Ethylene Dehydroaromatization over Ga-ZSM-5 Catalysts: Nature and Role of Gallium Speciation.

Bifunctional catalysis in zeolites possessing both Brønsted and Lewis acid sites offers unique opportunities to tailor shape selectivity and enhance catalyst performance. Here, we examine the impact of framework and extra-framework gallium species on enriched aromatics production in zeolite ZSM-5. We compare three distinct methods of preparing Ga-ZSM-5 and reveal direct (single step) synthesis leads to optimal catalysts compared to post-synthesis methods. Using a combination of state-of-the-art characterization, catalyst testing, and density functional theory calculations, we show that Ga Lewis acid sites strongly favor aromatization. Our findings also suggest Ga(framework)-Ga(extra-framework) pairings, which can only be achieved in materials prepared by direct synthesis, are the most energetically favorable sites for reaction pathways leading to aromatics. Calculated acid site exchange energies between extra-framework Ga at framework sites comprised of either Al or Ga reveal a site-specific preference for stabilizing Lewis acids, which is qualitatively consistent with experimental measurements. These findings indicate the possibility of tailoring Lewis acid siting by the placement of Ga heteroatoms at distinct tetrahedral sites in the zeolite framework, which can have a marked impact on catalyst performance relative to conventional H-ZSM-5.

In pursuit of advanced materials from single-source precursors based on metal carbonyls.

In this perspective, the development of single-source precursors and their relative advantages over multiple source approaches for the synthesis of metal pnictide solid state materials is explored. Particular efforts in the selective production of iron phosphide materials for catalytic applications are discussed, especially directed towards the hydrogen evolution and oxygen evolution reactions of water splitting.

Synthesis of Hexagonal FeMnP Thin Films from a Single-Source Molecular Precursor.

The first heterobimetallic phosphide thin film containing iron, manganese, and phosphorus, derived from the single-source precursor FeMn(CO)8 (µ-PH2 ), has been prepared using a home-built metal-organic chemical vapor deposition apparatus. The thin film contains the same ratio of iron, manganese, and phosphorus as the initial precursor. The film becomes oxidized when deposited on a quartz substrate, whereas the film deposited on an alumina substrate provides a more homogeneous product. Powder X-ray diffraction confirms the formation of a metastable, hexagonal FeMnP phase that was previously only observed at temperatures above 1200 °C. Selected area electron diffraction on single crystals isolated from the films was indexed to the hexagonal phase. The effective moment of the films (µeff =3.68 µB ) matches the previously reported theoretical value for the metastable hexagonal phase, whereas the more stable orthorhombic phase is known to be antiferromagnetic. These results not only demonstrate the successful synthesis of a bimetallic, ternary thin film from a single-source precursor, but also the first low temperature approach to the hexagonal phase of FeMnP.

A TiO2/FeMnP Core/Shell Nanorod Array Photoanode for Efficient Photoelectrochemical Oxygen Evolution.

A variety of catalysts have recently been developed for electrocatalytic oxygen evolution, but very few of them can be readily integrated with semiconducting light absorbers for photoelectrochemical or photocatalytic water splitting. Here, we demonstrate an efficient core/shell photoanode with a highly active oxygen evolution electrocatalyst shell (FeMnP) and semiconductor core (rutile TiO2) for photoelectrochemical oxygen evolution reaction. Metal-organic chemical vapor deposition from a single-source precursor was used to ensure good contact between the FeMnP and the TiO2. The TiO2/FeMnP core/shell photoanode reaches the theoretical photocurrent density for rutile TiO2 of 1.8 mA cm-2 at 1.23 V vs reversible hydrogen electrode under simulated 100 mW cm-2 (1 sun) irradiation. The dramatic enhancement is a result of the synergistic effects of the high oxygen evolution reaction activity of FeMnP (delivering an overpotential of 300 mV with a Tafel slope of 65 mV dec-1 in 1 M KOH) and the conductive interlayer between the surface active sites and semiconductor core which boosts the interfacial charge transfer and photocarrier collection. The facile fabrication of the TiO2/FeMnP core/shell nanorod array photoanode offers a compelling strategy for preparing highly efficient photoelectrochemical solar energy conversion devices.

High-Performance Hybrid Bismuth-Carbon Nanotube Based Contrast Agent for X-ray CT Imaging.

Carbon nanotubes (CNTs) have been used for a plethora of biomedical applications, including their use as delivery vehicles for drugs, imaging agents, proteins, DNA, and other materials. Here, we describe the synthesis and characterization of a new CNT-based contrast agent (CA) for X-ray computed tomography (CT) imaging. The CA is a hybrid material derived from ultrashort single-walled carbon nanotubes (20-80 nm long, US-tubes) and Bi(III) oxo-salicylate clusters with four Bi(III) ions per cluster (Bi4C). The element bismuth was chosen over iodine, which is the conventional element used for CT CAs in the clinic today due to its high X-ray attenuation capability and its low toxicity, which makes bismuth a more-promising element for new CT CA design. The new CA contains 20% by weight bismuth with no detectable release of bismuth after a 48 h challenge by various biological media at 37 °C, demonstrating the presence of a strong interaction between the two components of the hybrid material. The performance of the new Bi4C@US-tubes solid material as a CT CA has been assessed using a clinical scanner and found to possess an X-ray attenuation ability of >2000 Hounsfield units (HU).

Anionic Bismuth-Oxido Carboxylate Clusters with Transition Metal Countercations.

Six new anionic bismuth-oxido clusters containing trifluoroacetate ligands were prepared. These include two new Bi6O8 clusters: [M(NCMe)2(H2O)4]3[Bi6(µ3-O)4(µ3-OH)4(CF3CO2)12] with an octahedral Bi6O4(OH)4 core (M = Ni, 1a; Co, 1b) and four Bi4O2 clusters, {[Co(NCMe)6][Bi4(µ3-O)2(CF3CO2)10]}n (2a), {[Co{HC(MeCO)2(MeCNH)}2][Bi4(µ3-O)2(CF3CO2)10]·2[CF3CO2]·2[CF3CO2H]·2[H2O]}n (2b), {[Cu(NCMe)4]2[Bi4(µ3-O)2(CF3CO2)10]·2[CF3CO2H]}n (2c), and {[Me4N]2[Bi4(µ3-O)2(CF3CO2)10]·2[CF3CO2H]}n (2d). These are among the first bismuth-oxido anionic clusters synthesized, and the first to have transition metal countercations. The Bi6O8 anion in 1a and 1b is a high-symmetry octahedron. Additionally, two of the new Bi4O2 clusters are arranged in 1D polymeric structures via bridging carboxylate ligands. The cation in compound 2c had not been previously characterized and was also observed in the synthesis of [Co{HC(MeCO)2(MeCNH)}2][Bi(NO3)6] (3). The new compounds were characterized using single crystal X-ray crystallography and elemental analysis.

New Main-Group-Element-Rich nido-Octahedral Cluster System: Synthesis and Characterization of [Et4N][Fe2(CO)6(µ3-As){µ3-EFe(CO)4}2].

A series of clusters of the form [Et4N][Fe2(CO)6(µ3-As)}(µ3-EFe(CO)4)], where E is either P or As, were synthesized from [Et4N]2[HAs{Fe(CO)4}3] and ECl3. AsCl3 gives the As-only compound; PCl3 produces compounds having two As atoms with one P atom, or one As atom and two P atoms, and they can exist as two possible isomers, one of which is chiral. The As2P and AsP2 clusters cocrystallize, and their structure as determined by single-crystal X-ray diffraction is given along with the structure of the As-only cluster. Analytical data as well as density functional theory calculations support the formation and geometries of the new molecules.

Aluminum nanocrystals.

We demonstrate the facile synthesis of high purity aluminum nanocrystals over a range of controlled sizes from 70 to 220 nm diameter with size control achieved through a simple modification of solvent ratios in the reaction solution. The monodisperse, icosahedral, and trigonal bipyramidal nanocrystals are air-stable for weeks, due to the formation of a 2-4 nm thick passivating oxide layer on their surfaces. We show that the nanocrystals support size-dependent ultraviolet and visible plasmon modes, providing a far more sustainable alternative to gold and silver nanoparticles currently in widespread use.

Synthesis and structural studies of the simplest bismuth(III) oxo-salicylate complex: [Bi4(µ3-O)2(HO-2-C6H4CO2)8]·2Solv (Solv = MeCN or MeNO2).

Reaction of BiPh3 with salicylic acid (HO-2-C6H4CO2H, H2Sal) at room temperature in wet acetonitrile or nitromethane leads to the facile formation of an oxo cluster compound with formula [Bi4(µ3-O)2(HSal)8] solvated by either MeCN and MeNO2 (1·2MeCN or 1·2MeNO2). This simple procedure affords a convenient, high yield (>80%) synthesis of a single bismuth oxo cluster. Both adducts exhibit a nearly planar Bi4(µ3-O)2 core. The solvent ligands are situated in the same coordination sites in both but at long Bi-N and Bi-O distances. The ease of preparation as a pure compound makes this an ideal starting material for study of bismuth oxo-salicylate chemistry.

Hexaaquacobalt(II) and hexaaquanickel(II) bis(µ-pyridine-2,6-dicarboxylato)bis[(pyridine-2,6-dicarboxylato)bismuthate(III)] dihydrate.

The title complexes, hexaaquacobalt(II) bis(µ-pyridine-2,6-dicarboxylato)bis[(pyridine-2,6-dicarboxylato)bismuthate(III)] dihydrate, [Co(H(2)O)(6)][Bi(2)(C(7)H(4)NO(4))(4)]·2H(2)O, (I), and hexaaquanickel(II) bis(µ-pyridine-2,6-dicarboxylato)bis[(pyridine-2,6-dicarboxylato)bismuthate(III)] dihydrate, [Ni(H(2)O)(6)][Bi(2)(C(7)H(4)NO(4))(4)]·2H(2)O, (II), are isomorphous and crystallize in the triclinic space group P-1. The transition metal ions are located on the inversion centre and adopt slightly distorted MO(6) (M = Co or Ni) octahedral geometries. Two [Bi(pydc)(2)](-) units (pydc is pyridine-2,6-dicarboxylate) are linked via bridging carboxylate groups into centrosymmetric [Bi(2)(pydc)(4)](2-) dianions. The crystal packing reveals that the [M(H(2)O)(6)](2+) cations, [Bi(2)(pydc)(4)](2-) anions and solvent water molecules form multiple hydrogen bonds to generate a supramolecular three-dimensional network. The formation of secondary Bi...O bonds between adjacent [Bi(2)(pydc)(4)](2-) dimers provides an additional supramolecular synthon that directs and facilitates the crystal packing of both (I) and (II).

(N,N-Dimethyl-formamide-κO)bis-(3-hy-droxy-picolinato-κN,O)phenyl-bis-muth(III).

The title organometallic complex, [Bi(C(6)H(5))(C(6)H(4)NO(3))(2)(C(3)H(7)NO)], features a Bi(III) atom in a distorted pentagonal-pyramidal coordination by two N,O-donating bidentate 3-hy-droxy-picolinate (3-hpic) ligands, one monodentate dimethyl-formamide (dmf) mol-ecule and one phenyl ring. The C atom of the aryl ligand occupies the apical position of the BiCN(2)O(3) coordination polyhedron, while the equatorial plane is formed by one O atom of the dmf ligand and two sets of N and O atoms from the chelating 3-hpic ligands. Inter-molecular secondary Bi⋯O [3.485 (3) Å] and O-H⋯O hydrogen-bonding inter-actions connect the complexes into a three-dimensional network. Intramolecular O-H⋯O hydrogen bonds are also observed.

Selective arylation reactions of bismuth-transition metal salicylate complexes.

Heterometallic bismuth-niobium or -tantalum salicylate complexes react with sodium tetraphenylborate to produce complexes in which one or more aryl groups have been transferred from boron to bismuth with the concomitant displacement of a eta(2)-salicylato ligand. When the previously reported Bi(2)Ta(2)(sal)(4)(Hsal)(4)(OEt)(4) (1) and BiTa(4)(mu-O)(4)(sal)(4)(Hsal)(3)(O(i)Pr)(4) (2) are treated with an alcoholic solution of NaBPh(4), the compounds [PhBi(Hsal)Ta(sal)(2)(OEt)(2) x EtOH](2) (3) and PhBiTa(4)(mu-O)(4)(Hsal)(2)(sal)(4)(OEt)(4) x CH(2)Cl(2) (4) are produced (sal = O(2)CC(6)H(4)-2-O(2-), Hsal = O(2)CC(6)H(4)-2-OH(-)). The core geometries of the heterometallic complexes are retained. However, if preparations of compound 1 are treated with NaBPh(4) without prior isolation of 1, [Ph(2)BiNb(sal)(2)(OMe)(2)](infinity) (5) is produced instead. This compound was characterized both as a solvent-free crystalline form and as one containing a lattice diethyl ether. The compound exhibits a polymeric chain structure that can be viewed as alternating [Ph(2)Bi](+) and [Nb(sal)(2)(OMe)(2)](-) units connected via bridging carboxylate groups. The arylation of the bismuth(III) center proceeds smoothly under mild conditions at room temperature, affording a new means for the mild functionalization of bismuth-transition metal heterometallic complexes.

Magnetic-plasmonic core-shell nanoparticles.

Nanoparticles composed of magnetic cores with continuous Au shell layers simultaneously possess both magnetic and plasmonic properties. Faceted and tetracubic nanocrystals consisting of wustite with magnetite-rich corners and edges retain magnetic properties when coated with a Au shell layer, with the composite nanostructures showing ferrimagnetic behavior. The plasmonic properties are profoundly influenced by the high dielectric constant of the mixed iron oxide nanocrystalline core. A comprehensive theoretical analysis that examines the geometric plasmon tunability over a range of core permittivities enables us to identify the dielectric properties of the mixed oxide magnetic core directly from the plasmonic behavior of the core-shell nanoparticle.

Iron phosphide nanostructures produced from a single-source organometallic precursor: nanorods, bundles, crosses, and spherulites.

Single-source molecular precursors were found to produce iron phosphide materials. In a surfactant system of trioctylamine and oleic acid, H2Fe3(CO)9PtBu reacted to form Fe4(CO)12(PtBu)2, which decomposed to give Fe2P nanorods and "bundles." Control of the morphology obtained was possible by varying the surfactant system; addition of increasing amounts of oleic acid resulted in crystal splitting, while the addition of microliter amounts of an alkane enhanced the crystal splitting to give sheaflike structures. The different morphologies seen were attributed to imperfect crystal growth mechanisms.

Addition of the phenoxathiin cation radical to alkenes and nonconjugated dienes. Formation of (E)- and (Z)-(10-phenoxathiiniumyl)alkenes and (E)- and (Z)-(10-phenoxathiiniumyl)dienes on basic alumina.

Addition of phenoxathiin cation radical (PO*+) to acyclic alkenes in acetonitrile (MeCN) solution occurred stereospecifically to form bis(10-phenoxathiiniumyl)alkane adducts. Stereospecific trans addition is ascribed to the intermediacy of an episulfonium cation radical. The alkenes used were cis- and trans-2-butene, cis- and trans-2-pentene, cis- and trans-4-methyl-2-pentene, cis- and trans-4-octene, trans-3-hexene, trans-3-octene, trans-5-decene, cis-2-hexene, and cis-2-heptene. The erythro bisadducts (compounds 6) were obtained with trans-alkenes, while threo bisadducts (compounds 7) were obtained with cis-alkenes. The assigned structures of 6 and 7 were consistent with their NMR spectra and, in one case, 6c (the adduct of trans-4-methyl-2-pentene) was confirmed with X-ray crystallography. Additions of PO*+ to 1,4-hexa-, 1,5-hexa-, 1,6-hepta-, and 1,7-octadiene gave bis(10-phenoxathiiniumyl)alkenes (compounds 8), the assigned structures of which were consistent with their NMR spectra. Each of these adducts lost a proton and phenoxathiin (PO) when treated with basic alumina in MeCN solution. Compounds 6 (from trans-alkenes) gave mixtures of (Z)- (9) and (E)-(10-phenoxathiiniumyl)alkenes (10) in which the (Z)-isomers (9) were dominant. On the other hand, compounds 7 (from cis-alkenes) gave mixtures of 9 and 10 in which, with one exception (the adduct 7c of cis-4-methyl-2-pentene), compounds 10 were dominant. The path to elimination is discussed. The alkenes 9 and 10 were characterized with NMR spectroscopy and, in one case (9a), with X-ray crystallography. Reactions of 8b-d with basic alumina gave mixtures of (E)- (13) and (Z)-(10-phenoxathiiniumyl)dienes (14), in which compounds 13 were dominant. The configuration of the product from 8a (the adduct of 1,4-hexadiene) could not be settled. Noteworthy features in the coupling patterns and chemical shifts in the NMR spectra of some of the adducts and their products are discussed and related to adduct conformations.

Adducts of thianthrene- and phenoxathiin cation radical tetrafluoroborates to 1-alkynes. Structures and formation of 1-(5-thianthreniumyl)- and 1-(10-phenoxathiiniumyl)alkynes on alumina leading to alpha-ketoylides and alpha-ketols.

[structure: see text] Thianthrene cation radical tetrafluoroborate (Th*+ BF4(-)) added to the terminal alkynes 1-pentyne, 1-hexyne, 1-heptyne, 1-octyne, 1-nonyne, and 1-decyne to form trans-1,2-bis(5-thianthreniumyl)alkene tetrafluoroborates (1-6). Similarly, addition of phenoxathiin cation radical tetrafluoroborate (PO*+ BF4(-)) to the same alkynes gave 1,2-bis(10-phenoxathiiniumyl)alkene tetrafluoroborates (7-12). The trans configuration of two of the adducts (1 and 4) was shown with X-ray crystallography. When solutions of 1-6 in chloroform were stirred with activated alumina, cis elimination of a proton and thianthrene (Th) occurred with the formation of 1-(5-thianthreniumyl)alkyne tetrafluoroborates (1a-6a). Similar treatment of 8-12 caused elimination of a proton and phenoxathiin (PO) with formation of 1-(10-phenoxathiiniumyl)alkene tetrafluoroborates (8a-12a). Stirring of 1a-6a with alumina for short periods of time caused their conversion into 5-[(alpha-keto)alkyl]thianthrenium ylides (1b-6b) and alpha-ketols, RC(O)CH2OH (1c-6c).

Adducts of thianthrene- and phenoxathiin cation radical salts with symmetrical alkynes. Structure and formation of cumulenes on alumina leading to alpha-diketones, alpha-hydroxyalkynes, and alpha-acetamidoalkynes.

[reaction: see text] Thianthrene cation radical tetrafluoroborate (Th*+ BF4-) added to 2-butyne, 3-hexyne, 4-octyne, and 5-decyne in MeCN to form trans bisadducts R(Th+)C=C(Th+)R, where R = Me, Et, Pr, Bu (7a-d). Phenoxathiin cation radical tetrafluoroborate (PO*+ BF4-) added similarly to the last three alkynes to form adducts R(PO+)C=C(PO+)R, 8b-d. Cyclic monoadducts were not found. The trans structures of 7 and 8 were deduced with X-ray crystallography (7c) and NMR spectroscopy. When solutions of adducts in CHCl3 and MeCN were deposited on activated alumina, elimination of thianthrene (Th) and phenoxathiin (PO) occurred almost quantitatively. Detailed studies with (7b-d) indicated that a cumulene (15) was formed by the elimination of Th and that 15 was subsequently converted into small amounts of other products. In CHCl3, these products were the respective alkyne, thianthrene 5-oxide, an alpha-diketone (11), an alpha-hydroxyalkyne (12), and hydrogen. The same products were formed in MeCN along with an alpha-acetamidoalkyne (13). The formation of 15 and products derived from it is explained and was confirmed by preparation and reactions of 2,3,4-hexatriene.

Model platinum nucleobase and nucleoside complexes and antitumor activity: X-ray crystal structure of [PtIV(trans-1R,2R-diaminocyclohexane)trans-(acetate)2(9-ethylguanine)Cl]NO3.H2O.

A series of platinum(II) and (IV) monoadducts of the type [Pt(II)(DACH)LCl]NO3 and [Pt(IV)(DACH)trans-(X)2LCl]NO3 (where DACH=trans-1R,2R-diaminocyclohexane, L=adenine, guanine, hypoxanthine, cytosine, adenosine, guanosine, inosine, cytidine, 9-ethylguanine (9-EtGua), or 1-methylcytosine and X=hydroxo or acetato ligand) have been synthesized and characterized by elemental analysis and by 1H and 195Pt nuclear magnetic resonance (NMR) spectroscopy. The crystal structure of the model nucleobase complex [Pt(IV)(trans-1R,2R-diaminocyclohexane)trans-(acetate)2(9-EtGua)Cl]NO3.H2O was determined using a single crystal X-ray diffraction method. The compound crystallized in the monoclinic space group P2(1), with a=10.446(2) A, b=22.906(5) A, c=10.978(2) A, Z=4, and R=0.0718, based upon the total of 11,724 collected reflections. In this complex, platinum had a slightly distorted octahedron geometry owing to the presence of a geometrically strained five-member ring. The two adjacent corners of the platinum plane were occupied by the two amino nitrogen of DACH, whereas, the other two equatorial positions occupied by chloride ion and 9-ethylguanine. The remaining two axial positions were occupied by the oxygen atoms of acetato ligands. The DACH ring was in a chair configuration. An intricate network of intermolecular hydrogen bonds held the crystal lattice together. Some of these synthesized models of DACH-Pt-DNA adducts have good in vitro cytotoxic activity against the cisplatin-sensitive human cancer ovarian A2780 cell line (IC50=1-8 microM). Interestingly, a substituted nucleobase (9-ethylguanine) adduct was over 6-fold more potent than regular adducts. The cross-resistance factor against the 44-fold cisplatin-resistant 2780CP/clone 16 cells was about 3-9; thus, the cytotoxicity of adducts was indicative of low potency, but the resistance factors were also substantially low. These results suggest that DNA adducts of DACH-Pt are cytotoxic with low cross-resistance.

Heterobimetallic Bi(III)-Ti(IV) coordination complexes: synthesis and solid-state structures of BiTi4(sal)6(mu-OiPr)3(OiPr)4, and the cyclic isomers Bi4Ti4(sal)10(mu-OiPr)4(OiPr)4 and Bi8Ti8(sal)20(mu-OiPr)8(OiPr)8.

The reaction of a 1:2 mixture of bismuth(III) salicylate with titanium(IV) isopropoxide in refluxing toluene has been investigated and found to proceed with ligand exchange to produce the new heterobimetallic complexes BiTi(4)(sal)(6)(mu-O(i)Pr)(3)(O(i)Pr)(4) (1), Bi(4)Ti(4)(sal)(10)(mu-O(i)Pr)(4)(O(i)Pr)(4) (2), and Bi(8)Ti(8)(sal)(20)(mu-O(i)Pr)(8)(O(i)Pr)(8) (3). Complex 1 is the major product, while 2 and 3 were identified as minor products from the reaction. Compound 1 is produced pure and in high yield by employing stoichiometric amounts of reagents; its crystal structure consists of a [Ti(4)(sal)(6)(O(i)Pr)(7)](3)(-) ion capped by a Bi(3+) ion. Complexes 2 and 3 exhibit cyclic ring structures of bismuth and titanium atoms showing crystallographically imposed inversion symmetry. Both structures occlude large quantities of lattice solvent. The compositional and structural parameters from the single crystal studies indicate that complexes 2 and 3 may represent sequential steps in a ligand exchange process between the two metal species, while the reactivity patterns that were observed provide clues about the solution state structure of bismuth(III) salicylate itself. The 2D COSY (1)H NMR spectrum of 1 indicates retention of the asymmetric structure in solution as evidenced by the presence of 14 diastereotopic isopropoxide methyl resonances.