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Xianhui Bu

Publications and source records attributed to Xianhui Bu.

At least 19 recordsLinked to original sources
PubMed2006

Sodium zinc hydroxide sulfite with a novel Zn3OH geometry.

The synthesis and crystal structure of a new sodium zinc hydroxide sulfite, Na[(Zn(OH)]3(SO3)2, with novel structural features and bonding geometry are reported. In Na[(Zn(OH)]3(SO3)2, Zn2+ and O2- alternate to form an interesting corrugated hexagonal sheet with rings consisting of (ZnO)3. Another rare occurrence is the bonding geometry of one-third of the O sites within the sheet. These O sites form a planar Zn3O unit, unlike other known compounds, in which Zn3O is pyramidal.

Hydroxides↗
PubMed2006

Metal-organic frameworks from zinc sulfite clusters, chains, and sheets: 4-connected, (3,4)-connected 3-D frameworks and 2-D arrays of catenane-like interlocking rings.

Even though open-framework solids have been made in a variety of compositions such as silicates, phosphates, germanates, borates, and phosphites, few are known that are based on trigonal-pyramidal sulfite anions. We report here the first synthetic and structural studies of metal-organic framework materials in the zinc sulfite composition. It is demonstrated here that Zn2+ and SO32- can form various neutral inorganic subunits that can be 0-D clusters, 1-D chains, or 2-D sheets. These inorganic subunits of different dimensionality can subsequently be connected into extended frameworks of higher dimensionality through bifunctional ligands. In (ZnSO3)2en, infinite corrugated ZnSO3 layers are pillared by ethylenediamine (en) molecules into a 3-D network that can be classified as a (3,4)-connected net based on tetrahedral Zn nodes and trigonal-pyramidal S nodes. In (ZnSO3)pip, infinite ZnSO3 chains are cross-linked with piperazine molecules into a 3-D framework that can be classified as 4-connected net based on tetrahedral Zn nodes only. In (ZnSO3)2(TMDPy)2, (ZnSO3)2 dimers are doubly bridged by trimethylenedipyridine molecules into an infinite chain with a string of circles. Each circle along the chain is interlocked with another circle from a chain in the perpendicular direction, creating a 2-D pattern with an infinite-square array of catenane-like units.

Molecular Structure↗
PubMed2006

Two-dimensional indium sulfide framework constructed from pentasupertetrahedral p1 and supertetrahedral t2 clusters.

A new open-framework indium sulfide ([In12S24H2]10-) constructed from pentasupertetrahedral sulfide clusters ([In8S17H],9- P1) and supertetrahedral sulfide clusters ([In4S10H],7-) T2) has been prepared through hydrothermal synthesis. Unlike previously reported P1 clusters that require divalent metal cations, the P1 cluster reported here consists of only trivalent ions (In3+) and is the only known example of tetrahedral clusters with a core sulfur site bonded to four trivalent ions. Each P1 cluster is joined to three T2 clusters (vice versa) to form an infinite two-dimensional sheet stacked along the crystallographic c-axis. In contrast with known three-dimensional open-framework indium sulfides in which locations of extraframework amines are rarely known due to disorder, structure-directing amine molecules are much less disordered as a result of host-guest N-H...S hydrogen bonding. The UV-vis diffuse reflectance spectrum shows that this material is a wide band gap semiconductor.

Crystallography, X-Ray↗
PubMed2006

Solvothermal in situ ligand synthesis through disulfide cleavage: 3D (3,4)-connected and 2D square-grid-type coordination polymers.

Two novel coordination polymers, Cu3(4-pyt)3 (1) and Co(4-pyt)2 (2) (4-pyt = pyridine-4-thiolate), have been synthesized by in situ generation of a 4-pyt ligand from a 4,4'-dithiodipyridine precursor through reductive cleavage of the disulfide bond under solvothermal conditions. 1 and 2 exhibit a three-dimensional (3,4)-connected network and a two-dimensional square-grid-type structure, respectively.

Chemistry, Inorganic↗
PubMed2006

(3,4)-connected zincophosphites as structural analogues of zinc hydrogen phosphate.

The synthesis and crystal structures of three new open-framework zincophosphites with helical channels are reported here in the context of the synthetic design of an open architecture from three- and four-connected polyhedral centers. These zincophosphites were prepared under hydrothermal conditions from HF-containing media in mixed water-ethylene glycol solvents. Their three-dimensional frameworks consist of alternating ZnO4(6-) tetrahedra and HPO3(2-) trigonal pyramids with an overall framework composition of [Zn3(HPO3)4]2-. The topology was analyzed by converting these zincophosphites from their (3,4)-connected network into a four-connected framework. The symmetry and charge density of three different structure-directing agents dictate the symmetry and framework density of resulting inorganic frameworks. These zincophosphites are structural analogues of a known hydrogen phosphate, suggesting that the bonding difference between -P-H and -P-OH plays an insignificant role in the formation of phosphite and hydrogen phosphate open frameworks.

Crystallization↗
PubMed2006

Metal-chelate dye-controlled organization of Cd32S14(SPh)40(4-) nanoclusters into three-dimensional molecular and covalent open architecture.

Chalcogenide II-VI nanoclusters are usually prepared as isolated clusters and have defied numerous efforts to join them into covalent open-framework architecture with conventional templating methods such as protonated amines or inorganic cations commonly used to direct the formation of porous frameworks. Herein, we report the first templated synthesis of II-VI covalent superlattices from large II-VI tetrahedral clusters (i.e., [Cd32S14(SPh)38]2-). Our method takes advantage of low charge density of metal-chelate dyes that is a unique match with three-dimensional II-VI semiconductor frameworks in charge density, surface hydrophilicity-hydrophobicity, and spatial organization. In addition, metal-chelate dyes also serve to tune the optical properties of resulting dye semiconductor composite materials.

Journal Article↗
PubMed2005

One-dimensional assembly of chalcogenide nanoclusters with bifunctional covalent linkers.

Even though different approaches have been developed to achieve various 1D assemblies of nanocrystals, few studies have been done on the assembly of crystallographically well-defined chalcogenide nanoclusters. Here, by using bifunctional organic ligands as the directional linker, a series of one-dimensional assemblies of semiconducting chalcogenide nanoclusters have been prepared and characterized. The synthetic method allows for the preparation of differently sized tetrahedral nanoclusters that are joined together with organic linkers of different length and rigidity. Multiple linking modes between nanoclusters and organic ligands are revealed in four different assemblies that also exhibit size-dependent optical properties.

Journal Article↗
PubMed2005

Crystalline superlattices from single-sized quantum dots.

Despite the recent progress toward the synthesis of monodisperse semiconducting nanocrystals, it remains a challenge to prepare quantum dot structures with a precise number of atoms. Here, we report synthesis, crystal structure, and optical properties of a family of cadmium sulfide nanocrystal superlattices assembled through single-sized semiconducting clusters. Clusters of various sizes have been made. The largest cluster determined from single-crystal analysis has a total of 138 metal-chalcogen sites. It is the largest known single-sized II-VI quantum dot and is also the first one with more than 100 metal-chalcogen sites. X-ray powder diffraction (XRD) and optical absorption studies indicate the presence of even larger single-sized quantum dots (>200 metal-chalcogen sites). These clusters consist of cubic zinc blende-type core and hexagonal wurtzite-type corners and can exist in up to five isomeric forms that differ only in the position of the hexagonal-cubic interface.

Journal Article↗
PubMed2005

Chromium(III) complexes for photochemical nitric oxide generation from coordinated nitrite: synthesis and photochemistry of macrocyclic complexes with pendant chromophores, trans-[Cr(L)(ONO)(2)]BF(4).

Several new dinitritochromium(III) complexes of the type trans-[Cr(L)(ONO)(2)]BF(4), where L is a derivative of the macrocyclic ligand cyclam having pendant aromatic chromophores attached (L = 5,7-dimethyl-6-(substituted)-1,4,8,11-tetraazacyclotetradecane), have been prepared and characterized. Photoexcitation of aqueous solutions containing these complexes at wavelengths corresponding to the pendant chromophore absorption bands led to the generation of NO as detected by an electrochemical sensor. Photophysical data show that the expected fluorescence of the pendant chromophores is largely quenched when the macrocyclic ligand is coordinated to these Cr(III) centers, and this is interpreted in terms of fast energy transfer processes from the ligand-centered pipi states to the Cr(III)-centered ligand field states leading to subsequent cleavage of the Cr(III)-coordinated nitrito ligand. Thus, the chromophores tethered to the coordinated cyclam serve as light-gathering antennae for the intramolecular sensitization of the NO-generating photoreactions at the metal center.

Chromium↗
PubMed2005

Synthesis and luminescence properties of Cr(III) complexes with cyclam-type ligands having pendant chromophores, trans-[Cr(L)Cl(2)]Cl.

The synthesis and spectroscopic properties of new cyclam-type ligands 5,7-dimethyl-6-R-1,4,8,11-tetraazacyclotetradecane (L), where R is a pendant chromophore such as an anthracene derivative, are reported. These ligands were prepared according to a nickel(II) template procedure, and the X-ray crystal structures of several Ni(II) intermediates are described. Reaction of the free base ligands L with CrCl(3)x3THF resulted in facile formation of trans-[Cr(L)Cl(2)]Cl complexes, and the structures and spectroscopic characterizations of these complexes are also described. Examination of the photophysical properties of trans-[Cr(L)Cl(2)]Cl solutions at 77 K demonstrated the emission spectra to be dominated by phosphorescence from the ligand field doublet of the chromium(III) center. This also applies to the Cr(III) complex trans-[Cr(mac)Cl(2)]Cl, where mac is the anthracene derivative 5,7-dimethyl-6-anthracenylcyclam. Excitation into the pi-pi(*) states of the anthracene leads to marked quenching of the fluorescence from this chromophore and sensitized phosphorescence from the metal-centered doublet state.

Chromium↗
PubMed2005

Na5(In4S)(InS4)3.6H2O, a zeolite-like structure with unusual SIn4 tetrahedra.

A hydrated sodium indium sulfide, Na5(In4S)(InS4)3.6H2O, has been prepared by hydrothermal synthesis. This material contains a tetrahedral sulfur site coordinated to four trivalent indium ions, an unusual bonding pattern not previously observed in open framework chalcogenides. The structure is related to the perovskite (CaTiO3) type with simultaneous substitutions of Ti by SIn4, O by InS4, and Ca2+ by [Na5(H2O)6]5+. It is a wide-gap semiconductor and shows photocatalytic activity under UV light for hydrogen generation from aqueous solution without use of any cocatalyst.

Journal Article↗
PubMed2005

The interface chemistry between chalcogenide clusters and open framework chalcogenides.

One of the most exciting recent developments concerning molecular architectures is the emerging field of crystalline chalcogenide superlattices that bridges two traditional but distinct areas of research: chalcogenide clusters and porous materials. By combining synthetic and structural concepts in these two areas, many crystalline solids containing spatially organized chalcogenide clusters have been created that exhibit varied properties ranging from microporosity, fast ion conductivity, and photoluminescence to narrow and tunable electronic band gaps. The potential applications of these materials extend beyond traditional areas such as acid catalysis or adsorption-based separation to include shape- or size-selective photocatalysis, solid-state ionics, and electrochemistry.

Journal Article↗
PubMed2004

Tetrahedral chalcogenide clusters and open frameworks.

By integrating porosity with electrical or optical properties, microporous chalcogenides may have unique applications. Here we review recent advances and discuss concepts in the synthesis and crystal structure of tetrahedral clusters and their frameworks. These chalcogenides can be viewed as trivalent metal chalcogenides doped with tetra-, di-, or monovalent metal cations. Low-valent cations help to increase the cluster size, while high-valent cations have the opposite effect.

Journal Article↗