Structure and Magnetocaloric Effect of Two Kinds of Ln–Mn II Heterometallic Coordination Polymers Produced by Fractional Crystallization

Two series of Ln–Mn II heterometallic coordination polymers (HCPs), [Ln 8 Mn 3 (µ 3 ‐OH) 8 (IN) 14 Cl 6 (H 2 O) 16 ] n (OH) 2 n · 5 n DMF · 8 n H 2 O {Ln = Gd ( 1 ); Ln = Dy ( 2 )} and [Ln 2 Mn(IN) 6 Cl 2 (H 2 O) 4 ] n · 2 n DMF {Ln = Gd ( 3 ); Ln = Dy ( 4 ), IN = isonicotinic cation}, were synthesized by using fractional crystallization and structurally characterized. Polymers 1 and 2 are isostructural and form a 2D double layer of [Ln 4 (µ 3 ‐OH) 4 ] cubane and Mn(IN) 4 Cl 2 units, whereas 3 and 4 are isomorphic and form a four‐connected cds ‐type 3D framework assembled from paddle‐wheel binuclear Ln 2 (COO) 4 units and planar Mn(IN) 4 Cl 2 units. Polymers 1 – 4 exhibited large magnetic entropy changes of 42.0, 16.7, 31.5, and 16.6 J kg –1  K –1 , respectively (Δ H = 7 T). In addition, compounds 2 and 4 displayed field‐induced slow magnetic relaxation behavior.