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Two novel and tetranuclear gadolinium clusters, namely, [Gd4(L)2(dbm)6(CH3OH)2] (1) and [Gd4(L)2(dbm)6(C2H5OH)2] (2) (H3L = (6-Hydroxymethyl)-N′-((2,3-dihydroxyphenyl)-methylene)picolinohydrazide and dbm = dibenzoylmethane), were assembled by the reaction of a multidentate ligand H3L with Gd(dbm)3·2H2O in different solvent system. Both the two Gd4 clusters have an approximate linear-shaped arrangement and the four central Gd3+ ions are connected by six μ2-O atoms. Direct-current (dc) magnetic susceptibility measurements of clusters 1 and 2 indicated that the weak antiferromagnetic interactions between adjacent Gd3+ ions both exist in clusters 1 and 2. It's particularly significant that clusters 1 and 2 display significant cryogenic magnetocaloric effects with maximum −ΔSm values of 21.39 and 20.26 J kg−1 K−1 at 2.0 K and 7.0 T, respectively.

Two new Dy2 compounds, namely, [Dy2(dbm)4(H2L)(CH3O)(CH3OH)] (1) and [Dy2(dbm)5(H2L)] (2) (dbm = dibenzoylmethane, H3L = (2E,N′E)-2-(hydroxyimino)-N′-(pyridin-2-ylmethylene)propanehydrazide, based a polydentate Schiff base ligand have been synthesized, structurally and magnetically characterized. The single-crystal X-ray diffraction research show that both compounds 1 and 2 are binuclear structures. The only difference is that two methanol molecules coordinated to Dy(III) ion in 1 instead of a dbm− coordinated to Dy(III) ion in 2. Magnetic property measurements indicate that they exhibit distinct slow magnetic relaxation behaviors (ΔE/kB = 0.87 K for 1 and ΔE/kB = 18.68 K for 2). This work revealed that the different solvent induced slight disparate structural and magnetic behaviors of two Dy2 compounds, which may provide an effective approach for tuning slow magnetization relaxation behaviors in polynuclear Ln-clusters.

In search of simple approaches to rationally modulate the single-molecule magnet behaviors in polynuclear lanthanide clusters, a new system containing two structurally closely related rhombus-shaped Dy4 clusters, Dy4(tmhd)4L6(μ3-OH)2·5CH3CN (1) and Dy4(acac)4L6(μ3-OH)2 (2) (HL = 5-(4-ethyoxylbenzylidene)-8-hydroxylquinoline, Htmhd = 2,2,6,6-tetramethyl-3,5-heptanedione and Hacac = acetylacetonate), have been obtained by employing two dysprosium β-diketonate salts to react with a bidentate Schiff base ligand (HL). The two Dy4 clusters have similar structures and possess a structure in which four Dy3+ ions remain in a perfect plane with a rhombus-shaped geometric construction. Dynamic magnetic analysis revealed different single-molecule magnet (SMM) behaviors occurs in 1 and 2. Under zero direct-current (dc) field, 1 displays typical SMMs behavior with ΔE/kB = 39.6 K and τ0 = 2.1 × 10−6 s. However, for 2, a peculiar feature of the χ″ versus temperature curves is that more than two peaks that are frequency-dependent are revealed, indicating the occurrence of multifold relaxation processes that lead to two ΔE/kB (31.3 K and 81.6 K) and pre-exponential factors (τ0 = 3.1 × 10−6 s, τ0 = 2.2 × 10−7 s).

The reaction of the lanthanide(III) β-diketonate salt (Dy(beac)3·2H2O) with a bidentate chelating ligand 5-(2-hydroxy-5-methylbenzylidene)-8-hydroxylquinoline (HL) afforded the tetranuclear Dy(III) cluster, [Dy4(μ3-OH)2L6(beac)4]·10CH3CN (1). The elemental analysis (EA), powder X-ray diffraction (PXRD), single-crystal X-ray diffraction and magnetic properties of 1 have been characterized. The X-ray structural analysis reveals that cluster 1 contains one Dy4 center with a rhombus-shaped arrangement, and each Dy(III) ion of 1 is located in a distorted square antiprism geometrical configuration. Magnetic properties study indicate that 1 shows single-molecule magnet behavior with larger energy barrier (ΔE/kB) of 78.3 K and τ0 = 4.4 × 10−7 s.

Three dinuclear lanthanide complexes: {[Ln2(L)2(pbd)4]·2CH3CN} (Ln = Eu (1), Gd (2), Dy (3); HL = 2-(hydroxyimino)-N′-(pyridin-2-ylmethylene)propanehydrazonic acid, pbd = 1-phenylbutane-1,3-dione) were fabricated and structurally characterized. Compounds 1–3 are isostructural belonging to the monoclinic system with space group C2/c. Magnetic studies reveal that 2 exhibits cryogenic magnetic refrigeration property (−ΔSm = 21.20 J K−1 kg−1), whereas compound 3 displays slow relaxation of the magnetization. Additionally, solid-state luminescence measurements reveal that 1 displays the characteristic Eu (III) luminescence at room temperature.

Two novel tetranuclear lanthanide complexes, [Ln4(μ3-OH)2L6(tmhd)4] (Ln = Tb (1) and Dy (2)), were successfully synthesized by using 5-(2-hydroxylbenzylidene)-8-hydroxylquinoline (HL) and 2,2,6,6-tetramethyl-3,5-heptanedione (Htmbd). The investigation of single-crystal X-ray diffraction showed that the structures of 1 and 2 are both composed of butterfly-shaped [Ln4O2] clusters in the center, and of which four Ln(III) ions are all eight-coordinated. Moreover, the luminescence test reveal that 1 exhibits four characteristic peaks of Tb(III); while for 2, it is magnetically characterized and alternating-current (ac) magnetic susceptibility suggests slow magnetic relaxation behavior was occurred in 2 with the energy barrier (ΔE/kB) of 81.76 K.

Three dinuclear lanthanide complexes: {[Ln2(L)2(tmhd)2(CH3OH)2]·nCH3OH} (Ln = Sm (1, n = 1), Eu (2, n = 0), Dy (3, n = 0); H2L = 2-hydroxy-N′-(2-hydroxy-3-methoxybenzylidene)benzohydrazide, tmhd = 2,2,6,6-tetramethylheptane-3,5-dione) were fabricated and structurally characterized. Compounds 1–3 are isostructural belonging to the tetragonal system with space group I4(1)/a. Magnetic studies indicated that slow magnetic relaxation behaviors were observed in 3, with energy barrier (ΔE/kB) of 53.97 K and τ0 = 4.61 × 10−7 s. Additionally, solid-state luminescence measurements reveal that 2 and 3 display the characteristic lanthanide luminescence at room temperature.

Two tetranuclear lanthanide(III) clusters, [Gd4(μ3-OH)2L6(dbm)4]·solvent, (1, Ln = GdIII, solvent = 2CH3CN·2CH2Cl2 and 2, Ln = DyIII, solvent = 6CH3CN; HL = 5-(4-o-hydroxybenzylidene)-8-hydroxylquinoline; dbm = 1,3-diphenyl-1,3-propanedione), were characterized in terms of structure and magnetism. The X-ray structural analysis exhibit that clusters 1 and 2 contain one Ln4 center with rhombus-shaped arrangement, and each Ln(III) ion of them is located in a distorted square-antiprismatic coordination sphere. Magnetic measurements indicate that 1 show magnetic refrigeration (−ΔSm = 13.91 J kg−1 K−1 for ΔH = 7.0 T at 3.0 K) and 2 display single molecule magnets behaviors with energy barrier (ΔE/kB) of 52.65 K and τ0 = 7.01 × 10−7 s.

Two new LnIII4 clusters, namely, [Dy4(μ3-OH)2L6(beac)4] (1) and [Gd4(μ3-OH)2L6(acac)4]·4CH3CN (2), (HL = 5-(4-o-hydroxybenzylidene)-8-hydroxylquinoline; Hbeac = 1-benzoylacetone and Hacac = acetylacetone), were successfully obtained and structurally characterized. The X-ray structural analysis show that clusters 1 and 2 contain one Ln4 center with rhombus-shaped arrangement, and the four 8-coordinate central Ln(III) ion of them are located in a distorted square-antiprismatic coordination sphere. Magnetic measurements reveal that 1 displays slow magnetic relaxation behavior with energy barrier (ΔE/kB) of 83.38 K and τ0 = 1.51 × 10−7 s; while 2 shows magnetic refrigeration (−ΔSm = 19.65 J kg−1 K−1 for ΔH = 7.0 T at 2.0 K).

Two new three-dimensional lanthanide frameworks [Ln(BTB)(H2O)]n (Ln = Eu (1) and Dy (2)) based on 1,3,5-benzenetribenzoic acid (H3BTB) were synthesized and characterized. Structural analysis reveals that they were isostructural, in which two lanthanide ions are bridged by four carboxylic groups from different BTB3− in the modes of μ2-η1η1 and μ2-η1η2 to form a binuclear unit. The binuclear units are built into one-dimensional chain via two μ2-η1η1 carboxylic groups, which are further linked by BTB3− to generate three-dimensional frameworks. Compound 1 displays excellent solvent stability. The luminescent investigations suggest that 1 exhibits high sensitive sensing to aniline. Importantly, 1 as a promising luminescent detector for aniline can be recycled at least for four times. Additionally, magnetic studies reveal that 2 displays slow magnetic relaxation behaviors with the energy barrier (ΔE/kB) of 9.36 K under an external dc field (dc = 2500 Oe).

Seven new dinuclear centrosymmetric complexes, [Ln2(dbm)2L2(DMF)2]·2DMF (Ln = Nd (1), Eu (2), Tb (3), Dy (4), Er (5), Yb (6)) and [Dy2(dbm)2L2(CH3OH)2]·2CH3OH (7) (Hdbm = 1,3-diphenyl-1,3-propanedione, H2L = 2-[(2-(amino)benzhydrazide)-methyl]-8-hydroxylquinoline, DMF = dimethyl-formamide) have been synthesized and structurally characterized. Dynamic magnetic studies reveal the slow magnetic relaxation of complexes 4 and 7 are influenced by a fast quantum tunneling relaxation of the magnetization (QTM). However, the different magnetic relaxation behaviors were observed apparently in the two Dy2 complexes under a 3000 Oe dc field and modulated by the subtle change of solvents from DMF to CH3OH. For complex 7, the temperature dependence curves of in-phase (χ′) and out-of-phase (χ″) show better frequency-dependent signals, suggesting a slow relaxation of magnetization, typical of SMM behavior. Fitting the dynamic magnetic data of complex 7 to the Arrhenius law gives the energy barrier Ueff/kB = 44.06 K with the pre-exponential factor τ0 = 2.17 × 10−7 s under a 3000 Oe dc field.

A series of tetranuclear lanthanide(III) clusters, namely, [Ln4(μ3-OH)2L6(acac)4]·xCH3CN (Ln(III) = Tb(1), Dy(2) and Ho(3), HL = 5-(4-o-hydroxybenzylidene)-8-hydroxylquinoline; acac = acetylacetone), have been synthesized and completely characterized. The X-ray structural analysis exhibit that clusters 1–3 contain one Ln4 center with rhombus-shaped arrangement, and each Ln(III) ion of them is located in a distorted square-antiprismatic coordination sphere. Magnetic measurements indicated that single molecule magnets behaviors were observed in 2, with energy barrier (ΔE/kB) of 55.17 K and τ0 = 8.19 × 10−7 s. Additionally, luminescence properties study reveal that 1 and 2 display the characteristic TbIII and DyIII luminescence at room temperature.

Two new tetranuclear gadolinium clusters, [Gd4(μ3-OH)2(L1)6(beac)4] (1) and [Gd4(μ3-OH)2(L2)6(tmhd)4] (2) (HL1 = 5-(3-chlorobenzylidene)-8-hydroxylquinoline, HL2 = 5-(2-thenylidene)-8-hydroxylquinoline, beac = 1-benzoylaceton, tmhd = 2,2,6,6-tetramethyl-3,5-heptanedione), have been synthesized, then structurally and magnetically characterized. The X-ray structural analysis showed that both clusters 1 and 2 contain one Gd4 center with a rhombus-shaped arrangement, and all of the Gd(III) ions are located in a distorted square-antiprismatic coordination sphere. Magnetic property measurements indicate that 1 and 2 show magnetic refrigeration with −ΔSm = 20.43 J kg−1 K−1 for ΔH = 7 T at 2.0 K for 1 and −ΔSm = 19.94 J kg−1 K−1 for ΔH = 7 T at 2.5 K for 2.

Three new phenoxo-O-bridged dinuclear lanthanide(III) compounds, [Dy(bfa)2L1]2 (1), [Gd(hfac)3L2]2·C6H14 (2) and [Tb(hfac)3L2]2 (3) (bfa = benzoyltrifluoroacetone, hfac = hexafluoroacetylacetonate, HL1 = 2-[(3,4-dimethylaniline)-imino]methyl]−8-hydroxyquinoline and HL2 = 5-(2-thenylidene)-8-hydroxylquinoline), have been synthesized, then structurally and magnetically characterized. The X-ray structural analysis shows that 1–3 are phenoxo-O-bridged dinuclear compounds and the central eight-coordinated Ln(III) ions are in a slightly distorted dodecahedral geometry. Magnetic measurements indicated that slow magnetic relaxation behaviors were observed in 1 with an energy barrier (ΔE/kB) of 52.21 K and τ0 = 1.75 × 10−7 s; compound 2, however, exhibited magnetic refrigeration with −ΔSm = 15.06 J kg−1 K−1 for ΔH = 7.0 T at 2.0 K.

Two new tetranuclear Ln-based clusters, namely [Ln4(μ3-OH)2L6(beac)4] (Ln = Gd (1) and Dy (2)), were successfully assembled by employing 5-(2-thenylidene)-8-hydroxylquinoline (HL) and 1-benzoylacetone (Hbeac). They were structurally characterized by single crystal X-ray diffraction. In 1·Gd and 2·Dy, the structures of them are very similar with planar [Ln4O2] cluster at the center, four Ln(III) ions in which are further coordinated by six L− and four beac− anions in the modes of μ2-η2η1 for L− and μ2-η2η1 for beac−, respectively. Additionally, the magnetic measurement of them reveal that 1·Gd displays magnetic entropy change (−ΔSm) of 21.55(3) J K−1 kg−1 at 2 K for ΔH = 7 T. For 2·Dy, it exhibits slow magnetic relaxation behavior with the energy barrier (ΔE/kB) of 27.96(7) K.

A series of lanthanide based dinuclear compounds, namely, [Ln(bfa)2L]2 (Ln = Gd (1), Tb (2), and Dy (3), bfa = benzoyltrifluoroacetone and HL = 2-[5-methyl-1,2-oxazol-imino]methyl]-8-hydroxyquinoline), were synthesized by employing a multidentate 8-hydroxyquinoline Schiff base derivative ligands (HL) and a bidentate β-diketonate coligand (bfa). The elemental analysis (EA), powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA), single-crystal X-ray diffraction and magnetic properties of the three Ln2 compounds were completely characterized. Structures of 1–3 are similar to each other with a parallelogram Ln2O2 core. Magnetic properties study indicates that 1 exhibits antiferromagnetic exchange interaction between two nearby GdIII centers and shows magnetic refrigeration (−ΔSm = 17.78 J kg−1 K−1 for ΔH = 7 T at 2.0 K). Ac magnetic susceptibility measurements of 3 demonstrate that slow relaxation behavior is observed in 3, with effective energy barrier Ueff = 24.3 K and pre-exponential factor τ0 = 1.71 × 10−6 s.

A new cobalt(II) metal–organic framework (MOF), {[Co4(TDA)3(HCOO)2(TPT)2(DMF)2]·4DMF·2H2O}n (1) (H2TDA = thiophene-2,5-dicarboxylic acid and TPT = 2,4,6-tris(4-pyridyl)-1,3,5-triazine) has been synthesized via a mixed ligands approach and structurally characterized by elemental analysis, infrared spectra, powder X-ray diffraction, thermogravimetric analysis, and single crystal X-ray diffraction. Interestingly, two neighboring Co(II) ions of 1 can be connected via µ2-O from HCOO− anions and TPT ligands to form a 3D (3,3)-connected cationic net with a Schlafli symbol of {103}, which are further bridged by TDA2− ligands to generate a 3D (3,6)-connected net with a Schlafli symbol of {42·53·66·73·8}{52·6}. The magnetic property of 1 was studied in detail.

A series of dinuclear lanthanide(III) compounds, namely, [Ln2(tmhd)2L2(CH3OH)2] (Ln(III) = Sm (1), Eu (2), Dy (3) and Er (4); H2L = 2-amino-benzoic acid (8-hydroxy-quinolin-2-ylmethylene)-hydrazide, Htmhd = 2,2,6,6-tetramethyl-3,5-heptanedione), have been synthesized, structurally and magnetically characterized. The X-ray structural analysis exhibit that 1–4 are phenoxo-O-bridged dinuclear compounds and central Ln(III) ions are eight-coordinated with one bidentate tmhd−, one CH3OH and two μ2-O bridging Schiff base ligands. Magnetic measurements indicated that slow magnetic relaxation behaviors were observed in 3, with energy barrier (ΔE/kB) of 13.14 K and τ0 = 4.58 × 10−6 s, however, no out-of-phase (χ″) alternating current (ac) signals noticed in 1, 2 and 4. Additionally, solid-state luminescence properties reveal that 1–3 display the characteristic LnIII luminescence at room temperature.

In this paper, in search of an approach for tuning the single-molecule magnet behaviors in lanthanide polynuclear compounds, two new dinuclear dysprosium compounds based on an 8-hydroxyquinoline Schiff base and two different β-diketonate ligands, [Dy2(hfac)4L2] (1) and [Dy2(tfac)4L2] (2) (HL = 2-[[(4-iodophenyl)imino]methyl]-8-hydroxyquinoline, hfac = hexafluoroacetylacetonate and tfac = trifluoroacetylacetonate), have been synthesized, structurally and magnetically characterized. The two Dy2 compounds have very similar structures, however, magnetic studies reveal that 1 and 2 showed different SMM behaviors with energy barriers of 15.70 K for 1 and 6.57 K for 2. The different SMM behaviors mainly result from the different coordination environments of the central DyIII ions in 1 and 2.

A new rhombus-shaped tetranuclear dysprosium cluster, [Dy 4 (μ 3 -OH) 2 L 6 (tmhd) 4 ]·CH 2 Cl 2 ·8CH 3 CN ( 1 ) (HL = 5-(4-fluorobenzylidene)-8-hydroxylquinoline; tmhd = 2,2,6,6-tetramethyl-3,5-heptanedione), has been synthesized and completely characterized. The X-ray structural analysis exhibit that compound 1 contains one Dy 4 center with rhombus-shaped arrangement, and each Dy(III) ion of 1 is located in a distorted bicapped trigonal prism coordination sphere. Magnetic properties measurements indicate that 1 shows slow magnetic relaxation with energy barrier of 69.29 K and τ 0 = 6.18 × 10 −8 s.

Two series of new lanthanide dinuclear complexes having formulae, [Ln2(hfac)4(L1)2] (Ln = Tb (1), Er (2) and Lu (3), hfac = hexafluoroacetylacetone and HL1 = 2-[4-methylaniline-imino]methyl]-8-hydroxyquinoline) and [Ln2(hfac)4(L2)2] (Ln = Tb (4), Ho (5) and Er (6), hfac = hexafluoroacetylacetone and HL2 = 2-[(3,4-dimethylaniline)-imino]methyl]-8-hydroxyquinoline), have been successfully synthesized and studied interms of their magnetic properties. Magnetic studies reveal that 1 and 4 shows distinct slow magnetic relaxation. Indeed, no out-of-phase alternating current (ac) signal is noticed for 1, whereas 4 shows a slow relaxation of magnetization with energy barriers (ΔE/kB) of 6.84 K while application of an external dc field (2000 Oe).

Three new dinuclear lanthanide compounds, [Ln(hfac)2L]2 (Ln(III) = Gd (1), Tb (2) and Er (3), hfac = hexafluoroacetylacetonate and HL = 2-[(4-ethylphenyl)imino]methyl-8-hydroxyquinoline), have been synthesized and characterized by elemental analysis, IR, PXRD and single crystal X-ray diffraction. The X-ray structural analysis exhibit that 1–3 are phenoxo-O-bridged dinuclear complexes and central Ln(III) ions are eight-coordinated with two bidentate hfac− and two μ2-O bridging 8-hydroxyquinoline Schiff base ligands. Magnetic measurements indicate that 1 displays cryogenic magnetic refrigeration properties with maximum −ΔSm value of 19.94 J K−1 kg−1 at 2 K and 7 T; whereas 2 shows slow magnetic relaxation with energy barriers of 15.3 K and τ0 = 3.34 × 10−6 s. Additionally, solid-state photoluminescence property reveals that 2 displays the characteristic TbIII luminescence at room temperature.

One new tetranuclear dysprosium compound, namely [Dy4(μ3-OH)2(L)6(tmhd)4]·CH3CN (1) (HL = 5-(4-methylbenzylidene)-8-hydroxylquinoline; tmhd = 2,2,6,6-tetramethyl-3,5-heptanedione) was successfully synthesized and characterized. The structure of 1 was established by the single crystal X-ray diffraction technique, and the center Dy(III) ions was bridged by μ3-OH molecules and phenoxide oxygen atoms, displaying a ‘butterfly’ arrangement. Magnetic studies reveal that weak ferromagnetic interaction between adjacent Dy(III) exists in 1. Additionally, it also exhibits slow magnetic relaxation behaviors with the energy barrier of 46.4 K.

A 3d-4f cluster [Gd2Mn2(μ3-OH)2L4(NO3)4]·CH3CN (1) (HL = methyl 3-methoxysalicylate) was synthesized successfully, the structure and magnetical property of 1 were characterized and discussed. Cluster 1 possesses two defective cubic-type tetranuclear core which were connected by two μ3-O and four μ2-O. In cluster 1, the Gd(III) ion is nine-coordinated and the Mn(II) is six-coordinated. The magnetic property research suggests that a weak antiferromagnetic interaction exists in cluster 1. It is important that cluster 1 exhibits larger cryogenic magnetocaloric effect with a maximum -ΔSm of 40.59 J kg−1 K−1 for ΔH = 7 T at 2.0 K.