Deuteron Magnetic Resonance Study in Co(ND3)6Cl3

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Abstract
Deuteron quadrupole coupling tensors in Co(ND3)6Cl3 were determined at various temperatures. The observed quadrupole coupling shows that Co(ND3)63+ ions execute a rapid isotropic reorientation at high temperatures (above 320°K for one of the sites (the 4f sites) and above 190°K for another (the 2e sites), while at low temperatures (below 190°K for the 4f sites, and 170°K for the 2e sites), only a C3 axis reorientation of the ligand ND3 groups is present. The deuteron resonance spectra clearly show that Co(ND3)63+ ions in the 4f sites begin to reorient about one of the three C4 axes at intermediate temperatures (about 240°K). On the basis of the orientation of quadrupole tensors, probable orientations of Co(ND3)63+ ions in the 4f sites in the crystal are proposed. Additional measurements of the proton resonance on a single crystal of Co(NH3)6Cl3support the results obtained from the deuteron resonance. To obtain the reorientation rates and the activation energies of these reorientational motions, the deuteron resonance line width at the 4f sites is measured at various temperatures and at various crystal orientations. From the temperature dependence of the line width, the presence of two cations with slightly different rates at the 4f sites is suggested. However, because of the limits set by the various experimental conditions, reliable values of the reorientation rates and activation energies could not be obtained.

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