The main objectives of my Ph.D. work were to prepare transition metal complexes, to characterize them by analytical, spectroscopic, electrochemical and crystallographic methods, and also to investigate their catalytic activity and magnetic properties. I followed various kinds of synthetic routes to produce single crystals, solved their structures and studied kinetic & magnetic properties to realize the above mentioned goal. In particular, A novel Cu(II) complex was prepared with carbonato ligand, which was the first report of a polymer showing the rare tridentate mode exhibiting long-range ferromagnetic order. The macrocyclic hexanuclear Mn(III)-compound has been evaluated as the model system for the catechol oxidase enzyme. Many of these complexes exhibited novel supramolecular architectures through hydrogen bonds. Most of the synthesized complexes showed considerable photoluminescence; it opens up the opportunity for photochemical applications. The complexes with novel architectures have potential applications as catalysts, molecular magnets, photosensitizes, zeolite type materials etc. This study should be especially useful to professionals in transition metal chemistry field.