8-hydroxyquinoline Schiff Base Ligands Research Articles

Crystal structure, fluorescence, magnetic properties and DNA interaction of four novel binuclear LnⅢ2 compounds with Schiff ligand

Four new Ln2 compounds, [Ln2(H2L−)2(acac)2(CH3O)2] (Ln = Sm(1), Tb(2), Ho(3) and Er(4), H3L = 2‑hydroxy-N’-[(1E)-(8-hydroxyquinolin-2-yl)methylidene]benzohydrazide), were synthesized by using a multidentate Schiff ligand and lanthanide β-diketone salts via solvent evaporation methods. The X-ray structural analysis reveal that the four Ln2 compounds are dinuclear compounds and each Ln(Ⅲ) ion is eight-coordinated. The two central Ln(Ⅲ) ions are bridged by two μ2O atoms from 8-hydroxyquinoline Schiff base ligands, leading to a parallelogram Ln2O2 core. The magnetism investigation shows that compound 2 display slow magnetic relaxation behavior under zero dc field (ΔE/kB = 19.77 K and τ0 = 1.35 × 10−6 s). Subsequent studies strongly suggested that the four Ln2 compounds binded to Calf thymus DNA (CT-DNA) through intercalative mode and have pBR322 plasmid DNA cleavage ability. This work will provide more insights for the design and investigation of lanthanide-based SMMs, and has certain reference value to study the interaction between compound and DNA.

Modulating SMM behaviors in phenoxo-O bridged Dy2 compounds via different β-diketonate

Two new Dy2 compounds, [Dy(TTA)2L]2(1) and [Dy(dbm)2L]2 (2) (TTA = 2-thenoyltrifluoroacetone, and HL = 2-[(4-chlorophenyl)imino]methyl]-8-hydroxyquinoline and dbm = dibenzoylmethane), were synthesized via solvent evaporation method, and the structures and magnetic properties of them have been characterized. The X-ray structural analysis show that both 1 and 2 are binuclear dysprosium complexes with similar structure, and the two central Dy atoms are bridged by two phenoxo-O atoms of two 8-hydroxyquinoline Schiff base ligands. The only difference is the coordinate β-diketonate. Magnetic measurements indicated that the two Dy2 compounds display different single-molecular magnets (SMMs) behaviors with Ueff /kB = 29.4 K for 1 and Ueff /kB = 43.5 K for 2.

A phenoxo-O bridged Dy2 compound showing two-step magnetic relaxation processes behavior

A new dinuclear Dy(III)-based compound, [Dy(bfac)2L]2(1) ([bfac = benzoyltrifluoroacetone, and HL = 2-[(4-chlorophenyl)imino]methyl]-8-hydroxyquinoline), was synthesized, structurally and magnetically characterized. The X-ray structural analysis exhibits compound 1 is a binuclear dysprosium complex, in which Dy1 and Dy1a atoms are bridged by two phenoxo-O atoms of two 8-hydroxyquinoline Schiff base ligands. Magnetic properties research indicated that two magnetic relaxation processes were clearly observed in 1 under Hdc = 0 fild. It is a rare and interesting magnetic phenomenon in the reported dinuclear Ln(III)-based compounds.

Structures, luminescence and magnetic properties of four phenoxo-O bridged Ln2 compounds: Distinct single-molecule magnets behaviors were observed in two Tb2 compounds

Four new dinuclear lanthanide compounds, [Ln(hfac)2L]2 (Ln(III)=Eu (1) and Tb (2)) and [Ln(tfac)2L]2·(C7H16)x (Ln(III)=Tb (3), Yb (4), HL=2-[[(4-iodophenyl)imino]methyl]-8-hydroxyquinoline, hfac=hexafluoroacetylacetonate, tfac=trifluoroacetylacetonate), 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 two bidentate hfac− and two μ2-O bridging 8-hydroxyquinoline Schiff base ligands. Magnetic measurements indicated that slow magnetic relaxation behaviors were observed in 2 under 0dc field, with an optimized dc field of 2000Oe for 2, the quantum tunneling of the magnetization was suppressed with ΔE/kB of 6.72K. However, no evident ac magnetic signals were observed in 3 under 0dc field. The distinct single-molecule magnets behaviors are mainly due to the slight different coordination environments around central TbIII ions of 2 and 3.

Structures and magnetic properties of two series of phenoxo-O bridged Ln2 compounds: Two Gd2 compounds displaying magnetic refrigeration properties

Two series of lanthanide dinuclear compounds, namely[Ln(hfac)2L]2 (LnIII=Gd (1), Ho (2) and Er (3), hfac=hexafluoroacetylacetonate, HL=2-[[(4-iodophenyl)imino]methyl]-8-hydroxyquinoline) and [Ln(tfac)2L]2 (LnIII=Gd (4) and Tm (5), tfac=trifluoroacetylacetonate), have been synthesized and characterized by elemental analysis, IR, PXRD, UV–Vis and single crystal X-ray diffraction. Single-crystal X-ray diffraction analysis shows that the two series of Ln2 compounds have very similar structures and 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 ligands. The magnetic study reveals that 1 and 4 display cryogenic magnetic refrigeration properties with maximum −ΔSm values of 16.41 and 18.32JK−1kg−1 at 2.0K and 7.0T, respectively.

Comparative ethylene polymerization via imino-quinolinol catalysts

A series of zirconium catalysts based on tridentate 8-hydroxyquinoline Schiff base ligands were prepared and successfully used for polymerization of ethylene. The highest activities of the prepared catalysts were obtained at polymerization temperatures about 30–45oC. By increasing the [Al]/[Zr] molar ratio productivity of all the catalysts enhanced to an maximum value then decrease at higher [Al]/[Zr] molar ratio with the exception of catalyst 4, which showed no optimum activity in the range studied. Also, the activities and selectivities to produce low-carbon olefins were profoundly influenced by the catalysts structure indicating the dramatic effects of the substitution on the polymerizations behavior. Fouling of the reactor was strongly related to polymerization parameters like as monomer pressure and [Al]/[Zr] ratio in the homogeneous polymerization. Heterogeneous polymerization of ethylene using the catalysts and the MAO modified silica decreased the fouling. The obtained polyethylenes have a melting point of about 125–130°C, crystallinities of about 45–55% and PDI of 2.45–3.45.

Magnetic refrigeration and single-molecule magnet behaviour of two lanthanide dinuclear complexes (Ln = GdIII, TbIII) based on 8-hydroxyquinolin derivatives

Two dinuclear lanthanide(III) complexes, namely, [Ln2(bfa)4L2]·CH2Cl2 (Ln(III)=Gd (1) and Tb (2), bfa=benzoyltrifluoroacetone and HL=2-[[(4-methylphenyl)imino]methyl]-8-hydroxyquinoline), have been synthesized, structurally and magnetically characterized. 1 and 2 are phenoxo-O bridged dinuclear complexes and each center Ln(III) ion is eight-coordinated with two bidentate bfa and two μ2-O bridging 8-hydroxyquinoline Schiff base ligands. Magnetic studies reveal that 1 displays cryogenic magnetic refrigeration property (−ΔSm=18.5Jkg−1K−1 for ΔH=7T at 2K); while 2 exhibits single-molecule magnet behavior with the anisotropic barriers (ΔE/kB) of 9.93K.

Structures, luminescence properties, magnetocaloric effect and slow magnetic relaxation of three Ln (III) complexes based on 8‑hydroxyquinoline Schiff-base ligand

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 19.94JK−1kg−1 at 2K and 7T; whereas 2 shows slow magnetic relaxation with energy barriers of 15.3K and τ0=3.34×10−6s. Additionally, solid-state photoluminescence property reveals that 2 displays the characteristic TbIII luminescence at room temperature.

Two Gd2 compounds constructed by 8-hydroxyquinoline Schiff base ligands: Synthesis, structure, and magnetic refrigeration

Two new Gd2 compounds having formulae, [Gd2(hfac)4(L1)2] (1) and [Gd2(hfac)4(L2)2] (2) (hfac=hexafluoroacetylacetonate, HL1=2-[4-methylaniline-imino]methyl]-8-hydroxyquinoline and HL2=2-[(3,4-dimethylaniline)-imino]methyl]-8-hydroxyquinoline), have been successfully synthesized via applying two different 8-hydroxyquinoline Schiff base ligands, and further characterized by crystallography. Structural analysis shows that both of 1 and 2 are phenoxo-O bridged dinuclear complexes. The magnetic study reveal that 1 and 2 display cryogenic magnetic refrigeration properties with maximum −ΔSm=17.66Jkg−1K−1 at 2K and 7T for 1 and −ΔSm=14.81Jkg−1K−1 at 3K and 7T for 2.

Lanthanide dinuclear complexes constructed by 8-hydroxyquinoline Schiff base showing magnetic refrigeration and slow magnetic relaxation

Two dinuclear lanthanide(III) complexes based on 8-hydroxyquinoline Schiff base derivatives, [Ln2(hfac)6L2]·0.5C7H16 (Ln=Gd (1) and Dy (2), HL=5-(4-methylbenzylidene)-8-hydroxylquinoline and hfac=hexafluoroacetylacetonate), have been synthesized, structurally and magnetically characterized. Both 1 and 2 are phenoxo-O bridged dinuclear complexes, and center Ln(III) ions are eight-coordinated with three bidentate hfac and two μ2-O bridging 8-hydroxyquinoline Schiff base ligands. Magnetic studies reveal that 1 exhibits antiferromagnetic exchange interaction between nearby Gd(III) centers and shows magnetic refrigeration (−ΔSm=14.9Jkg−1K−1 for ΔH=7 T at 2K). Ac susceptibility measurements reveal that 2 exhibits slow magnetic relaxation behavior with the anisotropic barriers (ΔE/kB) of 3.0K.

Modulating dynamic magnetic behaviors of two Tb(III) dinuclear complexes by using two different β-diketonate coligands

Three dinuclear rare-earth complexes, [RE2(tfa)4L2] (RE=Y(1), Tb (2)) and [Tb2(dbm)4L2·CH3CN·CH2Cl2](3) (tfa=trifluoroacetylacetonate, dbm=dibenzoylmethane and HL=2-[(4-bromophenyl)-imino]methyl]-8-hydroxyquinoline), have been synthesized and structurally characterized. Complexes 1–3 are phenoxo-O bridged dinuclear complexes, RE(III) ions are eight-coordinated with two bidentate β-diketonate and two μ2-O bridging 8-hydroxyquinoline Schiff base ligands. Magnetic studies reveal that 2 shows single-molecule-magnet behavior with the anisotropic barriers (ΔE/kB) of 1.18K, while no out of-phase alternating-current (ac) signal is noticed for 3. The distinct magnetic behaviors of 2 and 3 are mainly due to the slightly different chemical environment around the center Tb(III) ions.

Single-molecule magnet behavior of a dinuclear dysprosium compound constructed by 8-hydroxyquinoline Schiff base and β-diketonate ligands

A dinuclear dysprosium compound, [Dy2(dbm)4L2]2(1) (Hdbm=1,3-diphenyl-1,3-propanedione, HL=2-[[(4-fluorophenyl)imino]methyl]-8-hydroxyquinoline), have been synthesized, structurally and magnetically characterized. The X-ray structural analysis exhibits that the compound 1 is phenoxo-O bridged binuclear compound, in which two DyIII ions are bridged by two phenoxido oxygen atoms of two 8-hydroxyquinoline Schiff base ligands. Each DyIII centers exhibit an eight-coordinated environment. Magnetic measurements indicated that slow relaxation of the magnetization was clearly observed in 1, typical of SMM behavior.