Three Gd-based magnetic refrigerant materials with high magnetic entropy: From di-nuclearity to hexa-nuclearity to octa-nuclearity

Magnetocaloric effect (MCE) is one of the most promising features of molecular-based magnetic materials. We reported three Gd-based magnetic refrigerant materials, namely, Gd2(L)(NO3)(H2O)‧CH3CN‧H2O (1, H2L = (Z)-N-[(1E)-(2-hydroxy-3-methphenyl)methylidene]pyrazine-2-carbohydrazonic acid), {Gd6(L)6(CO3)2(CH3OH)2(H2O)3Cl}Cl‧4CH3CN (2), and Gd8(L)8(CO3)4(H2O)8‧2H2O (3). Complex 1 contains two GdIII ions linked by two η 2:η 1:η 1:η 1:μ 2-L2- ligands, which are seven-coordinated in a capped trigonal prism, and complex 2 possesses six GdIII ions, contributing to a triangular prism configuration. For complex 3, eight GdIII ions form a distorted cube arrangement. Moreover, the large values of magnetic entropy in the three complexes prove to be excellent candidates as cryogenic magnetic coolants.

Magnetic cooling: a molecular perspective

The magnetocaloriceffect is considered as an energy-efficient and environmentally friendly technique which can take cooling technology to the next level. Apart from its commercial application at room temperature, magnetic refrigeration is an up-and-coming solution for the cryogenic regime, especially as an alternative to He³ systems. Molecular magnets reveal advantageous features for ultra-low cooling which are competitive with intermetallic and lanthanide alloys. Here, we present a guide to the current status of magnetocaloric effect research of molecular magnets with a theoretical background focused on the inverse magnetocaloric effect and an overview of recent results and developments, including the rotating magnetocaloric effect.

A magnetocaloric glass from an ionic-liquid gadolinium complex

[Gd 5 (L) 16 (H 2 O) 8 ](Tf 2 N) 15 was obtained from reaction of Gd 2 O 3 with 1-carboxymethyl-3-ethylimidazolium chloride (LHCl). The material was found to be an ionic liquid that freezes to glassy state on cooling to -30°C. Variable-temperature magnetic studies reveal the presence of weak magnetic intramolecular interactions in the glass. Isothermal variable-field magnetization demonstrates a magnetocaloric effect (MCE), which is the first finding of such an effect in a molecular glass. This MCE explainable by an uncoupled representation, with a magnetic entropy change of -11.36 J K -1 kg -1 at 1.8 K for a 0-7 T magnetic field change, and with a refrigerant capacity of 125.9 J kg -1 , in the 1.8-50 K interval.

Solvent Dependence of Crystal Structure and Dielectric Relaxation in Ferromagnetic [MnCr(oxalate)3]− Salt

[MnCr(oxalate)3]− possesses a two-dimensional ferromagnetic network that is an ideal system for the construction of multifunctional molecular materials based on ferromagnetism. This is because additional functions, such as ferroelectricity, can...

Gd(III)-based metal-organic frameworks and coordination polymers for magnetic refrigeration

As the alternatives of expensive and increasingly shortage 3He for ultralow-temperaturerefrigeration, molecule-based magnetorefrigerant materials have attracted much attention in the past decades. Among them, Gd(III)-based metal-organic frameworks and coordination polymers...

A Series of High-Nuclear Gadolinium Cluster Aggregates with a Magnetocaloric Effect Constructed through Two-Component Manipulation

The serialized expansion of high-nuclear clusters usually includes the controlled variable method and changes only a single variable. However, changing both variables will greatly increase the complexity of the reaction simultaneously. Therefore, the use of a two-component regulation reaction is rare. Herein, we used a diacylhydrazone ligand (H₄L¹) with multidentate chelating coordination sites for the reaction with Gd(NO₃)₃·6H₂O under solvothermal conditions to obtain an example of 16-nucleus disc-shaped cluster 1 with a brucite structure. The overall structure of cluster 1 can be regarded as an equilateral triangle, which is formed by three (L¹)^4- ions that can be regarded as "sides" and wrap the four-layer metal center Gd(III) ions. Notably, upon simultaneous regulation of the substituent of the ligand and the coordination anion, heptanuclear gadolinium cluster 2 was obtained. Cluster 2 can be regarded as a butterfly structure, which was formed by connecting two Gd₃L² molecules that were not in the same plane and through the central Gd(III) ion as an intersection. Moreover, hexanuclear gadolinium cluster 3 was obtained by changing the ligand substituent and adding an auxiliary ligand. Cluster 3 can be regarded as a chair structure, which was composed of two molecules of diacylhydrazone ligand (L²)^4- wrapping vacant cubane shared by four vertices. This study was the first to construct a series of high-nuclear gadolinium clusters through two-component regulation manipulation. The study of the magnetocaloric effect showed that the maximum values of -ΔS_m for clusters 1-3 were 34.05, 29.04, and 24.32 J kg^-1 K^-1, respectively, when T = 2 K and ΔH = 7 T.

Synthesis, structure and magnetocaloric properties of a new two-dimensional gadolinium(III) coordination polymer based on azobenzene-2,2',3,3'-tetracarboxylic acid

A new Gd3+ coordination polymer (CP), namely, poly[diaqua[μ4-1'-carboxy-3,3'-(diazene-1,2-diyl)dibenzene-1,2,2'-tricarboxylato]gadolinium(III)], [Gd(C16H7N2O8)(H2O)2]n, (I), has been synthesized hydrothermally from Gd(NO3)3·6H2O and azobenzene-2,2',3,3'-tetracarboxylic acid (H4abtc). The target solid has been characterized by single-crystal and powder X-ray diffraction, elemental analysis, IR spectroscopy and susceptibility measurements. CP (I) crystallizes in the monoclinic space group C2/c. The structure features a 4-connected topology in which Gd3+ ions are connected by carboxylate groups into a linear chain along the monoclinic symmetry direction. Adjacent one-dimensional aggregates are bridged by Habtc3- ligands to form a two-dimensional CP in the (10-1) plane. A very short hydrogen bond [O...O = 2.4393 (4) Å] links neighbouring layers into a three-dimensional network. A magnetic study revealed antiferromagnetic Gd...Gd coupling within the chain direction. CP (I) displays a significant magnetocaloric effect (MCE), with a maximum -ΔSm of 27.26 J kg-1 K-1 for ΔH = 7 T at 3.0 K. As the MCE in (I) exceeds that of the commercial magnetic refrigerant GGG (Gd3Ga5O12, -ΔSm = 24 J kg-1 K-1, ΔH = 30 kG), CP (I) can be regarded as a potential cryogenic material for low-temperature magnetic refrigeration.

Metal-Organic Frameworks Based on Group 3 and 4 Metals

Metal-organic frameworks (MOFs) based on group 3 and 4 metals are considered as the most promising MOFs for varying practical applications including water adsorption, carbon conversion, and biomedical applications. The relatively strong coordination bonds and versatile coordination modes within these MOFs endow the framework with high chemical stability, diverse structures and topologies, and interesting properties and functions. Herein, the significant progress made on this series of MOFs since 2018 is summarized and an update on the current status and future trends on the structural design of robust MOFs with high connectivity is provided. Cluster chemistry involving Y, lanthanides (Ln, from La to Lu), actinides (An, from Ac to Lr), Ti, and Zr is initially introduced. This is followed by a review of recently developed MOFs based on group 3 and 4 metals with their structures discussed based on the types of inorganic or organic building blocks. The novel properties and arising applications of these MOFs in catalysis, adsorption and separation, delivery, and sensing are highlighted. Overall, this review is expected to provide a timely summary on MOFs based on group 3 and 4 metals, which shall guide the future discovery and development of stable and functional MOFs for practical applications.

Tumor-Specific Endogenous FeII-Activated, MRI-Guided Self-Targeting Gadolinium-Coordinated Theranostic Nanoplatforms for Amplification of ROS and Enhanced Chemodynamic Chemotherapy

Low drug payload and lack of tumor-targeting for chemodynamic therapy (CDT) result in an insufficient reactive oxygen species (ROS) generation, which seriously hinders its further clinical application. Therefore, how to improve the drug payload and tumor targeting for amplification of ROS and combine it with chemotherapy has been a huge challenge in CDT. Herein, methotrexate (MTX), gadolinium (Gd), and artesunate (ASA) were used as theranostic building blocks to be coordinately assembled into tumor-specific endogenous Fe^II-activated and magnetic resonance imaging (MRI)-guided self-targeting carrier-free nanoplatforms (NPs) for amplification of ROS and enhanced chemodynamic chemotherapy. The obtained ASA-MTX-Gd^III NPs exhibited extremely high drug payload (∼96 wt %), excellent physiological stability, long circulating ability (half-time: ∼12 h), and outstanding tumor accumulation. Moreover, ASA-MTX-Gd^III NPs could be specifically uptaken by tumor cells via folate (FA) receptors and subsequently be disassembled via lysosomal acidity-induced coordination breakage, resulting in drug burst release. Most strikingly, the produced ASA could be catalyzed by tumor-specific overexpressed endogenous Fe^II ions to generate sufficient ROS for enhancing the main chemodynamic efficacy, which could exert a synergistic effect with the assistant chemotherapy of MTX. Interestingly, ASA-MTX-Gd^III NPs caused a lower ROS generation and toxicity on normal cell lines that seldom expressed endogenous Fe^II ions. Under MRI guidance with assistance of self-targeting, significantly superior synergistic tumor therapy was performed on FA receptor-overexpressed tumor-bearing mice with a higher ROS generation and an almost complete elimination of tumor. This work highlights ASA-MTX-Gd^III NPs as an efficient chemodynamic-chemotherapeutic agent for MRI imaging and tumor theranostics.

Slow magnetic relaxation in O–Se–O bridged manganese(iii) Schiff base complexes

Two new chain complexes consisting of a Mn(salen) building block bridged by O–Se–O units, [Mn₂(salen)₂(L)](ClO₄) (1) and {[Mn(salen)]₂(L)₂}·Y (2) (salen = N,N′-bis(salicylidene)-ethylenediamine, L = 3,4,5-trifluorobenzeneseleninic acid, Y = salicylaldehyde) have been synthesized and characterized structurally and magnetically.