Browsing by Subject "catalysts"

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Anisotropic Small-Polaron Hopping In W:Bivo4 Single Crystals
(2015-01) Rettie, Alexander J. E.; Chemelewski, William D.; Lindemuth, Jeffrey; McCloy, John S.; Marshall, Luke G.; Zhou, Jianshi S.; Emin, David; Mullins, C. Buddie; Rettie, Alexander J. E.; Chemelewski, William D.; Marshall, Luke G.; Zhou, Jianshi S.; Mullins, C. Buddie
DC electrical conductivity, Seebeck and Hall coefficients are measured between 300 and 450 K on single crystals of monoclinic bismuth vanadate that are doped n-type with 0.3% tungsten donors (W:BiVO4). Strongly activated small-polaron hopping is implied by the activation energies of the Arrhenius conductivities (about 300 meV) greatly exceeding the energies characterizing the falls of the Seebeck coefficients' magnitudes with increasing temperature (about 50 meV). Small-polaron hopping is further evidenced by the measured Hall mobility in the ab-plane (10(-1) cm(2) V-1 s(-1) at 300 K) being larger and much less strongly activated than the deduced drift mobility (about 5 x 10(-5) cm(2) V-1 s(-1) at 300 K). The conductivity and n-type Seebeck coefficient is found to be anisotropic with the conductivity larger and the Seebeck coefficient's magnitude smaller and less temperature dependent for motion within the ab-plane than that in the c-direction. These anisotropies are addressed by considering highly anisotropic next-nearest-neighbor (approximate to 5 angstrom) transfers in addition to the somewhat shorter (approximate to 4 angstrom), nearly isotropic nearest-neighbor transfers. (C) 2015 AIP Publishing LLC.
Circular Dichroism of Multi-Component Assemblies for Chiral Amine Recognition and Rapid ee Determination
(2011-08) Metola, Pedro; Anslyn, Eric V.; James, Tony D.; Bull, Steven D.; Metola, Pedro; Anslyn, Eric V.
Upon mixing a chiral amine, enantiopure BINOL, and o-formyl phenyl boronic acid, the three components assemble efficiently and rapidly into chiral host-guest structures that produce distinct circular dichroism signals for each enantiomer of the amine. Employing BINOL and two derivatives to create an array of receptors, the CD signals resulting from several a-chiral primary amines were processed by principal component analysis and linear discriminant analysis to give satisfactory discrimination of the amines studied. Not only was the system able to differentiate the analytes chemoselectively and enantioselectively, but it also allowed for the rapid determination of chiral amine
Graphite Oxide Activated Zeolite NaY: Applications in Alcohol Dehydration
(2013) Todd, Alexander D.; Bielawski, Christopher W.; Bielawski, Christopher W.
A mixture of graphite oxide (GO) and the zeolite NaY (Si/Al = 5.1) was used to dehydrate various alcohols to their respective olefinic products. Using conditions optimized for 4-heptanol (15 wt% GO-NaY (1:1 wt/wt), 150 degrees C, 30 min), a series of secondary and tertiary aliphatic alcohols were cleanly dehydrated in moderate to excellent conversions (27.5-97.2%). Several primary alcohols were also dehydrated, although higher catalyst loadings (200 wt% GO-NaY (1 : 1) and longer reaction times (3 h) were required. The enhanced dehydration activity was attributed to the ability of GO to convert NaY to an acidic form and without the need for ammonium cation exchange and/or high temperature calcination.
Phase and Redox Shifted Four Iron/Four Sulfur Clusters: Fluorous Analogs of Metalloenzyme Cofactors
(2015-07) Zhang, Cheng-Pan; Xi, Zhenxing; Mueller, Kory M.; Holliday, Bradley J.; Bazzi, Hassan S.; Gladysz, John A.; Mueller, Kory M.; Holliday, Bradley J.
Reactions of (1) [Q](2)[Fe4S4(SC(CH3)(3))(4)] and the fluorous thiols HS(CH2)(n)R-f8 (n = 2, 3; R-f8 = (CF2)(7)CF3)), or (2) [Na](2)[Fe4S4(S(CH2)(n)R-f8)(4)] (n = 2, 3) and [PhCH2P((CH2)(3)R-f6)(3)][Br] or [PPN][Cl] (PPN = Ph3P - N - PPh3), give the title compounds [Q] 2[Fe4S4(S(CH2) nRf8) 4], comprised of a fluorous dianion and in some cases fluorous cations, with (1) Q/n = Ph4P/2 (4, 67%), Ph4P/3 (5, 67%), Me4N/3 (69%), and Ph3P(CH2)(2)R-f6/2 (73%) or (2) PhCH2P((CH2)(3)R-f6)(3)/2 (14, 39%), PhCH2P((CH2)(3)R-f6)(3)/3 (15, 63%), and PPN/2 (36%). The educt [Ph3P(CH2)(2)Rf(6)](2)[Fe4S4(SC(CH3)(3))(4)] is in turn prepared from FeCl3, HSC(CH3)(3)/CH3ONa, and [Ph3P( CH2)(2)R-f6][I], and the educts [Na](2)[Fe4S4(S(CH2) nR(f8))(4)] from [Na](2)[Fe4S4(SC(CH3)(3))(4)] and HS(CH2) nRf8. The SCH2 H-1 and C-13 NMR signals of these paramagnetic salts appear 8.7-10.3 and 32.3-34.9 ppm downfield from those of the corresponding thiols, but the chemical shifts of other signals are nearly normal. The UV-visible spectra show bands similar to those of non-fluorous analogs (290-298 nm and 406-415 nm; e = 25 700 and 19 200 M-1 cm-1 for 5). The singly fluorous salts are soluble in organic solvents of moderate polarity, but not in fluorous solvents. The doubly fluorous salts 14, 15 are soluble in all fluorous solvents assayed, with partition coefficients of > 99.65 : < 0.35 (CF3C6F11/toluene) and 93.2-93.1 : 6.9-6.8 (FC-72/THF). Cyclic voltammograms carried out using a platinum working microelectrode show that 4 is 0.08 V thermodynamically easier to reduce than 5.
Photophysical Tuning of the Aggregation-Induced Emission of a Series of Para-Substituted Aryl Bis (Imino)Acenaphthene Zinc Complexes
(2015-05) Evans, Daniel A.; Lee, Lucia Myongwon; Vargas-Baca, Ignacio; Cowley, Alan H.; Evans, Daniel A.; Cowley, Alan H.
Bis(imino)acenaphthene (BIAN) zinc complexes with para-substituted aryl groups have been synthesized and investigated from the standpoint of their photophysical properties. Each complex was found to be nonemissive in solution. However, complexes 1-6 turned out to be emissive in the solid state, while complexes 7 and 8 remained nonemissive. The emissions for complexes 1-8 displayed color tunability ranging from red-yellow. A detailed crystallographic study of the "as-synthesized" structures revealed a distinct difference in the crystal packing environments of the emissive and nonemissive complexes. Furthermore, a solvatomorphic study provided further emission tunability via changes in the crystal packing environments of each solvatomorph. Lastly, TD-DFT calculations were performed in order to investigate the effect of different para-substituents on the flanking aryl rings of the BIAN ligand.
Synthesis and Structures of Mononuclear 3,4-Bis(Trifluoromethyl)Pyrrolyl Complexes of Rh(I) and Ni(II)
(2014-11) Rivers, Joseph H.; Jones, Richard A.; Rivers, Joseph H.; Jones, Richard A.
New mononuclear complexes of the 3,4-bis(trifluoromethyl)pyrrolyl ligand (3,4-(CF3)(2)-Pyr(-)) with Rh(I) and Ni(II) are reported. Reaction of 3,4-(CF3)(2)-PyrNa with [Rh(COD)Cl](2) produces [Rh(PMe3)(3)(3,4-(CF3)(2)(-)Pyr)] (1) while reaction of 3,4-(CF3)(2)-PyrH with [Ni(PMe3)(2)Me-2] (2) or [Ni(PMe3)(2)Ph-2] (4) gives [trans-Ni (PMe3)(2) (3,4-(CF3)(2)-Pyr)(CH3)] (3) or [trans-Ni(PMe3)(2)(C6H5)(3,4-(CF3)2-Pyr)] (5) respectively. Complexes 1, 3 and 5 have been characterized spectroscopically and all five compounds have been structurally characterized by single crystal X-ray diffraction studies.
Tuning Coordination Modes of Pyridine/Thioether Schiff Base (NNS) Ligands to Mononuclear Manganese Carbonyls
(2014-05) Lumsden, Simone E. A.; Durgaprasad, Gummadi; Muthiah, Keren A. Thomas; Rose, Michael J.; Lumsden, Simone E. A.; Durgaprasad, Gummadi; Muthiah, Keren A. Thomas; Rose, Michael J.
We have investigated the coordination modes of NNS Schiff base, thioether ligands to manganese(I) carbonyls. The ligands contain ortho substituted pyridines (H, CH3, OCH3, fluorophenyl) and varying substituents (H, CH3) at the Schiff base linkage. In general, reaction of [Mn(CO)(5)Br] with a tridentate NNS ligand in CH2Cl2 affords species in which the thioether-S may be bound or unbound to the manganese center, depending on the steric and electronic substitution in the ligand framework; as a result, the complexes exhibit two or three carbonyl ligands, respectively. Aldehyde-derived ligand frames (R1NHNS) generally afford complexes of type [(RNNS)Mn(CO)(3)Br] (1(CO), 2(CO), 3(CO); R = H, OCH3, CH3) that exhibit incomplete ligation of the chelate (S not bound) in X-ray structures. In contrast, use of the iminomethyl ligand (NMeNS) affords a complex of formula [(NMeNS) Mn(CO)(2)Br] (4(CO)), in which the mixed N/thioether-S stabilizes the {Mn(CO)(2)}(+) fragment. In solid state IR spectra, complexes of type [(RNNS)Mn(CO)(3)Br] (1(CO) through 3(CO)) afford three mu(CO) in the range similar to 2060-1865 cm(-1); the dicarbonyl complex [(NMeNS)-Mn( CO)(2)Br] (4(CO)) exhibits two carbonyl stretches in the range similar to 1920-1845 cm(-1). Prolonged storage of the tricarbonyl [(MeNNS) Mn(CO) 3Br] (3CO) in presence of trace dioxygen affords the dibromide species [(MeNNS)Mn(Br)(2)] (3(Br)), in which the thioether S reliably binds to the Mn(II) center. Complexes 1(CO)-3(CO) exhibit simple, diamagnetic 1H NMR spectra in CD2Cl2. The S-ligated complex 4(CO) exhibits spectra consistent with a mixture of an S-bound (6-coordinate) and S-unbound (5-coordinate) species as represented by [(NMeNS) Mn(CO)(2)Br] <-> [(NMeNS) Mn(CO)(2)Br]. Lastly, we obtained crystal structures of the S-bound and S-unbound conformers derived from the same ligand -the fluorophenyl derived FPhNNS, namely [(FPhNNS) Mn(CO)(3)Br] (5(CO-a)) and [(FPhNNS) Mn(CO)(2)Br] (5(CO-b)). This report represents several examples of a thioether-stabilized {Mn(CO)(2)}(+) fragment, a deviation from the usual 'piano stool' Mn(I) tricarbonyl motif. We highlight that coordination of these NNS ligands to Mn(I) carbonyls occurs on a soft conformational landscape, and that ligand substituents can be rationally employed to favor the desired coordination mode.