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1. 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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2. Binary Rare‐Earth Silicate Glasses Near Deep Eutectic: The Case for Sc ₂ O ₃ –SiO ₂ System

   https://doi.org/10.1111/jace.70869  

   Everson, Bryce; Chuang, Shih‐Yi; Hung, Ivan; Gan, Zhehong; McCormack, Scott J; Sen, Sabyasachi (May 2026, Journal of the American Ceramic Society)

   ABSTRACT Homogeneous glass formation in binary rare‐earth silicate systems has thus far been precluded due to the presence of extensive liquid–liquid immiscibility and a strong tendency of these liquids toward crystallization. In this study, we demonstrate homogeneous glass formation in the Sc₂O₃–SiO₂binary system within a narrow compositional window (37–39 mol% Sc₂O₃) near a deep eutectic between the compounds Sc₂Si₂O₇and Sc₂SiO₅, using containerless laser melting under aerodynamic levitation. The atomic structure of these unusual glasses is investigated using multinuclear (²⁹Si,⁴⁵Sc,¹⁷O) solid‐state nuclear magnetic resonance (NMR) and Raman spectroscopy. The spectroscopic results, when taken together, provide a comprehensive picture of the structure of these glasses characterized by pyrosilicate [Si₂O₇]⁶⁻anionic units interconnected by Sc cations in ScO₆coordination polyhedra, via Si–O–Sc linkages. A significant fraction (∼6%) of the oxygen atoms in the structure is present as free oxide (FO) ions in Sc–O–Sc linkages, providing connectivity between the ScO₆polyhedra. The formation of the FO species via oxygen disproportionation reaction is promoted by the uniquely high field strength of the Sc³⁺ions, and the resulting structural frustration is hypothesized to suppress crystallization of the stable pyrosilicate phase in these liquids, enabling glass formation in an otherwise non‐glass‐forming binary system. These findings highlight the critical role of rare‐earth cation field strength in controlling oxygen speciation, structure, and glass‐forming ability in this binary silicate system. 

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3. Atomic Transition Probabilities for Transitions of Si i and Si ii and the Silicon Abundances of Several Very Metal-poor Stars ^∗

   https://doi.org/10.3847/1538-4365/acb642  

   Den Hartog, E. A.; Lawler, J. E.; Sneden, C.; Roederer, I. U.; Cowan, J. J. (March 2023, The Astrophysical Journal Supplement Series)

   Abstract We report new measurements of branching fractions for 20 UV and blue lines in the spectrum of neutral silicon (Si i ) originating in the 3 s 2 3 p 4 s 3 P o 1,2 , 1 P o 1 , and 3 s 3 p 3 1 D o 1,2 upper levels. Transitions studied include both strong, nearly pure LS multiplets as well as very weak spin-forbidden transitions connected to these upper levels. We also report a new branching fraction measurement of the 4 P 1/2 – 2 P o 1/2,3/2 intercombination lines in the spectrum of singly ionized silicon (Si ii ). The weak spin-forbidden lines of Si i and Si ii provide a stringent test on recent theoretical calculations, to which we make comparison. The branching fractions from this study are combined with previously reported radiative lifetimes to yield transition probabilities and log( gf ) values for these lines. We apply these new measurements to abundance determinations in five metal-poor stars. 

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4. Composition-structure relationships for calcium aluminosilicate glasses

   https://doi.org/10.1617/s11527-025-02693-y  

   Panda, Subhashree; Liu, Meili; Purusottam, Rudra N; Walls, Jamie D; Pestana, Luis Ruiz; Suraneni, Prannoy (June 2025, Materials and Structures)

   Calcium aluminosilicate (CAS) glasses serve as ideal model systems for understanding the composition-structure relationships underpinning the performance of supplementary cementitious materials (SCMs) due to their simpler chemistry and reduced phase heterogeneity. Here, we investigate the structure of a broad compositional range of CAS glasses, including unprecedented high-CaO compositions, using X-ray diffraction (XRD), solid-state nuclear magnetic resonance (NMR), and Fourier transform infrared (FTIR) spectroscopy. With increasing CaO content, the XRD hump maxima shifts towards higher diffraction angles and causes downfield shifts in the 29Si and 27Al NMR isotropic shift maxima, indicating reduced interatomic distances and decreased electron density around Si and Al nuclei, respectively. These trends, consistent with a depolymerized structure that is more compact and contains a higher number of non-bridging oxygens, also correlate strongly with changes in Si–O-Si and Al–O–Al bond angles predicted by atomistic simulations. FTIR spectra reveals shifts in T-O-T' bond vibrations to lower wavenumbers with increasing CaO, signifying a transition to less polymerized Qn(Si, Al) species. Collectively, our results demonstrate the role of CaO in promoting network depolymerization, a crucial factor for SCM reactivity, and provide valuable insights into the structural evolution of CAS glasses as a function of composition. 

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5. Solid-state ¹¹ B NMR studies of coinage metal complexes containing a phosphine substituted diboraanthracene ligand

   https://doi.org/10.1039/d1dt02981a  

   Huynh, Winn; Taylor, Jordan W.; Harman, W. Hill; Conley, Matthew P. (October 2021, Dalton Transactions)

   Transition metal interactions with Lewis acids (M → Z linkages) are fundamentally interesting and practically important. The most common Z-type ligands contain boron, which contains an NMR active 11 B nucleus. We measured solid-state 11 B{ 1 H} NMR spectra of copper, silver, and gold complexes containing a phosphine substituted 9,10-diboraanthracene ligand (B 2 P 2 ) that contain planar boron centers and weak M → BR 3 linkages ([(B 2 P 2 )M][BAr F 4 ] (M = Cu (1), Ag (2), Au (3)) characterized by large quadrupolar coupling ( C Q ) values (4.4–4.7 MHz) and large span ( Ω ) values (93–139 ppm). However, the solid-state 11 B{ 1 H} NMR spectrum of K[Au(B 2 P 2 )] − (4), which contains tetrahedral borons, is narrow and characterized by small C Q and Ω values. DFT analysis of 1–4 shows that C Q and Ω are expected to be large for planar boron environments and small for tetrahedral boron, and that the presence of a M → BR 3 linkage relates to the reduction in C Q and 11 B NMR shielding properties. Thus solid-state 11 B NMR spectroscopy contains valuable information about M → BR 3 linkages in complexes containing the B 2 P 2 ligand. 

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