N14 Nuclear Magnetic Resonance Studies of Complex Rotation in Silver-Acetonitrile Solutions

Abstract

The complex [CH3CN•••Ag•••NCCH3]+ has been suggested for silver ions in acetonitrile.l H1 NMR data2 show that, for AgNO3 in CH3CN, the complexed CH3CN molecules and the CH3CN molecules in bulk solution exchange so rapidly that there is only one NMR line, with negligible line broadening due to exchange, down to at least -31°C. Nl4 nuclear magnetic resonance linewidth and chemical shift measurements were made for AgNO3 and AgClO4 solutions in CH3CN as functions of concentration and temperature. Assumption of a complex-solvent rapid exchange model with two possible environments for the CH3CN molecules permits calculation of rotational correlation times for the complex, if all of the line broadening is attributed to slower rotation of the CH3CN molecules in the complex. Chemical shift data are used to calculate the chemical shifts of the complex with respect to pure acetonitrile. For AgNO3 solutions it is found that equilibrium between the bis-CH3CN complex and higher order complexes must be taken into account for concentrations greater than .12 mole ratio AgNO3/CH3CN. Comparison of the results for linewidth and chemical shift measurements of AgNO3 and AgClO4 solutions shows that the NO3- ions are considerably more involved in complexing Ag+ ions than are ClO4- ions.