Articles you may be interested in Spin dynamics calculations of electron and nuclear spin relaxation times in paramagnetic solutionsThe proton relaxation time in solutions of paramagnetic ions depends, among other factors, on the relaxation time of the electron spins, T •• It is shown that the latter, for ions of the iron group, is determined mostly by the distortion of the hydrated complex by collisions with other water molecules. The theory provides a quantitative explanation for the decrease in T2 in Mn+ + (and other) solutions in very high magnetic fields. The experimentally observed field and temperature dependence of the proton relaxation times, Tl and T2, for ions of the iron group is compared with theory and the features which depend on T, are stressed.

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The temperature dependences of copper (II) EPR and 17 0 NMR spectra are analyzed in terms of a tetragonally distorted Cu(H20)e2+ ionic species in which only the equatorial water molecules form strong (1' bonds to copper (II). By reconstructing the EPR spectra at temperatures in the range _10° to 100°C the contributions to the linewidth from spin-lattice relaxation, tumbling of an ionic complex having an aclsotropic g factor and an anisotropic hyperfine coupling constant, and from isotropic hyperfine splitting, are separated. It is found that the spin-lattice relaxation time Tlo has components from both spin-rotational and Van Vleck processes. The 17 0 NMR linewidth is due to scalar hyperfine interaction with the copper (n) electron spin, and the spin-exchange correlation time T. for this mechanism is determined over the same temperature range. While Tlo and T. have similar temperature dependences, T. is 6-8 times smaller than T1., suggesting that it may be related to inversion of tetragonal distortion in the complex rather than to electron relaxation.'

Nuclear magnetic relaxation times for protons in dilute aqueous solutions of chromic, manganous nickel, cupric, and gadolinium ions were measured in the frequency range 1.9 to 60 Mc/sec. Results we:e interpreted in terms of Solomon's formulation of electron-nuclear dipole-dipole interaction and Bloembergen's expression for scalar coupling of electron and nuclear spins. In large magnetic fields relaxation times were found to be shorter than those expected on the basis of low field values, suggesting that the effective ion magnetic moments, electron spin relaxation times, and/or electron-nuclear spin exchange constants are field-dependent.

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The temperature dependences of the 17 0 NMR and CU(Il) EPR spectra of solutions of the ethylenediamine complex ions Cu(en) (H20) ,2+ and Cu(en),(H20)22+ are analyzed in terms of an octahedrally coordinated structure with tetragonal distortion. It is found that the 17 0 NMR spectrum is broadened and shifted by Cu(en) (H20).2+ through scalar hyperfine interaction with the copper (II) electron spin, while Cu(en)2(H20j.2+ has no effect. The Cu(II) EPR spectra of both species have linewidth contributions from spin-rotational relaxation, from tumbling of an ionic complex having an anisotropic g factor and an anisotropic hyperfine coupling constant, and from 63CU isotropic hyperfine and 14N isotropic extrahyperfine splitting. The results are discussed in terms of the antibonding molecular-orbital model for the Blg ground state of Cu(II) and compared with the previous study on Cu(H20)a2+.

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