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 (1), Ho (2), and Yb (3); H4pztc = pyrazine-2,3,5,6-tetracarboxylic acid], have been facilely synthesized. X-ray crystallographic analysis reveals that complexes 1–3 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 pztc4– ligands bridging metal ions, exhibiting 1D channels along the b axis. The magnetic analysis suggests that complexes 1 and 3 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.