Syntheses, Structures, and Magnetic Properties of Two Series of 3d-4f Heterometallic Coordination Polymers Derived from Pyrazine-2,3-dicarboxylic Acid.

Twenty 3d-4f heterometallic coordination polymers (CPs), namely, [Ln₂Co(2,3-pzdc)₄(H₂O)₆]·2H₂O [Ln = La (1), Pr (2), Nd (3), Sm (4), Eu (5), Gd (6), Tb (7)], [Ln₂Co(2,3-pzdc)₄-(H₂O)₄]·4H₂O [Ln = Dy (8), Er (9)], [Ln₂Cu(2,3-pzdc)₄(H₂O)6]·2H₂O [Ln = La (10), Pr (11), Nd (12), Sm (13), Eu (14), Gd (15), Tb (16)], [Dy₂Cu(2,3-pzdc)₄(H₂O)₄]·4H₂O (17), and [Ln₂Cu(2,3- pzdc)₄(H₂O)₄]·2H₂O [Ln = Er (18), Yb (19), Lu (20)], are synthesized successfully by the reactions of 2,3-H2pzdc with LnCl3·nH₂O/Ln(NO3)3·nH₂O and Co(NO3)2·3H₂O/CuCl₂·2H₂O under hydrothermal conditions. CPs 1-20 are isostructural, and only the coordination and interstitial water molecules, as well as the coordination numbers of Ln^III, are different from each other. In 1-20, the 2,3-pzdc anions link the Co^II/Cu^II and Ln^III ions by two coordination modes to form a three-dimensional (3D) framework with a 3,3,4,4-connected (4·62)2(42·62·82)- (6³)2(65·8)2 topology. CPs 6 and 7 manifest the weak ferromagnetic interactions between Co^II and Ln^III in the low-temperature range. CP 8 exhibits a field-induced slow magnetic relaxation behavior. CP 16 shows a magnetic transition between shortrange ferromagnetic ordering at 60 K and long-range ferromagnetic ordering below 26 K. CP 17 displays field-induced singlemolecule magnet (SMM) behavior, with a U_eff value of 102.4 K. [ABSTRACT FROM AUTHOR]