Separation of o-vanillin hydrazone isomers constructing a Dy2 single-molecule magnet and a Dy3 single-molecule toroic

Abstract

The elegant chemical modification of o-vanillin hydrazide simultaneously produces two hydrazone-based Z/E-isomers, HL-Z and HL-E, where HL-Z = ethyl (Z)-2-(2-(2-hydroxy-3-methoxybenzoyl)hydrazono)-2-(pyridin-2-yl)acetate and HL-E = (E)-2-(2-(2-hydroxy-3-methoxybenzoyl)hydrazono)-2-(pyridin-2-yl)acetate, which can be separated by column chromatography. Their structures are determined by NMR spectroscopy and SC-XRD analysis. Upon irradiation at 365 nm, HL-Z converted unidirectionally into HL-E with an E/Z ratio of 35 : 65. This isomerization process is thermally irreversible, i.e., HL-E retains its configuration on heating. The self-assembly of Dy(SCN)₃·6H₂O with HL-E or HL-Z affords two distinct complexes, one is a Dy(III)-based triangle Dy₃ ([Dy₃(μ₃-OH)₂(L-E)₃(EtOH)₂(SCN)₄]) and the other is dinuclear Dy₂ ([Dy₂(HL-Z)(L-Z)₂(SCN)₂]). Magnetic investigations reveal that Dy₂ behaves as a field-induced single-molecule magnet (SMM) with a U_eff of ca. 39 K under a 400 Oe dc field, while Dy₃ exhibits typical single-molecule toroic (SMT) properties.