X-RAY STRUCTURAL STUDY OF ORGANIC LIGANDS OF THE COMPLEXONE TYPE. III. CRYSTAL AND MOLECULAR STRUCTURE OF PHOSPHONOMETHYLGLYCINE AND IMINODIACETIC-MONOMETHYLPHOSPHONIC ACID

Article abstract of DOI:10.1007/BF00746199

An x-ray structural study of phosphonomethylglycine (I) and iminodiacetic-monomethylphosphonic acid (II) has been carried out (diffractometer, direct method, anisotropic method of least squares, R = 0.035 and 0.050, R_W = 0.040 and 0.052 from 1712 and 1113 reflections for compounds I and II respectively).The crystals of compound I are monoclinic and those of compound II triclinic; I: a = 8.681, b = 7.981, c = 9.893 Angstroem, β = 105.77 deg, d_calc = 1.702 g/nm³, Z = 4, space group P2₁/c; II: a = 5.590, b = 7.422, c = 10.648 Angstroem, α = 93.12, β = 95.03, γ = 90.40 deg, d_calc = 1.716 g/cm³, Z = 2, space group <*>.The geometric parameters of the molecules of compounds I and II are similar.Structural proof has been obtained for the first time to show that the nitrogen atom is protonated by the proton of the phosphonic acid group, and not the carboxyl group, for the Complexones I and II, containing comparing functional groups, in the crystalline state.Complexone I is obtained from Complexone II by removing one methylcarboxyl group and replacing it by a hydrogen atom.The result of this process is a change in compound I from the conformation of the molecule of compound II, directed towards the stabilization of a sterically favorable system of hydrogen bonds (HB), responsible for the similar structural motifs in the crystals of compounds I and II.This system includes HB O -H...O and N -H...O, forming dimeric ribbons, networks, and three-dimensional frameworks.In compound II, weak intramolecular HB are formed, leading to the formation of H-rings.