Separation of o-vanillin hydrazone isomers constructing Dy2 single-molecule magnet and 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)acetateethyl 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 spectra and SC-XRD analysis. Upon irradiation at 365 nm, HL-Z converted unidirectionally into HL-E with the E/Z ratio of 35:65. This isomerization process is thermally irreversible, i.e. HL-E retaining its configuration at heating. The self-assembly of Dy(SCN)3•6H2O with HL-E or HL-Z affords two distinct complexes, one is 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 Ueff of ca. 39 K under 400 Oe dc field while Dy3 exhibits typical single-molecule toroic (SMT) properties.