Di- and Tetranuclear Dysprosium Single-Molecule Magnets Bridged by Unprecedentedly Disassembled Nitrogen-Enriched Tetrazine Derivatives.

A series of di- and tetranuclear lanthanide complexes with the formulas [Dy 2 bmzch(tmhd) 5 (CH 3 OH)]·CH 3 OH ( 1 ), [Dy 2 bmzch(dbm) 4 (CH 3 O)(CH 3 OH)]·0.5CH 3 OH·0.5H 2 O ( 2 ), and Dy 4 bmzch(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.