Molecular nano magnets such as single-molecule magnets (SMMs) are a class of coordination complexes with numerous potential applications such as information storage devices, Q-bits in quantum computing and spintronics materials. One of the greatest challenges in taking these molecules to end-user applications lies in devising strategies to control and predict their magnetic properties. In this regard, lanthanide-based compounds are very attractive as they possess appealing magnetic properties such as very high barriers for magnetization reversal, very large blocking temperatures etc. Controlling the microscopic energy levels of lanthanide-based single-ion magnets (SIMs) is a challenging task and to obtain molecules having very large blocking temperatures, it is desirable to enhance the ground state-excited state gap between the mJ levels and also to quench the quantum tunnelling of magnetization that often circumvents the barrier height. One of the strategies that has been developed by us and others in this area is to employ a diamagnetic transition metal ion to achieve this goal. Over the years several diamagnetic ions such as ZnII, NiII (square planar), AlIII and CoIII have been successfully employed to obtain lanthanide-based SMMs with interesting properties. In this perspective, we discuss how incorporation of diamagnetic ion(s) in the cluster aggregation enhances the barrier height for magnetization reversal and hence improves the magnetic properties. We also discuss theoretical studies on such systems based on ab initio calculations performed using CASSCF level of theory. Such studies are helpful in affording an understanding of the role and limitation of the diamagnetic ions in enhancing the barrier height for magnetization reversal of molecular nanomagnets.