Preparation, Characterization, Thermal Degradation and X-Ray Structural Studies on Anhydrous and Hydrated Hydrazinium Lanthanide(III) Ethylenediaminetetraacetate

Abstract

Anhydrous hydrazinium lanthanide(III) ethylenediaminetetraacetates, [N₂H₅Ln(EDTA)], where Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb or Dy have been prepared by the reaction of the respective lanthanide(III) nitrate hydrate and dihydrazinium dihydrogen ethylenediaminetetraacetate in alcoholic medium. These complexes were characterized by CHN, hydrazine and metal analyses, spectral, thermal and X-ray diffraction studies. The infrared spectral studies reveal the multidentate coordination of EDTA^4- and monodentate coordination behaviour of N₂H₅⁺ cation. Thermal degradation studies in argon and oxygen atmospheres clearly show the formation of different end products. Attempt to recrystallize the anhydrous complexes in water yielded respective hydrated hydrazinium lanthanide(III) ethylenediaminetetraacetates as crystalline complexes. During this process the coordination sphere expanded from seven to nine by water coordination. However, in slightly acidic solution (pH = 4), simple lanthanide(III) ethylenediaminetetraacetate hydrates were formed. The formation and structures of the hydrated hydrazinium lanthanide(III) ethylenediaminetetraacetates were confirmed by comparing X-ray powder diffraction patterns with the previously reported complexes. The X-ray crystal structure of new hydrated samarium(III) ethylenediaminetetraacetate complex has been determined as a representative model for the confirmation of the composition and hydration.