Using a heterometallic approach the synthesis, structures, and magnetic properties are reported for the complexes [Ln(2)(III)Co(2)(III)(Ome)(2)(teaH)(2)(O2CPh)(4)(MeOH)(4)](NO3)(2)(MeOH)-Me-center dot center dot H2O {Ln = Gd (1a), Tb (2a), and Dy (3a)} and [Ln(2)(III)Co(2)(III)(OMe)(2)(teaH)(2)(O2CPh)(4)(MeOH)(2)-(NO3)(2)]center dot MeOH center dot H2O {Ln = Gd (1b), Tb (2b), and Dy (3b)}. Both compounds for the respective lanthanide ions are found to be isolated within the same crystal. Each Ln(III) dinuclear unit is incorporated within a diamagnetic Co-III/organic ligand backbone utilizing triethanolamine and benzoic acid as bridging ligands. Magnetic studies reveal an absence of any observable coupling interaction for the Gd case. The Dy analogue displays single molecule magnet (SMM) behavior with a large energy barrier to magnetization reversal of 88.8 K, and the quantum tunneling of the magnetization (QTM) is effectively suppressed because of the nonmagnetic exchange ground state of the molecule. Dilution of the Dy complex into an isostructural diamagnetic yttrium matrix allowed us to determine aspects of the relaxation mechanism within the system.