Su-Yuan Zeng

Family of Mixed 3d–4f Dimeric 14-Metallacrown-5 Compounds: Syntheses, Structures, and Magnetic Properties

An isomorphous family of mixed 3d-4f dodenuclear aggregates, {[Mn(III)8Ln4(Clshi)8(OAc)6(μ3-OCH3)2(μ3-O)2(CH3OH)12(H2O)2]·4CH3OH·xH2O)} (where Ln = Eu(III) (1), Gd(III) (2), Tb(III) (3), and Dy(III) (4); ClshiH3 = 5-chlorosalicylhydroxamic acid; x = 5 for 1 and 3; x = 6 for 2; x = 2 for 4), were synthesized and characterized. They were obtained from the reaction of ClshiH3 with Mn(OAc)2·4H2O and Ln(NO3)3·6H2O. These isomorphous mixed 3d-4f compounds represent a family of novel structures with lanthanide ions in the metallacrown (MC) ring. Each dodecanuclear aggregate contains two offset stacked 14-MC-5 units with M-N-O-M-N-O-Ln-O-N-M-O-N-M connectivity to capture one Ln(III) ion in the core of each MC. Two 14-MC-5 units are connected through O ions with four Mn ions and six O atoms arranged in a double Mn4O6 cubane. Magnetic measurement indicates that antiferromagnetic interactions are present between the metal ions. The Dy(III) analogue with high anisotropy and large spin shows slow magnetization relaxation at a direct-current field of 2 kOe.

A Pyridazine-Bridged Sandwiched Cluster Incorporating Planar Hexanuclear Cobalt Ring and Bivacant Phosphotungstate

A planar hexanuclear cobalt ring was clamped by two bivacant α1-[PW10O37](9-) with the assistance of the pyridazine bridges to form a novel sandwiched Co(II)-polyoxometalate cluster compound, [Na(H2O)6][Co3(OH) (pydz)4(H2O)7][Co6(PW10O37)2(pydz)4(H2O)6]·43H2O (1; pydz = pyridazine).This cluster was identified by X-ray single-crystal diffraction, elemental analysis, Fourier transform IR and UV-visible spectroscopies, and cyclic voltammetry (CV). Structural analysis reveals that 1 comprises a hexahydrated sodium, a trinuclear [Co3(OH) (pydz)4(H2O)7](5+) cationic cluster, and an anionic [Co6(PW10O37)2(pydz)4(H2O)6](6-) sandwiched cluster, thus giving an intrinsical intercluster compound. The isolation of such cluster was dependent on the in situ transformation of trivacant [α-P2W15O56](12-) to α1-[PW10O37](9-) under the hydrothermal condition. The CV shows reversible multielectron waves from the redox of W(VI) in 1. Cluster 1 exhibits remarkable electrocatalytic activity toward the reduction of nitrite. Magnetism studies indicated a weak anti-ferromagnetic exchange interaction between Co(II) ions within 1.

Study on the morphology-controlled synthesis of MnCO3 materials and their enhanced electrochemical performance for lithium ion batteries

In this work, monodispersed and high quality crystalline MnCO3 micro-peanuts and MnCO3 nano-shuttles were prepared by a simple hydrothermal method. A growth mechanism was proposed to elucidate the influence of reactant components on the morphology and size of the prepared MnCO3 samples. Both structures were employed as active electrode materials in lithium ion batteries. The electrochemical performance of the obtained MnCO3 samples was examined by analyzing the cyclic voltammograms, galvanostatic charge–discharge, rate performance and electrochemical impedance. At a current rate of 250 mA h g−1, the reversible capacity of the MnCO3 nano-shuttle electrode after 500 cycles was 605 mA h g−1, while that of the MnCO3 micro-peanut electrode was 463.4 mA h g−1. The results indicated that the MnCO3 samples synthesized by this method presented wonderful electrochemical properties, which could be used as promising active materials in lithium ion batteries.

Synthesis, structural versatility and magnetic properties of a series of copper(II) coordination polymers based on bipyrazole and various dicarboxylate ligands

Seven new copper(II) coordination networks combining flexible 3,3′,5,5′-tetramethyl-4,4′-bipyrazole (bpz) and diverse dicarboxylates, [Cu(bpz)0.5(adip)]n (1), [Cu2(bpz)4(sub)2]n (2), [Cu4(bpz)1.5(aze)·H2O]n (3), [Cu2(bpz)(pta)2(H2O)·H2O]n (4), [Cu2(bpz)(ipa)]n (5), [Cu2(bpz)(o-pda)2·H2O]n (6), and [Cu2(μ3-OH)(bpz)(p-pda)1.5·H2O]n (7) (H2adip = adipic acid, H2sub = suberic acid, H2aze = azelaic acid, H2pta = phthalic acid, H2ipa = isophthalic acid, H2o-pda = o-phenylenediacetic acid, H2p-pda = p-phenylenediacetic acid), have been obtained under solvothermal conditions and structurally verified by single-crystal X-ray diffraction analyses and further characterized by elemental analyses, powder X-ray diffraction (PXRD), infrared spectroscopy (IR), UV-vis spectroscopy and thermogravimetric analyses (TGA). Single crystal X-ray diffraction analysis revealed that both 1 and 6 are 6-connected pcu networks (point symbol: {412·63}) based on paddle-wheel [Cu2(COO)4] secondary building units (SBU). Complexes 2 and 4 are 2D 44-sql networks based on a single metal ion node and a binuclear [Cu2(COO)4(H2O)] SBU, respectively, while complex 3 features an extremely rare 3D 5-connected hxg-d-5-C2/c (point symbol: {42·67·8}) network. Complex 5 shows a 1D tape structure built from bpz sealed 1D helical Cu2(ipa) chains along the b axis, and 7 is a 3D 8-connected hex (point symbol: {36·418·53·6}) network based on a centrosymmetric [Cu4(μ3-OH)2(COO)4] SBU. A thorough structural comparison of these coordination networks suggests that the coordination fashions, conformations of dicarboxylates along with the different inorganic Cu(II) SBUs simultaneously play a significant role in constructing the diverse networks. Variable-temperature magnetic susceptibility data denote that 4 and 7 display antiferromagnetic interactions in binuclear [Cu2(COO)4(H2O)] and [Cu4(μ3-OH)2(COO)4] SBUs. Moreover, the thermal stability and UV-vis spectra of 1–7 are discussed in detail.

A facile in situ reduction route for preparation of spinel CoCr2O4 polycrystalline nanosheets and their magnetic properties

Considerable efforts have been exerted on the controllable synthesis of nanomagnetic materials due to their size- and morphology-dependent properties. Herein, a facile ethylene glycol in situ reduction strategy has been successfully employed in the preparation of CoCr2O4 nanosheets. X-ray diffraction patterns showed that the products have the cubic spinel structure. The electron microscopy analysis revealed that the obtained CoCr2O4 nanosheets consisted of nanoparticles with the diameters of 20–30 nm. Experiments proved that the volume ratio of ethylene glycol to water was crucial for the final morphology. The magnetization studies demonstrated that besides the long-range ferrimagnetic order below the Curie temperature (TC = 86 K), the sample exhibited two low-symmetry ordered states including the spiral magnetic order at TS = 20 K and the magnetic lock-in transition at TL = 13 K. The crystallinity- and size-dependent magnetic properties were also investigated. The temperature dependence of the specific heat revealed both phase transition at TC = 90 K and TS = 20 K, in line with the magnetic results.

Preparation and magnetic and microwave absorption properties of MnNb2O6 ellipsoid-like hierarchical structures

Great efforts have been made to synthesize columbite niobates due to their fascinating properties and applications. In this research, ellipsoidal MnNb2O6 crystals have been successfully prepared by a facile hydrothermal method. X-ray powder diffraction patterns showed that the products have the typical orthorhombic columbite structure. Electron microscopy analysis revealed that the obtained MnNb2O6 ellipsoids had a very rough surface, with flaky hierarchical structures composed of nanoparticles with diameters of 10–20 nm. Based on time-dependent experiments, a possible growth mechanism of the ellipsoidal hierarchitectures was also proposed. The magnetization studies demonstrate that the products exhibit antiferromagnetic behavior with a Neel temperature of about 4 K. The microwave absorption properties of the ellipsoidal MnNb2O6 hierarchical structures were also investigated with a vector network analyzer. The absorption peak position moves to a lower frequency with increasing thickness of the sample. The value of the minimum reflection loss is −11.6 dB at 7.8 GHz with a thickness of 3.5 mm, and a reflection loss lower than −10 dB can be obtained in the frequency range of 7.2–8.3 GHz.

Structural, electrochemical and magnetic analyses of a new octanuclear MnIII2MnII6 cluster with linked-defect cubane topology

The employment of the 3,5-dimethyl-1-(hydroxymethyl)-pyrazole (Hdmhmp) ligand in a manganese carboxylate cluster afforded the new mixed-valent octanuclear manganese cluster [MnIII2MnII6O2(PhCOO)10(dmhmp)4(H2O)2]·4CH3CN (1). Complex 1 was isolated by the reaction of Mn(ClO4)2·6H2O, Hdmhmp and benzoic acid in a mixed solvent of acetonitrile and methanol. The structure of 1 can be described as a μ4-O2−-linked pair of [Mn4O3] defect cubanes protected by ten PhCO2− and four μ3-dmhmp− ligands. Complex 1 is slightly soluble in acetonitrile, and high-resolution electrospray mass spectrometry (HRESI-MS) indicated that it could keep the [MnIII2MnII6O2] core integrity in solution but with detectable ligand exchange between PhCOO− and dmhmp−. The electrochemical studies show that 1 possesses a characteristic MnII → MnIII oxidation peak at +0.82 V and MnIII → MnII reduction peaks at −0.79 and −1.51 V (versus Fc/Fc+), respectively. A detailed magnetic properties investigation has revealed only a weak intramolecular antiferromagnetic interaction between the MnII and MnIII ions and no characteristic single-molecule magnetic properties.

The ferromagnetic–antiferromagnetic properties of Ni–Cr2O3 composite hollow spheres prepared by an in situ reduction method

Considerable efforts have been exerted on the facile synthesis of magnetic composite materials because of their unique properties and potential applications. Especially for ferromagnetic–antiferromagnetic systems, the magnetic exchange bias effect is essential for the development of magneto-electronic switching devices and magnetic storage media. In this research, a facile ethylene glycol in situ reduction strategy has been successfully employed in the preparation of Ni–Cr2O3 composite hollow spheres. X-Ray powder diffraction was used to determine the phase composition. Scanning electron microscopy and transmission electron microscopy was employed to characterize the morphologies of the as-prepared samples. Experiments proved that the volume ratio of ethylene glycol to water played a determinative role in the final morphology of the products. The magnetization vs. temperature results revealed a spin-glass-like behavior with blocking temperature of about 150 K for the as-prepared Ni–Cr2O3 composites. Induced by the coupling between ferromagnetic Ni and antiferromagnetic Cr2O3, a small exchange bias effect could be observed in the magnetic hysteresis loops. At lower temperature, a larger exchange bias field and coercivity are obtained. A high surface area of 145.1 m2 g−1 was obtained for the prepared porous hollow spheres.

Octanuclear Ni(II) cubes based on halogen-substituted pyrazolates: synthesis, structure, electrochemistry and magnetism

The employment of halogen-substituted pyrazole ligands in nickel(II) clusters afforded three anionic Ni(II) cubes, (HNEt3)2[Ni8(Xpz)12(OH)6] (X = Cl, 1·2CH3CN; X = Br, 2·2CH3CN; X = I, 3·12CH3CN; pz = pyrazolate). Clusters 1–3 are isolated as dianionic compounds which have similar cube geometry with each vertex occupied by a Ni(II) atom and eight μ4-OH− capped on eight square faces. The Xpz ligands adopt a bidentate mode to bind paired Ni(II) atoms on the edge of the cube. Interestingly, the three Ni8 cubes have similar symmetry, size and shape but pack together to form different lattice symmetry, which should be dictated by the halogen-related supramolecular interactions (C–X⋯H, C–X⋯π and X⋯X halogen bonding) in different crystals. The electrochemistry of 1–3 showed a Ni(II)/Ni(I) redox couple with E1/2 at ca. 900 mV and the oxidization potential order is 1 > 3 > 2 depending on the halogen substituents. 1–3 exhibit excellent electrocatalytic performances toward the oxidation of nitrite. The different packing of Ni8 cubes in 1–3 also has an important influence on their magnetic behaviors. Complex 2 showed antiferromagnetic couplings between the Ni(II) ions within the cubes, whereas 1 and 3 exclusively exhibited mixed ferromagnetic and antiferromagnetic properties, leading to frustration and typical spin glass behavior.

Self-assembly, structures, magnetic properties and solution behaviors of six mixed-valence cobalt clusters

The introduction of multidentate chelating ligands and secondary small inorganic anions into a variable-valence cobalt synthesis system led to the formation of six novel mixed-valence cobalt clusters, namely, [CoII2CoIII2(mdea)2(OH)2(2,2′-bipy)2(CH3CN)4]·4ClO4·2H2O (SD/Co1), [CoII2CoIII2(dmhmp)6(CH3CN)4]·4ClO4·4CH3CN (SD/Co2), [CoIICoIII4(mdea)4(N3)4(piv)2] (SD/Co3), [CoII2CoIII2Na(mdea)2(N3)(piv)8] (SD/Co4), [CoII4CoIII2(dea)2(Hdea)4(piv)4]·2piv (SD/Co5), and [CoII2CoIII2(mdea)2(dmpea)2(OH)2(CH3CN)2(H2O)2]·4ClO4·2H2O (SD/Co6) (H2dea = diethanolamine, H2mdea = N-methyldiethanolamine, 2,2′-bipy = 2,2′-bipyridine, Hdmhmp = 3,5-dimethyl-1-(hydroxymethyl)-pyrazole, Hpiv = pivalic acid and dmpea = 1-(3,5-dimethyl-1H-pyrazol-1-yl)-ethanimine). Among them, compounds SD/Co1, SD/Co2 and SD/Co6 have a similar cationic tetranuclear core motif {Co4O6} consisting of two CoIII and two CoII mixed-valence ions. Compound SD/Co3 has two similar neutral pentanuclear {Co5O8} clusters co-crystallized in one asymmetric unit that each contains four CoIII ions and one CoII ion. Compound SD/Co4 consists of a bimetallic pentanuclear calyx-like {Co4Na} skeleton including two CoIII and two CoII ions, while compound SD/Co5 has a cationic hexanuclear rod-like cluster {Co6O8} consisting of two CoIII and four CoII ions. In addition, the high-resolution electrospray ionization mass spectrometry (HRESI-MS) technique was introduced to detect their solution behaviors and reveal their evolutional processes. Magnetic measurements indicated that these cobalt clusters show distinct magnetic behaviors at low temperature.