From dinuclear to two-dimensional Dy(iii) complexes: single crystal–single crystal transformation and single-molecule magnetic behavior

Abstract

Regulating the magnetic properties through structural transformation and multifunctional magnetic bistable materials attracts increasing interest in the research area of molecular magnets. Herein, we have obtained a two-dimensional Dy³⁺ metal–organic framework {[Dy₂(H₂L)₂(H₂O)(CH₃OH)](ClO₄)₂·H₂O}_n (1) and three dinuclear Dy₂ complexes 2–4 based on the new diacylhydrazone ligand H₄L. The structural analyses show that the Dy³⁺ ions have a coordination geometry of Hula-hoop (C_2v) and are coordinated by one or two trans phenoxy groups of the ligand H₃L⁻ or H₂L²⁻ with Dy–O_phenoxy bond distances in the range of 2.175–2.252 Å. The 2D complex (1) exhibits excellent thermal stability, a broad ligand-based fluorescence emission band and selective adsorption capacity for rhodamine B. The dinuclear Dy₂ complexes (2–4) undergo consecutive single-crystal to single-crystal transformation in the mother liquor. Alternating-current (ac) susceptibility measurements reveal that 1–3 display typical single-molecule magnetic properties with effective energy barriers of 91.6 K, 106.3 K and 91.9 K, respectively. Ab initio calculations evidence good magnetic anisotropy with the calculated energy of the first excited state as high as 392.5 K (272.8 cm⁻¹) for 1, 257.5 K (179.0 cm⁻¹) for 2 and 250.2 K (173.9 cm⁻¹) for 3, respectively.