Molecular motion in cis- and trans-dichlorotetra-amminecobalt(III) chloride by proton magnetic resonance

Abstract

The second moments of cis- and trans-dichlorotetra-amminecobalt(III) chloride have been obtained between 77 and 300 K from CW spectra. Spin-lattice relaxation times for the trans isomer and “null times” for the cis isomer have been obtained between 77 and 440 K from pulse spectrometer measurements. The results suggest that in the trans complex one of the ammine ligands is unique, reorienting more slowly at a given temperature than the others, but that in the cis complex all the ammine ligands have about the same reorientation frequency at a particular temperature. Whole ion rotation occurs in the trans isomer, apparently about two different axes at two different crystal sites. Although whoel ion rotation, with a frequency which would narrow the n.m.r. line, does not occur in the cis isomer, libration does, and the second moment of the cis compound is interpreted in terms of such a torsional oscillation.