| Abstract | Two new ligands, 4-hydroxy coumarin-3-thiosemicarbazone (H2L1) and 4-hydroxy coumarin-3-semicarbazone (H2L2) were synthesized and used for the preparation of a series of transition metal complexes (Cr3?, Co2?, Ni2?, Cu2?, and Fe3?), derived from these ligands. These complexes have the forms [ML1Cl2]!nX (1–5) and [ML2Cl]!Nx (6 9) (X = H2O or ethanol). The structures of these complexes were elucidated by elemental analyses, IR, UV–Vis, and electrical conductivity, as well as magnetic susceptibility measurements and thermal analyses. IR spectral data indicates that in all complexes, the ligands act as monobasic tridentate, coordinated through keto oxygen or sulfur, azomethine nitrogen and deprotonated phenolic oxygen atom. On the basis of other physicochemical investigations, tetrahedral or square planar geometries are assigned for Cu2? complexes in monomeric structures. In the case of the Co2?, Ni2? and Fe3? complexes, octahedral stereochemistries in monomeric structures are suggested. The dissociation constants of the ligands and the stability constants of their Cu(II), Co(II), Ni(II), and Fe(III) complexes have been also determined using potentiometric pH-metric titration in mixed solvents of dioxane: H2O and DMF: H2O with different ratios and different temperatures. |