Novel 3D Alkali–Lanthanide Heterometal–Organic Frameworks with Pyrazine-2,3,5,6-tetracarboxylic Acid: Synthesis, Structure, and Magnetism

Three novel alkali–lanthanide heterometal–organic frameworks, namely, [K₅Ln₅­(pztc)₅­(H₂O)₁₉]·​7H₂O [Ln = Dy (<b>1</b>), Ho (<b>2</b>), and Yb (<b>3</b>); H₄pztc = pyrazine-2,3,5,6-tetracarboxylic acid], have been facilely synthesized. X-ray crystallographic analysis reveals that complexes <b>1</b>–<b>3</b> are isostructural, featuring unique 3D open frameworks, which possess a rare (4,8)-connected net with the Schläfli symbol of (4¹⁵·6¹²·8)­(4⁵·6)₂. The 3D coordination framework involves a ladder-like square column structure by pztc^4– ligands bridging metal ions, exhibiting 1D channels along the <i>b</i> axis. The magnetic analysis suggests that complexes <b>1</b> and <b>3</b> exhibit frequency-dependent out-of-phase signals in alternating current magnetic susceptibility measurements, indicating their slow magnetic relaxation characteristics. It is the first report of slow magnetic relaxation behavior existing in Yb³⁺-based HMOFs