Ling-Yu Guo

Embedding MnO@Mn3O4 Nanoparticles in an N-Doped-Carbon Framework Derived from Mn-Organic Clusters for Efficient Lithium Storage

The first synthesis of MnO@Mn3 O4 nanoparticles embedded in an N-doped porous carbon framework (MnO@Mn3 O4 /NPCF) through pyrolysis of mixed-valent Mn8 clusters is reported. The unique features of MnO@Mn3 O4 /NPCF are derived from the distinct interfacial structure of the Mn8 clusters, implying a new methodological strategy for hybrids. The characteristics of MnO@Mn3 O4 are determined by conducting high angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and electron energy loss spectroscopy (EELS) valence-state analyses. Due to the combined advantages of MnO@Mn3 O4 , the uniform distribution, and the NPCF, MnO@Mn3 O4 /NPCF displays unprecedented lithium-storage performance (1500 mA h g-1 at 0.2 A g-1 over 270 cycles). Quantitative analysis reveals that capacitance and diffusion mechanisms account for Li+ storage, wherein the former dominates. First-principles calculations highlight the strong affiliation of MnO@Mn3 O4 and the NPCF, which favor structural stability. Meanwhile, defects of the NPCF decrease the diffusion energy barrier, thus enhancing the Li+ pseudocapacitive process, reversible capacity, and long cycling performance. This work presents a new methodology to construct composites for energy storage and conversion.

Core–Shell {Mn7⊂(Mn,Cd)12} Assembled from Core {Mn7} Disc

Postsynthetic decoration of the Mn7, {MnIII⊂MnII6}, core with CdII in the outer shell to form the next generation Mn13Cd6, {MnIII⊂MnIII3MnII3⊂ MnII6CdII6}, core-shell disc was achieved and confirmed by single-crystal X-ray diffraction. The formation of Mn13Cd6 has only been successful with CdII and if the Cd salt is added within the first half hour window when the inner Mn7 has formed. EDX and ICP-AES gave the accurate content and confirm the average found by X-ray diffraction. HR-ESI-MS was even more precise by revealing three prominent molecular species, Mn13Cd6, Mn14Cd5 and Mn15Cd4, having a distribution of metals. The presence of nonmagnetic metal on the periphery reduces the exchange between these clusters as well as the low magnetic moment decreases the dipolar interaction resulting in a paramagnet compared to the ferrimagnetism found for the parent Mn19, {MnIII⊂MnIII3MnII3⊂MnII12}, disc. This study opens the way for the syntheses of heterometallic core-shell clusters in a controllable fashion.

Robust Cluster Building Unit: Icosanuclear Heteropolyoxocopperate Templated by Carbonate

The encapsulation of carbonate derived from atmospheric CO2 has resulted in an icosanuclear heteropolyoxocopperate, isolated as a metal-organic 1D chain, 2D sheet, or 3D framework, in which the Cu20 nanocluster represents the first eight-capped α-Keggin polyoxometalate with the late-transition-metal Cu(II) as the polyatom, CO3(2-) as the heteroanion, and OH(-) and suc(2-) or glu(2-) (H2suc=succinic acid; H2glu=glutaric acid) as the terminal ligands, which suggests a conceptual similarity to classical polyoxometalates. Even in the presence of competitive SO4(2-) in the assembly system, the CO3(2-) anion is still captured as a template to direct the formation of the Cu20 nanocluster, which indicates the stronger templation ability of CO3(2-) compared with SO4(2-). When other aliphatic dicarboxylates, such as glutaric acid, were used as ligands, the CO3(2-)-templated Cu20 nanocluster was maintained and acted as a cluster building unit (CBU) to be linked by two glutarate bridges to generate a distinct 1D metal-organic chain. This report presents not only a rare example of a huge anion-templated transition-metal cluster, but also its use as a robust CBU to construct novel coordination architectures. Variable-temperature magnetic susceptibility studies revealed that an antiferromagnetic interaction exists within the Cu20 nanocluster. The correlation between the coordination structure and the electron paramagnetic resonance spectra recorded of both powder and single-crystal samples are discussed in detail.

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.

Tunable Aggregation-Induced Emission of Polyoxometalates via Amino Acid-Directed Self-Assembly and Their Application in Detecting Dopamine

In this work, through the aqueous phase self-assembly of an Eu-containing polyoxometalate (POM), Na9[EuW10O36]·32H2O (EuW10) and different amino acids, we obtained spontaneously formed vesicles that showed luminescence enhancement for EuW10 and arginine (Arg), lysine (Lys), or histidine (His) complexes, but luminescence quenching for EuW10 and glutamic acid (Glu) or aspartic acid (Asp) complexes. The binding mechanisms between them have been explored at the molecular level by using different characterization techniques. It was found that EuW10 acted as polar head groups interact with the positively charged residues for alkaline amino acids, protonated amide groups for acidic amino and nonpolar acid aminos through electrostatic interactions, and the remaining segments of amino acids served as relatively hydrophobic parts aggregated together forming bilayer membrane structures. Moreover, the different influences of amino acids on the fluorescence property of EuW10 revealed that the electrostatic interaction between the positive charged group of amino acid and the polyanionic cluster dominates the fluorescence properties of assemblies. Furthermore, a turn-off sensing application of the EuW10/Arg platform to probe dopamine (DA) against various other biological molecules such as neurotransmitters or amino acids was also established. The concept of combining POMs with amino acids extends the research category of POM-based functional materials and devices.

Heptanuclear CoII5CoIII2 Cluster as Efficient Water Oxidation Catalyst

Inspired by the transition-metal-oxo cubical Mn4CaO5 in photosystem II, we herein report a disc-like heptanuclear mixed-valent cobalt cluster, [CoII5CoIII2(mdea)4(N3)2(CH3CN)6(OH)2(H2O)2·4ClO4] (1, H2mdea = N-methyldiethanolamine), for photocatalytic oxygen evolution. The topology of the Co7 core resembles a small piece of cobaltate protected by terminal H2O, N3-, CH3CN, and multidentate N-methyldiethanolamine at the periphery. Under the optimal photocatalytic conditions, 1 exhibits water oxidation activity with a turnover number (TON) of 210 and a turnover frequency (TOFinitial) of 0.23 s-1. Importantly, electrospray mass spectrometry (ESI-MS) was used to not only identify the possible main active species in the water oxidation reaction but also monitor the evolutions of oxidation states of cobalt during the photocatalytic reactions. These results shed light on the design concept of new water oxidation catalysts and mechanism-related issues such as the key active intermediate and oxidation state evolution in the oxygen evolution process. The magnetic properties of 1 were also discussed in detail.

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.

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.