To evaluate the capability of pyrophosphate ion as a carrier of fertilizer trace elements, pyrophosphato complexes with manganous, cupric, ferrous and zinc ions were studied by spectrophotometry and polarography.
The soluble complexes of Mn²⁺, Cu²⁺, Fe²⁺ and Zn²⁺ with pyrophosphate ion appeared to be [Mn(HxP₂O₇)₂]^(6-2x)-, [Cu(HxP₂O₇)₂]^(6-2x)-, [Fe(HxP₂O₇)₂]^(6-2x)- and [ZnH_xP₂O₇]^(2-x)-, and the logarithmic values of their stability constants were measured to be 1.79, 3.45, 5.08 and 6.43 at pH 10, respectively.
However, by adding excess corresponding metal ion, the soluble pyrophosphato complexes were ultimately changed to amorphous precipitates.