Magnetocaloric Effect of Two Isostructural Heterometallic Organic Frameworks Based on {MII GdIII 2 } Clusters (MII =Mn, Ni).

Abstract

Two isostructural heterometallic coordination polymers (HCPs) based on {MII GdIII 2 } clusters (MII =Mn and Ni) have been obtained from the conventional one-pot self-assembly of GdIII ions and H4 abtc ligands (H4 abtc=3,3',5,5'-azobenzenetetracarboxylic acid) with corresponding transition-metal ions in mixed N,N-dimethylformamide (DMF)/H2 O solvents. The formulas are expressed as {[NH2 (CH3 )2 ]2 [MII GdIII 2 (HCOO)2 (abtc)2 ]}n (MII =Mn for 1 and Ni for 2). The common features of both HCPs are that two GdIII ions and one MII ion interconnected through abtc4- ligands present "hourglass"-type {MII GdIII 2 } clusters, which are further linked by HCOO- and abtc4- ligands to produce 3D (4,4,10)-connected topological frameworks. Magnetic results reveal that both 1 and 2 possess remarkable magnetocaloric effects (MCE) with maximum -ΔSm values of 31.9 and 29.5 J kg-1 K-1 at 3.0 K for an applied field of 70 kOe, respectively. Furthermore, the skeletons of two HCPs were stable up to at least 310 °C as supported by thermogravimetric (TG) analyses and in situ variable-temperature powder X-ray diffraction (PXRD) patterns.