Caprylic hydrazide ligands are ideal ligands for the synthesis of novel polynuclear metal complexes, because they contain many N,O coordination atoms with a strong coordination ability, abundant hydrogen-bond donors, acceptors, and large conjugation systems. Here, we successfully obtained one dodecanuclear cobalt nanocluster [(Co8Co4III)-Co-II(L1)(4)(Py)(12)(CH3OH)(4)(CH3COO)(4)]center dot(CH3OH)(13) (1) and one octadecanuclear cobalt nanocluster [Co-18(II)(L2)(6)(Py)(48)]center dot(DMF)(5)center dot(CH3OH)(8) (2) by using H(6)L1 and H(6)L2 ligands, respectively (Py = pyridine; DMF = dimethylformamide). The cyclic cobalt nanocluster 1 can be regarded as two pentanuclear cobalt units (Co-5(N-N)(4)) connected by two cobalt ions, and it is a mixed-valent Co nanocluster. Every H(6)L1 ligand contains 10 coordination atoms, each of which coordinates with the Co ions. And every two H(6)L1 ligands form a structure similar to a handshake. The abnormal cylindrical cobalt nanocluster 2 can be regarded six trinuclear cobalt units Co-3(N-N)(2) connected by one L2(6-) ligand, and every L2(6-) ligand splits the structure on both sides, with a twisted cyclohexane in the middle. AC magnetic susceptibilities show that nanocluster 1 exhibits no frequency-dependent behavior, but nanocluster 2 shows an obviously single-molecule magnetic behavior, and the relaxation process of the energy barrier is 20.4 K.