摘要

Molecular refrigeration is found to be of great interest in the field of coordination chemistry, and Gd~(III) ion based complexes are particularly attractive, as they exhibit a large magneto-caloric effect (MCE). As the magnetic coupling in Gd~(III) clusters is difficult to control, other avenues to enhance the MCE values have been explored and incorporation of 3d metal ions in the cluster aggregation with Gd~(III) yielding {3d-Gd} clusters are targeted. Among the transition-metal ions, the Cu~(II) ion is particularly attractive, as it does not possess any anisotropy, and in this regard, several di- and polynuclear {Cu-Gd} clusters are reported to yield attractive MCE values. While the role of near-neighbor {Cu-Gd} interactions in the MCE has been explored in detail, how the next-nearest-neighbor interaction influences the MCE has not been explored. To explore the importance of next-nearest-neighbor (1,3) {Cu-Cu} interaction, we have undertaken detailed density functional studies on five trinuclear {Cu~(II)-Gd~(III)-Cu~(II)} complexes that are reported in the literature. In addition, we also report the synthesis and magnetic and EPR studies of a novel complex [(CuSALen)_(2)Gd(NO_(3))_(3)] ( 6 ; where SALen is N , N ′-ethylenebis(salicylaldiminato)). Both magnetic and EPR studies reveal an S = 9/2 ground state for 6 with a very small zero-field splitting parameter (+0.01 cm~(–1)), which aid in the achievement of a large MCE value for this molecule. Magnetization data collected for 6 yield a magnetic entropy change (?Δ S _(m)) of 17 J kg~(–1) K~(–1) at 3.5 K by employing a 7 T magnetic field. Our calculations on all six complexes reveal that {Cu-Gd} exchange is ferromagnetic in nature, while the next-nearest-neighbor {Cu-Cu} exchange is found to vary from a weak ferromagnetic to a moderate antiferromagnetic interaction. In all of the cases studied, simulated susceptibility data are in excellent agreement with the experimental data, offering confidence in the comp