Chemical shift anisotropy and second-sphere hydrogen bondin in Cobalt (III) Complexes
Abstract
The linewidths of the 59Co NMR resonances of 22 Co(III) complexes were measured at fields of 2.114, 5.872, and 9.395 T. The linewidths for octahedral complexes show no field dependence. Less symmetric compounds show differences in linewidth of as much as 10 kHz between the highest field and the lowest field. The linewidth changes parallel the chemical shift anisotropies calculated from optical absorption spectral data. For complexes with high symmetry the increase in width is proportional to the square of the field strength. For complexes of lower symmetry, plots against field squared show a pronounced curvature. If the increase in linewidth is calculated from the chemical shift anisotropies obtained from optical data (or from single-crystal measurements reported in the literature) and correlation times derived from quadrupole coupling constants the calculated increases in width are more than two orders of magnitude smaller than the observed increases. Correlation times of the order 10 -9 to 10 -10 sec rather than the accepted 10 -11 sec for rotational correlation times are required to fit the data. It is suggested that these long correlation times are associated with the lifetimes of hydrogen bonds with second-sphere solvent molecules.
- Publication:
-
Journal of Magnetic Resonance
- Pub Date:
- 1983
- DOI:
- 10.1016/0022-2364(83)90162-2
- Bibcode:
- 1983JMagR..52..351A