Single-molecule magnet (SMM) properties of terbium(iii)-phthalocyaninato and porphyrinato mixed ligand triple-decker complexes, [(TTP)Tb(Pc)Tb(TTP)] (1) and [(Pc)Tb(Pc)Tb(TTP)] type (2), were studied and were compared with those of the TbIII homoleptic triple-decker complex [(obPc)Tb(obPc)Tb(obPc)] (3) in order to elucidate the relationship between octa-coordination environments and SMM properties (TbIII = terbium(iii), TTP2- = tetraphenylporphyrinato, Pc2- = phthalocyaninato, obPc2- = 2,3,9,10,16,17,23,24-octabutoxyphthalocyaninato). By combining TTP2- and Pc2- with TbIII ions, it is possible to make three octa-coordination environments: SP-SP, SAP-SP and SAP-SAP sites, where SAP is square-antiprismatic and SP is square-prismatic. The direction and magnitude of the ligand field (LF) strongly affect the magnetic properties. Complexes 2 and 3, which have SAP-SAP sites, undergo dual magnetic relaxation processes in the low temperature region in a direct current magnetic field. On the other hand, 1, which has an SP-SP environment, undergoes a single magnetic relaxation process, indicating that the octa-coordination environments strongly influence the SMM properties. The SMM behaviour of dinuclear TbIII SMMs 1-3 were explained by using X-ray crystallography and static and dynamic susceptibility measurements. This work shows that the SMM properties can be fine-tuned by introducing different octa-coordination geometries with the same TbIII-TbIII distances.