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 Å. From alternating current magnetic studies on TbCdCdTb, the activation energy for spin reversal (Δ) increased with an increase in the direct current magnetic field (Hdc). This behavior is similar to that of TbCdTb, although the increase in Δ for TbCdTb is smaller. On the other hand, for TbTb, which has shortest Tb(III)-Tb(III) distance, Δ did not depend on Hdc, 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.