Synthesis and Complexation Properties of 2-Hydroxy-5-methoxyphenylphosphonic Acid .sub.2] Complex

2-Hydroxy-5-methoxyphenylphosphonic acid (H.sub.3L.sup.1) and the complex [Cu(H.sub.2L.sup.1).sub.2(H.sub.2O).sub.2] were synthesized and characterized by IR spectroscopy, thermogravimetry, and X-ray diffraction analysis. The polyhedron of the copper atom is an axially elongated square bipyramid with oxygen atoms of phenolic and of monodeprotonated phosphonic groups at the base and oxygen atoms of water molecules at the vertices. The protonation constants of the H.sub.3L.sup.1 acid and the stability constants of its Cu.sup.2+ complexes in water were determined by potentiometric titration. The protonation constants of the acid in water are significantly influenced by the intramolecular hydrogen bond and the methoxy group. The H.sub.3L.sup.1 acid forms complexes CuL.sup.â and CuL.sub.2.sup.4â with Cu.sup.2+ in water.