¹⁴N Nuclear Magnetic Resonance Relaxation of the Nitrate Ion and Ion Pairing in Aqueous Solution

Abstract

¹⁴ N n.m.r. spin-lattice relaxation times of four metal nitrate salts were measured as a function of concentration in aqueous solution. The concentration dependence of T₁ was attributed to the formation of ion pairs with increasing concentration in these solutions. The T₁ data, allowing for viscosity corrections, were treated by a two-state model of 'free' and 'bound' nitrate ions and to both possibilities of slow and fast exchange between the two states. In the equilibrium expressions estimates of the relevant activity coefficients were included. The slow nitrate exchange mechanism was favoured and the values obtained for this particular mechanism compared well with those derived from alternative measurements.