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 LnIII, are different from each other. In 1–20, the 2,3‐pzdc anions link the CoII/CuII and LnIII 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 CoII and LnIII in the low‐temperature range. CP 8 exhibits a field‐induced slow magnetic relaxation behavior. CP 16 shows a magnetic transition between short‐range ferromagnetic ordering at 60 K and long‐range ferromagnetic ordering below 26 K. CP 17 displays field‐induced single‐molecule magnet (SMM) behavior, with a Ueff value of 102.4 K.
