I. Hindered rotation in solid hexamminecobalt(III) chloride. II. Automatic coulometric titrations involving an amperometric end point

Abstract

Part I: A study has been made of the unusual behavior that solid hexamminecobalt(III) chloride exhibits when examined by the technique of nuclear magnetic resonance absorption. From the examples of substances exhibiting similar behavior to this one, the conclusion is reached that some sort of internal motion is taking place within the solid. On the basis of the structure of the hexamminecobalt(III) ion, and from information gathered on related ions, it is postulated that the motion involved is the rotation of the whole complex ion in the crystal lattice. From a study of the nuclear magnetic resonance absorption line width for the protons in the complex ion as a function of temperature, the motion is described in terms of a rate process. The general theory of nuclear magnetic resonance is discussed, and in particular the application of this technique to the study of rate processes. The design and construction of a nuclear magnetic resonance spectrograph are described. Part II: An instrument has been developed for automatic control of coulometric titrations employing the dual indicator electrode amperometric end point. The instrument is capable of detecting the end of the titration and stopping the generation, freeing the analyst of this task. The titration is stopped at a pre-set indicator current, either as a dead stop end point or as a preliminary operation to determining the exact end point by extrapolation of the post end point current to zero. The operation of the instrument on three different types of coulometric titrations is described.