Journal of Physical Chemistry, Vol.100, No.20, 8057-8060, 1996
Effect of Cobalt-59 Self-Decoupling on the Solid-State P-31 CP/MAS NMR-Spectra of Cobaloximes
Phosphorus-31 NMR spectra of three solid cobaloxime complexes containing phosphorus donor ligands have been examined. At room temperature, the P-31 CP/MAS NMR spectra of PBu(3)Co(DH)(2)Cl (I) are broad and rather featureless, while PPh(3)Co(DH)(2)CH3 (II) and P(OEt)(3)Co(DH)(2)N-3 (III) exhibit well-resolved eight-peak patterns which result from Co-59 (spin 7/2), P-31 spin-spin coupling. Variable temperature measurements on compound I indicate that the peak broadening observed at room temperature results from the onset of Co-59 self-decoupling. At 155 K, the Co-59 spin-lattice relaxation time is sufficiently long that well-resolved octets are observed. The experimental P-31 CP/MAS NMR spectra were simulated using the first-order perturbation approach of Olivieri and the information available from these simulations is discussed in detail. The P-31 NMR spectra of compound I provide the first reported example of recoupling of the direct and indirect spin-spin interactions between a quadrupolar nucleus and a spin 1/2 nucleus in the solid state by means of low temperature CP/MAS NMR experiments.