Hai-Yun Shen

Ligand Field Affected Single-Molecule Magnet Behavior of Lanthanide(III) Dinuclear Complexes with an 8-Hydroxyquinoline Schiff Base Derivative as Bridging Ligand

New dinuclear lanthanide(III) complexes based on an 8-hydroxyquinoline Schiff base derivative and β-diketonate ligands, [Ln2(hfac)4(L)2] (Ln(III) = Gd (1), Tb (2), Dy (3), Ho (4), Er (5)), [Ln2(tfac)4(L)2] (Ln(III) = Gd (6), Tb (7), Dy (8), Ho (9)), and [Dy(bfac)4(L)2·C7H16] (10) (L = 2-[[(4-fluorophenyl)imino] methyl]-8-hydroxyquinoline, hfac = hexafluoroacetylacetonate, tfac = trifluoroacetylacetonate, and bfac = benzoyltrifluoroacetone), have been synthesized. The single-crystal X-ray diffraction data show that complexes 1-10 are phenoxo-O-bridged dinuclear complexes; each eight-coordinated center Ln(III) ion is in a slightly distorted dodecahedral geometry with two bidentate β-diketonate coligands and two μ2-O bridging 8-hydroxyquinoline Schiff base derivative ligands. The magnetic study reveals that 1 and 6 display cryogenic magnetic refrigeration properties, whereas complexes 3, 8, and 10 show different SMM behaviors with energy barriers of 6.77 K for 3, 19.83 K for 8, and 25.65 K for 10. Meanwhile, slow magnetic relaxation was observed in 7, while no out-of-phase alternating-current signals were found for 2. The different dynamic magnetic behaviors of two Tb2 complexes and the three Dy2 complexes mainly derive from the tiny crystal structure changes around the Ln(III) ions. It is also proved that the β-diketonate coligands can play an important role in modulating magnetic dynamics of the lanthanide 8-hydroxyquinoline Schiff base derivative system.

Modulating single-molecule magnet behaviour of phenoxo-O bridged lanthanide(III) dinuclear complexes by using different β-diketonate coligands

Three dinuclear Dy(III) complexes, [Dy2(tfa)4L2] (1), [Dy2(TTA)4L2] (2) and [Dy2(dbm)4L2·2CH3CN·0.5H2O] (3) (tfa = trifluoroacetylacetonate, TTA = 2-thenoyltrifluoroacetone, dbm = dibenzoylmethane and HL = 2-[((4-bromophenyl)-imino)methyl]-8-hydroxyquinoline, have been synthesized, and structurally and magnetically characterized. The Dy(III) ions are eight-coordinated with two bidentate β-diketonate and two μ2-O bridging 8-hydroxyquinoline Schiff base ligands. Magnetic studies reveal that 1–3 exhibit different magnetic relaxation behaviors with the anisotropic barriers of 9.61 K (1), 54.81 K (2) and 30.98 K (3), respectively. The different magnetic relaxation behaviors of the three Dy2 complexes originate from the different chemical environments of the central Dy3+ ions with different β-diketonate coligands.

Near-infrared luminescence and SMM behaviors of a family of dinuclear lanthanide 8-quinolinolate complexes

A new family of lanthanide complexes, [Ln2(dbm)4(OQ)2(CH3OH)2] (Ln = Nd (1), Tb (2), Dy (3), Ho (4); dbm = dibenzoylmethanate, OQ = 8-quinolinolate), and [Er2(dbm)4(OQ)2(CH3OH)]·CH3COCH3 (5) were synthesized and characterized using single-crystal X-ray diffraction, elemental analysis (EA), thermal gravimetric analysis (TGA), powder X-ray diffraction (PXRD) and UV-vis spectra. X-ray crystallographic analyses reveal that 1–5 are μ-phenol bridged dinuclear complexes. For complexes 1–4, each LnIII ion is eight-coordinated with two bidentate dbm and two μ-phenol bridging OQ ligands and one methanol molecule. Complex 1 in the solid-state displays the typical emissions of the NdIII ions in the NIR region. Magnetic measurements were carried out on complexes 1–5. Dynamic magnetic studies reveal single-molecule magnet (SMM) behavior for complex 3. Fitting the dynamic magnetic data to the Arrhenius law gives the energy barrier ΔE/kB = 109.5 K and pre-exponential factor τ0 = 4.23 × 10−9 s under 3000 Oe dc field.

Modulation of the relaxation dynamics of linear-shaped tetranuclear rare-earth clusters through utilizing different solvents

Nine new tetranuclear centrosymmetric linear complexes, [RE4(dbm)8L2(DMF)2]·nCH2Cl2·mC2H3N (RE = Y (1), Tb (2), Dy (3), Ho (4), Er (5), Lu (6)) and [RE4(dbm)8L2(C2H5OH)2]·nCH3CN (RE = Tb (7), Dy (8), Ho (9)) (HL = 2-[(2-(hydroxyimino)propanehydrazide)methyl]-8-hydroxyquinoline and dbm = 1,3-diphenyl-1,3-propanedione) have been synthesized. Complexes 1-9 are tetranuclear complexes. Magnetic studies reveal that both DyIII-based complexes (3 and 8) exhibit single-molecule magnet (SMM) behavior under a zero dc field. Furthermore, complex 3 presents one relaxation process under a zero dc field, while application of an external dc field (1500 Oe) induces multi-relaxation signals of the ac magnetic susceptibility.

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.

Fine-tuning the magnetocaloric effect and SMMs behaviors of coplanar RE4 complexes by β-diketonate coligands

By introducing different β-diketonate coligands 1,3-diphenyl-1,3-propanedione (dbm) and acetylacetonate (acac), two series of new tetranuclear rare earth (RE) complexes [RE4(dbm)4L6(μ3-OH)2]·xCH3CN·yCH2Cl2 (RE = Y (1), Gd (2), Tb (3), Dy (4), Ho (5), Er (6) and Lu (7)) and [RE4(acac)4L6(μ3-OH)2]·xCH3CN (RE = Gd (8), Tb (9) and Dy (10)) based on 8-hydroxyquinoline Schiff base have been synthesized and characterized. RE4 clusters display subtle variation in the coordination geometry of REIII ion, but display remarkably dissimilar magnetic behaviors. Magnetic studies show that 2 and 8 act as cryogenic magnetic refrigerants, while 4 and 10 exhibit different slow magnetic relaxation. With the optimized dc fields, two Dy4 clusters both show multiple magnetic relaxation processes by comparing with the zero dc field due to the quantum tunneling of magnetization is mostly suppressed. Interestingly, complex 10 displays two-step relaxation processes occur with Ueff = 37.49 K (FR) and 89.89 K (SR) in the absence of an external field, and one with Ueff = 116.20 K in the presence of a 1500 Oe optimum field. These diversities originate from the substituent group (–C6H5 and –CH3) of β-diketonate coligands in the differences between steric hindrance and electron-donating effect. Additionally, the luminescence properties of 1, 3, 7, and 9 were investigated.

Dinuclear Ln(III) complexes constructed from an 8-hydroxyquinoline Schiff base derivative with different terminal groups show differing slow magnetic relaxation

Two series of dinuclear LnIII complexes, namely, [Ln(tfa)2(L)]2 (Ln = Gd (1), Tb (2), Dy (3), Ho (4), Er (5)) and [Ln(tfa)2(L′)]2 (Ln = Gd (6), Tb (7), Dy (8), Ho (9), Er (10)) (tfa = trifluoroacetylacetonate, HL = 2-[[(4-methylphenyl)imino]methyl]-8-hydroxyquinoline and HL′ = 2-[[(4-ethylphenyl)imino]methyl]-8-hydroxyquinoline), were synthesized, and structurally and magnetically characterized. Measurements of alternating-current (ac) susceptibility revealed that complexes 3 and 8 display significant zero-field single-molecule magnetic (SMM) behaviors with barrier energies of Ueff/kB = 9.14 K, τ0 = 4.76 × 10−6 s and Ueff/kB = 17.50 K, τ0 = 3.96 × 10−6 s, respectively. The magnetic studies also revealed that 1 and 6 feature a magnetocaloric effect with magnetic entropy change of −ΔSm values for 1 and 6 of 19.72 J kg−1 K−1 and 19.37 J kg−1 K−1 at T = 2 K and ΔH = 7 T, respectively.

Luminescence and magnetocaloric effect of Ln4 clusters (Ln = Eu, Gd, Tb, Er) bridged by CO32− deriving from the spontaneous fixation of carbon dioxide in the atmosphere

The synthesis and characterization of a new family of neutral tetranuclear Ln(III) complexes, [Eu4L4(CO3)(acac)2(H2O)2(CH3OH)2]·5H2O·2CH3OH (1), [Gd4L4(CO3)(acac)2 (CH3OH)4]·2CH3OH·CH2Cl2 (2), [Tb4L4(CO3)(acac)2(H2O)2(CH3OH)2]·3H2O·CH3OH (3), and [Er4L4(CO3)(acac)2(H2O)2(CH3OH)(DMF)]·H2O·CH3OH (4) (where acac− is acetylacetonate, H2L is 2-(hydroxyimino)-2-[(5-methyl-2-hydroxyphenyl)methylene]hydrazide and DMF = N,N-dimethyl formamide) are reported. For complexes 1–4, by absorbing and fixing CO2 spontaneously under atmospheric conditions, with CO32− as a bridging tetradentate ligand, the four LnIII ions are bridged by two μ2-O oxygen atoms from CO32− to form a Ln4 cluster. X-ray diffraction data reveal that the non-centrosymmetric (1, 3 and 4) or centrosymmetric (2) unit has two distinct LnIII ions, nine-coordinated LnIII ions in distorted spherical capped square antiprism geometry and eight-coordinated LnIII ions in distorted triangular dodecahedron geometry. Magnetic study indicates that complex 2 can act as a cryogenic magnetic refrigerant and the magnetocaloric effect (MCE) was detected with the magnetic entropy change of −ΔSm = 21.43 J kg−1 K−1 at ΔH = 7 T and 5 K. Furthermore, the fluorescence properties of complexes 1 and 3 were also investigated. The results prove that complex 3 can show TbIII characteristic emission peaks, while for complex 1, EuIII typical emission peaks were not observed.

Modulating the magnetization dynamics of four phenoxo-O bridged Dy2 complexes based on a Schiff base derived from 8-hydroxyquinoline

Four novel μ-O bridged dinuclear Dy2 clusters have been synthesized successfully by utilizing an 8-hydroxyquinoline (8-HQ) Schiff base ligand and four different co-ligands: [Dy2(bfa)2(L)2(H2O)2]·4CH3OH (1), [Dy2(TTA)2(L)2(H2O)2]·4CH3OH (2), [Dy2(acac)2(L)2(H2O)2]·2H2O (3) and [Dy2(PhCOO)2(L)2(H2O)2] (4) (Hbfa = benzoyl trifluoroacetylacetone, HTTA = thiophene trifluoroacetylacetone, Hacac = acetylacetone, PhCOOH = benzoic acid, H2L = 2-[(4-pyridinebenzoylhydrazone)methyl]-8-hydroxyquinoline). Magnetic studies show that only complex 1 exhibits SMM behavior under a zero dc field with a magnetic relaxation barrier of 68.89 K. When a dc field of 1500 Oe is applied, the value of ΔE/kB increases to 72.63 K. The different dynamic magnetic behaviors of the four Dy2 complexes mainly originate from the tiny changes of the coordination environment and magnetic coupling interaction of the central ions caused by the different co-ligands. Meanwhile, it proves that the co-ligands play an important role in modulating the magnetic properties of Dy-SMMs based on 8-HQ derivatives.