A Six-Coordinate Dysprosium Single-Ion Magnet with Trigonal-Prismatic Geometry.

A mononuclar six-coordinate dysprosium complex was synthesized and structurally and magnetically characterized. X-ray structural analyses show trigonal-prismatic coordination geometry of the DyIII center. Slow relaxation of magnetization in the absence of a direct-current field and magnetic hysteresis up to 3.0 K could be observed, indicating its single-ion-magnet behavior. Arrhenius fitting and ab initio calculations suggest that the magnetic relaxation process may not occur through the Orbach process at high temperatures under the experimental conditions.

Hydroxide-bridged five-coordinate DyIII single-molecule magnet exhibiting the record thermal relaxation barrier of magnetization among lanthanide-only dimers.

A hydroxide-bridged centrosymmetric DyIII dimer with each DyIII being five-coordinated has been synthesized using bulky hindered phenolate ligands. Magnetic studies revealed that this compound exhibits a slow magnetic relaxation of a single-ion origin together with a step-like magnetic hysteresis of the magnetic coupled cluster. The thermal relaxation barrier of magnetization is 721 K in the absence of a static magnetic field, while the intramolecular magnetic interaction is very large among reported 4f-only dimers. CASSCF calculations with a larger active space were performed to understand the electronic structure of the compound. The thermal relaxation regime and the quantum tunneling regime are well separated, representing a good model to study the relaxation mechanism of SMMs with intramolecular Dy-Dy magnetic interactions.

Gadolinium(III) Porpholactones as Efficient and Robust Singlet Oxygen Photosensitizers.

Construction of Gd(III) photosensitizers is important for designing theranostic agents owing to the unique properties arising from seven unpaired f electrons of the Gd(3+) ion. Combining these with the advantages of porpholactones with tunable NIR absorption, we herein report the synthesis of Gd(III) complexes Gd-1-4 (1, porphyrin; 2, porpholactone; 3 and 4, cis- and trans-porphodilactone, respectively) and investigated their function as singlet oxygen ((1) O2 ) photosensitizers. These Gd complexes displayed (1) O2 quantum yields (ΦΔ s) from 0.64-0.99 with the order Gd-1

Can Non-Kramers Tm(III) Mononuclear Molecules be Single-Molecule Magnets (SMMs)?

In recent years, plentiful lanthanide-based (Tb(III) , Dy(III) , and Er(III) ) single-molecule magnets (SMMs) were studied, while examples of other lanthanides, for example, Tm(III) are still unknown. Herein, for the first time, we show that by rationally manipulating the coordination sphere, two thulium compounds, 1[(Tp)Tm(COT)] and 2[(Tp*)Tm(COT)] (Tp=hydrotris(1-pyrazolyl)borate; COT=cyclooctatetraenide; Tp*=hydrotris(3,5-dimethyl-1-pyrazolyl)borate), can adopt the structure of non-Kramers SMMs and exhibit their behaviors. Dynamic magnetic studies indicated that both compounds showed slow magnetic relaxation under dc field and a relatively high effective energy barrier (111 K for 1, 46 K for 2). Magnetic diluted 1 a[(Tp)Tm0.05 Y0.95 (COT)] and 2 a[(Tp*)Tm0.05 Y0.95 (COT)] even exhibited magnetic relaxation under zero dc field. Relativistic ab initio calculations combined with single-crystal angular-resolved magnetometry measurements revealed the strong easy axis anisotropy and nearly degenerated ground doublet states. The comparison of 1 and 2 highlights the importance of local symmetry for obtaining Tm SMMs.

Structural phase transition in a multi-induced mononuclear Fe(II) spin-crossover complex.

Herein, we report the investigation of a mononuclear spin-crossover complex [Fe(II)L2][ClO4]2 (L = 2,6-bis{4,4-dimethyl-4,5-dihydrooxazol-2-yl}pyridine). This compound undergoes a structural phase transition around 173 K, accompanying with an abrupt spin-transition process. Interestingly, it exhibits a multi-induced spin-crossover behavior mediated by heat, light, pressure and solvent.

A large cryogenic magnetocaloric effect exhibited at low field by a 3D ferromagnetically coupled Mn(II)-Gd(III) framework material.

The large cryogenic magnetocaloric effect of a 3D oxydiacetate-bridged gadolinium-manganese MOF material, [Mn(H(2)O)(6)][MnGd(oda)(3)](2)·6H(2)O (1), was evaluated by magnetization and heat capacity measurements. A maximum -ΔS(m) of 50.1 J kg(-1) K(-1) for ΔH = 70 kG along with significant entropy change at lower field was found on account of the weak Mn···Gd ferromagnetic interactions and the small molecular mass. This suggests that 1 could be considered as a potential coolant for liquid helium temperature applications.

Heterometallic cubane-like {M2Ln2} (M = Ni, Zn; Ln =, Gd, Dy) and {Ni2Y2} aggregates. Synthesis, structures and magnetic properties.

The syntheses, structural determinations and magnetic studies of tetranuclear M(II)Ln(III) complexes (M = Ni, Zn; Ln = Y, Gd, Dy) involving an in situ compartmentalized schiff base ligand HL derived from the condensation of o-vanillin and 2-hydrazinopyridine as main ligand are described. Single-crystal X-ray diffraction reveals that all complexes are closely isostructural, with the central core composed of distorted {M(2)Ln(2)O(4)} cubes of the formulas [Ni(2)Ln(2)(µ(3)-OH)(2)(L)(2)(OAc)(4)(H(2)O)(3.5)](ClO(4))(2)·3H(2)O (Ln = Y 1 and Gd 2), [Ni(2)Dy(2)(µ(3)-OH)(2)(L)(2)(OAc)(5)(EtOH)(H(2)O)(1.5)](ClO(4))·EtOH·H(2)O (3) and [Zn(2)Ln(2)(µ(3)-OH)(2)(L)(2)(OAc)(5)(EtOH)(H(2)O)](ClO(4))·2EtOH·1.5H(2)O (Gd 4 and Dy 5). The Ln(III) ions are linked by two hydroxo bridges and each M(II) ion is also involved in a double phenoxo-hydroxo bridge with the two Ln(III) ions, so that each hydroxo group is triply linked to the two Ln(III) and one M(II) ions. The magnetic properties of all complexes have been investigated. Ni(2)Y(2) (1) has a ferromagnetic Ni(II)Ni(II) interaction. A weak ferromagnetic Ni(II)Ln(III) interaction is observed in the Ni(2)Ln(2) complexes (Ln = Gd 2, Dy 3), along with a weak antiferromagnetic Ln(III)Ln(III) interaction, a D zero-field splitting term for the nickel ion and a ferromagnetic Ni(II)Ni(II) interaction. The isomorphous Zn(2)Ln(2) (Ln = Gd 4, Dy 5) does confirm the presence of a weak antiferromagnetic Ln(III)Ln(III) interaction. The Ni(2)Dy(2) complex (3) does not behave as a SMM, which could result from a subtractive combination of the Dy and Ni anisotropies and an increased transverse anisotropy, leading to large tunnel splittings and quantum tunneling of magnetization. On the other hand, Zn(2)Dy(2) (5) exhibits a possible SMM behavior, where its slow relaxation of magnetization is probably attributed to the presence of the anisotropic Dy(III) ions.

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.

Pure trinuclear 4f 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.

Pentacobalt(II) cluster based pcu network exhibits both magnetic slow-relaxation and hysteresis behaviour.

A pentacobalt(II) cluster based 3D pcu network, [Co(5)(µ(3)-OH)(2)(bpdc)(4)(dabco)(H(2)O)(2)] (bpdc = benzophenone-2,4'-dicarboxylate and dabco = 1,4-diazabicyclo[2,2,2] octane), exhibiting both slow magnetic relaxation and hysteresis behavior, has been hydrothermally synthesized.

Reactivity of 4-amino-3,5-bis(pyridin-2-yl)-1,2,4-triazole, structures and magnetic properties of polynuclear and polymeric Mn(II), Cu(II) and Cd(II) complexes.

Five new complexes were obtained from solution or hydrothermal reactions of M(OAc)(2) (M = Mn, Cu and Cd) or CuCl(2) with 4-amino-3,5-bis(pyridin-2-yl)-1,2,4-triazole (abpt) and NaN(3) or 1,3,5-benzenetricarboxylic acid (btcH(3)) in different molar ratios. Structural analysis reveals that Cd(abpt) units in [Cd(abpt)(mu(1,1)-N(3))(2)](n) (1) are bridged by double mu(1,1) end-on (EO) azides into 1D zigzag coordination chains. Similar structural motifs, i.e. the chelation of abpt to the metal center and the double bridges of EO azides, are found in [Mn(4)(abpt)(4)(mu(1,1)-N(3))(8)(H(2)O)(2)] (2). The terminal aqua molecules and the monodentate N(3)(-) groups lead to the formation of a tetranuclear complex rather than a polymeric compound. The abpt underwent deamination in the presence of copper ions during the process of coordination and became 3,5-bis(pyridin-2-yl)-1,2,4-triazolate (bpt-H) in 3-5. [Cu(4)(bpt-H)(4)(N(3))(4)].4.5H(2)O (3) is a neutral tetranuclear grid-like complex, in which the azides act as monodentate ligands. A similar [Cu(4)(bpt-H)(4)](4+) grid-like unit was found in [Cu(4)(bpt-H)(4)(mu-btcH)Cl(2)].2H(2)O (4) and a pair of symmetry-related copper atoms are bridged by the mu-btcH(2)(-) coligand in a butterfly-shaped structure. In [Cu(2)(bpt-H)(mu(6)-btc)(H(2)O)](n) (5), the tetranuclear {Cu(4)(mu-bpt-H)(2)(mu(3)-carboxylate)(2)}(4+) units are bridged by mu(6)-btc(3-) ligands in a 2D step-like layer structure. Temperature-dependent magnetic susceptibility measurements reveal that the double mu(1,1)-N(3)(-) bridges in 2 transmit the ferromagnetic interactions between Mn(2+) centers (J(1) = J(2) = +3.09(4) cm(-1), g(Mn(II)) = 2.02(1)), and the mu-(bpt-H)(-) bridges transmit moderate antiferromagnetic interactions in both 3 (J = -12.78(13) cm(-1)) and 4 (J(1) = -14.96(11) cm(-1)). In 4 the antiferromagnetic coupling via the mu-btcH(2-) bridge was found as the second coupling pathway (J(2) = -9.48(7) cm(-1)). The coexistence of ferromagnetic and antiferromagnetic coupling between four Cu(2+) centers occurs in 5 (J(1) = -0.88(3) cm(-1) and J(2) = +5.01(2) cm(-1)). The magneto-structural relationship for tetranuclear copper pyrazolate/triazolate compounds has been discussed.