A nuclear magnetic resonance study of aqueous solutions of several nitrate salts

Abstract

Rotational correlation times for the end-over-end rotation of the C3 symmetry axis of the nitrate anion in the temperature range 3–80 °C are studied by nuclear magnetic resonance spectroscopy for a variety of nitrate salts in aqueous solution. The counterion is found to retard the rotation of the anion in the following order: Sc3+ > La3+ > Pb2+ > Ca2+, Sr2+ > Al3+, K+, Na+, (CH3)4N+ > Zn2+, Mg2+, Li+, NH4+, H3O+. This relative order is discussed in terms of the association of the nitrate ion with the cation. Oxygen-17 nmr spin-lattice relaxation times in combination with 14N nmr T1values are used to derive rotational diffusion constants for the in-plane rotations of the nitrate anion. In all cases the in-plane rotations are found to be slower than the corresponding end-over-end motion.