Metal Complexes with N-(Phosphonomethyl)glycine (Glyphosate): the Preparation and Characterization of the Group 2 Metal Complexes with Glyphosate and the Crystal Structure of Barium Glyphosate Dihydrate

Abstract

A series of the Group 2 metal complexes with the herbicide N-(phosphonomethyl)glycine (glyphosate, H₃L) with general formula [M(HL)·2H₂O] has been prepared and characterized by using infrared spectroscopy and in the case of the Ba analogue, by single-crystal X-ray diffraction. Crystals are monoclinic, space group P2₁/n, with four molecules in a cell having dimensionsa 9.516(3), b 7.609(2), c 12.826(5) Å, b 103.00(3)˚, and the structure was refined to a residual R 0.057 for 1655 observed reflections. The polymer structure is based on a centrosymmetric dimeric {[Ba(HL)(H₂O)₂]₂} repeating unit with each irregular BaO₈ centre bridged by bisglyphosate [O(phosphonate), O(carboxylate)] ligands, with the carboxylate groups also bidentate and bridging. The two water molecules, together with further interdimer bridges, complete the coordination about Ba [Ba–O range: 2.656–2.947(8) Å; mean, 2.774 Å]. Infrared spectroscopy has been used to show that the Ba and Sr complexes are similar but both are significantly different from the previously reported calcium analogue with the same general formula {[Ca(HL)(H₂O)₂]₂}_n, while all are significantly different from the magnesium analogue which has the probable formula [Mg₄(₃-OH)₄(H₂O)₁₂] [Mg₂(L)₂(-HL)(H₂O)₂].