3 NH + ). Calculations confirm that the Sn( ii ) lone pair is localized within the 5s orbital and reveal that the Sn 5p x LUMO is energetically inaccessible, which effectively abates reactivity. 

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2. Observing Metallic Carriers in Highly Faceted Plasmonic Cd 2 SnO 4 Inverse Spinel Nanocrystals

   https://doi.org/10.1002/adom.202400388  

   Ortega, Raul_E ; Smith, Robert_B ; Kuszynski, Jason_E ; Bayles, Aaron ; McGill, Stephen_A ; Halas, Naomi_J ; Schurko, Robert_W ; Strouse, Geoffrey_F ( June 2024 , Advanced Optical Materials)

   Correlating data from optical, structural, and theoretical methods allows the properties of highly faceted Cd₂SnO₄(CTO) inverted spinel plasmonic semiconductor nanocrystals (PSNCs) to be fully evaluated. The use of Sn(II) in the colloidal reaction for CTO results in reproducible octahedral PSNCs with an aspect ratio of 1.30. Correlating extinction spectra with magnetic circular dichroism yields a carrier density (n = 5.19 × 10¹⁹ cm⁻³) and carrier effective mass (m* = 0.022m_e) respectively.¹¹³Cd and¹¹⁹Sn solid‐state NMR experiments show clear evidence of metallic‐like carriers in CTO NCs based upon the observation of Knight shifts. These data suggest that carrier formation in CTO arises from Sn antisite occupation of octahedral Cd sites (Sn_Cd)_.From a broader perspective, the results point to wide‐bandgap spinels as being an important but understudied class of plasmonic PSNCs.

    

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3. Understanding Soap Formation in Paint Films by 207Pb, 119Sn, and 13C Solid-State NMR

   Catalano, J. ; Yao, Y. ; Murphy, A. ; Zumbulyadis, N. ; Centeno, S.A. ; Dybowski, C. ( October 2014 , Materials science and technology)

   The formation of lead carboxylates (lead soaps) has been identified as the cause of deterioration of hundreds of oil paintings. Soaps form when heavy metal-containing pigments, for example lead white and lead-tin yellow, react with saturated fatty acids in the oil medium. Understanding the mechanism of the reactions requires chemical information, which can be obtained with solid-state ²⁰⁷Pb, ¹¹⁹Sn and ¹³C NMR spectroscopy. Using the chemical-shift tensors determined by solid-state NMR we can gain structural insights on the coordination environment of the lead carboxylates and identify and quantify components in a paint film mixture. We have examined the spectroscopy of lead-containing pigments, lead carboxylates, and model paint films that were subjected to accelerated aging. We have also begun to investigate the dynamics of soap formation by ¹³C NMR spectroscopy. The NMR methods applied to the model paint systems could also be applied to other lead-containing materials. 

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4. Segmental Labeling: Applications to Protein NMR and DNP

   https://doi.org/10.1002/9780470034590.emrstm1613  

   Ghosh, Rupam ; Madrid, Carla L ; Frederick, Kendra K. ( March 2020 , eMagRes)

   Magic‐angle spinning (MAS) NMR coupled with dynamic nuclear polarization (DNP) has the possibility to increase the sensitivity of MAS NMR by several orders of magnitude. While DNP enables many experiments that are sensitivity limited, such as those on dilute samples or those that measure long‐range distances, interpretation of DNP NMR spectra is often limited by broad lines and chemical shift degeneracy. Segmental isotopic labeling using split intein technology can provide an opportunity to overcome this issue. Isotopic labeling of only a segment of a protein that is otherwise unlabeled reduces the chemical shift degeneracy. In this article, we describe the current state of the art for producing segmentally isotopically labeled proteins using split inteins. We discuss some of the potential applications of segmental isotopic labeling, particularly those that exploit the increased experimental sensitivity of DNP‐enhanced MAS NMR spectroscopy 

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5. NMR Crystallography: Evaluation of Hydrogen Positions in Hydromagnesite by 13 C{ 1 H} REDOR Solid‐State NMR and Density Functional Theory Calculation of Chemical Shielding Tensors

   https://doi.org/10.1002/ange.201813306  

   Cui, Jinlei ; Olmsted, David L. ; Mehta, Anil K. ; Asta, Mark ; Hayes, Sophia E. ( February 2019 , Angewandte Chemie)

   Solid‐state NMR measurements coupled with density functional theory (DFT) calculations demonstrate how hydrogen positions can be refined in a crystalline system. The precision afforded by rotational‐echo double‐resonance (REDOR) NMR to interrogate¹³C–¹H distances is exploited along with DFT determinations of the¹³C tensor of carbonates (CO₃²⁻). Nearby¹H nuclei perturb the axial symmetry of the carbonate sites in the hydrated carbonate mineral, hydromagnesite [4 MgCO₃⋅Mg(OH)₂⋅4 H₂O]. A match between the calculated structure and solid‐state NMR was found by testing multiple semi‐local and dispersion‐corrected DFT functionals and applying them to optimize atom positions, starting from X‐ray diffraction (XRD)‐determined atomic coordinates. This was validated by comparing calculated to experimental¹³C{¹H} REDOR and¹³C chemical shift anisotropy (CSA) tensor values. The results show that the combination of solid‐state NMR, XRD, and DFT can improve structure refinement for hydrated materials.

    

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