Two Dy(III) single-ion magnets with a trigonal dodecahedron (D-2d) for 1 and an approximately square-antiprismatic (SAP, D-4d) N2O6 coordination environment for 2,, formulated as [Dy(Phen)(tfmb)(3)] (1) and [Dy(Phen)-(tfmb)(3)]-0.5(1,4-dioxane),(2) (tfmb = 4,4,4-trifluoro-1-(4-methylphenyl)-1,3-butanedione, Phen = 1,10-phenanthroline), were obtained. Therein, complex 1 was transformed to. 2 in 1,4-dioxane solution: Structural analysis shows that complexes 1 and 2 have differing local symmetry of Dy(III) ions. Magnetic studies indicate that the barrier heights (Delta E/k(B)) of 1 and 2 are 63.56 and 102.82 K under zero dc field as well as 118.50 and 164.55 K under 1200 Oe do field, respectively. Based on the frequency dependencies of the ac susceptibilities, the effective barriers (Delta E/k(B)) and the pre-exponential factors (tau(0)) are 67:05 K and 4.57 x 10(-6) s for 1 and 95.88 K and 2.39 x 10(-7) s for 2 under zero dc field. The present work illustrates that guest-determined notable structure change results in different barrier heights.