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.

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.

Five new tetranuclear complexes based on an 8-hydroxyquinoline Schiff base derivative and the β-diketone coligand, [Ln4(acac)4L6(μ3-OH)2]·CH3CN·0.5CH2Cl2 (Ln = Gd (1), Tb (2), Dy (3), Ho (4) and Er (5); HL = 5-(benzylidene)amino-8-hydroxyquinoline; acac = acetylacetonate) have been synthesized, and structurally and magnetically characterized. Complexes 1–5 have similar tetranuclear structures. Each LnIII ion is eight coordinated and its coordination polyhedra can be described as being in a distorted square-antiprismatic geometry. The magnetic studies reveal that 1 features the magnetocaloric effect (MCE) with the magnetic entropy change of −ΔSm(T) = 25.08 J kg−1 K−1 at 2 K for ΔH = 7 T, and 3 displays the slow magnetic relaxation behavior of Single Molecule Magnets (SMMs) with the anisotropic barrier of 86.20 K and the pre-exponential factor τ0 = 2.99 × 10−8 s.

•A 2D Cobalt(II) compound (1) has been synthesized and characterized.•The crystal structure analysis showed that 1 contains a helical Co(II) chain.•1 exhibits weak ferromagnetic at low temperature.•1 showed slow magnetic relaxation behavior under 0 Oe direct current field.A new Co(II) complex, {[Co(MPA)(4,4′-bpy)(H2O)]·2H2O}n (1) (H2MPA = 4-methylphthalic acid, 4,4′-bpy = 4,4′-bipyridine), has been prepared under solvothermal condition and fully characterized. The X-ray crystallography test demonstrates that 1 exhibits two-dimensional (2D) layer structure in which the helical Co(II) chains linked by syn-anti carboxylate bridges are connected by 4,4′-bpy ligands. Weak ferromagnetism was observed on direct-current (dc) susceptibility due to the collective effects of the helical chain structure and antiferromagnetic couplings between Co(II) ions transmitted by μ2-1,3-carboxylate groups. Interestingly, slow magnetic relaxation was observed in 1 at liquid helium temperatures without an external dc field.Download high-res image (430KB)Download full-size image

Five tetranuclear rare-earth complexes, [RE4(dbm)4L6(μ3-OH)2] [HL = 5- (4-fluorobenzylidene)-8-hydroxylquinoline; dbm = 1,3-diphenyl-1,3-propanedione; RE = Y (1), Eu (2), Tb (3), Dy (4), Lu (5)], have been synthesized and completely characterized. The X-ray structural analyses show that each [RE4] complex is of typical butterfly or rhombus topology. Each REIII center exists in an eight-coordinated square-antiprism environment. Magnetic studies reveal that complex 4 displays single-molecule-magnet behavior below 10 K under a zero direct-current field, with an effective anisotropy barrier (ΔE/kB = 56 K). The fluorescence properties of complexes 1–5 were also investigated. Complexes 2–4 showed their characteristic peaks for the corresponding REIII center, while complexes 1 and 5 showed the same emission peaks with the ligand when they were excited at the same wavelength.

Seven dinuclear complexes based on 8-hydroxyquinoline Schiff base derivatives and β-diketone ligands, [RE2(hfac)4L2] (RE = Y (1), Gd (2), Tb (3), Dy (4), Ho (5), Er (6) and Lu (7); hfac− = hexafluoroacetylacetonate; HL = 2-[(4-chloro-phenylimino)-methyl]-8-hydroxyquinoline), have been synthesized, and structurally and magnetically characterized. Complexes 1–7 have similar dinuclear structures, in which each REIII ion is eight coordinated by two L− and two hfac− ligands in a distorted dodecahedron geometry. The luminescence spectra indicate that complex 3 exhibits characteristic TbIII ion luminescence, while 1 and 7 show HL ligand luminescence. The magnetic studies reveal that 2 features a magnetocaloric effect with the magnetic entropy change of −ΔSm = 16.83 J kg−1 K−1 at 2 K for ΔH = 8 T, and 4 displays slow magnetic relaxation behavior with the anisotropic barrier of 6.7 K and pre-exponential factor τ0 = 5.3 × 10−6 s.

•A new 3D framework based on {Co6} cluster has been synthesized.•Framework 1 showed an 8-connected bcu topology.•Two coordination modes of the trz− ligand are observed in 1.•Compound 1 displays high thermal stability.•Compound 1 exhibits antiferromagnetic interaction among the CoII spin carries.A new 3D framework 1 based on {Co6} cluster as node was successfully synthesized and fully characterized, which showed an 8-connected bcu topology with the Schläfli symbol of {424,64}. Furthermore, the thermal stability and magnetic property reveal that 1 displays high thermal stability and antiferromagnetic interaction among the CoII spin carries.A new 3D framework 1 based on {Co6} cluster as node was successfully synthesized, which showed an 8-connected bcu topology. The thermal stability and magnetic property reveal that 1 display high thermal stability and antiferromagnetic interaction among the CoII spin carries.

•Two novel coordination polymers have been synthesized and characterized.•Coordination polymer 1 contains a rarely reported 1D CuII chain.•Non-coordinated groups of the ligands greatly influence the formations of 1 and 2.•1 and 2 exhibit very different antiferromagnetic dominant behaviors.Two coordination polymers: {[Cu3(MPA)2(trz)(μ3-OH)(H2O)]∙2H2O}n (1) and {[Cu6(NPA)4(trz)2(μ3-OH)2(H2O)2]∙H2O}n (2) (H2MPA = 4-methylphthalic acid, Htrz = 1H-1,2,4-triazole, H2NPA = 4-nitrophthalic acid) were synthesized under identical reaction conditions by changing the non-coordinated methyl group to nitro group of phthalic acid and characterized by elemental analysis, powder X-ray diffraction (PXRD), IR spectrum, thermo-gravimetric (TG) analysis and single crystal X-ray diffraction. Direct-current magnetic susceptibility measurements reveal that relatively strong antiferromagnetic couplings between the CuII spin carriers exist in 1 and 2.By employing the mixed-linker synthetic strategy, two novel two-dimensional (2D) coordination polymers (1 and 2) were obtained. 1 and 2 exhibit strong antiferromagnetic interactions between CuII carriers.

Three metal–organic frameworks (MOFs) with d10 metal ions, namely, {[Zn3(TDA)2(bpy)3]·(bpy)·10.5H2O}n (1), {[Zn3(TDA)2(azopy)2.5(H2O)]·4H2O}n (2) and {[Cd2K3(TDA)(HTDA)2(H2O)4]}n (3) (KH2TDA = potassium 1H-1,2,3-triazole-4,5-dicarboxylic acid, bpy = 4,4′-bipridine, azopy = 4,4′-azobispridine), have been successfully synthesized from KH2TDA with the aid of three different length-controllable auxiliary ligands and characterized by infrared spectra, elemental analysis, thermogravimetric analysis, powder X-ray diffraction and single-crystal X-ray diffraction. MOF 1 shows an interesting three-dimensional (3D) (3,4,4,4)-connected KAVGAQ framework with a Schläfli symbol of {63}2{64·102}{64·82}2, which can be extended by 2D layers and bpy pillars. MOFs 2 and 3 also display 3D framework structures, corresponding to a 6-connected {44·611} net and a (6,12)-connected {312·430·520·64}{36·48·5} net, respectively. Moreover, a novel coordination mode of H3TDA is observed in 3. The luminescence properties of 1–3 are investigated.

Seven dinuclear complexes based on 8-hydroxyquinoline Schiff base derivatives and β-diketone ligands, [RE2(hfac)4L2] (RE = Y (1), Gd (2), Tb (3), Dy (4), Ho (5), Er (6) and Lu (7); hfac− = hexafluoroacetylacetonate; HL = 2-[(4-chloro-phenylimino)-methyl]-8-hydroxyquinoline), have been synthesized, and structurally and magnetically characterized. Complexes 1–7 have similar dinuclear structures, in which each REIII ion is eight coordinated by two L− and two hfac− ligands in a distorted dodecahedron geometry. The luminescence spectra indicate that complex 3 exhibits characteristic TbIII ion luminescence, while 1 and 7 show HL ligand luminescence. The magnetic studies reveal that 2 features a magnetocaloric effect with the magnetic entropy change of −ΔSm = 16.83 J kg−1 K−1 at 2 K for ΔH = 8 T, and 4 displays slow magnetic relaxation behavior with the anisotropic barrier of 6.7 K and pre-exponential factor τ0 = 5.3 × 10−6 s.

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.

Five new tetranuclear complexes based on an 8-hydroxyquinoline Schiff base derivative and the β-diketone coligand, [Ln4(acac)4L6(μ3-OH)2]·CH3CN·0.5CH2Cl2 (Ln = Gd (1), Tb (2), Dy (3), Ho (4) and Er (5); HL = 5-(benzylidene)amino-8-hydroxyquinoline; acac = acetylacetonate) have been synthesized, and structurally and magnetically characterized. Complexes 1–5 have similar tetranuclear structures. Each LnIII ion is eight coordinated and its coordination polyhedra can be described as being in a distorted square-antiprismatic geometry. The magnetic studies reveal that 1 features the magnetocaloric effect (MCE) with the magnetic entropy change of −ΔSm(T) = 25.08 J kg−1 K−1 at 2 K for ΔH = 7 T, and 3 displays the slow magnetic relaxation behavior of Single Molecule Magnets (SMMs) with the anisotropic barrier of 86.20 K and the pre-exponential factor τ0 = 2.99 × 10−8 s.