3-[3-Carboxyethyl-4,5-dimethylthiophene-2-yl)azo]pent-2,4-dione was
synthesized by coupling diazotized 2-amino-3-carboxyethyl-
4,5-dimethylthiophene with acetylacetone. Based on various spectral studies
and elemental analysis, an intramolecularly hydrogen bonded azoenol
structural form was assigned for the ligand. This ligand is versatile in
forming a series of lanthanide(III) complexes viz, lanthanum(III),
cerium(III), praseodymium(III), neodymium(III), samarium(III) and
gadolinium(III), which were characterized through various spectral studies,
elemental analysis, magnetic susceptibility measurements, molar conductance
and thermal analysis. The spectral data revealed that the ligand acted as a
neutral tridentate, coordinating to the metal ion through one of the azo
nitrogen atoms, the ester carbonyl and the enolic oxygen of the acetylacetone
moiety, without deprotonation. Molar conductance values adequately supported
their non-electrolytic nature. The ligand and lanthanum(III) complexes were
subjected to X-ray diffraction studies. In addition, the lanthanum(III)
complex underwent a facile transesterification reaction on refluxing with
methanol for a long period. The thermal behavior of the lanthanum(III)
complex was also examined.