Polymeric Perturbation to the Magnetic Relaxations of the <i>C</i>_2<i>v</i>-Symmetric [Er(Cp)₂(OBu)₂]⁻ Anion

To test the coordination symmetry effect on the magnetization-reversal barrier trend of Er^III-based single-ion magnets, the <i>C</i>_2<i>v</i>-symmetric organolanthanide anion [Er­(Cp)₂(O^<i>t</i>Bu)₂]⁻ has been incorporated with different countercations, resulting in two structures, namely, the discrete [K₂(Cp)­(18-C-6)₂]­[Er­(Cp)₂(O^<i>t</i>Bu)₂] (<b>1</b>) and the polymeric [ErK₂(Cp)₃(O^<i>t</i>Bu)₂(THF)₂]_n (<b>2</b>), where 18-C-6 = 18-crown-6 ether and Cp = cyclopentadienide. Surprisingly, the polymeric <b>2</b> exhibits much stronger field-induced magnetization relaxing behavior compared to the monomeric <b>1</b>. Such disparate dynamic magnetism is attributable to the subtle coordination environmental perturbations of the central Er^III ions

Polymeric Perturbation to the Magnetic Relaxations of the <i>C</i>_2<i>v</i>-Symmetric [Er(Cp)₂(OBu)₂]⁻ Anion

To test the coordination symmetry effect on the magnetization-reversal barrier trend of Er^III-based single-ion magnets, the <i>C</i>_2<i>v</i>-symmetric organolanthanide anion [Er­(Cp)₂(O^<i>t</i>Bu)₂]⁻ has been incorporated with different countercations, resulting in two structures, namely, the discrete [K₂(Cp)­(18-C-6)₂]­[Er­(Cp)₂(O^<i>t</i>Bu)₂] (<b>1</b>) and the polymeric [ErK₂(Cp)₃(O^<i>t</i>Bu)₂(THF)₂]_n (<b>2</b>), where 18-C-6 = 18-crown-6 ether and Cp = cyclopentadienide. Surprisingly, the polymeric <b>2</b> exhibits much stronger field-induced magnetization relaxing behavior compared to the monomeric <b>1</b>. Such disparate dynamic magnetism is attributable to the subtle coordination environmental perturbations of the central Er^III ions

Disklike Hepta- and Tridecanuclear Cobalt Clusters. Synthesis, Structures, Magnetic Properties, and DFT Calculations

The synthesis, structure and magnetic properties are reported of two disklike mixed-valence cobalt clusters [Co^IIICo^II₆(thmp)₂­(acac)₆(ada)₃] (<b>1</b>) and [Co^III₂Co^II₁₁­(thmp)₄(Me₃CCOO)₄­(acac)₆(OH)₄­(H₂O)₄]­(Me₃CCOO)₂·H₂O (<b>2</b>). Heptanuclear complex <b>1</b> was prepared by solvothermal reaction of cobalt­(II) acetylacetonate (Co­(acac)₂), 1,1,1-tris­(hydroxymethyl)-propane (H₃thmp), and adamantane-1-carboxylic acid (Hada), whereas by substituting Hada with Me₃CCO₂H, tridecanuclear complex <b>2</b> was obtained with an unexpected [Co^III₂Co^II₁₁] core. The core structures of <b>1</b> and <b>2</b> are related to each other: that of <b>1</b> arranges as a centered hexagon of a central Co^III ion surrounded by a [Co^II₆] hexagon, while that of <b>2</b> can be described as a larger oligomer based on two vertex-sharing [Co^IIICo^II₆] clusters. Variable-temperature direct-current magnetic susceptibility measurements demonstrated overall ferromagnetic coupling between the Co^II ions within both clusters. The magnetic exchange (<i>J</i>) and magnetic anisotropy (<i>D</i>) values were quantified with appropriate spin-Hamiltonian models and were also supported by density functional theory calculations. The presence of frequency-dependent out-of-phase (χ_M<i>″</i>) alternating current susceptibility signals at temperatures below 3 K suggested that <b>2</b> might be a single-molecule magnet

Polynuclear and Polymeric Gadolinium Acetate Derivatives with Large Magnetocaloric Effect

Two ferromagnetic μ-oxo_acetate-bridged gadolinium complexes [Gd₂(OAc)₂(Ph₂acac)₄(MeOH)₂] (<b>1</b>) and [Gd₄(OAc)₄(acac)₈(H₂O)₄] (<b>2</b>) and two polymeric Gd­(III) chains [Gd­(OAc)₃(MeOH)]_<i>n</i> (<b>3</b>) and [Gd­(OAc)₃(H₂O)_0.5]_<i>n</i> (<b>4</b>) (Ph₂acacH = dibenzoylmethane; acacH = acetylacetone) are reported. The magnetic studies reveal that the tiny difference in the Gd–O–Gd angles (Gd···Gd distances) in these complexes cause different magnetic coupling. There exist ferromagnetic interactions in <b>1</b>–<b>3</b> due to the presence of the larger Gd–O–Gd angles (Gd···Gd distances), and antiferromagnetic interaction in <b>4</b> when the Gd–O–Gd angle is smaller. Four gadolinium acetate derivatives display large magnetocaloric effect (MCE). The higher magnetic density or the lower <i>M</i>_W/<i>N</i>_Gd ratio they have, the larger MCE they display. Complex <b>4</b> has the highest magnetic density and exhibits the largest MCE (47.7 J K^–1 kg^–1). In addition, complex <b>3</b> has wider temperature and/or field scope of application in refrigeration due to the dominant ferromagnetic coupling. Moreover, the statistical thermodynamics on entropy was successfully applied to simulate the MCE values. The results are quite in agreement with those obtained from experimental data

Mentha angustifolia

A family of high-nuclearity [Ln^III₆Mn^III₁₂] (Ln = Gd, Tb) nanomagnets has been synthesized, of which two are in <i>D</i>₂ molecular symmetry and the other two are in <i>C</i>₁ symmetry. X-ray crystallography shows that each of them contains a similar {Mn^III₈O₁₃} unit, four marginal Mn^III ions, and two linear {Ln^III₃} units with parallel or perpendicular orientation for high- and low-symmetry cores, respectively. For [Gd^III₆Mn^III₁₂], the distinct spins of the {Mn^III₈O₁₃} unit lead to different spin ground states (<i>S</i>_T = 23 for the high-symmetry one and <i>S</i>_T = 16 for the low-symmetry one), and significant magnetocaloric effects are observed in a wide temperature range [full width at half-maximum (FWHM) of −Δ<i>S</i>_m > 18 K] that can maximizes the refrigerant capacity, which may be attributed to the ferromagnetic interactions. By replacement of isotropic Gd^III with anisotropic Tb^III, they behave as single-molecule magnets, with the high-symmetry one possessing a larger effective barrier (36.6 K) than the low-symmetry one (19.6 K)

A Six-Coordinate Ytterbium Complex Exhibiting Easy-Plane Anisotropy and Field-Induced Single-Ion Magnet Behavior

The field-induced blockage of magnetization behavior was first observed in an Yb^III-based molecule with a trigonally distorted octahedral coordination environment. Ab initio calculations and micro-SQUID measurements were performed to demonstrate the exhibition of easy-plane anisotropy, suggesting the investigated complex is the first pure lanthanide field-induced single-ion magnet (field-induced SIM) of this type. Furthermore, we found the relaxation time obeys a power law instead of an exponential law, indicating that the relaxation process should be involved a direct process rather than an Orbach process

The First {Dy₄} Single-Molecule Magnet with a Toroidal Magnetic Moment in the Ground State

A toroidal magnetic moment in the absence of a conventional total magnetic moment was first observed in a novel tetranuclear dysprosium cluster with <i>nonmagnetic</i> ground state. The toroidal state is quite robust with respect to variations of the exchange parameters

Incomplete Spin Crossover versus Antiferromagnetic Behavior Exhibited in Three-Dimensional Porous Fe(II)-Bis(tetrazolate) Frameworks

Two three-dimensional (3D) Fe­(II) porous metal–organic frameworks (MOFs) [Fe₂(H_0.67bdt)₃]·13H₂O (<b>1</b>·13H₂O) and [Fe₃(ox)­(H_0.67bdt)₃(H₂O)₂]·solvent (<b>2</b>·solvent) (H₂bdt = 5,5′-(1,4-phenylene)­bis­(1H-tetrazole); H₂ox = oxalic acid; solvent = 10H₂O and 9CH₃OH for <b>2</b>·9MeOH and 6H₂O and 5C₄H₉OH for <b>2</b>·5<i>n</i>-BuOH) were solvothermally synthesized and characterized. The X-ray structure analysis reveals that complex <b>1</b>·13H₂O is constructed from one-dimensional (1D) {Fe­(tz)₃}_<i>n</i> (tz = tetrazolate) chains which are linked through the phenyl tethers of the bdt ligands into a 3D microporous framework. In the case of complex <b>2</b>·solvent, the linear trinuclear [Fe₃(tz)₆] units are linked by ox^2– bridges to form 1D {Fe₃(tz)₆(ox)}_<i>n</i> chains, which are also extended into a 3D microporous framework linked by the bdt ligands. Their frameworks can be simplified as the same topological network (4⁶,6⁶,8³)­(4²,6³,8). The substructure of the 1D {Fe­(tz)₃}_<i>n</i> chain in <b>1</b>·13H₂O consists of spin-crossover (SCO) active Fe1 ions and low spin (LS) Fe2 ions alternately, while the trinuclear unit in <b>2</b>·solvent contains a partial high spin (HS) Fe1 ion and two terminal HS Fe2 ions. Magnetic susceptibility measurements reveal that complex <b>1</b>·13H₂O presents an incomplete gradual SCO behavior. Although complex <b>2</b>·solvent also has the SCO active Fe1 ions, the spin state change is extremely small and the antiferromagnetic property is primarily observed

Two new clusters with Mn^II-Mn^IV magnetic exchange from the use of polyalcohol ligands

<p>Two mixed-valence Mn(II,IV) complexes, [Mn^II₄Mn^IV₃(teaH)₃(tea)(thmeH)₃(thme)](ClO₄)₂·3MeCN (<b>1</b>) and [Mn^II₂Mn^IV₂(edteH)₂(peolH)₂]·4MeOH (<b>2</b>), where H₄edte = N,N,N′,N′-tetrakis(2-hydroxyethyl)ethylenediamine, teaH₃ = tris(2-hydroxyethyl)amine, H₄peol = pentaerythritol, and H₃thme = 1,1,1-tris(hydroxymethyl)ethane, were prepared from the corresponding manganese salts and mixed ligands with polyalcohols. The two clusters consist of a trapped-valence polynuclear core comprising 4Mn^II and 3Mn^IV for <b>1</b>, 2Mn^II and 2Mn^IV ions for <b>2</b>. Complex <b>1</b> crystallizes in the rhombohedral space group <i>R</i>3c, while <b>2</b> crystallizes in the monoclinic space group <i>P</i>2₁/c. Complex <b>1</b> consists of a near-planar Mn₇ unit that comprises a Mn₆ hexagon of alternating Mn^II and Mn^IV ions surrounding a central Mn^II ion. The remaining coordinated sites are occupied by eight different deprotonation degrees of H₃tea or H₃thme. The tetranuclear cluster of <b>2</b> consists of a fused defective dicubane Mn₄O₆ core, and the four Mn ions are coordinated by oxygens from edteH³⁻ and peolH³⁻ into an unusual butterfly-like [Mn^II₂Mn^IV₂] topology. The two clusters are also characterized by mass spectra and X-ray photoelectron spectroscopy. Direct current magnetization studies reveal ferromagnetic interactions within both Mn clusters.</p

The First {Dy₄} Single-Molecule Magnet with a Toroidal Magnetic Moment in the Ground State

A toroidal magnetic moment in the absence of a conventional total magnetic moment was first observed in a novel tetranuclear dysprosium cluster with <i>nonmagnetic</i> ground state. The toroidal state is quite robust with respect to variations of the exchange parameters