Investigation of complexing in the systems of HCOOLi-(HCOO)2Zn(Cd)-H2O and HCOOLi-HCOOCs(NH4)-H2O by the NMR method

By the method of nuclear spin echo, investigations into relaxation of Li7 nuclei in solutions of HCOOLi-(HCOO)2Zn(Cd)-H2O (at 25 and 50 deg C) and HCOOLi-HCOONH4-H2O (at 25 deg C) systems are carried out. For solutions of HCOOLi-HCOOCs-H2O system, relaxation times are measured both for Li7 and Cs133 nuclei. The relaxation curves reflect all the peculiar points of the solubility isothermic lines. There are sharp bends in them at the points corresponding to minima of the solubility curves, which results from changes in lithium ion environment in the solution. Increase in complex formation in the solution with increasing temperature is fixed on the relaxation curves by sharper bends at 50 deg C than at 25 deg C. It is shown for the case of HCOOLi-HCOOCs-H2O system that measurement of relaxation of both cations makes it possible to judge a composition of the complex in solution and its correspondence to the composition of the crystallized solid phase