Search

Based on a β-diketiminate ligand, an iron(III) tetrahedral high-spin complex, [LFeIII(Cl)2] (1), and an iron(II) high-spin triangular planar complex, [LFeIICl] (2), have been synthesized and structurally characterized. Also, complex 1 can be considered as a precursor to produce 2via a reduction process, with a concomitant change in its magnetic anisotropy. Combined experiments and ab initio calculations support the observation of field-induced single-ion magnet (SIM) behaviour for 2 with an effective spin-reversal energy barrier of Ueff = 40.02 K, as a direct consequence of the large intrinsic magnetic anisotropy (easy axis) arising from out-of-state spin-orbit coupling in the trigonal planar FeII complex. Noteworthy butterfly hysteresis loops were observed from 2 up to 8 K, which represents the first case in Fe(II) complexes. [ABSTRACT FROM AUTHOR]

A series of linear sandwich single-ion magnets containing [Er(COT)]+ fragment were selected to probe the magneto-structural correlations using ab initio methods. For prolate shaped ErIII ion, an equatorially coordinating geometry is preferable to achieve high axial anisotropy. Our calculations confirm that the increasing transversal crystal field (CF) induced by equatorial ligands truly enhances the energy barrier. However, if we continue to strengthen the transversal CF in the equatorial plane, the energy barrier inversely decreases. Our further results show that a medium ligand ring of benzene is preferable for prolate shaped ErIII ion, which can induce the modest energy splitting and the small temperature-assisted quantum tunneling of magnetization. Although the obtained energy barrier of 343.1 cm−1 for our created model [(C6H6)Er(COT)]+ is the largest, it is also much smaller than the DyIII-based compounds. [ABSTRACT FROM AUTHOR]

A series of five mononuclear β-diketonate-Dy(III) complexes, with formulas Dy(ntfa)3(Br-bpy) (1), Dy(ntfa)3(Br2-bpy) (2), Dy(ntfa)3(5,5-(CH3)2-bpy) (3), Dy(ntfa)3(4,4-((CH3)3)2-bpy) (4) and Dy(ntfa)3(4,4-(CH3)2-bpy) (5) (ntfa = 4,4,4-trifluoro-1-(2-naphthyl)-1,3-butanedione, Br-bpy = 5-bromo-2,2′-bipyridine, Br2-bpy = 4,4′-dibromo-2,2′-bipyridine, 5,5-(CH3)2-bpy = 5,5′-di-methyl-2,2′-bipyridine, 4,4-((CH3)3)2-bpy = 4,4′-di-tert-butyl-2,2′-bipyridine, and 4,4-(CH3)2-bpy = 4,4′-di-methyl-2,2′-bipyridine), have been prepared by altering the capping N-donor coligands. Dy(III) ions in all complexes possess N2O6 octa-coordinated environments, displaying a distorted square antiprismatic D4d symmetry in complexes 1–4, as well as a triangular dodecahedron D2d symmetry in 5. Magnetic investigations evidence the SIM behavior in the five complexes with the energy barriers (Ueff) of 104.19 K (1), 122.93 K (2), 84.20 K (3), 64.16 K (4) and 80.23 K (5) under zero applied dc field. The potential QTM effects in the title complexes are successfully suppressed in the presence of the extra applied fields. The crystal field parameters and orientations of the magnetic easy axes were obtained from the simulation of the magnetic data and the electrostatic model calculation. The distinct electronic effects originating from the subtle changes of the substituents on the capping N-donor coligands induce varying coordination microenvironments and geometries on the Dy(III) sites, further drastically impacting the overall magnetic properties of the title complexes. The disparities of the uniaxial anisotropy and the magnetic dynamics for 1–5 have been elucidated by ab initio calculations as well. [ABSTRACT FROM AUTHOR]

Four DyIII complexes, [Dy2(NO3)4(L)2(H2O)2]·2MeCN (1), [Dy2(NO3)4(L)2(H2O)2]·2(NO3)·DMBD·2MeOH (2), [Dy2(NO3)4(L)2(TPO)2]·2MeCN (3) and [Dy2(L′)6(H2O)2]·4MeCN (4), were elaborately synthesized, structurally characterized and magnetically investigated (HL = 2,6-dimethoxyphenol, HL′ = 4-hydroxy-3,5-dimethoxybenzaldehyde, DMBD = 1,1′-dimethyl-[4,4′-bipyridine]-1,1′-diium and TPO = phosphine triphenyl oxide). In 1–3, the nearly planar molecular structures consisting of two DyIII ions and two L ligands are almost perpendicular to four nitrate ligands, which provides an opportunity to introduce auxiliary ligands (H2O or TPO) at the terminal position along the Dy⋯Dy orientation of [Dy2]. The slightly discrepant coordination environment around the DyIII ion with different terminal ligands plays a key role in tuning the magnetic anisotropy, and further strongly affects the magnetic properties of 1–4. The magnetic studies reveal that they all behave as single-molecule magnets (SMMs) at zero dc field with ferromagnetic dipole–dipole interaction between DyIII ions. The dynamic magnetic investigations give the energy barriers of 107.5 (1), 127.1 (2), 168.7 (3) and 251.9 K (4), respectively. The magnetic axis orientation of the ground state gradually verges on the Dy–Oaux bond from 1 to 4, leading to the stronger uniaxial anisotropy of DyIII ions and better SMM properties of 3 and 4. In addition, complexes 3 and 4 possess higher energy barriers than reported dinuclear DyIII-SMMs also constructed from HL or HL' with β-diketone. It is believed that the ligands coordinating to the DyIII ion at both terminals of the Dy⋯Dy linkage improve the SMM properties of dinuclear DyIII complexes. This design may provide a new strategy for obtaining dinuclear DyIII-based SMMs. [ABSTRACT FROM AUTHOR]

Based on a multidentate Schiff-base ligand, N,N′-bis(2-hydroxy-5-methyl-3-formylbenzyl)-N,N′-bis-(pyridin-2-ylmethyl)ethylenediamine (H2L), two binuclear DyIII compounds, with formulas [Dy2(L)(NO3)3(CH3O)] (1) and [Dy2(L)(NO3)3(CH3CH2O)] (2), have been synthesized under different solvent systems. The DyIII ions in 1 and 2 adopt monocapped square antiprism coordination geometries, while different structural distortions can be observed. The two DyIII ions in 1 and 2 are bridged by two phenoxide atoms of one L2− ligand and one bridged CH3O−/CH3CH2O− oxygen node, leading to an approximate fusiform Dy2O3 core. The different DyIII–Obridged node distances, DyIII–Obridged node–DyIII angles and DyIII⋯DyIII distances can be observed. Magnetic studies reveal that 1 and 2 display slow magnetic relaxation behaviours under a zero direct-current field with the effective energy barriers (Ueff) of 114.17 K and 171.23 K, respectively. Furthermore, compound 2 possesses the highest Ueff in nine-coordinated Dy2 compounds. The M versus H data exhibit weak butterfly-shaped hysteresis loops at 2 K for 2. The rare CH3O−/CH3CH2O−-bridged nine-coordinated binuclear DyIII single-molecule magnets (SMMs) significantly regulate and enhance the Ueff of compounds 1 and 2. To deeply understand their different magnetic behaviours, the magnetic anisotropies and magnetic interactions of 1 and 2 were studied by ab initio calculations. These findings demonstrate an efficient approach for regulating and enhancing the magnetic anisotropy barriers using a bridged CH3O− anion or CH3CH2O− anion. [ABSTRACT FROM AUTHOR]

Complexation of dysprosium(III) ions with a multidentate hydrazone ligand, N-[(E)-pyridin-2-ylmethylideneamino]pyridine-2-carboxamide (L), in the presence of different β-diketonate coligands, leads to the formation of two novel DyIII dimers, with formulas Dy2(BTFA)4(L)2 (1) and Dy2(TTA)4(L)2 (2) (BTFA = 3-benzoyl-1,1,1-trifluoroacetone and TTA = 4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedionate). They exhibit slightly different coordination geometries around DyIII centers and discrepant binuclear motifs – as a result of altering the β-diketonate coligands – which has an impact on the magnetic interactions between metal centers, the local tensor of anisotropy on each DyIII site and their relative orientations, therefore contributing to distinct magnetization dynamics. Compared to 2, complex 1 exhibits a more significant slow magnetic relaxation of SMM behavior in the absence of a dc field. The QTM effect is effectively repressed under a static field, resulting in the energy barriers of 57 K for 1 and 38 K for 2. Ab initio calculations clarify that, strong single-ion magnetic anisotropies exist in both complexes, whereas intermetallic ferromagnetic interaction and antiferromagnetic interaction are observed in 1 and 2, respectively, therefore resulting in dissimilar magnetization dynamics. [ABSTRACT FROM AUTHOR]

The utilization of two isomorphic ligands with different substituents leads to two centrosymmetric DyIII dimers, namely, [Dy2(bfbpen)2(H2O)2]·2I− (1) and [Dy2(bcbpen)2(H2O)2]·2I−·0.5H2O (2) (H2bfbpen = N,N′-bis-(2-hydroxy-5-fluoro-benzyl)-N,N′-bis-(pyridin-2-ylmethyl)ethylenediamine and H2bcbpen = N,N′-bis-(2-hydroxy-5-chloro-benzyl)-N,N′-bis-(pyridin-2-ylmethyl)ethylenediamine). Although Dy ions in both compounds uniformly exhibit a square-antiprism geometry, the critical difference found in the terminal substituents of the two ligands fine-tunes the local crystal field around Dy centers and the dinuclear molecular structures of 1 and 2. Magnetic investigations unveil that both 1 and 2 display dynamic magnetic relaxation of single-molecule magnet (SMM) behaviour with different energy barriers of 20.9 K for 1 and 72.7 K for 2 under a zero direct-current (dc) field, as well as 26.9 K for 1 under a 1200 Oe dc field. Compared to 1, the stronger uniaxial anisotropy and magnetic exchange in 2 render it a better SMM as evidenced by the higher energy barrier. Ab initio calculations are also performed on both Dy2 compounds to rationalize the observed discrepancy in their magnetic behaviours. The contribution illustrates that the SMM behaviour could be effectively enhanced by means of deliberate local structural manipulation. [ABSTRACT FROM AUTHOR]

We showcase the coordination anion substitution effect on the relaxation dynamics of defect dicubane Zn2Dy2 tetranuclear clusters. On utilization of the coordination similarity of acetate and nitrate anions, we successfully isolated two defect dicubane Zn2Dy2 tetranuclear clusters with formulas [Zn2Dy2(L)4(NO3)2(CH3OH)2]·2CH3COCH3 (1) and [Zn2Dy2(L)4(CH3COO)2(CH3CH2OH)2]·4CH3COCH3 (2), where L denotes the fully deprotonated H2L ligand (E)-4-(tert-butyl)-2-((2-hydroxy-3-methoxybenzylidene)amino)phenol. Such a subtle change in the coordination anion around the DyIII site imposes a significant effect on the distinct relaxation dynamics in 1 and 2. Their magnetic properties were characterized through SQUID magnetometry and theoretical calculations to determine the effective energy barrier, energy levels, magnetic anisotropy and intracluster magnetic exchange coupling interactions. Both tetramers display frequency dependence of the out-of-phase ac magnetic susceptibility signal under zero applied dc field associated with single-molecule magnetic behaviour. The effective energy barriers of 1 and 2 are 108 and 40 cm−1, respectively. Theoretical calculations suggest that the different relaxation dynamics between them are mainly ascribed to the variation of the coordination anion around the DyIII site. [ABSTRACT FROM AUTHOR]