The carboxamide [–C(O)NH–] group, ubiquitous throughout nature in the primary structure of proteins, is an important ligand construction unit for coordination chemists. However, carboxamides have anticancer and anti-inflammatory activities. There are several important biological and industrial application with amid functional group, such as drug preparation (pencilline and folic acid) and dye synthesis(indigo). On the other hand, 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. The coordination chemistry of cobalt is of considerable interest since cobalt (II) and cobalt (III) complexes derived from Schiff bases are reported to be biologically active. Vitamin B 12 , which is involved in the production of red blood cells is a cobalt (III) complex with a substituted corrin macrocycle. Cobalt (III) complexes have shown specific hypoxic radiosensitization and thermosensitization as well as antitumor activity in vivo. The antitumor action of cobalt (III) complexes with tetradentate Schiff bases derived from aliphatic beta-diketones and diamines was observed in the case of ascite form of Erlich carcinoma. Cobalt(III)- schiff base complexes are found to be potential antiviral agents. On the other hand, azide is a versatile ligand since it exhibits a variety of coordination modes such as monodentate, end-on bridging mode (?-1, 1), end-to-end bridging mode (?-1, 3) etc among many others. Azide acts as an inhibitor for several enzymes like ATPases. So, the study of metal-azido complexes and especially Cobalt-azide complexes with carboxamide or Schiff base ligands are very useful for the understanding of biological processes. Therefore, in this thesis, we describe preparation of two kind of important cobalt (III)-azide complexes.