L. O. Morgan

Magnetic Resonance Studies on Copper(II) Complex Ions in Solution. I. Temperature Dependences of the 17O NMR and Copper(II) EPR Linewidths of Cu(H2O)62

The temperature dependences of copper (II) EPR and 17O NMR spectra are analyzed in terms of a tetragonally distorted Cu(H2O)62+ ionic species in which only the equatorial water molecules form strong σ 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 anisotropic g factor and an anisotropic hyperfine coupling constant, and from isotropic hyperfine splitting, are separated. It is found that the spin—lattice relaxation time T1e has components from both spin—rotational and Van Vleck processes. The 17O NMR linewidth is due to scalar hyperfine interaction with the copper (II) electron spin, and the spin‐exchange correlation time τe for this mechanism is determined over the same temperature range. While T1e and τe have similar temperature dependences, τe is 6–8 times smaller than T1e, suggesting that it may be related to inversion of tetragonal distortion in the complex, rather than to electron relaxation.The temperature dependences of copper (II) EPR and 17O NMR spectra are analyzed in terms of a tetragonally distorted Cu(H2O)62+ ionic species in which only the equatorial water molecules form strong σ 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 anisotropic g factor and an anisotropic hyperfine coupling constant, and from isotropic hyperfine splitting, are separated. It is found that the spin—lattice relaxation time T1e has components from both spin—rotational and Van Vleck processes. The 17O NMR linewidth is due to scalar hyperfine interaction with the copper (II) electron spin, and the spin‐exchange correlation time τe for this mechanism is determined over the same temperature range. While T1e and τe have similar temperature dependences, τe is 6–8 times smaller than T1e, suggesting that it may be related to inversion of tetragonal distortion in th...

Electron Spin Relaxation in Solvated Manganese(II) Ion Solutions

Electron spin resonance (ESR) spectra were obtained for solutions of manganese(II) perchlorate in dimethylformamide (DMF), diethylformamide (DEF), dimethylsulfoxide (DMSO), and water. Variation of line shape with solvent and temperature was obtained and interpreted at low temperatures in terms of a model in which solvent fluctuations about the solvated ion modulate the ligand field and relax the electron spin through spin—orbit interaction. Relaxation times for Δms=1 transitions of the S=52 system were calculated using a semiclassical density‐matrix formalism. In DMF, DEF, and DMSO solutions another contribution to relaxation was observed at high temperatures which may be attributable to ligand exchange or to internal motion in the complex ion. The high‐temperature process was not observed in aqueous manganese(II) solutions.

Magnetic‐Resonance Studies on Copper(II) Complex Ions in Solution. II. Oxygen−17 NMR and Copper(II) EPR in Aqueous Solutions of Cu(en)(H2O)42+ and Cu(en)2(H2O)22+

The temperature dependences of the 17O NMR and Cu(II) EPR spectra of solutions of the ethylenedi‐amine complex ions Cu(en)(H2O)42+ and Cu(en)2(H2O)22+ are analyzed in terms of an octahedrally coordinated structure with tetragonal distortion. It is found that the 17O NMR spectrum is broadened and shifted by Cu(en)(H2O)42+ through scalar hyperfine interaction with the copper (II) electron spin, while Cu(en)2(H2O)22+ 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 B1g ground state of Cu(II) and compared with the previous study on Cu(H2O)62+.

Electron Spin Resonance Linewidths of Manganese(II) Ions in Concentrated Aqueous Solutions

ESR spectra of concentrated solutions of manganese(II) perchlorate (1–3.2M) do not indicate strong spin exchange and the dipole—dipole interaction is considered to be the predominant intermolecular‐relaxation process. A model of the ESR spectrum is constructed using 30 Lorentzian distribution functions positioned according to a relation developed by Hurd, Sachs, and Hershberger. Ratios of the second moment for the various electron‐magnetic transitions are used to approximate the linewidth ratios of the transitions and thereby reduce the number of linewidth parameters to one, ΔHD½, the dipolar‐linewidth contribution to the −½→½ absorption. ΔHD½ is calculated from the experimental spectra by trial and error. The variations of ΔHD½ with increasing temperature indicates that for concentrations less than 1.9M a simple rapid‐motion diffusion model is sufficient to explain the narrowing of the spectrum. Above 1.9M, ΔHD½ follows a modified exponential function, ΔHD½=AD—BD exp(—u/kT), in which AD varies linearly w...

Magnetic Resonance Studies on Copper (II) Complex Ions in Solution. III. NMR and EPR in Concentrated Ethylenediamine Solutions

Measurements of the proton and 14N NMR linewidths in ethylenediamine—water solutions of Cu(II) combined with EPR studies of Cu(II) in these media demonstrate that the first sphere relaxation and residence times both make singificant contributions to the over‐all relaxation of protons and 14N by Cu(II). Moreover, the results are consistent with the view that protons and 14N both experience the Cu(II) evironment through exchange of the ethylenediamine molecule as a whole between the bulk solvent and the Cu(II) first sphere. From the temperature dependence of the Cu(II) EPR linewidth it is further concluded that the relaxation of the electron spin occurs predominantly via the spin—rotational process at higher temperatures. At lower temperatures the EPR linewidth is broadened both by tumbling of a tetragonally distorted complex with an anisotropic g factor and hyperfine coupling constant and by the same fast chemical exchange process which provides 14N and proton relaxation in ethylenediamine.