Self-assembly of polydentate Schiff base 2,6-diformyl-4-methylphenol di(benzoylhydrazone) (H3L), with dysprosium thiocyanate and sodium azide, affords two novel trinuclear triangular circular helicate dysprosium(III) complexes, [Dy-3(mu(3)-OCH3)(2)(HL)(3)(SCN)]center dot 4CH(3)OH center dot 2CH(3)CN center dot 2H(2)O (1) or [Dy-3(mu(3)-N-3)(mu(3)-OH)(H2L)(3)(SCN)(3)](SCN)center dot 3CH(3)OH center dot H2O (2), depending on the presence or absence of base. Single-crystal X-ray analyses show that two mu(3)-methoxy oxygens cap the Dy-3 triangle in complex 1 and that one mu(3)-OH and one mu(3)-N-3(-) cap the Dy-3 triangle of complex 2, representing the first example of a mu(3)-N-3(-)-capped lanthanide complex reported to date. Ac susceptibility measurements reveal that multiple relaxation processes and the onset of slow magnetization relaxation occur for complex 1 and 2, respectively. Theoretical calculations are required to elucidate the underlying mechanism; however, the different magnetic anisotropy of the respective structures, which is dictated by the coordination environment of Dy-III ions and structural parameters of the triangles, is mostly responsible for the distinctive relaxation dynamics observed.