Quadrupolar cobalt

A study of labeled compounds derived from ethylcobalt(m) oetaethylporphyrin and other porphyrins indicated that the NMR resonances of the carbon atoms bound to cobalt were quite broad and were upheld shifted. The anomalous features of the NMR spectra were ascribed to the quadrupolar cobalt nucleus, and to the paramagnetic contact shifts that arose from thermal population ground state instead of agostic bond. ... 

Similar to the situation for quadrupole-induced relaxation, the quadrupole splitting in liquid crystals is zero if the molecular symmetry is tetrahedral or higher. Electric field gradients are zero for such symmetries so there can be no quadrupolar interaction. However, one expects to see small splittings from tetrahedral or octahedral derivatives because of structural distortions. These predominately arise from specific interactions with extraneous materials such as lipophilic headgroups in surfactant systems, as seen, for instance, in both cationic and anionic octahedral cobalt(III) species [23], Much larger splittings will be expected from other structure... 

In some cases, when a spin-1/2 nucleus such as P, or is coupled to a quadrupolar nucleus, the simulation by a computer program of the unusual lineshape of the spin-1/2 may provide information about the chemical shift anisotropy, the quadrupole coupling constant and the indirect scalar spin-spin coupling constant involving the metal atom. This method has been applied to the P spectra of phosphines bound to cobalt in heteronuclear clusters [17]. 

In addition to mechanistic studies, Co is the transition metal that has found most widespread use in thermal measurements. Since it is a quadrupolar nucleus, a symmetric chemical environment around the central cobalt nucleus is necessary to observe narrow lineshapes for precise temperature measurements. Co... 

Finally, we note as a general observation for the fluorinated alkyl cobaloximes that i F NMR resonances for the a-F atoms generally are broadened due to incomplete averaging of coupling to the quadrupolar 59Co (I = 7/2) nucleus. This broadening is evident for the CF=CF2 complexes as well, where the F atom on the carbon atom attached to cobalt is severely broadened and the F atom trans to the cobalt is slightly broadened (25),... 

Chemical shift anisotropy has also been noted for cobalt complexes as a Bg-dependent component to relaxation which, for quadrupolar nuclei, is otherwise dominated by the quadrupolar relaxation mechanism T2 (1-i- /3)Tc, where... 

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