Magnetocaloric Effect of Two Isostructural Heterometallic Organic Frameworks Based on {MIIGd2III} Clusters (MII=Mn, Ni)

Two isostructural heterometallic coordination polymers (HCPs) based on {(MGd2III)-Gd-II} clusters (M-II = Mn and Ni) have been obtained from the conventional one-pot self-assembly of Gd-III ions and H(4)abtc ligands (H(4)abtc= 3,3',5,5'-azobenzenetetracarboxylic acid) with corresponding transition-metal ions in mixed N,N-dimethylformamide (DMF)/H2O solvents. The formulas are expressed as {[NH2(CH3)(2)](2)[(MGd2III)-Gd-II(HCOO)(2)(abtc)(2)]}(n) (M-II = Mn for 1 and Ni for 2). The common features of both HCPs are that two Gd-III ions and one M-II ion interconnected through abtc(4-) ligands present hourglass-type {(MGd2III)-Gd-II} clusters, which are further linked by HCOO- and abtc(4-) 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 -Delta S-m values of 31.9 and 29.5 Jkg(-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 degrees C as supported by thermogravimetric (TG) analyses and in situ variable-temperature powder X-ray diffraction (PXRD) patterns.