Single-molecule magnet (SMM) properties of terbium(III)-phthalocyaninato quintuple-decker complex TbCdCdTb were studied and were compared with those of other multiple-decker complexes (triple-decker: TbTb, quadruple-decker: TbCdTb) to elucidate the relationship between magnetic dipole interactions and SMM properties. From X-ray crystallography performed with synchrotron radiation, the Tb-III-Tb-III distance in TbCdCdTb was determined to be 9.883 angstrom. From alternating current magnetic studies on TbCdCdTb, the activation energy for spin reversal (Delta) increased with an increase in the direct current magnetic field (H-dc). This behavior is similar to that of TbCdTb, although the increase in Delta for TbCdTb is smaller. On the other hand, for TbTb, which has shortest Tb-III-Tb-III distance, Delta did not depend on H-dc, indicating that there is a correlation between SMM properties and the strength of the Tb-III-Tb-III interactions. By comparing the Zeeman diagrams for multiple-decker complexes, we found that the Tb-III-Tb-III interactions affected the magnetic field regions where quantum tunnelling of the magnetization was active. The results obtained from Zeeman diagrams are consistent with the results obtained from the magnetic studies.