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Chen, Baojin; Yao, Linchao; Feng, Cuidi; Zhang, Huaming; Xiao, Wenbo
doi: 10.1002/mrc.5311pmid: 36097252
The electron paramagnetic resonance (EPR) parameters—g factors gi (i = || and ⊥) and hyperfine structure constants Ai (M) and Ai(N), with M and N belonging to isotopes 63Cu2+ and 65Cu2+—and local structure of Cu2+ ion occupying W6+ site in CaWO4 crystal are theoretically studied based on the perturbation formulas of these parameters for a 3d9 ion under tetragonally elongated tetrahedra. In these formulas, the ligand orbital (LO) and spin–orbit coupling (SOC) contributions are included due to the shorter impurity‐ligand distance R (≈1.83 Å) and hence the strong covalency of the studied [CuO4]6− cluster, and the related molecular orbital coefficients are quantitatively determined from the cluster approach in a uniform way; meanwhile, the required crystal field (CF) parameters for the tetragonally distorted tetrahedron (TDT) are estimated from the superposition model and the local structure of the impurity Cu2+ center. According to the calculation, the bond angle θ between the four equivalent Cu2+‐O2− bonds and the C4 axis in the CaWO4:Cu2+ is found to be about 2.1° smaller than that (θ0 ≈ 54.74°) for an ideal tetrahedron due to the Jahn–Teller (JT) effect and the size mismatch. The fitted results agree well with the observed values, and the validity of the present assignment for the local structure of the Cu2+ center is also discussed.
Bakhmutov, Vladimir I.; Contreras‐Ramirez, Aida; Drake, Hannah; Zhou, Hong‐Cai
doi: 10.1002/mrc.5313pmid: 36117432
The phosphorus chemical shift anisotropies, 31PΔcs, and asymmetry parameters η were measured by the 31P{1H} NMR experiments in static and low‐frequency spinning samples of the zirconium phosphates and phosphonates and also in the mixed Zr (IV)/Sn (IV) phosphate/phosphonate material. The data obtained have shown a 111 connectivity in the HPO4 and PO3 groups, which does not change at modification and intercalation of the materials. The 31PΔcs values of the phosphonate groups (43–49 ppm) significantly surpass the values characterizing the HPO4 groups (23–37 ppm). The 31P Δcs values obtained for the metal (IV) phosphates were discussed in terms of P‐O distances. The 31P chemical shift anisotropy parameters can help at elucidation of local structures in phosphate and phosphonate materials.
Wood, Jared S.; Dal Poggetto, Guilherme; Wang, Xiao; Reibarkh, Mikhail; Williamson, R. Thomas; Cohen, Ryan D.
doi: 10.1002/mrc.5316pmid: 36166190
Chloride is the most common counterion used to improve aqueous solubility and enhance stability of small molecule active pharmaceutical ingredients. While several analytical techniques, such as titration, HPLC with charged aerosol detection, and ion chromatography, are currently utilized to assay the level of chloride, they have notable limitations, and these instruments may not be readily available. Here, we present a generally applicable 35Cl solution NMR method to assay the level of chloride in pharmaceutical compounds. The method uses KClO4 as an internal standard for improved accuracy in comparison with external standard methods, and it was found to be robust, linear over three orders of magnitude, precise (<3% RSD), and accurate (<0.5% absolute error).
Montes, Luciana F.; Morgan, Vinícius G.; Kock, Flávio V. C.; Castro, Eustáquio V. R.; Barbosa, Lúcio L.
doi: 10.1002/mrc.5317pmid: 36196655
Crude oil distillates are a highly useful industrial product, mainly for energy generation. Unfortunately, they are rarely studied, mainly due to the low accessibility to products directly obtained from the distillation process, which is a laborious, expensive, and time‐consuming operation. This work presents and discusses the use of time‐domain nuclear magnetic resonance (TD‐NMR) as a simple, affordable, and straightforward tool for the development of correlations supported on the transverse relaxation time (T2) and boiling temperature. The results point out a high convergence between TD‐NMR experimental data and the ASTM D2892 method for distillates from light, medium, and heavy oils, with up to 52.20% of accumulated mass and boiling point temperature (Tb) up to 400°C. Furthermore, an unprecedented relationship between T2 values and the accumulated mass of the distillates is first demonstrated. This new insight opens new perspectives for future prediction of accumulated mass for unknown crude oils, placing the TD‐NMR relaxometry as an appeal spectroscopy approach with a potential to meaningfully contribute to the daily refining petrochemical industry field operations.
Liu, Li; Yang, Zhangzhang; Fu, Jia; Wan, Zhitao
doi: 10.1002/mrc.5319pmid: 36200650
The defect structure, spin Hamiltonian parameters (SHPs: anisotropic g factors g‖ and g⊥ and the hyperfine structure constants A‖ and A⊥), and their compositional dependence of Cu2+ in xCuO−(68−x)V2O5−32TeO2 ( x = 5, 10, 20, 30 mol%) glasses are quantitatively analyzed by using the higher‐order perturbation formula of octahedral complex with tetrahedral elongation distortion. Due to the Jahn–Teller effect, the [CuO6]10− group is subjected to tetragonal elongation distortion of varying degrees. Dq,N,ρ,κ, and H show nonlinear changes with the concentrations of Cu2+. When x = 10 mol% CuO, the degree of distortion ( ρ≈0.1%) is the smallest; when x = 30 mol% CuO, the degree of distortion ( ρ≈15%) is the largest, which indicates that excessive distortion leads to the appearance of Z‐axis oxygen vacancies and the coordination number of copper ions from six to four. The increasing tendency of the evaluated N and H reveals decreasing covalency of the whole glass system. Present theoretical studies would be useful to the explore the structural properties and optical applications of glass with different CuO concentrations.
Nawrocka, Ewa K.; Prus, Agnieszka; Owarzany, Rafał; Koźmiński, Wiktor; Kazimierczuk, Krzysztof; Fijalkowski, Karol J.
doi: 10.1002/mrc.5309pmid: 36082753
We report a detailed 1H NMR and 11B NMR study of as synthesised Li(BH3NH2BH2NH2BH3) obtained in a novel dry‐synthesis method. A combination of 1D and 2D single‐ and triple‐quantum techniques was used for the assignment of all observed signals. Minor side‐products and reactants were detected in the product: NH3BH3, Li(NH2BH3), Li(BH4), and two yet unknown salts containing 7‐membered chain anions: (BH3NH2BH2NH2BH2NH2BH3)− and (BH(NH2BH3)3)−. We believe the assignment provided within this study might be helpful when analysing the mixtures containing numerous ammonia borane derivatives, which often give overlapping signals that are hard to distinguish.
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