Zinc-67 NMR study of zinc ions in water and in some nonaqueous and mixed solvents
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Solutions of zinc salts in water, methanol (MeOH), dimethylformamide (DMF) and binary mixtures of water with the two nonaqueous solvents were studied by zinc-67 NMR measurements. Anhydrous zinc nitrate solutions in DMF and MeOH show upfield, concentration independent, chemical shifts at −27 and −19 ppm, respectively, vs. the aqueous solution standard. Addition of DMF or MeOH to an aqueous solution of a zinc salt results in a diamagnetic shift but for the addition of acetonitrile a paramagnetic shift results. In all cases the signal was broadened very considerably, e.g., in ZnCl2 solution the linewidth increased from ∼40 to ∼600 Hz in going from water to 35% aqueous MeOH. Both67Zn and13C NMR failed to show any complexation of Zn2+ ion by crown ethers in aqueous solution. A gradual addition of EDTA, of diaza-18-crown-6 or of tetraazacyclotetradecane resulted in an immediate broadening of the67Zn signal which became undetectable when one equivalent of a ligand was added.
Key wordsZinc-67 NMR nonaqueous solution zinc complexes crown ethers EDTA methanol dimethylformamide
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