Synthesis and properties of complexes of lead(II), cadmium(II), and zinc(II) with N-phosphonomethylglycine

Sparingly water soluble complexes of lead(II), cadmium(II), and zinc(II) wi th N-phosphonomethylglycine (glyphosate, NPMG) of the general formulae C3H6 O5NPPb, C3H6O5NPCd . 2H(2)O, and C3H6O5NPZn were synthesized. The complexes were also precipited from a dilute Roundup solution, and their solubility in water was determined. Thermal, diffractometric, and IR spectrophotometri c analyses were carried out. It was found that the metal is bonded to glyph osate through the oxygen atoms of the carboxylic and phosphonate groups; me tal-nitrogen binding is absent in the above compounds. Studying the complex ing behaviour in solution by UV spectrophotometry pointed out that a comple x of the composition Pb(II):NPMG = 1:1 with an absorption band at 232nm is formed. Its stability constant as determined by Job's method is logK = 5.9 +/- 0.1. Using potentiometric techniques, the dissociation constant of N-ph osphonomethylglycine and the stability constants of its complexes with cadm ium (II) and zinc (II) were determined.