cun Li

Slow magnetic relaxation in lanthanide complexes with chelating nitronyl nitroxide radical.

Two rare-earth radical complexes [Ln(hfac)(3)NIT-2Py].0.5C(7)H(16) [Ln = Tb (1), Dy (2)] have been synthesized and characterized structurally as well as magnetically. Both complexes are isomorphous, in which the NIT-2Py radical is coordinated to the Ln(III) ion in a chelating manner. Magnetic studies reveal that complex 1 shows a frequency-dependent, alternating-current magnetic susceptibility typical of a single-molecule magnet, whereas slow magnetic relaxation is observed in 2 under an applied direct-current field.

Four new lanthanide-nitronyl nitroxide (Ln(III) = Pr(III), Sm(III), Eu(III), Tm(III)) complexes and a Tb(III) complex exhibiting single-molecule magnet behavior.

Five new complexes based on rare-earth-radical [Ln(hfac)(3)(NIT-5-Br-3py)](2) (Ln = Pr (1), Sm (2), Eu (3), Tb (4), Tm (5); hfac = hexafluoroacetylacetonate; NIT-5-Br-3py = 2-(4,4,5,5-tetramethyl-3-oxylimidazoline-1-oxide)-5-bromo-3-pyridine) have been synthesized and characterized by X-ray crystal diffraction. The single-crystal structures show that these complexes have similar structures, in which a NIT-5-Br-3py molecule acts as a bridging ligand linking two Ln(III) ions through the oxygen atom of the N-O group and nitrogen atom from the pyridine ring to form a four-spin system. Both static and dynamic magnetic properties were measured for complex 4, which exhibits single-molecule magnetism behavior.

Slow Magnetic Relaxation in Novel Dy4 and Dy8 Compounds

Two novel dysprosium(III) clusters have been prepared and structurally characterized. One has a tetranuclear core with a rare zigzag arrangement, and the other is an unprecedented octanuclear cluster with six triangular Dy(3) units sharing vertices. Both dysprosium(III) clusters possess frequency-dependent on alternating-current magnetic susceptibilities, indicating possible single-molecule magnet behavior.

Structural transformation mediated by o-, m-, and p-phthalates from two to three dimensions for manganese/phthalate/4,4′-bpy complexes (4,4′-bpy = 4,4′-bipyridine)

Three isomers of o-, m-, and p-phthalate are used to link together Mn centres, resulting in [Mn(phth)(H2O)x]n moieties (phth = phthalate dianion) with single-chain, double-chain and sheet structures, respectively, which predetermine the extended structures derived from the crosslinkage of 4,4′-bipyridine, and show the influence of isomerism of the phthalate on topological changes of the final polymers from two dimensional (2D) single-layer, double-layer to 3D network architectures. These structural changes in topology are correlated with the differences in the magnetic and optical properties of the polymers.

Modulating spin dynamics of cyclic LnIII-radical complexes (LnIII = Tb, Dy) by using phenyltrifluoroacetylacetonate coligand

Three novel ring-like compounds formulated as [Ln(Phtfac)(3)(NITpPy)](2) (Ln(III) = Gd 1, Tb 2, Dy 3; HPhtfac = 4,4,4-trifluoro-1-phenylbutane-1,3-dione; NITpPy = 2-(4-pyridyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazolyl-1-oxyl-3-oxide) were synthesized and structurally and magnetically characterized. Three compounds possess cyclic dimer structure in which each pyridine substituted radical links two different metal ions through the oxygen of nitroxide group and the pyridine nitrogen. DC magnetic studies show the Ln(III) ion interacts ferromagnetically with the directly bonding nitronyl nitroxide. Both Tb(III) and Dy(III) clusters show frequency-dependent ac magnetic susceptibilities, indicating single-molecule magnet behavior. It is demonstrated that the β-diketonate coligand may play an important role in determining the magnetic relaxation for the lanthanide-radical system.

Structure and magnetic behaviour of a novel alternating one-dimensional chain compound {[Cu(phen)(μ1,1-N3)]2(μ-ta)}n

Abstract A new one-dimensional alternating chain compound {[Cu(phen)(μ1,1-N3)]2(μ-ta)}n (phen=1,10-phenanthroline, ta=terephthalato dianion) has been prepared and characterised by X-ray crystallography and magnetic measurements. The structure consists of copper chains in which the copper(II) ions are alternatively bridged by terephalato and double end-on azido bridges. In the temperature range 4–300 K, the variable temperature magnetic susceptibility of the title compound can be modelled as a dimeric copper species within which the exchange interaction is ferromagnetic.

Structural diversity and properties of M(II) 4-carboxyl phenoxyacetate complexes with 0D-, 1D-, 2D- and 3D M-cpoa framework

Nine new metal complexes with an asymmetric H2cpoa ligand, [Co(Hcpoa)2(bpe)2(H2O)2] (1), [Co(cpoa)(bpe)1.5(H2O)]·H2O (2), [Co(Hcpoa)2(4,4′-bpy)2] (3), [Co(4,4′-bpy)(H2O)4]·[Co(cpoa)2(H2O)2]·2H2O (4), [Ni(cpoa)(4,4′-bpy)(H2O)2] (5), [Ni(cpoa)(bpe)1.5(H2O)]·H2O (6), [Zn2(cpoa)2(bpe)(H2O)] (7), [Zn(cpoa)(bpe)0.5]·0.5(i-C3H7OH) (8) and [Zn(cpoa)(bpe)0.5]·0.5(n-C3H7OH) (9) (H2cpoa = 4-carboxyphenoxy acetic acid, bpe = 1,2-bis(4-pyridyl)ethane, 4,4′-bpy = 4,4′-bipyridine) were synthesized under hydro/solvothermal conditions. X-ray single-crystal structural analyses reveal that they have metal–organic frameworks ranging from 0D (1), 1D (3, 4), 2D (5, 7, 8) to 3D structure (2, 6, 9). The reaction of the CoCl2/H2cpoa/bpe (1 : 1 : 1) system results in the formation of complex 1 at the starting pH of ca. 8, and complex 2 at 12. The reaction of CoCl2/H2cpoa/4,4′-bpy (1 : 1 : 1) forms complex 3 with a 1D chain structure, while a molar ratio of 1 : 1 : 0.5 leads to the formation of complex 4 with two 1D metal–organic frameworks of rarely reported homometal complex ion pairs. By changing the added organic solvent, the 2D layer framework of complex 8 and the microporous 3D framework of complex 9 were obtained under the same reaction conditions. The guest n-C3H7OH molecules occupy 1D channels in 9. Thermogravimetric and powder X-ray diffraction analyses show that the microporous 3D framework of 9 is maintained after the removal of the guest molecule. And a reversible dealcoholization/realcoholization process can be observed. The magnetic measurements show antiferromagnetic interactions between the metal ions in 2, 4 and 5, and antiferromagnetic interaction in the range of 300–18 K and ferromagnetic interaction between Ni(II) ions below 18 K in 6.

Nitronyl nitroxide–metal complexes as metallo-ligands for the construction of hetero-tri-spin (2p–3d–4f) chains

A novel approach for the preparation of hetero-tri-spin magnetic compounds is described. It consists in using preformed metal-nitronyl nitroxide complexes as metallo-ligands in an assembling process involving an additional metal centre. This is illustrated by two unprecedented radical-Cu-Ln chain compounds (Ln = Gd(3+), Tb(3+)).

Unprecedented nitronyl nitroxide bridged 3d-4f complexes: structure and magnetic properties.

Two novel 2p-3d-4f compounds, {Ln(hfac)3[Cu(hfac)2]3(NITPhPyrim)2} [Ln = Gd (1), Dy (2)], have been obtained by reacting phenyl pyrimidyl nitronyl nitroxide with Cu(hfac)2 and Ln(hfac)3. These two compounds are the first examples of two-dimensional 3d-4f complexes bridged by nitronyl nitroxide radicals. Overall ferromagnetic behaviors were observed in both compounds.

A family of lanthanide–nitronyl nitroxide complexes: syntheses, crystal structures and magnetic properties

Seven Ln(III) complexes based on a novel nitronyl nitroxide radical have been synthesized and characterized structurally and magnetically: [Ln(hfac)3(NITNapOMe)2] (Ln = Pr(1), Gd(2), Tb(3), Dy(4), Ho(5), Er(6), Tm(7); hfac = hexafluoroacetylacetonate; NITNapOMe = 2-6′-methoxy-2′-naphthyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide). The single-crystal analyses show that these complexes have similar mononuclear tri-spin structures, in which central Ln(III) ions are eight coordinated by three hfac molecules and two NITNapOMe radicals. The variable-temperature magnetic susceptibility studies reveal the ferromagnetic interactions between Ln(III) ion and radicals in complexes 3, 4, and 7 and antiferromagnetic interactions in complexes 1, 2, 5, and 6.