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The synthesis, structures, and magnetic properties of a family of air-stable star-shaped CoIICo3III complexes were investigated. These complexes contain only one paramagnetic Co(II) ion with the approximate D3 coordination environment in the center and three diamagnetic Co(III) ions in the peripheral. Magnetic studies show their slow magnetic relaxation in the absence of an applied dc field, which is characteristic behavior of single-molecule magnets (SMMs), caused by the individual Co(II) ion with approximate D3 symmetry in the center. Most importantly, it was demonstrated that the anisotropy energy barrier can be finely tuned by the periphery substituent of the ligand and the countercation. The anisotropy energy barrier can be increased significantly from 38 K to 147 K. [ABSTRACT FROM AUTHOR]

Through investigation of the origin of the relaxation barriers and the magneto-structural correlations in three (DMF)4MReIVCl4(CN)2 (DMF = dimethylformamide; M = MnII (1), NiII (2), and CoII (3)) single-chain magnets (SCMs) in the intermediate regime between the Ising and the Heisenberg limits using hybrid functional theory (B3LYP) and complete active space second-order perturbation theory (CASPT2) methods, we succeeded in obtaining the magnetic anisotropy and correlation energy barriers DA and Dx in terms of D (magnetic anisotropy parameter), J (magnetic exchange coupling constant), and S (spin value). B3LYP calculations show that the antiferromagnetic ReIV-MnII coupling interactions decrease with the increase of the Mn-N-C angle, while the ferromagnetic ReIV-NiII coupling interactions increase with the increase of the Ni-N-C angle. But, the ReIV-CoII exchange interactions with the variation of the Co-N-C angle are almost the same. The total energy barriers Dt of 1 and 2 mainly come from the contribution of the transverse anisotropy of ReIV, while the MnII and NiII ions only transmit the exchange coupling between ReIV and almost have no contributions. For 3, however, both of the ReIV and CoII ions have contributions to the total energy barrier. [ABSTRACT FROM AUTHOR]

A novel 1D dysprosium complex was synthesized by employing a pyridine-N-oxide ligand. It exhibits slow magnetic relaxation with an energy barrier of 227 K under zero dc field. [ABSTRACT FROM AUTHOR]

Until now, the expressions of the anisotropic energy barriers Δξ and ΔA, using the uniaxial magnetic anisotropy D, the intrachain coupling strength J, and the high-spin ground state S for single-chain magnets (SCMs) in the intermediate region between the Ising and the Heisenberg limits, were unknown. To explore this relationship, we used density functional theory and ab initio methods to obtain expressions of Δξ and ΔA in terms of D, J, and S of six R4FeII-ReIVCl4(CN)2 (R = diethylformamide (1), dibutylformamide (2), dimethylformamide (3), dimethylbutyramide (4), dimethylpropionamide (5), and diethylacetamide (6)) SCMs in the intermediate region. The ΔA value for compounds 1-3 was very similar to the magnetic anisotropic energy of a single Fe'', while the value of Δξ was predicted using the exchange interaction of FeII with the neighboring ReIV, which could be expressed as 2JSReSFe. Similar to compounds 1-3, the anisotropy energy barrier ΔA of compounds 4 and 5 was also equal to (Di - Ei)SFe², but the correlation energy Δξ was closely equal to 2JSReSFe(cos 98.4 - cos 180) due to the reversal of the spins on the opposite FeII. For compound 6, one unit cell of ReIVFeII was regarded as a domain wall since it had two different ReIV-FeII couplings. Thus, the Δξ of compound 6 was expressed as 4JnSRe1Fe1SRe2Fe2, where Jn was the coupling constant of the neighboring unit cells of Re1Fe1 and Re2Fe2, and ΔA was equal to the anisotropic energy barrier of one domain wall given by DRe1Fe1(S²Re1Fe1 - 1/4). [ABSTRACT FROM AUTHOR]

Three ion-pair complexes based on spin-crossover [Mn(5-Br-sal-N-1,5,8,12)]ClO4 with TBA2[Ni(mnt)2], TBA2[Pt(mnt)2] (mnt = maleonitriledithiolate) and TBA[Ni(dmit)2] respectively (dmit = 2-thioxo-1,3- dithiole-4,5-dithiolato) have been synthesized and structurally characterized. Complexes 1 [Mn(5-Br-sal- N-1,5,8,12)]2[Ni(mnt)2] and 2 [Mn(5-Br-sal-N-1,5,8,12)]2[Pt(mnt)2] are isomorphic and show the axial compression of the octahedral coordination environment of MnIII ions. With the temperature increasing the equatorial metal-ligand bond lengths show significant elongation, but the axial bond lengths remain unchanged. Complex 3 [Mn(5-Br-sal-N-1,5,8,12)][Ni(dmit)2].CH3CN contains π-π, p-π and H-bonds weak interactions. Magnetic investigation shows the spin-crossover phenomena for 1 and 2, and T1/2 has been increased by 230 K comparing with the reactant complex. However, no spin-crossover was observed in complex 3, and theoretical calculations show that there are weak antiferromagnetic couplings mediated through π-π interactions. [ABSTRACT FROM AUTHOR]

A density functional theory (DFT) study of the magnetic coupling interactions and magnetic anisotropy in a family of experimentally synthesized Ni9MoV and Ni9WV systems is presented. Our calculations show that for all of our selected Ni9M6 systems, the intramolecular magnetic coupling interactions are ferromagnetic, and the ground-state spins are 12. All of the D values of Ni9W6 systems come mainly from the contribution of the Di of W6(CN)48Ni extracted from Ni9W6, and the influence of the eight surrounding Ni including the ligands on their magnetic anisotropy is very small. Although the surrounding Ni bounded by different ligands have a small influence on all D values for our selected complexes, they decide on the core structures of W6(CN)48Ni, which dominate their magnetic anisotropy. Thus, to obtain a Ni9W6 system having a large negative D, we can use different ligands bound to Ni to obtain a good core structure of W6(CN)48Ni with a large negative D value. All D values of Ni9Mo6 systems also come mainly from the contribution of Di of the Mo6(CN)48Ni, which is positive or negative but very small; most of these systems do not behave as single-molecule magnets. [ABSTRACT FROM AUTHOR]

The ferromagnetic couplings were observed in an unpublished crystal that consists of binuclear copper(ii) complexes, namely, [Cu2(μ1,3-SCN)2(PhenOH)(OCH3)2(HOCH3)2] (PhenOH = 2-hydroxy-1,10-phenanthroline), and in the binuclear complex Cu(ii) ion assumes a distorted octahedral geometry and thiocyanate anion functions as a μ1,3-SCN−equatorial–axial (EA) bridging ligand. The analysis for the crystal structure indicates that there are three types of magnetic coupling pathways, in which two pathways involve π–π stacking between the adjacent complexes and the third one is the μ1,3-SCN−bridged pathway. The fitting for the data of the variable-temperature magnetic susceptibilities shows that there is a ferromagnetic coupling between adjacent Cu(ii) ions with J= 50.02 cm−1. Theoretical calculations reveal that the two types of π–π stacking resulted in ferromagnetic couplings with J= 4.16 cm−1and J= 2.75 cm−1, respectively, and the bridged thiocyanate anions pathway led to a weaker ferromagnetic interaction with J= 0.88 cm−1. The theoretical calculations also indicate that the ferromagnetic coupling sign from the two types of π–π stacking does not accord with McConnell I spin-polarization mechanism. The analysis for the Wiberg bond indexes that originate from the π–π stacking atoms indicates that the Wiberg bond indexes are relevant to the associated magnetic coupling magnitude and the Wiberg bond index is one of the key factors that dominates the associated magnetic coupling magnitude. [ABSTRACT FROM AUTHOR]

A theoretical density functional study of the relationship between the nearest-neighbor constants and the number of peripheral complexes in the cyano-bridged CrCNMn(salen)(H2O)63and (5-Brsalen)2(H2O)2Mn2Cr(CN)6clusters is presented. Two approaches show that the antiferromagnetic coupling interactions between nearest neighbors decrease with the increase of the number of peripheral complexes, although the second approach provides better results using several exchange-correlation functionals. The first approach consisted of evaluating the exchange coupling constant Jijbetween two paramagnetic metal centers iand jin the hexanuclear molecule by calculating the energy differences between the highest and broken-symmetry spin states of a model molecule in which metal atoms except for iand jare substituted by diamagnetic Zn(II) cations, while the second consisted of calculating the different spin-state energies of hexanuclear complexes and using the Heisenberg Hamiltonian to obtain the exchange coupling constants between different metal centers. Moreover, Kahn's qualitative theory succeeded in being applied to interpret the trend. [ABSTRACT FROM AUTHOR]

Magnetic coupling constants J for the complete structures of [Gd(capro)2(H2O)4Cr(CN)6]•H2O (capro represents caprolactam) (a) and trans-[Fe(CN)4(μ-CN)2Gd(H2O)4(bpy)]•4H2O•1.5bpy (b) have been calculated using hybrid density functional theory (DFT) B3LYP combined with a modified broken symmetry approach (BS). The calculated J value of -0.24 cm-1 for a is very close to the experimental -0.33 cm-1. They both show the antiferromagnetic interaction between Gd(III) and Cr(III). For b, although the sign of the calculated J value of 4.24 cm-1 is different from that of the experimental -0.38 cm-1, the two values both show the weak magnetic coupling interaction between Gd(III) and Fe(III). The spin density distributions are discussed on the basis of Mulliken population analysis. For complexes a and b, both transition metal (Fe(III) or Cr(III)) and rare earth Gd(III) display a spin polarization effect on the surrounding atoms, where a counteraction of the opposite polarization effects leads to a low spin density on the bridging ligand C1N1. For the compounds Gd(III)-Cr(III) (a) and Gd(III)-Fe(III) (b) in the HS states, Cr(III) has stronger spin polarization influence on the bridging atoms than Fe(III) even causing the positive spin population on the bridging atom N1. [ABSTRACT FROM AUTHOR]

A half-sandwich organolanthanide complex, [(C6Me6)Dy(AlCl4)3], in which Dy(III) is coordinated with a π-bonded arene was synthesized and magnetically characterized. This complex displays slow magnetic relaxation and a hysteresis loop associated with single-ion magnet behavior. The orientation of the magnetic anisotropy axis is analyzed using ab initio calculations. [ABSTRACT FROM AUTHOR]

We report a method for synthesizing single-molecule magnets through a single-crystal to single-crystal transformation. This process yields two single-molecule magnets with similar triangular Dy3 cores but distinct solvents and space groups achieved via solvent exchange. Magnetic properties reveal that both Dy3 molecules exhibit similar toroidal moments but manifest diverse multiple magnetization dynamic behaviors owing to the spin–lattice coupling influence from different solvent molecules. [ABSTRACT FROM AUTHOR]