Exploring the Sources of the Magnetic Anisotropy in a Family of Cyanide-Bridged Ni₉Mo₆ and Ni₉W₆ Systems: A Density Functional Theory Study

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

On the Origin of Magnetic Anisotropy in Cyanide-Bridged Co₉M₆ (M = Mo^V or W^V) Systems: A DFT Study

Our calculations show that the substitution of metal ions using CoII is not the main reason that CoII9M6 (M = MoV or WV) exhibits single-molecule-magnet behavior, whereas the unsymmetrical distribution of three CH3OH ligands surrounding each CoII is the main one

Unexpectedly Strong Magnetic Anisotropy in a Mononuclear Eight-Coordinate Cobalt(II) Complex: a Theoretical Exploration

Ab initio methods have been used to explore the unexpectedly strong magnetic anisotropy and the magnetostructural correlations in mononuclear eight-coordinate complex [Co^II(12-crown-4)₂]²⁺. Our calculations showed that both decreasing α and increasing φ may enhance its magnetic anisotropy, which was rationalized by the qualitative theory proposed by Long and co-workers. Moreover, we deduced that the |<i>D</i>| value of [Co^II(12-crown-4)₂]²⁺ with α = 52° and φ = 43° is the largest one

Largely Enhancing the Blocking Energy Barrier and Temperature of a Linear Cobalt(II) Complex through the Structural Distortion: A Theoretical Exploration

Complete-active-space self-consistent field and N-electron valence second-order perturbation theory have both been employed to investigate the magnetic anisotropy of one two-coordinate cobalt­(II) compound via altering the Co–C bond lengths and twist angle φ. The calculated energy barrier Ueff decreases with the decrease in the Co–C bond lengths due to the gradually increasing interaction between the 3d orbitals of CoII and the coordination ligand field and then to the decrease in the ground orbital angular moment L of CoII. Thus, we cannot improve Ueff simply by shortening the Co–C bond lengths. However, by rotating the twist angle φ from 60 to 0°, it is surprising to find that the energy barrier and blocking temperature can be enhanced up to 1559.1 cm–1 and 90 K, respectively, with φ = 0°, which are prominent even among lanthanide-based single-molecule magnets

Understanding the Magnetic Relaxation Mechanism in Mixed-Valence Dilanthanide Complexes with Metal–Metal Bonding: A Theoretical Investigation

Theoretical investigations on mixed-valence dilanthanide complexes (CpiPr5)2Ln2I3 (Ln = Tb, Dy, and Ho) indicate that the total spin of the 4f shell couples preferentially to the σ electron spin and then to the orbital angular momentum, improving the strength of spin–orbit coupling (SOC) for each magnetic center. On the other hand, the concentration of negative charges containing the delocalized σ electron in the axial direction leads to a large crystal-field (CF) splitting. Both strong SOC and large CF splitting lead to the largest energy barrier Ueff of such complexes up to now. In addition, our calculations show that the introduction of σ electron can better suppress the quantum tunneling of magnetization in the ground spin–orbit state, and the Ueff of (CpiPr5)2Ln2I3 is expected to originate from the contribution of both Ln ions under such strong Ln−σ exchange coupling

Series of Benzoquinone-Bridged Dicobalt(II) Single-Molecule Magnets

Mononuclear complexes within a particular coordination geometry have been well recognized for high-performance single-molecule magnets (SMMs), while the incorporation of such well-defined geometric ions into multinuclear complexes remains less explored. Using the rigid 2-(di(1H-pyrazol-1-yl)methyl)-6-(1H-pyrazol-1-yl)pyridine (PyPz3) ligand, here, we prepared a series of benzoquinone-bridged dicobalt(II) SMMs [{(PyPz3)Co}2(L)][PF6]2, (1, L = 2,5-dioxo-1,4-benzoquinone (dhbq2–); 2, L = chloranilate (CA2–); and 3, L = bromanilate (BA2–)), in which each Co(II) center adopts a distorted trigonal prismatic (TPR) geometry and the distortion increases with the sizes of 3,6-substituent groups (H (1) 2) 3)). Accordingly, the magnetic study revealed that the axial anisotropy parameter (D) of the Co ions decreased from −78.5 to −56.5 cm–1 in 1–3, while the rhombic one (E) increased significantly. As a result, 1 exhibited slow relaxation of magnetization under a zero dc field, while both 2 and 3 showed only the field-induced SMM behaviors, likely due to the increased rhombic anisotropy that leads to the serious quantum tunneling of the magnetization. Our study demonstrated that the relaxation dynamics and performances of a multinuclear complex are strongly dependent on the coordination geometry of the local metal ions, which may be engineered by modifying the substituent groups

Probing the Effect of Axial Ligands on Easy-Plane Anisotropy of Pentagonal-Bipyramidal Cobalt(II) Single-Ion Magnets

We herein reported the synthetic, structural, computational, and magnetic studies of four air-stable heptacoordinated mononuclear cobalt­(II) complexes, namely, [Co^II(tdmmb)­(H₂O)₂]­[BF₄]₂ (<b>1</b>), [Co^II(tdmmb)­(CN)₂]·2H₂O (<b>2</b>), [Co^II(tdmmb)­(NCS)₂] (<b>3</b>), and [Co^II(tdmmb)­(SPh)₂] (<b>4</b>) (tdmmb = 1,3,10,12-tetramethyl-1,2,11,12-tetraaza[[3]­(2,6)­pyridino[3]­(2,9)-1,10-phenanthrolinophane-2,10-diene; SPh^– = thiophenol anion). Constrained by the rigid pentadentate macrocyclic ligand tdmmb, the Co^II centers in all of these complexes are in the heptacoordinated pentagonal-bipyramidal geometry. While the equatorial environments of these complexes remain very similar to each other, the axial ligands are systematically modified from C to N to O to S atoms. Analyses of the magnetic data and the ab initio calculations both reveal large easy-plane magnetic anisotropy (<i>D</i> > 0) for all four complexes. While the experimentally obtained <i>D</i> values do not show any clear tendency when the axial coordinated atoms change from C to N to O atoms (complexes <b>1</b>–<b>3</b>), the largest value is for the heavier and softer S-atom-coordinated complex <b>4</b>. Because of significant magnetic anisotropy, all four complexes are field-induced single-ion magnets. This work represents a delicate modification of the magnetic anisotropy by tuning the chemical environment of the metal centers

Probing the Effect of Axial Ligands on Easy-Plane Anisotropy of Pentagonal-Bipyramidal Cobalt(II) Single-Ion Magnets

We herein reported the synthetic, structural, computational, and magnetic studies of four air-stable heptacoordinated mononuclear cobalt­(II) complexes, namely, [CoII(tdmmb)­(H2O)2]­[BF4]2 (1), [CoII(tdmmb)­(CN)2]·2H2O (2), [CoII(tdmmb)­(NCS)2] (3), and [CoII(tdmmb)­(SPh)2] (4) (tdmmb = 1,3,10,12-tetramethyl-1,2,11,12-tetraaza[[3]­(2,6)­pyridino[3]­(2,9)-1,10-phenanthrolinophane-2,10-diene; SPh– = thiophenol anion). Constrained by the rigid pentadentate macrocyclic ligand tdmmb, the CoII centers in all of these complexes are in the heptacoordinated pentagonal-bipyramidal geometry. While the equatorial environments of these complexes remain very similar to each other, the axial ligands are systematically modified from C to N to O to S atoms. Analyses of the magnetic data and the ab initio calculations both reveal large easy-plane magnetic anisotropy (D > 0) for all four complexes. While the experimentally obtained D values do not show any clear tendency when the axial coordinated atoms change from C to N to O atoms (complexes 1–3), the largest value is for the heavier and softer S-atom-coordinated complex 4. Because of significant magnetic anisotropy, all four complexes are field-induced single-ion magnets. This work represents a delicate modification of the magnetic anisotropy by tuning the chemical environment of the metal centers

Five-Coordinated Dysprosium Single-Molecule Magnet Functionalized by the SMe Group

A five-coordinate mononuclear Dy(III) complex with a C4v geometry (square-pyramid), [Dy(X)(DBP)2(TMG(H))2] [X = 3-(methylthio)-1-propoxide, DBP = 2,6-di-tert-butylphenoxide, and TMG(H) = 1,1,3,3-tetramethylguanidine] (1), was designed and synthesized. The complex displays a large anisotropy barrier of 432 cm–1 in the absence of a dc magnetic field benefiting from the strong interaction between the phenolate and Dy(III) ion. Ab initio calculations reveal that the most possible relaxation pathway is going through the second excited state. The terminal SMe group in the apical position furnishes the possibility of depositing it on the Au surface by the strong Au–S bond