The complex chemistry of N-(phosphonomethyl)glycine (glyphosate): preparation and characterization of the ammonium, lithium, sodium (4 polymorphs) and silver(I) complexes

Abstract

A series of complexes with the herbicide glyphosate [N-(phosphonomethyl)glycine = H₃L] has been synthesized and characterized using infrared spectroscopy, and in the case of five of these, by single crystal X-ray diffraction. The compounds are ammonium glyphosate [NH₄][H₂L] 1, lithium glyphosate Li(H₂L) 2, sodium glyphosate hemi-hydrate Na(H₂L)·0.5H₂O 3, sodium glyphosate monohydrate Na(H₂L)·H₂O 4, sodium glyphosate dihydrate Na(H₂L)·2H₂O 5, disodium glyphosate nonahydrate Na₂(HL)·9H₂O 6 and disilver glyphosate Ag₂(HL) 7. The crystal structures of 1, 3, 4, 6 and 7 have been determined. Compound 1 consists of a hydrogen-bonded lattice structure in which all of the available ammonium protons are involved in hydrogen bonding, together with the zwitterionic amine group and the single phosphonate proton. Compounds 3 and 4 are both polymeric and based on dimeric repeating units with six-co-ordinate sodium centres. Complex 6 is based on both discrete octahedral [Na(HL)(H₂O)₅]⁻ anionic complex units with the unidentate glyphosate ligand bonded via a carboxylate oxygen, together with a cationic [Na₂(H₂O)₈]²⁺ ribbon polymer. All structures have extensive hydrogen bonding interactions. The silver complex 7 is a polymer structure which involves the phosphonate ligands in linear chains joined through the carboxyl group at one end (via bis-O,O′ bridged silver dimers) and silver co-ordinated phosphonate oxygens at the other.