59Co second-order quadrupolar effects in the13C cross-polarization magic angle spinning NMR spectra of the cobaltocenium salts [Cp*2Co]+[PF6]− and [Cp*CpCo]+[PF6]−

Abstract

were studied by 13 C cross-polarization magic angle spinning NMR spectroscopy. The ring carbon signals ofshowed splitting patterns which are a signature of the hitherto unknown 59 Co, 13 C dipolar coupling. In contrast, a unique signal was found for the remaining cations. The dependence of the patterns on the field, the rotor spinning rate and the temperature was investigated, and full-matrix diagonalization treatment was used to fit the spectra. The patterns were better resolved at lower fields and to some extent at lower spinning rates. Self-decoupling was observed for [Cp Ł CpCo] C [PF 6 ] above 360 K. Visual fitting yielded dipolar and indirect isotropic 59 Co, 13 C coupling constants of 530 and 40 Hz, respectively. When the counter ion of [Cp Ł CpCo] C was changed from [PF 6 ] to Cl or [TCNE] 2 the dipolar coupling pattern was not present, probably because of self-decoupling.

A Solid-State NMR, X-ray Diffraction, and Ab Initio Investigation into the Structures of Novel Tantalum Oxyfluoride Clusters

“…In addition, if this type of Ta-F dipolar coupling were significant we would expect it to be observable in all of the materials investigated, not simply the TAF16-PYR cluster. Although residual dipolar couplings to quadrupolar nuclei have been documented in a range of different materials, ,, we do not feel that for the TAF materials reported here the residual dipolar coupling between 19 F and 181 Ta is observed. Perhaps a fast T 1 relaxation of the quadrupolar 181 Ta nucleus has resulted in a self-decoupling from the 19 F nucleus.…”

“…Increasing the field strength by a factor of 1.5 should have reduced the 19 F line splitting, but this effect was not observed. It is noted that the high-field approximation holds for situations where υ I ≫ C Q , such that analysis for larger C Q values require complete diagonalization of the interaction Hamiltonian. , The C Q for TaF materials is not know, but in TaO 3 compounds has been estimated as high as 250 GHz, clearly outside the high-field approximation. Regardless of the C Q magnitude, some variation of the line shape and splitting with changes in magnetic field strength is expected if a residual dipolar coupling between Ta and F were present.…”

Structural Insights from 59Co Solid‐State NMR Experiments on Organocobalt(I) Catalysts

“…From these spectra, both peaks were simulated simultaneously using the QUEST software to obtain highly precise C Q ( 59 Co) and η Q values, which are reported in Table . The C Q ( 59 Co) values in this series of Co I catalysts are similar in magnitude to the values previously reported for Co I ‘sandwich’ compounds, Co(C 2 B 9 H 11 ) 2 − and Co(C 5 H 5 ) 2 + , as well as for cobaltocenium derivatives, which, taken together, suggests that the C Q ( 59 Co) values for Co I compounds tend to be larger than those for Co III compounds…”

Inter- and Intramolecular Spin Transfer in Molecular Magnetic Materials. Solid-State NMR Spectroscopy of Paramagnetic Metallocenium Ions

“…This is illustrated by the 13 C MAS NMR spectra of [(C 5 Me 5 ) 2 Co] + salts in Figure . The methyl and ring carbon signals of the [PF 6 ] - salt appear at 8.1 and 95.3 ppm, respectively, the latter signal featuring second-order dipolar coupling to the quadrupolar nucleus 59 Co . In the [TCNE] - salt at 298 K, these signals are shifted to high frequencies by 18.8 and 26.3 ppm, respectively.…”