A series of three beta-diketone mononuclear dysprosium complexes, namely, Dy(TFI)(3)(H2O)(2) (1), Dy(TFI)(3)(bpy) (2), and [Dy(TFI)(3)(Phen)]center dot 0.02CHCl(3) (3) (TFI = 2-(2,2,2-trifluoroethyl)-1-indone, bpy = 2,2'-bipyridine, phen = 1,10-phenanthroline) have been designed and synthesized. Crystal structure analysis reveals that complexes 1-3 have haveisomorphic structures in which the central Dy(III) ion is eight-coordinated by six oxygen atoms from three TFI ligands and two O/N atoms from auxiliary ligands, forming a distorted bicapped trigonal prismatic geometry for 1, a distorted dodecahedral geometry for 2, and a distorted square antiprismatic geometry for 3, respectively. Magnetic studies indicate that complex 2 with D-2d symmetry and 3 with D-4d symmetry exhibit slow magnetic relaxation with barrier heights (U-eff/k(B)) of 48.8 K for 2 and 57.9 K for 3. Strikingly, the relaxation time (tau) of 0.0258 s for 3 is about 20 times that for 2, which is presumably associated with larger rotation of the SAP surroundings for 3. Further, complexes 2 and 3 exhibit essential magnetic hysteresis loops at 1.8 K. These extend the recent reports of the single-ion magnets (SIMs) of beta-diketone mononuclear dysprosium complexes.