A coordination compound with the composition CoLCl 2 ·H 2 O ( L = bis-condensation product of diacetyl and 2-hydrazinyl-4,6-dimethylpyrimidine) was synthesized, in which the Co( ii ) ion was hexacoordinated. Under applied DC fields, this compound exhibited single-ion magnet behavior. Two relaxation processes were observed when increasing the applied magnetic field from 1000 to 3200 Oe. The first relaxation (high-frequency) was observed both at 1000 Oe and 3200 Oe, while the second relaxation was only registered under a field of 3200 Oe at low frequencies (<1 Hz) and low temperatures (<5 K). Modeling of the magnetic DC properties using the Griffith Hamiltonian accompanied by quantum chemical calculations revealed easy-axis-type magnetic anisotropy with weak rhombic contributions. This study presents the novel hexacoordinated Co( ii ) mononuclear complex with SIM behavior.