Fixing CO2 from the air to assemble Dy8 zero-field single-molecule magnet and Gd8 magnetocaloric molecular material

Abstract

Assembling Ln(III) clusters by capturing and fixing CO₂ from the air is a unique and eco-friendly approach to multinuclear single-molecule magnets and magnetocaloric molecular materialss. However, the conditions or factors required to facilitate this process are still unclear. When synthesizing Ln(III) complexes using a hydrazone Schiff base (H₂L_schiff) condensed from o-vanillin and 3-aminopyrazine-2-carbohydrazide, LiOH plays a decisive role in the formation of [Dy₈(L_schiff)₈(CO₃)₄(H₂O)₈]·4DMA·4H₂O (1) by capturing and fixing CO₂ from the air, as using Et₃N under the same conditions only yields a normal product [Dy₂(L_schiff)₂(DMA)₃(H₂O)₃](CF₃SO₃)₂·3DMA·H₂O (2). Either 1 or 2 exhibits intramolecular ferromagnetic interactions, and both perform as good zero-field single-molecule magnets. Furthermore, an analog of 1, complex [Gd₈(L_schiff)₈(CO₃)₄(H₂O)₈]·4DMA·4H₂O (3) was obtained using a synthesis method similar to that of 1, exhibiting a good magnetocaloric effect. Therefore, choosing the appropriate alkali is a necessary prerequisite for automatically fixing CO₂ from the air to assemble polynuclear Ln(III) SMMs and magnetocaloric molecular materials.