Wen-Min Wang

Modulating single-molecule magnet behavior towards multiple magnetic relaxation processes through structural variation in Dy4 clusters

Three Dy4 clusters, [Dy4(tmhd)8(L)2(CH3OH)2]·CH3OH (1), [Dy4(hfac)8(L)2(DMF)2]·C7H16 (2) and [Dy4(dbm)6(L)2(μ3-OH)2]·CH2Cl2 (3) (tmhd = 2,2,6,6-tetramethyl-3,5-heptanedione, hfac = hexafluoroacetylacetonate, dbm = 1,3-diphenyl-1,3-propanedione, HL = 2-[(2-(hydroxyimino)propanehydrazide)methyl]), have been successfully synthesized by using three different β-diketonate salts (Dy(tmhd)3·2H2O, Dy(hfac)3·2H2O, and Dy(dbm)3·2H2O) to react with HL and by changing the solvent. The X-ray structural analysis shows that four DyIII ions in clusters 1 and 2 are linearly arranged; however, cluster 3 contains one Dy4 center with a rhombus-shaped arrangement. The different structures of three Dy4 clusters were profoundly affected by these minor changes in β-diketonate or a change in the solvent. Magnetic studies reveal that Dy4 clusters 1–3 exhibit different single-molecule magnet (SMM) behaviors under a zero dc field. 1 and 2 display slow magnetic relaxation behaviors with effective energy barriers ΔE/kB = 1.44 K for 1 and ΔE/kB = 50.96 K for 2, while for 3, two distinct slow magnetic relaxation processes are observed, with effective energy barriers ΔE/kB = 40.45 K for the fast relaxation process and ΔE/kB = 113.63 K for the slow relaxation process. This study shows that the β-diketonate coligands play an important role in modulating molecular structures and further affecting the magnetic dynamics of the lanthanide clusters towards multiple magnetic relaxation processes.

Butterfly-shaped tetranuclear Ln4 clusters showing magnetic refrigeration and single molecule-magnet behavior

Three new Ln4 clusters based on a bidentate Schiff base ligand having formulae [Ln4(μ3-OH)2L6(acac)4]·xCH3CN (Ln(III) = Eu(1), Gd(2) and Dy(3), x = 1 for 1, x = 2 for 2, and x = 0 for 3, HL = 5-(4-o-hydroxybenzylidene)-8-hydroxylquinoline and acac = acetylacetone) have been successfully synthesized and completely characterized. The structures of 1–3 are similar to each other except for the nature of the central ion and the number of free acetonitrile molecules. The four LnIII ions are coplanar and clusters 1–3 have a butterfly-shaped arrangement. Magnetic studies show that cluster 2 displays a weak antiferromagnetic exchange interaction between nearby GdIII centers and exhibits magnetic refrigeration with maximum −ΔSm = 18.85 J kg−1 K−1 (ΔH = 7.0 T at 2.5 K). Alternating current (ac) magnetic susceptibility measurement of 3 indicates that 3 demonstrates SMMs behavior under a zero direct-current (dc) field, with an effective energy barrier (ΔE/kB) of 79.15 K and a pre-exponential factor τ0 = 5.82 × 10−8 s.

Self-assembly of tetra-nuclear lanthanide clusters via atmospheric CO2 fixation: interesting solvent-induced structures and magnetic relaxation conversions

Two systems of carbonate complexes were constructed by employing a newly prepared Schiff based ligand (H2L; H2L = 2-(hydroxyimino)-2-[(3-methoxyl-2-hydroxyphenyl)methylene]hydrazide) and Ln(acac)3·H2O (Hacac = acetylacetone) in different reaction solutions, namely [Ln4(CO3)(L)4(acac)2(H2O)4]·2CH3CN (Ln = Gd(1), Dy(2)) and [Ln4(CO3)(L)4(acac)2(CH3OH)2(H2O)2]·CH3OH·H2O (Ln = Gd(3), Dy(4)). Interestingly, complexes 1–4 are nearly structurally identical except for the coordinated solvent molecules. All of them consist of a Ln4 cluster in the center, in which four Ln(III) ions are bridged by two μ2-O atoms from the in situ formed CO32− through spontaneous fixation of atmospheric CO2. Magnetic investigation suggests that complexes 1 and 3 display magnetic refrigeration behaviors with maximum values of magnetic entropy changes of 31.23 J kg−1 K−1 and 27.06 J kg−1 K−1, respectively. Additionally, the energy barriers of the magnetization reversal were significantly improved from 2.73 K for 2 to 23.79 K for 4 by deliberately using methanol to replace the coordinated H2O molecule. It should be noted that the divergence in structures and magnetic properties could be mainly ascribed to the different solvent effects in the synthesis process.

CCDC 1845003: Experimental Crystal Structure Determination

Related Article: Yun-Shan Xue, Ting-Ting Kang, Huan-Huan Zhang, Xin-Yi Qiao, Wen-Ying Hou, Fei Pan, Wen-Min Wang|2018|Polyhedron|154|480|doi:10.1016/j.poly.2018.08.033