Particular attention has recently been paid to the synthesis and study of diimino tetradentate Schiff base ligands and their complexes. Interest in the design, synthesis and characterization of transition metal complexes of unsymmetrical Schiff base ligands stems from the fact that the central metal ions in natural systems are unsymmetrical. These complexes are used in some chemical processes as catalysts and also as biological models in understanding the structure of biomolecules and biological processes. Synthesis of such ligands is rather difficult compared to their symmetrical counterparts. Moreover, during the formation of metal complexes of unsymmetrical quadridentate Schiff base ligands, one of the major problems which is commonly encountered is the hydrolysis process which leads to the unsymmetrical to symmetrical rearrangements of the Schiff base. On this basis, in this thesis a new ligand, H 2 pyrabza, and its metal complexes, which may have biochemical and photochemical applications, are synthesized, characterized and studied. (1) [Ni II (pyrabza)] (4) [Co III (pyrabza)(py) 2 ]BPh 4 (2) [Cu II (pyrabza)] (5) [Co III (pyrabza)(3-Mepy) 2 ]BPh 4 (3) [Zn II (L 1 ) 2 (OAc) 2 ] (6) [Co III (pyrabza)(4-Mepy) 2 ]BPh 4 (7) [Co III (pyrabza)(N-MeIm) 2 ]BPh 4 Changes in the electronic properties can also affect the reactivity of the central metal ion. There fore, only complexes with two ? donor and ? acceptor ligands in the axial positions were successfully synthesized. In addition, The steric demand of the ligand pyrabza, led to the formation of [Cu II (pyrabza)] with a distorted square planar structure. Due to the steric hindrance imposed by the pyrabza ligand, the structure of Co(III) complexes is also, distorted octahedral. Selective hydrolysis of one of the imine bond in the presence of zinc metal causes a interesting and rare structure for complexe 3. The H 2 pyrabza and its complexes were characterized by UV-Vis, FT-IR, 1 H-NMR and Elemental Analysis. Complexes (2), (3), (4), (7) were structurally characterized by X-Ray Diffraction.