Rong-Bin Huang

High-nuclearity 3d-4f clusters as enhanced magnetic coolers and molecular magnets

Four 52-metal-ion 3d-4f cluster complexes featuring a common core of Ln(42)M(10) (Ln = Gd(3+), Dy(3+); M = Co(2+/3+), Ni(2+)) were obtained through self-assembly of the metal ions templated by mixed anions (ClO(4)(-) and CO(3)(2-)). Magnetic studies revealed that the Gd(42)Co(10) and Gd(42)Ni(10) clusters exhibit the largest magnetocaloric effect (MCE) among any known 3d-4f complexes. Replacement of Gd(3+) ions with anisotropic Dy(3+) ions caused significant changes in the magnetic behavior of the clusters; both Dy(42)Co(10) and Dy(42)Ni(10) displayed slow relaxation of the magnetization.

Synthesis of Trisoctahedral Gold Nanocrystals with Exposed High-Index Facets by a Facile Chemical Method

National Natural Science Foundation of China [20725310, 20721001, 20673085, 20671079, J0630429]; National Basic Research Program of China [2007CB815303, 2009CB939804]; Fujian Province of China [2005HZ013]

A 48-Metal Cluster Exhibiting a Large Magnetocaloric Effect†

NNSFC[20825103, 20901064, 90922031, 2007CB815304, 21021061]; Fundamental Research Funds for the Central Universities[2010121016]

Keeping the Ball Rolling: Fullerene-like Molecular Clusters

The discovery of fullerenes in 1985 opened a new chapter in the chemistry of highly symmetric molecules. Fullerene-like metal clusters, characterized by (multi)shell-like structures, are one rapidly developing class of molecules that share this shape. In addition to creating aesthetically pleasing molecular structures, the ordered arrangement of metal atoms within such frameworks provides the opportunity to develop materials with properties not readily achieved in corresponding mononuclear or lower-nuclearity complexes. In this Account, we survey the great variety of fullerene-like metal-containing clusters with an emphasis on their synthetic and structural chemistry, a first step in the discussion of this fascinating field of cluster chemistry. We group the compounds of interest into three categories based on the atomic composition of the cluster core: those with formal metal-metal bonding, those characterized by ligand participation, and those supported by polyoxometalate building blocks. The number of clusters in the first group, containing metal-metal bonds, is relatively small. However, because of the unique and complex bonding scenarios observed for some of these species, these metalloid clusters present a number of research questions with significant ramifications. Because these cores contain molecular clusters of precious metals at the nanoscale, they offer an opportunity to study chemical properties at size ranges from the molecular to nanoscale and to gain insights into the electronic structures and properties of nanomaterials of similar chemical compositions. Clusters of the second type, whose core structures are facilitated by ligand participation, could aid in the development of functional materials. Of particular interest are the magnetic clusters containing both transition and lanthanide elements. A series of such heterometallic clusters that we prepared demonstrates diverse magnetic properties including antiferromagnetism, ferrimagnetism, and ferromagnetism. Considering the diversity of their composition, their distinct electronic structures, and the disparate coordination behaviors of the different metal elements, these materials suggest abundant opportunities for designing multifunctional materials with varied structures. The third type of clusters that we discuss are based on polyoxometalates, in particular those containing pentagonal units. However, unlike in fullerene chemistry, which does not allow the use of discrete pentagonal building blocks, the metal oxide-based pentagonal units can be used as fundamental building blocks for constructing various Keplerate structures. These structures also have a variety of functions, including intriguing magnetic properties in some cases. Coupled with different linking groups, such pentagonal units can be used for the assembly of a large number of spherical molecules whose properties can be tuned and optimized. Although this Account focuses on the topological aspects of fullerene-like metal clusters, we hope that this topical review will stimulate more efforts in the exploratory synthesis of new fullerene-like clusters. More importantly, we hope that further study of the bonding interactions and properties of these molecules will lead to the development of new functional materials.

Solvent-Induced Transformation of Single Crystals of a Spin-Crossover (SCO) Compound to Single Crystals with Two Distinct SCO Centers

The long-sought-after crystal structure of Fe(tpa)(NCS)(2) (1, tpa = tris(2-pyridylmethyl)amine), an otherwise well-studied spin-crossover (SCO) complex, has been obtained, and its one-step, incomplete spin transition was correlated to its solid-state structures at different temperatures. Upon exposure to methanol vapor, single-crystal-to-single-crystal transformation of 1 to a new SCO compound, 2, formulated as {[Fe(tpa)(NCS)(2)] x [Fe(tpa)(NCS)(2) x CH(3)OH]}, occurs with a dramatic color change from yellow to red. Crystallographic studies revealed that the asymmetric unit of the structure of 2 contains two independent Fe(II) centers. Studies by magnetic measurements and Mossbauer spectroscopy revealed a two-step complete spin transition for compound 2, between LS-LS and HS-HS, via an unambiguous intermediate LS-HS phase; the two SCO centers of disparate spin states were resolved crystallographically. That a significant portion of the original crystal structure is maintained indicates that the present approach is a more subtle means of altering the properties associated with SCO phenomenon than by changing counteranions or crystallization using different solvents. Furthermore, the dramatic changes in crystal structure and SCO behaviors triggered by mere solvent sorption suggest that this approach is rather efficient in modifying and hopefully fine-tuning and optimizing properties of SCO compounds. Coupled with the aforementioned gentleness and subtlety, the present approach of heterogeneously introducing perturbations to pre-existing supramolecular arrays of SCO units is more conducive to systematic studies aiming at the discovery of new SCO systems and phenomenon toward their ultimate materials applications.

pH-Dependent Ag(I) coordination architectures constructed from 4-cyanopyridine and phthalic acid: from discrete structure to 2D sheet

Four mixed-ligand Ag(I) coordination complexes (CCs), namely, [Ag(cnpy)2(Hpta)] (1), [Ag2(cnpy)2(Hpta)2] (2), [Ag4(cnpy)2(pta)2(H2O)]n (3) and [Ag2(inta)2(pta)·3H2O]n (4), (cnpy = 4–cyanopyridine, H2pta = phthalic acid, inta = isonicotinamide) have been synthesized through a one-pot ultrasonic reaction of silver(I) oxide, cnpy and H2pta under different pH values and structurally characterized. Complexes 1 and 2 formed at lower pH values (5.0 for 1 and 6.9 for 2) exhibit zero-dimensional (0D) mononuclear and tetranuclear motifs, respectively. Reaction at pH = 8.8 leads to a two-dimensional (2D) structure of 3 in which completely deprotonated H2pta shows two kinds of coordination modes: μ5-η1:η1:η1:η3 and μ6-η1:η1:η1:η3. A further increase of the pH value to 9.4 results in the in situhydrolysis of cnpy and produces complex 4 as a one-dimensional (1D) chain structure. Of particular interest, a well-resolved chair-like centrosymmetric hexamer water cluster, (H2O)6, which is stabilized by 1D chains through six dangling hydrogen bonds, exists in 4. Comparing the experimental results, it is comprehensible that the pH value plays a crucial role in the formation of the resulting structures. Additionally, results about IR spectra, thermogravimetric curves and photoluminescence spectra were discussed.

The Designed Assembly of Augmented Diamond Networks From Predetermined Pentanuclear Tetrahedral Units

One of the most important goals in the synthesis of new materials is to achieve real “design” and to obtain tailor-made compounds with expected structures and properties starting from well-characterized inorganic and organic precursors. To this end, secondary building units (SBUs), which have the advantage of allowing the topologies of structures to be predicted, are widely used to design and construct the extended frameworks that are attracting much interest in materials science, chemistry, and crystallography. SBUs usually possess attributes, such as the necessary shape and geometry, metal coordination environments, and desired directionality, that offer the possibility to assemble predefined building units into network structures with expected topologies. For example, some solid materials based on SBUs (trimetallic octahedra with a common m3-O center [3] or polymeric clusters) linked through polycarboxylate and polypyridyl ligands have been obtained. TCNQ (7,7,8,8tetracyano-p-quinodimethane) has attracted much attention as a polytopic bridge in recent years as this redox-active ligand can act as a good electronic acceptor or donor depending on whether its valence is 0, 1, or 2. TCNQbridged complexes generally also display unusual electrical, optical, and magnetic properties. A large number of extended frameworks based on some specific SBUs have been designed and synthesized over the past two decades, although little attention has been focused on investigating the role of the SBU precursors and/or the reaction intermediates in the assembly of metal–organic frameworks. An EXAFS study by F9rey et al. has provided direct evidence that Fe3O building units remain intact during the crystallization of starting materials into products. Similarly, electrospray ionization mass spectrometry (ESIMS) has been used to identify intermediates in solutions prior to the formation of networks, thereby providing an effective method of following the assembly process. Herein, we utilize two pentanuclear metal clusters with predetermined shapes, sizes, and geometries, namely [M5(btz)6(NO3)4(H2O)4] (btz= benzotriazolate; M=Co (1), Ni (2)), as the SBUs and the radical anion TCNQC as the organic linker to realize the stepby-step synthesis of two twofold interpenetrated threedimensional diamond networks with formula [M5(btz)6(TCNQC )4(H2O)4]·nH2O (3 : M=Co, n= 2; 4 : M=Ni, n= 3.5). Complex 1 (or 2) was prepared from btz-CH2OH and Co(NO3)2·6H2O (or Ni(NO3)2·6H2O) in acetone solution. The CH2OH group at the 2-position of btz is lost during the reaction. Single-crystal X-ray diffraction analysis revealed that 1 and 2 are isomorphous and crystallize in the space group I4̄. The structure of 1 is shown in Figure 1. The

Shape-Dependent Antibacterial Activities of Ag2O Polyhedral Particles

Ag(2)O particles with different polyhedral shapes including octahedron, truncated octahedron, and cube were successfully synthesized by a simple wet-chemical method using silver nitrate, ammonia, and sodium hydroxide as raw materials at room temperature. Simply by tuning the concentration of starting materials, the shape of Ag(2)O particles evolved from octahedron to cube, and the size gradually decreased from 1-2 microm to 400-700 nm. As examples for promising applications, the antibacterial activities of the as-prepared Ag(2)O polyhedral particles were preliminarily studied. It has been found the antibacterial activity of Ag(2)O particles against E. coli depends on the shape of Ag(2)O particles, demonstrating that the surface structure of Ag(2)O particles affects the antibacterial activity.

Single-crystal-like hematite colloidal nanocrystal clusters: synthesis and applications in gas sensors, photocatalysis and water treatment

A facile and efficient one-pot solvothermal synthetic route based on a simplified self-assembly is proposed to fabricate spherical hematite colloidal nanocrystal clusters (CNCs) of uniform shape and size. The as-prepared hematite CNCs are composed of numerous nanocrystals of approximately 20 nm in size, and present a single-crystal-like characteristic. A possible formation process based on the nucleation–oriented aggregation–recrystallization mechanism is proposed. Our experiments demonstrated that both the surfactant and the mixed solvent play very critical roles in controlling the size of primary nanocrystals and the final morphology of single-crystal-like spherical CNCs. Compared with other hematite nanostructures, the spherical hematite CNCs show outstanding performance in gas sensing, photocatalysis and water treatment due to their large surface area and porous structure. In addition, interesting tertiary CNCs formed by further assembly of secondary spherical CNCs were observed for the first time.

p-Dimethylaminobenzaldehyde thiosemicarbazone: a simple novel selective and sensitive fluorescent sensor for mercury(II) in aqueous solution.

A novel and simple fluorophore, p-dimethylaminobenzaldehyde thiosemicarbazone (DMABTS), was prepared in order to find available fluorescent chemosensor for mercuric ion in aqueous solution. DMABTS emitted fluorescence at 448 nm in aqueous solution and its fluorescence intensity was completely quenched upon interaction with Hg(2+) ions, which should be attributed to the 1:1 complex formation between DMABTS and Hg(2+). The binding constant of the complex was determined as 7.48 x 10(6)mol l(-1). The linear range of quantitative detection of 0 to 5.77 x 10(-6)mol l(-1) and the detection limit of 7.7 x 10(-7)mol l(-1) for Hg(2+) in the 6.3 x 10(-6)mol l(-1) DMABTS aqueous solution were obtained from a calibration curve. The coexistence of several transition metal ions and anions did interfere the fluorometric titration of Hg(2+) ion by less than 4% in the emission change.