[MnIII4LnIII4] Calix[4]arene Clusters as Enhanced Magnetic Coolers and Molecular Magnets

Fine-tuning the magnetocaloric effect and SMMs behaviors of coplanar RE4 complexes by β-diketonate coligands

By introducing different β-diketonate coligands, Gd₄ complexes show cryogenic magnetic refrigeration properties, whereas Dy₄ clusters exhibit different SMMs behaviors.

Syntheses, crystal structures, and magnetic properties of a family of heterometallic octanuclear [Cu6Ln2] (Ln = Dy(iii), Tb(iii), Ho(iii), Er(iii), and Gd(iii)) complexes

Five novel [Cu₆Ln₂] complexes were synthesized, wherein Ln^III ions are seven-coordinate and coordinated by one triethanolamine and three di-2-pyridyl ketone ligands, without coordinated solvent molecules and small anions.

The remarkable influence of N,O-ligands in the assembly of a bis-calix[4]arene-supported [MnIV2MnIII10MnII8] cluster

Bis-calix[4]arene is a highly versatile ligand that is capable of forming a range of polymetallic clusters. Use of an N,O-chelating co-ligand affords a very high nuclearity mixed-valence Mn cluster (shown here) that displays coordination modes relative to each ligand type.

Molecular rare earth metal alumosilicates

The resulting structure of the rare-earth metal alumosilicates depends strongly on the lanthanide radii and the acidity of Al–OH and Si–OH groups.

Ligand-directed synthesis of {MnIII5} twisted bow-ties

3,5-Diamino-1,2,4-triazole derivatives direct the assembly of {MnIII5} twisted bow-ties.

Anion-directed supramolecular chemistry modulating the magnetic properties of nanoscopic Mn coordination clusters: from polynuclear high-spin complexes to SMMs

We report a supramolecular approach to mixed-valent Mn coordination clusters that demonstrates how halide ions can be applied to influence the assembly of distinct tetranuclear building units to produce a number of related Mn coordination clusters with dense core structures that derive from a cuboctahedral arrangement of Mn ions. In all compounds the alignment of the Jahn-Teller axes of the Mn^III centers coincides with the positions of the stabilizing chloride ligands. Thus, the relative chloride concentrations in the reaction mixtures allow us to modify the symmetry and magnetic anisotropy of this basic core structures resulting in isotropic polynuclear high-spin complexes at high Cl^- concentrations and Single-Molecule Magnets at lower relative Cl^- concentrations.

Unusual Mn(III/IV)4 Cubane and Mn(III)16M4 (M = Ca, Sr) Looplike Clusters from the Use of Dimethylarsinic Acid

Three complexes are reported from the initial use of dimethylarsinic acid (Me2AsO2H) in Mn(III/IV) cluster chemistry, [Mn4O4(O2AsMe2)6] (3; 2Mn(III), 2Mn(IV)), and [Mn16X4O8(O2CPh)16(Me2AsO2)24] (X = Ca(2+) (4) or Sr(2+) (5); 16Mn(III)). They were obtained from reactions with [Mn12O12(O2CR)16(H2O)4] (R = Me, Ph) either without (3) or with (4 and 5) the addition of X(2+) salts. Complex 3 contains a [Mn4O4](6+) cubane, whereas isostructural 4 and 5 contain a planar loop structure comprising four Mn4 asymmetric "butterfly" units linked by alternating anti,anti μ-O2AsMe2 and {X2(O2AsMe2)(O2CPh)2} units. Variable-temperature magnetic susceptibility (χM) data were collected on dried microcrystalline samples of 3-5 in the 5.0-300 K range in a 0.1 T (1000 G) direct-current (dc) magnetic field. Data for 3 were fit to the appropriate Van Vleck equation (using the [Formula: see text] = -2JŜi·Ŝj convention) for a cubane of virtual C2v symmetry, giving J33 = 0.0(1) cm(-1), J34 = -3.4(4) cm(-1), J44 = -9.8(2) cm(-1), and g = 1.99(1), where the Jij subscripts refer to the oxidation states of the interacting Mn atoms. The ground state thus consists of two coupled Mn(IV) and two essentially noninteracting Mn(III). For 4 and 5, low-lying excited states from the high nuclearity and weak couplings prevent fits of dc magnetization data, but in-phase alternating current susceptibility χ'MT data down to 1.8 K indicate them to possess S = 4 ground states, if considered single Mn16 units. If instead they are treated as tetramers of weakly coupled Mn4 units, then each of the latter has an S = 2 ground state. Complexes 4 and 5 also exhibit very weak out-of-phase χ″M signals characteristic of slow relaxation, and magnetization versus dc field scans on a single crystal of 4·15MeCN at T ≥ 0.04 K showed hysteresis loops but with unusual features suggesting the magnetization relaxation barrier consists of more than one contribution.

Filling the gap between the quantum and classical worlds of nanoscale magnetism: giant molecular aggregates based on paramagnetic 3d metal ions

In this review, aspects of the syntheses, structures and magnetic properties of giant 3d and 3d/4f paramagnetic metal clusters in moderate oxidation states are discussed. The term "giant clusters" is used herein to denote metal clusters with nuclearity of 30 or greater. Many synthetic strategies towards such species have been developed and are discussed in this paper. Attempts are made to categorize some of the most successful methods to giant clusters, but it will be pointed out that the characteristics of the crystal structures of such compounds including nuclearity, shape, architecture, etc. are unpredictable depending on the specific structural features of the included organic ligands, reaction conditions and other factors. The majority of the described compounds in this review are of special interest not only for their fascinating nanosized structures but also because they sometimes display interesting magnetic phenomena, such as ferromagnetic exchange interactions, large ground state spin values, single-molecule magnetism behaviour or impressively large magnetocaloric effects. In addition, they often possess the properties of both the quantum and the classical world, and thus their systematic study offers the potential for the discovery of new physical phenomena, as well as a better understanding of the existing ones. The research field of giant clusters is under continuous evolution and their intriguing structural characteristics and magnetism properties that attract the interest of synthetic Inorganic Chemists promise a brilliant future for this class of compounds.

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.

Seven phenoxido-bridged complexes encapsulated by 8-hydroxyquinoline Schiff base derivatives and β-diketone ligands: single-molecule magnet, magnetic refrigeration and luminescence properties

Seven dinuclear complexes based on 8-hydroxyquinoline Schiff base derivatives and β-diketone ligands have been synthesized, and structurally and magnetically characterized.

Two unprecedented decanuclear heterometallic [MnII2MnIII6LnIII2] (Ln = Dy, Tb) complexes displaying relaxation of magnetization

The synthesis and magnetic properties of two novel [Mn₈Ln₂] complexes containing the gem-diol form of di-2-pyridyl ketone and triethanolamine were investigated.

Core expansion of bis-calix[4]arene-supported clusters

Stoichiometric control allows for remarkable expansion of the cores of two known bis-calix[4]arene-supported clusters, with concomitant changes to the magnetic properties.

Dodecanuclear 3d/4f-metal clusters with a ‘Star of David’ topology: single-molecule magnetism and magnetocaloric properties

The first dodecanuclear [M^II₆Ln^III₆] clusters with a ‘Star of David’ metal topology have been synthesized with a variety of different divalent 3d-metal ions and lanthanides, and exhibited single-molecule magnetism and magnetic refrigeration.

An octanuclear MnIII4DyIII4 cluster connected via two μ5-NO3− bridges with slow relaxation of magnetization

An octanuclear MnIII4DyIII4 cluster was connected by two μ₅-NO₃⁻ bridges.

Synthesis, structure, magnetic and magnetocaloric properties of a series of {CrIII4LnIII} complexes

Magnetic properties and magnetocaloric effect of rare heterometallic Cr(iii)–Ln(iii) complexes are reported.

A high-nuclearity metal-cyanide cluster [Mo6Cu14] with photomagnetic properties

A high-nuclearity metal-cyanide cluster [Mo₆Cu₁₄] has been prepared and its photomagnetic properties investigated.

Dodenuclear [Mn(III)(8)Ln(III)(4)] clusters with 2-(hydroxymethyl)pyridine: syntheses, structures, and magnetic properties

A new family of isostructural Mn/Ln dodenuclear clusters: [Mn8Ln4(O)8(hmp)4(O2CPh)12(NO3)4(PhCO2H)(C2H5OH)] [Ln = La (1), Pr (2), Nd (3), Gd (4), Dy(5), hmpH = 2-(hydroxymethyl)pyridine] have been synthesized by the reaction of Mn(NO3)2 and Ln(NO3)3·6H2O with hmpH and benzoic acid as co-ligands. Compounds 1-5 possess a spindle-shaped core of [MnLn(μ4-O)4(μ3-O)4(μ3-OR)2(μ2-OR)8](10+), which is composed of six face-sharing defected cubane units and two square-pyramidal units. The compounds represent the highest nuclearity Mn/Ln clusters with the use of hmpH to date. That the ferromagnetic interactions dominated within complexes 1-4 were suggested by solid-state dc magnetic susceptibility analyses. Compound 4 displays a magnetic-caloric effect (MCE) with 13.94 J kg(-1) K(-1) as the entropy change at 6 K for ΔH = 8 T. Compounds 1 and 5 exhibit an out-of-phase χ''M peak maximum above 2.0 K. Fitting of the ac susceptibility data to an Arrhenius law gives an energy barrier Ueff = 6.88/7.44 K for compounds 1 and 5 respectively.

Nitronyl nitroxide based 2p-3d-4f chains with the magnetocaloric effect and slow magnetic relaxation

Four new nitronyl nitroxide radical based hetero-tri-spin one-dimensional compounds, namely [{Ln(hfac)3}3{Cu(hfac)2}{NIT-Ph(OMe)2}4]n (Ln = Gd (1), Tb (2), Dy (3), Er (4); hfac = hexafluoroacetylacetonate; NIT-Ph(OMe)2 = 2-(2',4'-dimethoxyphenyl)-4,4,5,5-tetramethyl-imidazolyl-1-oxyl-3-oxide) have been successfully prepared. Single crystal X-ray crystallographic analysis reveals that complexes 1-4 possess a 1D chain structure with a repeating [Cu-Rad-Ln-Rad-Ln-Rad-Ln-Rad] moiety in which Ln(hfac)3 and Cu(hfac)2 units are bridged by nitronyl nitroxide radicals through the NO groups. DC magnetic studies found that ferromagnetic interactions between metals and the coordinated NO groups are active in all four compounds. The Tb derivative displays frequency dependent ac magnetic susceptibilities, indicating slow magnetic relaxation behavior. The Gd complex shows an important cryogenic magnetocaloric effect with the entropy change (-ΔSm) of 13.5 J kg(-1) K(-1) at 2 K and a magnetic field of 7 T, representing the first example of Gd-radical molecular species exhibiting the magnetocaloric effect.

Magnetic and magnetocaloric properties of an unusual family of carbonate-panelled [Ln(III)(6)Zn(III)(2)] cages

The reaction of the pro-ligand H4L, which combines the complementary phenolic oxime and diethanolamine moieties within the same organic framework, with Zn(NO3)2·6H2O and Ln(NO3)3·6H2O in a basic methanolic solution generates a family of isostructural heterometallic coordination compounds of general formula [Ln6Zn2(CO3)5(OH)(H2L)4(H3L)2(H4L)]NO3·xMeOH [Ln = Gd, x = 30 (), Ln = Dy, x = 32 (), Ln = Sm, x = 31 (), Ln = Eu, x = 29 (), Ln = Tb, x = 30 ()]. The octametallic skeleton of the cage describes a heavily distorted [Gd] octahedron capped on two faces by Zn(II) ions. The metal core is stabilised by a series of μ3- and μ4-CO3(2-) ions, originating from the serendipitous fixation of atmospheric CO2. The magnetic properties of all family members were examined via SQUID magnetometry, with the χMT product and VTVB data of the Gd analogue () being independently fitted by numerical diagonalisation to afford the same best-fit parameter JGd-Gd = -0.004 cm(-1). The MCE of complex was elucidated from specific heat data, with the magnetic entropy change reaching a value of 22.6 J kg(-1) K(-1) at T = 1.7 K, close to the maximum entropy value per mole expected from six Gd(III) spins (SGd = 7/2), 23.7 J kg(-1) K(-1).

A Strongly Spin-Frustrated Fe(III) 7 Complex with a Canted Intermediate Spin Ground State of S=7/2 or 9/2

A disk-shaped [Fe(III) 7 (Cl)(MeOH)6 (μ3 -O)3 (μ-OMe)6 (PhCO2 )6 ]Cl2 complex with C3 symmetry has been synthesised and characterised. The central tetrahedral Fe(III) is 0.733 Å above the almost co-planar Fe(III) 6 wheel, to which it is connected through three μ3 -oxide bridges. For this iron-oxo core, the magnetic susceptibility analysis proposed a Heisenberg-Dirac-van Vleck (HDvV) mechanism that leads to an intermediate spin ground state of S=7/2 or 9/2. Within either of these ground state manifolds it is reasonable to expect spin frustration effects. The (57) Fe Mössbauer (MS) analysis verifies that the central Fe(III) ion easily aligns its magnetic moment antiparallel to the externally applied field direction, whereas the other six peripheral Fe(III) ions keep their moments almost perpendicular to the field at stronger fields. This unusual canted spin structure reflects spin frustration. The small linewidths in the magnetic Mössbauer spectra of polycrystalline samples clearly suggest an isotropic exchange mechanism for realisation of this peculiar spin topology.

Linked supramolecular building blocks for enhanced cluster formation

Methylene-bridged calix[4]arenes have emerged as extremely versatile ligand supports in the formation of new polymetallic clusters possessing fascinating magnetic properties. Metal ion binding rules established for this building block allow one to partially rationalise the complex assembly process. The ability to covalently link calix[4]arenes at the methylene bridge provides significantly improved control over the introduction of different metal centres to resulting cluster motifs. Clusters assembled from bis-calix[4]arenes and transition metal ions or 3d-4f combinations display characteristic features of the analogous calix[4]arene supported clusters, thereby demonstrating an enhanced and rational approach towards the targeted synthesis of complex and challenging structures.

Experimental and theoretical investigations of four 3d–4f butterfly single-molecule magnets

Experimental and theoretical investigations of four 3d–4f defect-dicubane single-molecule magnets.