Slow magnetic relaxation of a three-dimensional metal–organic framework featuring a unique dysprosium(iii) oxalate layer

Abstract

A novel lanthanide metal–organic framework was yielded by a hydrothermal reaction of 5-chloro-6-hydroxypyridine-3-carboxylic acid (5-Cl-6-HOPy-3-CO₂H) and Dy₂O₃ in the presence of oxalic acid [H₂(OX)], namely, {[Dy₂(1H-5-Cl-6-Opy-3-CO₂)₂(OX)₂(H₂O)]·2H₂O}_∞ (1, 1H-5-Cl-6-Opy-3-CO₂⁻ = 1-hydro-5-chloro-6-oxopyridine-3-carboxylate, which was formed by the autoisomerization of single deprotonated 1H-5-Cl-6-HOpy-3-CO₂⁻ anion). The dysprosium(III) ions are bridged by oxalate anions to construct an interesting 4-connected layer network with a Schälfli topology symbol of (3²·5²) (3·5³), such layers are connected with each other by the 1H-5-Cl-6-HOpy-3-CO₂⁻ anions to form a three-dimensional framework. Magnetic investigations indicated that 1 is a field-induced single-molecule magnet, displaying two-step thermal magnetic relaxation, with an effective thermal barrier of 37.6 K. Surprisingly, a zigzag chain-like gadolinium(III) complex, {[Gd(1H-5-Cl-6-Opy-3-CO₂)₂(OX)_0.5(H₂O)₃]·6H₂O}_∞ (2), was isolated using Gd₂O₃ instead of Dy₂O₃ owing to the lanthanide contraction effect. Notebaly, a unique F-shaped (H₂O)₆ supramolecular aggregate exists in the crystal structure of 2.