Nitrogen-15 NMR Study of Solid Cobaloximes Containing <sup>15</sup>N-Labeled Pyridine and Aniline
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Bibliographic record
Abstract
Solid-state 15 N NMR spectra of spinning and stationary samples of four cobaloximes containing either pyridine- 15 N or aniline- 15 N as ligands are presented. The cobaloximes investigated are pyCo(DH) 2 Cl ( 1 ), pyCo(DH) 2 Br ( 2 ), pyCo(DH) 2 CH 3 ( 3 ), and anilCo(DH) 2 Cl ( 4 ) where DH = the dimethylglyoxime anion, py = pyridine, and anil = aniline. Nitrogen-15 CPMAS NMR spectra exhibit 15 N, 59 Co residual dipolar coupling, due to the breakdown of the high-field approximation for the 59 Co ( S = 7/2) nuclei. These spectra are analyzed to yield the one-bond cobalt-nitrogen indirect spin−spin coupling constant, 1 J ( 59 Co, 15 N), as well as the magnitude and sign of the 59 Co nuclear quadrupole coupling constant, C Q, and the orientation of the electric field gradient tensor at the 59 Co nucleus with respect to the molecular frame. Nitrogen-15 NMR spectra of stationary samples are analyzed using the dipolar-chemical shift method, providing the principal components of the nitrogen chemical shift tensors and information concerning their orientations with respect to the molecular frame. The sign of 1 J ( 59 Co, 15 N) is also determined from these spectra. The ab initio gauge-independent atomic orbital (GIAO) method is used to calculate the nitrogen chemical shielding tensors for three of the cobaloximes, as well as for free pyridine and aniline. Comparison of experimental and theoretical data reveals qualitative agreement, and supports the experimentally proposed nitrogen chemical shielding tensor orientations. The nitrogen coordination shifts and chemical shielding tensor orientations of pyridine- and aniline-substituted cobaloximes can qualitatively be accounted for using molecular orbital theory.
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Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
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Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
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