It is crucial to understand and elucidate the self-assembly mechanism in solution systems for the construction of Dy-III-based single-molecule magnets (SMMs). Herein, through fine-tuning of the anion and solvent, we prepared three nine-coordinate mononuclear dysprosium compounds, [Dy(2,3'-pcad)(NO3)(2)(CH3OH)(2)] (1), [Dy(2,3'-Hpcad)(2)(H2O)(3)]center dot 3Cl center dot 5H(2)O (2), and [Dy(2,3'-pcad)(NO3)(H2O)(4)]center dot NO3 center dot H2O (3) [2,3'-Hpcad = N-3-(2-pyridoyl)-3-pyridinecarboxamidrazone]. The reactions of formation for 1-3 are in situ thermodynamically monitored by isothermal titration calorirnetry. Magnetic data analysis reveals that 2 shows SMM behavior under a zero direct-current (dc) field, whereas 1 and 3 exhibit distinct slow magnetic relaxation processes upon a 1200 Oe dc field. To deeply understand the different magnetic behaviors, the magnetic anisotropy of 1-3 has been systematically studied by ab initio calculations, which is consistent with the experimental observations. Moreover, the semiconductor behaviors of 1-3 have been investigated by experimental measurements of UV-vis spectroscopy.