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Xianhui Bu

Publications and source records attributed to Xianhui Bu.

31 records · Page 2Linked to original sources
PubMed2003

Synthetic design of crystalline inorganic chalcogenides exhibiting fast-ion conductivity.

Natural porous solids such as zeolites are invariably formed with inorganic cations such as Na(+) and K(+) (refs 1, 2). However, current research on new porous materials is mainly focused on the use of organic species as either structure-directing or structure-building units; purely inorganic systems have received relatively little attention in exploratory synthetic work. Here we report the synthesis of a series of three-dimensional sulphides and selenides containing highly mobile alkali metal cations as charge-balancing extra-framework cations. Such crystalline inorganic chalcogenides integrate zeolite-like architecture with high anionic framework polarizability and high concentrations of mobile cations. Such structural features are particularly desirable for the development of fast-ion conductors. These materials demonstrate high ionic conductivity (up to 1.8 x 10(-2) ohm(-1) cm(-1)) at room temperature and moderate to high humidity. This synthetic methodology, together with novel structural, physical and chemical properties, may lead to the development of new microporous and open-framework materials with potential applications in areas such as batteries, fuel cells, electrochemical sensors and photocatalysis.

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PubMed2003

Synthesis and photophysical properties of new chromium(III) complexes of N-derivatized 1,4,8,11-tetraazacyclotetradecane ligands cis-[Cr(1,8-R(2)cyclam)Cl(2)]Cl, where R is a pendant chromophore. exclusive formation of the cis isomer.

Several new chromium(III) complexes have been synthesized utilizing derivatives of the macrocyclic ligand cyclam (1,4,8,11-tetraazacyclotetradecane) with various N-substituted chromophores in the 1 and 8 positions (1,8-R(2)cyclam) where R = CH(3), CH(2)Ph, CH(2)Nph (Nph = naphthyl), and CH(2)Anth (Anth = anthracyl). X-ray crystal structures were determined for all four complexes, and these are formed exclusively in the cis configuration with the two tertiary amines in the "hinge" positions (i.e., along the folding axis) of the coordinated ligand. As a result, the cis isomers appear to be inert to isomerization under conditions dramatically more forcing than needed to effect the cis to trans isomerization of the unsubstituted Cr(cyclam)Cl(2)(+) ion. Photophysical studies demonstrated that emission occurs solely from the metal-centered ligand field doublet excited states regardless of whether initial excitation is into the quartet ligand field bands or into the pi-pi bands of the pendant chromophore. Thus, excitation of the pendant chromophore results in efficient intramolecular energy transfer to the metal centered ligand field excited states.

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PubMed2003

Templated assembly of sulfide nanoclusters into cubic-C3N4 type framework.

Here we report a new type of nanocluster superlattice in which each four-connected cluster ([M4In16S31],6- M = Fe, Co, Zn, and Cd) alternates with a three-connected sulfur anion (S2-) to form a rare and yet theoretically important non-centrosymmetric and non-interpenetrating (3,4)-connected net topologically identical to that of the hypothetical cubic carbon nitride type net. These materials have a ring size consisting of 16 tetrahedral atoms. Because of the large cluster size and the elimination of structural intergrowth, the volume fraction of the inorganic framework is as low as 38%. A strong photoluminescent emission has also been observed.

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PubMed2003

Nonaqueous synthesis and selective crystallization of gallium sulfide clusters into three-dimensional photoluminescent superlattices.

A low-temperature, nonaqueous synthesis approach is described that produces a series of gallium sulfide and polysulfide three-dimensional superlattices from binary Ga-S and ternary Zn-Ga-S supertetrahedral clusters. The diversity of superlattices is achieved by modifying the cluster size, the cluster composition, and the inter-cluster linkage mode. Both pure T3 (Ga10S186-) (denoted as UCR-7GaS) and pure T4 (Zn4Ga16S3310-) (denoted as UCR-5ZnGaS) superlattices with ring sizes of 18 and 24 tetrahedral atoms have been made. Of particular interest is the synthesis of the T3-T4 hybrid superlattice (denoted as UCR-19) with an odd ring size of 21 tetrahedral atoms. Another unprecedented feature is the occurrence of the -S-S-S- polysulfide linkage between supertetrahedral clusters in UCR-18. The fluorescent emission wavelength of these materials ranges from 440 to 500 nm and fills the previously observed gap between open-framework oxides and indium sulfides. A comparative study shows that open-framework gallium sulfides are more thermally stable than indium sulfides. They can also undergo ion exchange. It is suggested here that supertetrahedral clusters of different types coexist in a solution and can be selectively crystallized out with a proper choice of structure-directing agents.

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PubMed2002

Microporous and photoluminescent chalcogenide zeolite analogs.

Crystalline semiconducting sulfide and selenide zeolite analogs were synthesized that possess four-connected, three-dimensional tetrahedral networks built from tetravalent (M4+ = Ge4+ or Sn4+, where M = meta) and trivalent (M3+ = Ga3+ or In3+) cations. Microporous materials were obtained in all four combinations of M4+ and M3+, and some of them were thermally stable up to at least 380 degrees C. These materials exhibit framework topologies with pore size ranging from 12 to 24 tetrahedral atoms, high surface area, high framework charge density and ion exchange capacity, and tunable electronic and optical properties.

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PubMed2002

Pushing up the size limit of chalcogenide supertetrahedral clusters: two- and three-dimensional photoluminescent open frameworks from (Cu(5)In(30)S(54))(13-) clusters.

Direct band gap copper indium chalcogenides are of great technological importance in part because of their high photovoltaic conversion efficiency. Covalent superlattices constructed from copper indium chalcogenide clusters are of particular interest because they may combine open framework architecture with semiconducting properties. Here two photoluminescent covalent superlattices built from core-shell type copper indium sulfide supertetrahedral clusters are reported. Each cluster consists of 35 metal cations and is so far the largest known supertetrahedral cluster with a metal-to-metal distance of 1.6 nm. In addition, this is the first example of supertetrahedral clusters in heterometallic copper indium chalcogenides. The preparation of these large clusters has narrowed down the size gap between colloidal nanoclusters and small supertetrahedral clusters and revealed new possibilities in the construction of nanoporous semiconducting superlattices with tunable pore size. Through the combination of metal ions with different oxidation states to provide both overall and local charge neutrality, an effective approach has been demonstrated in the rational synthesis of chalcogenide open framework materials with large and unprecedented supertetrahedral clusters.

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PubMed2002

Nanocluster with one missing core atom: a three-dimensional hybrid superlattice built from dual-sized supertetrahedral clusters.

In addition to having size-dependent properties, nanoclusters also behave like large pseudo-atoms and serve as building blocks for the construction of superlattices with properties that differ from either individual clusters or the bulk. While colloidal nanoparticles usually self-assemble into close-packed lattices, supertetrahedral clusters that are regular fragments of the zinc blende-type lattice can form covalent lattices with large pore size and high pore volume. Unfortunately, the size of the known supertetrahedral cluster is still small, and only a few types are currently known. In addition, their superlattices invariably consist of clusters of identical size. Here we report an open framework sulfide (denoted as UCR-15) that extends the cluster size from 20 metal ions in a T4 supertetrahedron to 34 metal ions in a novel T5 supertetrahedron with a missing core atom, [In34S54]6-. T5 clusters are joined by smaller T3 clusters (i.e., [In10S18]6-) to form an extended superlattice. UCR-15 is the first example of a covalent open framework built from supertetrahedral clusters of different sizes, thus revealing new possibilities in the construction of crystalline nanoporous semiconducting superlattices. It is proposed here that the formation of the dual-sized T3 and T5 hybrid framework is related to the host-guest charge density matching.

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PubMed2002

Self-assembly of novel dye molecules and [Cd8(SPh)12]4+ cubic clusters into three-dimensional photoluminescent superlattice.

The use of organic multidentate ligands to organize inorganic species is an effective method to prepare porous solids with tunable pore sizes. However, thus far, inorganic building units are generally limited to individual metal ions (e.g., Zn2+) or their oxide clusters (e.g., Zn4O6+). To expand applications of porous materials to electronic, electrooptic, or optical areas, the organization of semiconducting chalcogenide nanoclusters is desirable. Here we report the organization of cubic [Cd8(SPh)12]4+ clusters by in-situ-generated tetradentate 1,2,4,5-tetra(4-pyridyl)benzene molecules. The structure consists of three-dimensional inorganic-organic open framework with large unidimensional channels. The combination of dye molecules and inorganic cluster units in the same material creates a synergetic effect that enhances the emission of the inorganic cluster at 580 nm. Such an emission can be excited by a broad spectral range down to the UV, which is believed to result from the absorption of dye molecules and the subsequent energy transfer. The inorganic double four-ring cluster, [Cd8(SPh)12]4+, is formed from conversion of supertetrahedral clusters, while the novel tetradentate dye molecule is formed by oxidative coupling of two diamines.

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PubMed2002

Photochemical nitric oxide precursors: synthesis, photochemistry, and ligand substitution kinetics of ruthenium salen nitrosyl and ruthenium salophen nitrosyl complexes.

Described are syntheses, characterizations, and photochemical reactions of the nitrosyl complexes Ru(salen)(ONO)(NO) (I, salen = N,N'-ethylenebis(salicylideneiminato) dianion), Ru(salen)(Cl)(NO) (II), Ru((t)Bu(4)salen)(Cl)(NO) (III,(t)Bu(4)salen = N,N'-ethylenebis(3,5-di-tert-butylsalicylideneiminato) dianion), Ru((t)Bu(4)salen)(ONO)(NO) (IV), Ru((t)Bu(2)salophen)(Cl)(NO) (V, (t)Bu(2)salophen = N,N'-1,2-phenylenediaminebis(3-tert-butylsalicylideneiminato) dianion), and Ru((t)Bu(4)salophen)(Cl)(NO) (VI, (t)Bu(4)salophen = N,N'-1,2-phenylenebis(3,5-di-tert-butylsalicylideneiminato) dianion). Upon photolysis, these Ru(L)(X)(NO) compounds undergo NO dissociation to give the ruthenium(III) solvento products Ru(L)(X)(Sol). Quantum yields for 365 nm irradiation in acetonitrile solution fall in a fairly narrow range (0.055-0.13) but decreased at longer lambda(irr). The quantum yield (lambda(irr) = 365 nm) for NO release from the water soluble complex [Ru(salen)(H(2)O)(NO)]Cl (VII) was 0.005 in water. Kinetics of thermal back-reactions to re-form the nitrosyl complexes demonstrated strong solvent dependence with second-order rate constants k(NO) varying from 5 x 10(-4) M(-1) s(-1) for the re-formation of II in acetonitrile to 5 x 10(8) M(-1) s(-1) for re-formation of III in cyclohexane. Pressure and temperature effects on the back-reaction rates were also examined. These results are relevant to possible applications of photochemistry for nitric oxide delivery to biological targets, to the mechanisms by which NO reacts with metal centers to form metal-nitrosyl bonds, and to the role of photochemistry in activating similar compounds as catalysts for several organic transformations. Also described are the X-ray crystal structures of I and V.

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PubMed2002

Modeling the catalytic site of vanadium bromoperoxidase: synthesis and structural characterization of intramolecularly H-bonded vanadium(V) oxoperoxo complexes, [VO(O(2))((NH)2pyg(2))]K and [VO(O(2))((BrNH)2pyg(2))]K.

Vanadium haloperoxidases (VHPO) catalyze the peroxidative halogenation of organic substrates. Crystallographic studies suggest that hydrogen bonding from a lysine side chain to the vanadium(V)-bound peroxo group may facilitate oxidation of halides (Cl(-), Br(-), I(-)). A ligand with pendant NH(2) functionality, N-(2-pyridylmethyl-6-amino) iminodiacetic acid (H(2)(NH)2pyg(2).2HCl) has been designed to explore the effects that H-bonding from Lys may have on peroxide activation. The first structural characterization of VBrPO model complexes [VO(O(2))((NH)2pyg(2))]K and [VO(O(2))((BrNH)2pyg(2))]K which demonstrate direct intramolecular H-bonding between an amine functionality and V(V)-bound peroxide is reported. The distances between NH(2) proton and bound peroxo moiety [(d(N(1)-H.O): 2.637(4) A in [VO(O(2))((NH)()2pyg(2))]K, and 2.640(8) and 2.6919(8) A in [VO(O(2))((BrNH)2pyg(2))]K] are indicative of intramolecular H-bonding. The intramolecular H-bond strength in [VO(O(2))((BrNH)2pyg(2))](-) is estimated at 6 kcal/mol by (1)H NMR studies and demonstrates that the H-bond interaction is also significant in solution.

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PubMed1997

Synthesis and Structural Characterization of Several Ruthenium Porphyrin Nitrosyl Complexes.

The synthesis, X-ray crystal structures, and some spectroscopic and chemical properties of the nitrosylruthenium(II) porphyrin complexes Ru(TPP)(NO)(ONO), Ru(TPP)(NO)(OH), Ru(OEP)(NO)(ONO), and Ru(OEP)(NO)(OH) (TPP = tetraphenylporphyrinato dianion; OEP = octaethylporphyrinato dianion) derived from the analogous Ru(II) carbonyl complexes are reported. Also described are experiments which quantitatively demonstrate that N(2)O is formed as a product of the synthesis scheme and that NO serves as the principal oxidant in the transformation of N(II) to N(III). The two TPP complexes are isostructural and consist of columns of molecules stacked along the c axis. The two OEP complexes are also isostructural and can be considered as layers of OEP complexes stacked along the b axis with solvent molecules situated at the cavities between layers. The nitrite ions are coordinated in a unidentate fashion through the oxygen atom. Crystal data for Ru(TPP)(NO)(ONO) (1): M = 789.79, space group I4/m (No. 87), a = 13.6529(6) Å, c = 9.7904(5) Å, V = 1825.0(2) Å(3), Z = 2, rho = 1.437 g cm(-)(3), purple bipyramid, 2theta(max) = 50.0 degrees, R(F) = 4.87% for 86 parameters and 838 reflections with I > 2sigma(I). Crystal data for Ru(TPP)(NO)(OH) (2): M = 760.79, space group I4/m (No. 87), a = 13.5423(4) Å, c = 9.7150(4) Å, V = 1781.7(1) Å(3), Z = 2, rho = 1.418 g cm(-)(3), dark red plate, 2theta(max) = 50.0 degrees, R(F) = 3.92% for 83 parameters and 811 reflections with I > 2sigma(I). Crystal data for Ru(OEP)(NO)(ONO).CH(2)Cl(2) (3): M = 794.77, space group P2(1) (No. 4), a = 10.7687(2) Å, b = 21.0320(2) Å, c = 8.5936(2) Å, beta = 102.683(1) degrees, V = 1898.85(6) Å(3), Z = 2, rho = 1.390 g cm(-)(3), black plate, 2theta(max) = 50.0 degrees, R(F) = 6.23% for 453 parameters and 4702 reflections with I > 2sigma(I). Crystal data for Ru(OEP)(NO)(OH).C(2)H(5)OH (4): M = 726.91, space group P2(1) (No. 4), a = 10.8474(7) Å, b = 21.002(1) Å, c = 8.3646(5) Å, beta = 103.571(1) degrees, V = 1852.4(2) Å(3), Z = 2, rho = 1.303 g cm(-)(3), brown plate, 2theta(max) = 45.0 degrees, R(F) = 6.74% for 421 parameters and 3527 reflections with I > 2sigma(I).

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