Abstract
The spin-lattice relaxation time (T1) of7Li+ was measured in solutions of LiCl and LiClO4 in protic (MeOH, EtOH,n-PrOH,i-PrOH,n-BuOH, sec-BuOH, formamide, N-methylformamide) and aprotic (MeCN, acetone, methyl ethyl ketone, propylene carbonate, dimethyl sulfoxide, dimethylformamide, hexamethylphosphotriamide) solvents and in mixtures of H2O-formamide, H2O−N-methylformamide, H2O−N,N-dimethylformamide, H2O-DMSO, H2O-hexamethylphosphotriamide, and formamide-N,N-dimethylformamide at 25°C. The values of (1/T1)0 obtained by extrapolation are discussed in terms of current theories of the magnetic relaxation of ionic nuclei. Linear correlations were found between (1/T1)0 and Gutmann's donor numbers and Kosower's Z-values. These correlations indicate that relaxation of7Li+ is dominated by donor-acceptor interaction of the cation with solvent molecules. Concentration dependences of 1/T1 for LiCl and LiClO4 differ from one another in a given solvent, a fact which is accounted for by a specific cation-anion short-range potential. The quantity 1/T1 of7Li+ atC=1 mole per 55.5 moles of mixed solvent as a function of solvent composition show characteristic features, which are discussed in terms of the relaxation mechanism proposed.
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