The coordination chemistry of vanadium complexes received much more attention due to its several biological activities such as insulin mimetic, DNA binding, photo-induced DNA cleavage in the inhibition of cancer cell proliferation, as an anti-inflammatory, antibiotic, and antifungal agent. Apart from the biological importance of vanadium, the magnetic properties of molecular compounds are important in bioinorganic chemistry when one tries to correlate them with structural parameters. One likely reason for this could be their similarities to biochemical molecules such as metalloproteins and their possible utilization as models in unraveling their mode of function within biological systems. Just like vanadium(IV) compounds, the cobalt(II) complexes also exhibit good magnetic properties. It is because of their importance in a variety of research fields, including single-molecule magnets (SMMs), quantum computing, molecular spintronics, and high-density information storage. Despite significant advancements in mononuclear Co(II)-based SMMs over the past few years, it is still difficult to establish a proper correlation between magnetic properties and their structural parameters in cobalt complexes. To be able to achieve this, it is beneficial to understand the basic mechanism through which the interactions occur, and this is expected to facilitate the improved design of such materials based on an in-depth understanding. These observations have motivated me to focus on my thesis work which comprises designing and synthesizing novel vanadium(IV/V) and cobalt(II) complexes featuring O, and N donor ligands emphasizing their biological and magnetic properties.