A series of di- and tetranuclear lanthanide complexes with the formulas [Dy2bmzch(tmhd)5 (CH3OH)]·CH3OH (1), [Dy2bmzch(dbm)4 (CH3O)(CH3OH)]·0.5CH3OH·0.5H2O (2), and Dy4bmzch(btfa)10 (3), where tmhd = 2,2,6,6-tetramethyl-3,5-heptanedionate, dbm = dibenzoylmethane, btfa = benzoyltrifluoroacetone, and bmzch = (Z)-N-[(E)-pyrimidin-2-ylmethylene]pyrimidine-2-carbohydrazonate, were structurally and magnetically characterized. More strikingly, although the nitrogen-enriched bridged ligand 3,6-di(pyrimidin-2-yl)-1,2,4,5-tetrazine (bmtz) was initially adopted, the structures of the complexes obtained indicated that bmtz underwent unprecedented asymmetric ring opening and generated a new ligand bmzch. Combined with different β-diketonates, di- and tetranuclear dysprosium complexes were constructed in which the structural patterns are very sensitive to the selected β-diketonates. In view of this, the bilateral and unilateral dinuclear Dy2 complexes 1 and 2 and tetranuclear Dy4 complex 3 were obtained by choosing different β-diketonates. Magnetic test results reveal that both complexes 1 and 3 showcase typical slow magnetic relaxation behavior without an external direct-current field and the effective energy barrier of the latter is almost twice that of the former, while complex 2 only displays in-field single-molecule-magnetic behavior. Also of note is that these are the first tetrazine-type dysprosium-based single-molecule-magnets undergoing in situ asymmetric ring-opening reaction of this ligand that are formed.