Ferromagnetic Homometallic Mn19 Cluster and Heterometallic Na2Mn15 Cluster with Large Spin State as Magnetic Refrigerants

Ferromagnetic Archimedean polyhedra {Fe24M18} (M = Fe, Ni, and Mn) with tunable electron configurations

Three symmetric nanocages {Fe24M18} that mimic the Archimedean polyhedra, namely pseudo-rhombicuboctahedron, were synthesized. Their electron configurations depend highly on the changes of metal ions and the deprotonation of auxiliary ligands.

New Highly Charged Iron(III) Metal-Organic Cube Stabilized by a Bulky Amine

In this work, we report a new octanuclear cluster based on Fe^III and the ligand 1H-imidazole-4,5-dicarboxylic acid, [Et₃NH]₁₂[Fe₈(IDC)₁₂]·10DMF·13H₂O (1), with a metal core containing eight Fe^III connected by only one type of organic ligand. A peak at 573 m/z in the mass spectra of the compound suggests the adduct species {[Fe₈(IDC)₁₂]+8H}^4-. By X-ray photoelectron spectroscopy, the oxidation state of the iron cation was confirmed to be 3+, also identifying the presence of a quaternary nitrogen species, which act as a countercation of the anionic metal core [Fe₈(IDC)₁₂]^12-. Mössbauer spectra recorded at different temperatures show an isomer shift and quadrupole splitting parameters that confirm the existence of only Fe^III-HS in the structure of 1. X-ray analysis reveals that compound 1 crystallizes in the orthorhombic system space group Ibam, confirming a molecular cluster structure with an almost regular cube as geometry, with the Fe^III atoms located at the corners of the cube and connected by μ-1κ² N,O:2κ² N',O‴-IDC^3- bridges. Additionally, the magnetic measurements reveal a weak antiferromagnetic coupling in the Fe₈ ^III coordination cluster (J = -3.8 cm^-1). To the best of our knowledge, 1 is the first member of the family of cubes assembled with 1H-imidazole-4,5-dicarboxylic acid and Fe^III cation, exhibiting high pH stability over a broad pH range, making it an ideal candidate for the design of supramolecular structures and metal-organic frameworks.

Syntheses, crystal-solution structures and magnetic properties of a series of decanuclear heterometallic [LnCoCo] (Ln = Eu, Gd, Tb, Dy) clusters

Four unprecedented decanuclear heterometallic [Ln2CoII4CoIII4] clusters based on a diethanolamine ligand (H2dea), namely [Eu2CoII4CoIII4(dea)8(HCOO)4(OH)2(Cl)2(CH3OH)2]Cl2·4CH3OH·2H2O (1), [Gd2CoII4CoIII4(dea)8(HCOO)4(OH)2(Cl)2(CH3OH)2]Cl2·4CH3OH·2H2O (2), [Tb2CoII4CoIII4(dea)8(HCOO)4(OH)2(Cl)2(CH3OH)2]Cl2·2CH3OH·4H2O (3) and [Dy2CoII4CoIII4(dea)8(HCOO)4(OH)2(Cl)2(CH3OH)2]Cl2·2CH3OH·4H2O (4) were synthesized through a facile solution method. Single-crystal X-ray diffraction analyses reveal that complexes 1-4 consist of a [Ln2CoII4CoIII4] core, which is constructed by bridging a quasi-double cuboidal [Ln2CoII2CoIII2] core with two [CoIICoIII] units. Electrospray ionization mass spectrometry (ESI-MS) using methanol solution reveals that complexes 1-4 are stable in the solution, and the clusters undergo three different substitution reactions (Cl- replaced by OH-, OH- replaced by CH3O- and HCOO- replaced by OH-/CH3O-) at the same time in the ionization state. Magnetic susceptibilities reveal ferromagnetic couplings within complexes 3 and 4, and the magnetocaloric effect (MCE) for 2 was also evaluated and the maximum entropy change (-ΔSm) value reaches 16.3 J kg-1 K-1 at about 3 K and 5 T.

A new approach to fabricate the Mn(ii)-based magnetic refrigerant through incorporation of a diamagnetic {LiO4} spacer

A new 3D MOF [MnLi₂(ip)₂(H₂O)₂] (1) with a 1D heterometallic inorganic Mn(ii)-Li(i) chain is reported. With the assistance of diamagnetic {LiO₄} connectors, which separate the paramagnetic Mn(ii) ions and act as magnetic spacers, very weak magnetic interactions were obtained. Remarkably, 1 showed a significant magnetocaloric effect (MCE) with a large entropy change value of 30.4 J kg^-1 K^-1 for ΔH = 8 T at 2 K.

High-nuclearity silver ethynide clusters containing polynucleating oxygen donor ligands

Three high-nuclearity heterometallic ethynide clusters were constructed with various polynucleating oxygen donor ligands.

Syntheses, structures, and chiroptical and magnetic properties of chiral clusters built from Schiff bases: a novel [MnIIMnIII6NaI2] core

Enantiomeric pairs of clusters with Mn^IIMnIII3Na^I and the unprecedented Mn^IIMnIII6NaI2 cores have been synthesized employing enantiomerically pure Schiff bases.

Coordination-Cluster-Based Molecular Magnetic Refrigerants

Coordination polymers serving as molecular magnetic refrigerants have been attracting great interest. In particular, coordination cluster compounds that demonstrate their apparent advantages on cryogenic magnetic refrigerants have attracted more attention in the last five years. Herein, we mainly focus on depicting aspects of syntheses, structures, and magnetothermal properties of coordination clusters that serve as magnetic refrigerants on account of the magnetocaloric effect. The documented molecular magnetic refrigerants are classified into two primary categories according to the types of metal centers, namely, homo- and heterometallic clusters. Every section is further divided into several subgroups based on the metal nuclearity and their dimensionalities, including discrete molecular clusters and those with extended structures constructed from molecular clusters. The objective is to present a rough overview of recent progress in coordination-cluster-based molecular magnetic refrigerants and provide a tutorial for researchers who are interested in the field.

Quantum signatures of a molecular nanomagnet in direct magnetocaloric measurements

Geometric spin frustration in low-dimensional materials, such as the two-dimensional kagome or triangular antiferromagnetic nets, can significantly enhance the change of the magnetic entropy and adiabatic temperature following a change in the applied magnetic field, that is, the magnetocaloric effect. In principle, an equivalent outcome should also be observable in certain high-symmetry zero-dimensional, that is, molecular, structures with frustrated topologies. Here we report experimental realization of this in a heptametallic gadolinium molecule. Adiabatic demagnetization experiments reach ~200 mK, the first sub-Kelvin cooling with any molecular nanomagnet, and reveal isentropes (the constant entropy paths followed in the temperature-field plane) with a rich structure. The latter is shown to be a direct manifestation of the trigonal antiferromagnetic net structure, allowing study of frustration-enhanced magnetocaloric effects in a finite system.

The magnetocaloric effect is well understood in spin-frustrated low-dimensional systems, and should be observable in certain high-symmetry molecular structures. Here, the authors report the experimental observation of sub-Kelvin cooling with a molecular magnet, and probe the low-temperature spin behaviour.

High-nuclearity 3d-4f clusters as enhanced magnetic coolers and molecular magnets

Four 52-metal-ion 3d-4f cluster complexes featuring a common core of Ln(42)M(10) (Ln = Gd(3+), Dy(3+); M = Co(2+/3+), Ni(2+)) were obtained through self-assembly of the metal ions templated by mixed anions (ClO(4)(-) and CO(3)(2-)). Magnetic studies revealed that the Gd(42)Co(10) and Gd(42)Ni(10) clusters exhibit the largest magnetocaloric effect (MCE) among any known 3d-4f complexes. Replacement of Gd(3+) ions with anisotropic Dy(3+) ions caused significant changes in the magnetic behavior of the clusters; both Dy(42)Co(10) and Dy(42)Ni(10) displayed slow relaxation of the magnetization.