Abstract
A review of the previous work on the properties of the phosphate group: as a ligand in cobalt(III) complexes, has shown not only that such work was very limited in scope, but that the conclusions reached were in conflict. The object of the present studies was to gain a fuller understanding of the role of the phosphate group as a ligand. Attempts have been made to introduce the phosphate group into the cobalt(III)ammine complexes by the use of various methods and various starting materials. Each product has been, examined systematically in an attempt to deduce its structure. The methods of investigation used were : Chemical analysis (including a determination of the proportion of the phosphate present in an ionic form), studies of the effect of heat on the solid materials, together with spectrophotometric and conductivity measurements on their aqueous solutions. The results have shown that all the attempts to obtain phosphatotriammine and pentammine-cobalt(III) complexes were unsuccessful, but that attempts to prepare phosphata-tetra]mine-cobalt(III) complexes were more successful and that in fact two such compounds were isolated These results were confirmed by phase diagram studies of the systems : [CO(NH3)5H2O]2 O3-P2O5-H2O and [CO(NH[3])[4](H[2]O)[2]][2] O[3]-P[2]O[5]-H[2]O ; in the first case two aquo-pentanmine-cobalt(III) phosphates were the only solid phases identified whereas, in the second case not only were the solid phases present found to be phosphato-tetrammine-cobalt(III) compounds, but the species present in solutions appeared to be of the same type Phase diagram and other physico-chemical studies were carried out on [CO(NH[3])[6]]PO[4],[4]H[2]O as well for purposes of comparison. These results are discussed in terms of the co-ordinating properties of the phosphate group as a ligand .