Three novel alkali-lanthanide heterometal-organic frameworks, namely, [K5Ln5(pztc)5(H2O) 19]·7H2O [Ln = Dy (1), Ho (2), and Yb (3); H 4pztc = 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. © 2014 American Chemical Society.
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