Lanthanide-Based Porous Coordination Polymers: Syntheses, Slow Relaxation of Magnetization, and Magnetocaloric Effect

Construction of a High Nuclear Gadolinium Cluster with Enhanced Magnetocaloric Effect through Structural Transition

Starting from a dinuclear complex {Gd₂(L)₂(NO₃)₄(H₂O)₂}·2(CH₃CN) (1) based on 2,6-dimethoxyphenol (HL), a nonanuclear cluster {Gd₉(L)₄(μ₄-OH)₂(μ₃-OH)₈(μ₂-OCH₃)₄(NO₃)₈ (H₂O)₈}(OH)·2H₂O (2) was obtained via modulating the amount of the ligand and base. Both of them have been structurally and magnetically characterized. Complex 1 decorates the Gd₂ core bridged by double μ₂-phenoxyl oxygen atoms and coordinated neutral CH₃CN molecules, while 2 features the Gd₉ core with a sandglass-like topology. Magnetic investigations reveal that the weaker antiferromagnetic interactions between adjacent metal ions exist in complex 2 than in 1, which is in agreement with the theoretical results. Meanwhile, the magnetocaloric effect with a maximum -ΔS _m value changes from 27.32 to 40.60 J kg^-1 K^-1 at 2 K and 7 T.

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.

Reversible Switching of Single-Molecule Magnetic Behaviour by Desorption/Adsorption of Solvent Ligand in a New Dy(III)-Based Metal Organic Framework

Two metal-organic frameworks (MOFs), [Dy(BDC)(NO₃)(DMF)₂] _n (1, H₂BDC = terephthalic acid) and [Dy(BDC)(NO₃)] _n (1a), were synthesized. The structures of MOFs 1 and 1a are easy to be reversibly transformed into each other by the desorption or adsorption of coordination solvent molecules. Accordingly, their magnetic properties can also be changed reversibly, which realizes our goals of manipulating on/off single-molecule magnet behaviour. MOF 1 behaves as a single-molecule magnet either with or without DC field. Contrarily, no slow magnetic relaxation was observed in 1a both under zero field and applied field.

Field-induced slow magnetic relaxation and magnetocaloric effects in an oxalato-bridged gadolinium(iii)-based 2D MOF

The coexistence of field-induced slow magnetic relaxation and moderately large magnetocaloric efficiency in the supra-Kelvin temperature region occurs in the 2D compound [Gd(ox)₃(H₂O)₆]_n·4nH₂O (1), a feature that can be exploited in the proof-of-concept design of a new class of slow-relaxing magnetic materials for cryogenic magnetic refrigeration.

Radii-dependent self-assembly of chiral lanthanide complexes: synthesis, chirality, and single-molecule magnet behavior

A pair of 3-methoxysalicylhydrazone-based homochiral ligands constructed chiral trinuclear and pentanuclear complexes with La^III and Dy^III ions, respectively, which indicates that the radii controlled the self-assembled structures. Chiral transfer during the self-assembly processes was confirmed by crystal structure analysis and CD spectroscopy. Then, magnetic investigations demonstrated that the chiral Dy₅ complexes exhibited typical single-molecule magnet behavior.

Remarkable Energy Barrier for Magnetization Reversal in 3D and 2D Dysprosium-Chloranilate-Based Coordination Polymers

Herein, two coordination polymers (CPs) [{Dy(Cl₂ An)_1.5 (CH₃ OH)}⋅4.5 H₂ O]_n (1) and [Dy(Cl₂ An)_1.5 (DMF)₂ ]_n (2), in which Cl₂ An is chloranilate (2,5-dihydroxy-1,4-benzoquinone dianion), exhibiting field-induced single-molecule magnet behavior with moderate barrier of magnetization reversal are reported. Detailed structural and topological analysis disclosed that 1 has a 3D network, whereas 2 has a 2D layered-type structure. In both CPs, magnetic measurements showed weak antiferromagnetic exchange interaction between the dysprosium centers and field-induced slow magnetic relaxation with barriers of 175(9)K and 145(7)K for 1 and 2, respectively. Notably, the energy barriers of magnetization reversal of 1 and 2 are remarkable for metal-chloranilate-based 3D (1) and 2D (2) CPs. The temperature and field dependence of relaxation time indicate the presence of multiple relaxation pathways, such as direct, quantum tunneling of magnetization, Raman, and Orbach processes, in both CPs. Ab initio theoretical calculations reinforced the experimentally observed higher energy barrier in 1 as compared with 2 due to the presence of large transverse anisotropy in the ground state in the latter. The average transition magnetic moment between the computed low-lying spin-orbit states also rationalized the relaxation as Orbach and Raman processes through the first excited state. BS-DFT calculations were carried out for both CPs to provide more insight into the exchange interaction.

Three coordination polymers with regulated coordination interactions as fluorescent sensors for monitoring purine metabolite uric acid

A facile optical sensor for uric acid (UA), an early pathological signature for the metabolic function of humans, was developed based on water-stable coordination polymers (CPs). Herein, three new isostructural fluorescent CPs, [Ln(TCPB)(DMF)3]n (Ln = La, CP 1; Ce, CP 2 and Pr, CP 3; H3TCPB = 1,3,5-tris(1-(2-carboxyphenyl)-1H-pyrazol-3-yl)benzene), with various metal ions were solvothermally synthesized. Significantly, by regulating the metal-organic coordination interactions, the fabricated CP 3 can quantitatively recognize UA with higher sensitivity compared with CP 1 and CP 2. The mechanism for the sensing properties further demonstrates the best performance of CP 3 and the excellent selectivity for UA monitoring. This work represents the strategy of designing fluorescent CP sensors to determine UA and provides a convenient approach for developing analysis platforms for the assessment of related disease progress and human health monitoring.

Regulating the structural dimensionality and dynamic properties of a porous dysprosium coordination polymer through solvent molecules

The solvent molecules can regulate the structural dimensionality of a porous dysprosium coordination polymer from three to two and its dynamic behavior, as evidenced by the increase of the effective energy barriers and slowdown of quantum tunneling.

Mononuclear lanthanide(iii)-oxamate complexes as new photoluminescent field-induced single-molecule magnets: solid-state photophysical and magnetic properties

Lanthanide(iii)-oxamate complexes can switch into Light Conversion Molecular Devices (LCMDs) or field-induced Single-Molecule Magnets (SMMs) depending on the external stimulus.

3D isomorphous lanthanide coordination polymers displaying magnetic refrigeration, slow magnetic relaxation and tunable proton conduction

Four lanthanide 3D coordination frameworks with 1D hydrophilic channels along the crystallographic c direction have been investigated for their proton conduction and magnetic properties.

The slow magnetic relaxation regulated by the coordination, configuration and intermolecular dipolar field in two mononuclear DyIII single-molecule magnets (SMMs)

Tuning the magnetic dynamics of single-molecule magnets (SMMs) is a crucial challenge for chemists.