Two cobalt complexes with similar structures were synthesized using quinoline-2-carboxylic acid (HL) as the ligand. Both complexes are six-coordinated in antitriangular prism coordination geometries. There are one and four molecule units per cell for 1 and 2, respectively, with nearest Co-Co distances of 7.129 and 5.855 angstrom, respectively, which lead to their intermolecular interactions zj'. Both complexes are field-induced single-ion magnets. Complex 1 shows single slow relaxation under H-dc = 1.5 kOe attributed to the moment reversal, while complex 2 shows double slow relaxation resulting from intermolecular dipolar interaction and moment reversal, respectively.