Crystal structures, solution conformations and zinc(II) complex-forming abilities of two uncommon phosphonic derivatives of glutamic acid

The crystal structures of two new phosphonic derivatives of glutamic acid have been determined by X-ray diffraction. In water solutions the preferred conformers have been established by the means of the NMR method. In the crystal, the 3-amino-4-phosphonobutyric acid appears as the gauche–gauche conformer, while in solution the preferred conformation is trans–gauche. The 4-amino-2-phosphonobutyric acid exists in the extended trans–trans conformation in both solution and solid state. The solution studies of the protonation equilibria, co-ordination modes and stabilities of the complexes of zinc(II) with both compounds are reported. In contrast to the majority of simple aminophosphonic acids no tendency for cyclization upon the action of zinc(II) has been observed. q 2003 Elsevier B.V. All rights reserved