Fu-Sheng Guo

Polynuclear and polymeric gadolinium acetate derivatives with large magnetocaloric effect.

Two ferromagnetic μ-oxo(acetate)-bridged gadolinium complexes [Gd(2)(OAc)(2)(Ph(2)acac)(4)(MeOH)(2)] (1) and [Gd(4)(OAc)(4)(acac)(8)(H(2)O)(4)] (2) and two polymeric Gd(III) chains [Gd(OAc)(3)(MeOH)](n) (3) and [Gd(OAc)(3)(H(2)O)(0.5)](n) (4) (Ph(2)acacH = 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 1-3 due to the presence of the larger Gd-O-Gd angles (Gd···Gd distances), and antiferromagnetic interaction in 4 when the Gd-O-Gd angle is smaller. Four gadolinium acetate derivatives display large magnetocaloric effect (MCE). The higher magnetic density or the lower M(W)/N(Gd) ratio they have, the larger MCE they display. Complex 4 has the highest magnetic density and exhibits the largest MCE (47.7 J K(-1) kg(-1)). In addition, complex 3 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.

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 nonmagnetic ground state. The toroidal state is quite robust with respect to variations of the exchange parameters.

Pure Trinuclear 4 f Single-Molecule Magnets: Synthesis, Structures, Magnetism and Ab Initio Investigation

A family of linear Dy(3) and Tb(3) clusters have been facilely synthesized from the reactions of DyCl(3), the polydentate 3-methyloxysalicylaldoxime (MeOsaloxH(2) ) ligand with auxiliary monoanionic ligands, such as trichloroacetate, NO(3)(-), OH(-), and Cl(-). Complexes 1-5 contain a nearly linear Ln(3) core, with similar Ln···Ln distances (3.6901(4)-3.7304(3) Å for the Dy(3) species, and 3.7273(3)-3.7485(5) Å for the Tb(3) species) and Ln···Ln···Ln angles of 157.036(8)-159.026(15)° for the Dy(3) species and 157.156(8)-160.926(15)° for the Tb(3) species. All three Ln centers are bridged by the two doubly-deprotonated [MeOsalox](2-) ligands and two of the four [MeOsaloxH](-) ligands through the N,O-η(2)-oximato groups and the phenoxo oxygen atoms (Dy-O-Dy angles=102.28(16)-106.85(13)°; Tb-O-Tb angles=102.00(11)-106.62(11)°). The remaining two [MeOsaloxH](-) ligands each chelate an outer Ln(III) center through their phenoxo oxygen and oxime nitrogen atoms. Magnetic studies reveal that both Dy(3) and Tb(3) clusters exhibit significant ferromagnetic interactions and that the Dy(3) species behave as single-molecule magnets, expanding upon the recent reports of the pure 4f type SMMs.

Symmetry related [DyIII6MnIII12] cores with different magnetic anisotropies

Two heterometallic [DyIII6MnIII12] clusters comprising of the same [MnIII8O13] fragment, four isolated MnIII ions and two linear [DyIII3] units have been synthesised. Except for the same composition, the main difference of these two cores lies in the coordination environment and the orientations of the linear [DyIII3] units. This difference leads to an alternation in the symmetry of the two cores that significantly modulates their magnetic properties including ground spin state and slow relaxation behavior.

Multifunctional DyIII4 Cluster Exhibiting White‐Emitting, Ferroelectric and Single‐Molecule Magnet Behavior

Significant attention has been paid to the investigation of single-molecule magnets (SMMs) since the first Mn12 cluster with such properties was reported in 1993. During the past two decades, SMMs have experienced three generations of development, from the initially studied 3d metal clusters to mixed 3d–4f clusters, and now to 4f-based species. The drastically increased interest in 4f-based SMMs is because of their significant magnetic anisotropy originating from large unquenched orbital angular momenta. On the other hand, lanthanide-based complexes are also the subject of intense investigation as luminescent materials as a result of their large Stokes shifts and the very narrow emission bands observed. Recently, some pioneering studies have combined both properties to improve the performance and enlarge the application scope. A few Dy and Yb complexes have recently been shown to be luminescent SMMs. To further miniaturize molecule-based devices, multifunctional SMMs combining versatile physical properties, such as ferroelectricity, dielectricity, and chirality may be useful. The large inherent anisotropy of the Dy ion has made it an ideal candidate for the manufacture of a series of SMMs. Additionally, Dy can function as a yellow-light emitter. The combination of a yellow-emitting Dy unit and a blueemitting organic chromophore will result in dual-color Y/B emission from a single molecule that can be used to generate white-light emission. At the same time, the blue-lightemitting ligand (Figure S1 in the Supporting Information), 3,5-bis(pyridin-2-yl)-1,2,4-trizole (Hbpt), exhibits potential chirality because of the presence of torsion angles between aromatic rings, which may lead to a chiral structure from the Dy–Hbpt reaction system. Following the above-designed strategy, solvothermal reactions of DyACHTUNGTRENNUNG(NO3)3, Hbpt, and NEt3 have been carried out in different solvents. Luckily, colorless block-shaped crystals of chiral complex 1 (D-1 and L-1 are the two enantiomers), [Dy4ACHTUNGTRENNUNG(m-bpt)4ACHTUNGTRENNUNG(m3-OH)2ACHTUNGTRENNUNG(m-OMe)2ACHTUNGTRENNUNG(NO3)4]·3 MeOH, were obtained from a solution in methanol at 120 8C, which are very different from those obtained from solutions in ethanol. The phase purity of bulk 1 was confirmed by comparison of its powder diffraction pattern with that calculated from the single crystal study (Figure S2 in the Supporting Information). Single-crystal X-ray structure analysis reveals that complex 1 crystallizes in the monoclinic space group P21. The molecular structures are depicted in Figure 1 and show that all Dy ions possess distorted square-antiprismatic geometries with N4O4 coordination environments (Figure S3 in the

Symmetry-Related [LnIII6MnIII12] Clusters toward Single-Molecule Magnets and Cryogenic Magnetic Refrigerants

A family of high-nuclearity [Ln(III)(6)Mn(III)(12)] (Ln = Gd, Tb) nanomagnets has been synthesized, of which two are in D(2) molecular symmetry and the other two are in C(1) symmetry. X-ray crystallography shows that each of them contains a similar {Mn(III)(8)O(13)} unit, four marginal Mn(III) ions, and two linear {Ln(III)(3)} units with parallel or perpendicular orientation for high- and low-symmetry cores, respectively. For [Gd(III)(6)Mn(III)(12)], the distinct spins of the {Mn(III)(8)O(13)} unit lead to different spin ground states (S(T) = 23 for the high-symmetry one and S(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 -ΔS(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).

Switching of the Magnetocaloric Effect of MnII Glycolate by Water Molecules

The transformation of Mn(II) glycolates (glc) between the three-dimensional coordination polymer [Mn(glc)2]n (1) and discrete mononuclear phase [Mn(glc)2 (H2O)2] (2) can be reversibly switched by water molecules, which dramatically change the magnetocaloric effect (MCE) of Mn(II) glycolates from the maximum of 6.9 J kg(-1)  K(-1) in 1 to 60.3 J kg(-1)  K(-1) in 2. This case example reveals that the effect of magnetic coupling on MCE plays a dominant role over that of other factors such as magnetic density for 3d-type magnetic refrigerants.

Lanthanide oxide clusters: from tetrahedral [Dy4(μ4-O)](10+) to supertetrahedral [Ln20(μ4-O)11]38+ (Ln = Tb, Dy, Ho, Er).

Supertetrahedral clusters: A family of lanthanide oxide supertetrahedral T3{Ln20} clusters (Ln = Tb, Dy, Ho, Er; see figure) were obtained from the solvothermal reaction of lanthanide(III) salts with polytriazolate ligands that could be methylated and oxidized in situ.

Enhanced spin-crossover behavior mediated by supramolecular cooperative interactions.

Three one-dimensional (1D) hetereobimetallic coordination polymers [Fe(II)(L)2(AgCN)2]·Solv (L = bpt(-), 1; L = Mebpt(-), Solv = 1.75EtOH, 2; L = bpzt(-), 3) with in situ generated AgCN species were synthesized by solvothermal reactions of Fe(II) salt, K[Ag(CN)2], and the corresponding ligands [bptH = 3,5-bis(pyridin-2-yl)-1,2,4-triazole, MebptH = 3-(3-methyl-2-pyridyl)-5-(2-pyridyl)-1,2,4-triazole, and bpztH = 3,5-bis(pyrazin-2-yl)-1,2,4-triazole]. They were further characterized by X-ray crystallography, magnetic and photomagnetic measurements, and differential scanning calorimetry. Single-crystal X-ray analyses show that they are isostructural with 1D zigzag chain structures with rhombus {Fe2Ag2} units, in which the substituted bpt(-) ligand connects the Fe(II) ion and AgCN species in a cis bridging mode. Then the zigzag chains are packed into three-dimensional supramolecular structures by π···π interactions. Most importantly, weak Ag···N interactions (2.750 Å at 150 K) between the π-stacked neighboring chains present in complex 3. Magnetic susceptibility measurements exhibit that complex 1 displays characteristic paramagnetic behavior in the temperature range investigated. Complex 2 undergoes a gradual spin-crossover (SCO) with critical temperatures T(1/2)↓ = 232 K and T(1/2)↑ = 235 K, whereas 3 exhibits an abrupt SCO with critical temperatures T(1/2)↓ = 286 K and T(1/2)↑ = 292 K. The magnetostructural relationships suggest that the magnetic behaviors can be modulated from paramagnetic behavior to abrupt and hysteretic SCO near room temperature through adjustment of the electronic substituent effect and intermolecular interactions.