An organometallic building block strategy was employed to investigate the magnetic properties of a Ln(III) organometallic single-ion magnet (SIM) and subsequent single-molecule magnet (SMM) after coupling two of the monomeric units. New homoleptic (DyCOT2)-C-III '' and Ln(2)(III)COT(3)'' (Ln = Gd, Dy) complexes have been synthesized. DFT calculations of the bimetallic Dy-III complex indicate strong metal ligand covalency and uneven donation to the Dy-III ions by the terminal and internal COT ''(2-) (cyclooctatetraenide) rings that correlate with the respective bond distances. Interestingly, the studies also point to a weak covalent interaction between the metal centers, despite a large separation. The ac susceptibility data indicates that both (DyCOT2)-C-III '' and (Dy2COT3)-C-III '' act as an SIM and an SMM, respectively, with complex multiple relaxation mechanisms. Ab initio calculations reveal the direction of the magnetic anisotropic axis is not perpendicular to the planar COT '' rings for both (DyCOT2)-C-III '' and (Dy2COT3)-C-III '' complexes due to the presence of trimethylsilyl groups on the COT '' rings. If these bulky groups are removed, the calculations predict reorientation of the anisotropic axis can be achieved.