IS STATISTICAL LACK OF FIT A RELIABLE CRITERION FOR CHEMICAL COMPLEXITY

Complexations of Fe-III and Co-II ions with thiocyanate in water-aceto ne-ethanol ternary mixtures are investigated using multivariate statis tical techniques. Simplex lattice and hexagonal mixture designs lead t o model equations resulting in similar conclusions. The Fe-III thiocya nate complex exhibits a very simple dependence (quadratic) on the tern ary mixture composition. On the other hand this dependence is much mor e complex for the Co-II thiocyanate complex since even a full cubic mi xture model shows a significant lack of fit at the 95% confidence leve l. These results indicate that the different possible symmetries of th e Co-II complexes are more sensitive to the ternary mixture compositio n than are the multistep Fe-III complex equilibria.