A three-dimensional, highly symmetric sphere like nano cage was synthesized using a terpyridine (tpy)-based, flexible tris-dentate ligand and characterized by single crystal X-ray analysis. To introduce more rigidity, one of the tpy units of the tris-dentate ligand was preblocked by stable connectivity to form the corresponding Ru2+-dimer. The complexation between Ru2+-dimer and Fe2+ demonstrates an unexpected temperature-dependent assembly between two irreversible isomeric 3D nanocages. Investigation of the coordination process and structural configurations of the metal ligand framework, affected by the introduction of rigidity and in the presence of external stimuli (temperature), is reported.