Achieving Magnetic Refrigerants with Large Magnetic Entropy Changes and Low Magnetic Ordering Temperatures.

Adiabatic demagnetization refrigeration (ADR) is a promising cooling technology with high efficiency and exceptional stability in achieving ultralow temperatures, playing an indispensable role at the forefront of fundamental and applied science. However, a significant challenge for ADR is that existing magnetic refrigerants struggle to concurrently achieve low magnetic ordering temperatures (T0) and substantial magnetic entropy changes (-ΔSm) at ultralow temperatures. In this work, we propose the combination of Gd3+ and Yb3+ to effectively regulate both -ΔSm and T0 in ultralow temperatures. Notably, the -ΔSm values for Gd0.1Yb0.9F3 (1) and Gd0.3Yb0.7F3 (2) in the 0.4-1.0 K range exceed those of all previously reported magnetic refrigerants within this temperature interval, positioning them as the most efficient magnetic refrigerants for the third stage to date. Although the -ΔSm values for Gd0.5Yb0.5F3 (3) in 1-4 K are less than those of the leading magnetic refrigerant Gd(OH)F2, the -ΔSm values for Gd0.7Yb0.3F3 (4) in 1-4 K at 2 T surpass those of all magnetic refrigerants previously documented within the same temperature range, making it the superior magnetic refrigerant for the fourth stage identified thus far.

Accurate Prediction of the Magnetic Ordering Temperature of Ultralow-Temperature Magnetic Refrigerants.

Adiabatic demagnetization refrigeration is known to be the only cryogenic refrigeration technology that can achieve ultralow temperatures (≪1 K) at gravity-free conditions. The key indexes to evaluate the performance of magnetic refrigerants are their magnetic entropy changes (-ΔSm) and magnetic ordering temperature (T0). Although, based on the factors affecting the -ΔSm of magnetic refrigerants, one has been able to judge if a magnetic refrigerant has a large -ΔSm, how to accurately predict their T0 remains a huge challenge due to the fact that the T0 of magnetic refrigerants is related to not only magnetic exchange but also single-ion anisotropy and magnetic dipole interaction. Here, we, taking GdCO3F (1), Gd(HCOO)F2, Gd2(SO4)3·8H2O, GdF3, Gd(HCOO)3 and Gd(OH)3 as examples, demonstrate that the T0 of magnetic refrigerants with very weak magnetic interactions and small anisotropy can be accurately predicted by integrating mean-field approximation with quantum Monte Carlo simulations, providing an effective method for predicting the T0 of ultralow-temperature magnetic refrigerants. Thus, the present work lays a solid foundation for the rational design and preparation of ultralow-temperature magnetic refrigerants in the future.

pH-Driven Rotational Configuration of Keggin-Fe13 Clusters and Their Transformations.

Keggin-Fe13 clusters are considered foundational building blocks or prenucleation precursors of ferrihydrite. Understanding the factors that influence the rotational configuration of these clusters, and their transformations in water, is vital for comprehending the formation mechanism of ferrihydrite. Here, we report syntheses and crystal structures of four lanthanide-iron-oxo clusters, namely, [Dy6Fe13(Gly)12(µ2-OH)6(µ3-OH)18(µ4-O)4(H2O)17]·13ClO4·19H2O (1), [Dy6Fe13(Gly)12(µ3-OH)24(µ4-O)4(H2O)18]·13ClO4·14H2O (2), [Pr8Fe34(Gly)24(µ3-OH)28(µ3-O)30(µ4-O)4(H2O)30]·6ClO4·20H2O (3), and [Pr6Fe13(Gly)12(µ3-OH)24(µ4-O)4(H2O)18]·13ClO4·22H2O (4, Gly = glycine). Single-crystal analyses reveal that 1 has a ß-Keggin-Fe13 cluster, marking the first documented instance of such a cluster to date. Conversely, both 2 and 4 contain an α-Keggin-Fe13 cluster, while 3 is characterized by four hexavacant ε-Keggin-Fe13 clusters. Magnetic property investigations of 1 and 2 show that 2 exhibits ferromagnetic interactions, while 1 exhibits antiferromagnetic interactions. An exploration of the synthetic conditions for 1 and 2 indicates that a higher pH promotes the formation of α-Keggin-Fe13 clusters, while a lower pH favors ß-Keggin-Fe13 clusters. A detailed analysis of the transition from 3 to 4 emphasizes that lacunary Keggin-Fe13 clusters can morph into Keggin-Fe13 clusters with a decrease in pH, accompanied by a significant change in their rotational configuration.

A Doped Lanthanide-Based Coordination Polymer Exhibiting High Relative Sensitivity to Ratiometric Luminescent Thermometers at 440 K.

Ratiometric luminescent thermometers with excellent performance often require the luminescent materials to possess high thermal stability and relative sensitivity (Sr). However, such luminescent materials are very rare, especially in physiological (298-323 K) and high-temperature (>373 K) regions. Here we report the synthesis and luminescent property of [Tb0.995Eu0.005(pfbz)2(phen)Cl] (3), which not only exhibits high Sr in physiological temperature but also has a Sr up to 7.47% K-1 at 440 K, the largest Sr at 440 K in known lanthanide-based coordination compound luminescent materials.

A Gd-based borate-carbonate framework exhibiting a large magnetocaloric effect at a low magnetic field.

A 3D borate-carbonate framework, GdB(OH)4CO3 (1), was synthesized. Magnetic study reveals that its MCE is up to 33.5 J kg-1 K-1 at 2 K and 2 T, due to the introduction of a long magnetic exchange path of Gd-O-B-O-Gd leading to 1 exhibiting weak magnetic interaction.

Magnetocaloric Effect and Thermal Conductivity of a 3D Coordination Polymer of [Gd(HCOO)(C2O4)]n.

A 3D coordination polymer, [Gd(HCOO)(C2O4)]n was prepared. Its magnetocaloric effect (MCE) (32.7 J K-1 kg-1 at 2 K and 2 T) is significantly larger than that of commercial Gd3Ga5O12 (GGG) (14.6 J kg-1 K-1 at 2 K and 2 T), while its thermal conductivity (9.9 W m-1 K-1 at 3 K) is comparable to that of the commercial GGG (about 10 W m-1 K-1 at 3 K).

Lanthanide-Titanium Oxo Clusters as the Luminescence Sensor for Nitrobenzene Detection.

A luminescent lanthanide-titanium oxo cluster of Eu2Ti4(µ2-O)2(µ3-O)4(phen)2(tbza)10·4CH3CN (1, Eu2Ti4-phen-tbza, phen = 1,10-phenanthroline, Htbza = 4-tert-butylbenzoic acid) was prepared through the reaction of phen, Htbza, Eu(Ac)3·xH2O, and Ti(OiPr)4 in acetonitrile. Its overall absolute quantum yield is 65.4% in solid state and 30.2% in CH2Cl2, and the detection limit of 1 for the nitrobenzene (NB) is 10.5 ppb. When the concentration of NB is 40 ppm, the luminescence quenching of 1 can be observed with the naked eye. Time-resolved excited-state decay measurements indicate that the static quenching process is dominated across the NB concentration of 0-9 ppm. The distinguishable shifts in 1H NMR spectra of NB together with 1 confirm the presence of π···π stacking interactions between the organic ligands in 1 and the NB, which plays a key contribution for the quenching of luminescence.