Low‐Dimensional Carboxylate‐Bridged Gd^III Complexes for Magnetic Refrigeration

Abstract

Four carboxylate-bridged Gd(III) complexes (1-4) with 1D/2D structures have been synthesized by using the hydrothermal reaction of Gd2O3 with various carboxylate ligands. Compounds 1 and 2 contained the same [2n] Gd(III)-OH ladders, but with different crystallographically independent Gd(III) ions, whilst the structures of compounds 3 and 4 were composed of [Gd4(μ3-OH)2(piv)8(H2O)2](2+) units and 1D ladder Gd(III) chains, respectively. Antiferromagnetic interactions occurred in compounds 1-3, owing to their small Gd-O-Gd angles, whereas ferromagnetic coupling occurred in compound 4, in which the Gd-O-Gd angles were larger. These complexes exhibited a distinct magnetocaloric effect (MCE), which was affected by their different magnetic densities and exchange interactions. Among these compounds, complex 4 presented the largest MCE (-ΔS(m)(max)=43.6 J kg(-1) K(-1)), the lowest M(w)/N(Gd) ratio (the highest magnetic density), and weak ferromagnetic coupling. Therefore, a lower M(w)/N(Gd) ratio and weaker exchange interactions (a smaller absolute value of θ) between Gd(III) ions resulted in a larger MCE for the Gd(III) complexes.

Coordination‐Cluster‐Based Molecular Magnetic Refrigerants

“…Among Ln ions, the Gd III ion is usually chosen to construct molecular magnetic refrigerants; this may be attributes to the Gd III ion having a large single‐ion spin ( S =7/2) and negligible anisotropy, resulting from the lack of orbital contribution. Furthermore, the coupled interactions between Gd III ions are always weak, which is fit for acquiring a large MCE to work as an ideal molecular magnetic refrigerant (Tables and ) 25,27,39–57…”

“…Compared with discrete 4f‐metal‐cluster‐based molecular magnetic refrigerants,39–50 the numbers and types of pure 4f‐metal‐cluster‐based extended structures serving as molecular magnetic refrigerants are greater (Table );51–67 this may be because Ln ions possess various coordinated geometries and high coordination numbers, as well as minimal stereochemical preferences.…”

Counterion‐Directed Assembly of Praseodymium(III) Compounds based on the Flexible Ligand 5‐Aminotetrazole‐1‐propionic Acid (Hatzp)

“…While choosing metal ions, it is recognized that lanthanide coordination compounds stems have diverse structures, [4,[6][7][8] along with potential applications as advanced functional materials, in the field of luminescence, catalysis, gas storage and so on. [9][10][11][12] In addition, many factors, such as counterions, pH value, solvent system, temperature are likely to influence the eventual structures of the targeted molecules and add to the novelty of the structures.…”

Layered gadolinium hydroxides for low-temperature magnetic cooling

“… 13 , 14 In order to maximize the MCE, weak superexchange interactions in materials having high density of magnetic centres are highly desired; along this front the use of geometric spin frustration, like 2D triangular AF lattices, gives rise to regions of high density of states. 15 Thus, the highly dense, almost hexagonal, 2D lattice of lanthanide cations bridged by hydroxide ligands present in LLHs, together with its low diamagnetic content, is a promising alternative to the list of extended materials with short bridges reported so far with MCE, which includes, among others, formates, 16 , 17 phosphates 18 and carbonates, 19 being [Gd(HCOO)(OAc) 2 (H 2 O) 2 ], 20 [Gd(C 4 O 4 )(OH)(H 2 O) 4 ] n , 21 [Gd(C 2 O 4 )(H 2 O) 3 Cl], 22 and [Gd(cit)(H 2 O)], 23 the only 2D structures. Importantly, the ability of LLHs to be delaminated 3 provides additional advantages for rapid heat dissipation, as the delaminated material could be placed on a substrate thus enhancing heat transportation.…”