A new symmetric bidentate Schiff baseN, N′bis(4-fluorobenzal-dehydene)-1,2-diaminoethane(L) and its complexes with general formula MLX₂(M= Zn(II), Cd(II) and Hg(II) and X=chloride, bromide, iodide, thiocyanate and azide) have been prepared. The ligand and complexes have been established by microanalysis, electronic, FT-IR,¹H and¹³C NMR spectra, and by molar conductivity measurements. All compounds are non-electrolytes in chloroform or DMSO-d₆. The thermal behavior of the complexes shows weight loss by decomposition of the anions and ligand segments in the subsequent steps. Some activation thermodynamic parameters such as E*, ∆H*, ∆S* and ∆G* were calculated from thermal analysis.