Use of U-shaped donor-bridge-acceptor molecules to study electron tunneling through nonbonded contacts

A systematic determination of electronic coupling matrix elements in U-shaped molecules is demonstrated. The unique architecture of these systems allows for the determination of the electronic coupling through a pendant molecular moiety that resides between the donor and acceptor groups; this moiety quantifies the efficiency of electron tunneling through nonbonded contacts. Experimental electron-transfer rate constants and reaction free energies are used to calibrate a molecular-based model that describes the solvation energy. This approach makes it possible to experimentally determine electronic couplings and compare them with computational values.     

Polysulfonylamine. CLXIII [1] Kristallstrukturen von Metall‐di(methansulfonyl)amiden. 12 [1] Das orthorhombische Doppelsalz Na2Cs2[(CH3SO2)2N]4·3H2O: Ein dreidimensionales Koordinationspolymer aus (Caesium‐Anion‐Wasser)‐Schichten und intercalierten Natriumionen

Polysulfonylamines. CLXIII. Crystal Structures of Metal Di(methanesulfonyl)amides. 12. The Orthorhombic Double Salt Na₂Cs₂[(CH₃SO₂)₂N]₄·3H₂O: A Three‐Dimensional Coordination Polymer Built up from Cesium‐Anion‐Water Layers and Intercalated Sodium Ions The packing arrangement of the three‐dimensional coordination polymer Na₂Cs₂[(MeSO₂)₂N]₄·3H₂O (orthorhombic, space group Pna2₁, Z′ = 1) is in some respects similar to that of the previously reported sodium‐potassium double salt Na₂K₂[(MeSO₂)₂N]₄·4H₂O (tetragonal, P4₃2₁2, Z′ = 1/2). In the present structure, four multidentately coordinating independent anions, three independent aquo ligands and two types of cesium cation form monolayer substructures that are associated in pairs to form double layers via a Cs(1)—H₂O—Cs(2) motif, thus conferring upon each Cs⁺ an irregular O₈N₂ environment drawn from two N, O‐chelating anions, two O, O‐chelating anions and two water molecules. Half of the sodium ions occupy pseudo‐inversion centres situated between the double layers and have an octahedral O₆ coordination built up from four anions and two water molecules, whereas the remaining Na⁺ are intercalated within the double layers in a square‐pyramidal and pseudo‐C₂ symmetric O₅ environment provided by four anions and the water molecule of the Cs—H₂O—Cs motif. The net effect is that each of the four independent anions forms bonds to two Cs⁺ and two Na⁺, two independent water molecules are involved in Cs—H₂O—Na motifs, and the third water molecule acts as a μ₃‐bridging ligand for two Cs⁺ and one Na⁺. The crystal cohesion is reinforced by a three‐dimensional network of conventional O—H···O=S and weak C—H···O=S/N hydrogen bonds.     

On-column polymer-imbedded graphite inlet electrode for capillary electrophoresis coupled on-line with flow injection analysis in a poly(dimethylsiloxane) interface

A method for coupling an electrophoretic driven separation to a liquid flow, using conventional fused-silica capillaries and a soft polymeric interface is presented. A novel design of the electrode providing high voltage to the electrophoretic separation was also developed. The electrode consisted of a conductive polyimide/graphite imbedded coating immobilized onto the capillary electrophoresis (CE) column inlet. This integrated electrode gave the same separation performance as a commonly used platinum electrode. The on-column electrode also showed good electrochemical stability in chronoamperometric experiments. In addition, with this electrode design, the electrode position relative to the inlet end of the CE column will always be constant and well defined. The on-line flow injection analysis (FIA)-CE system was used with electrospray ionization (ESI)-time of flight (TOF)-mass spectrometry detection. The preparation of the PDMS (poly(dimethylsiloxane)) interface for FIA-CE is described in detail and used for initial tests of the on-column polymer-imbedded graphite inlet electrode. In this interface, a pressure-driven liquid flow, a make up CE electrolyte and a CE column inlet meet in a two-level cross (95 microm ID) in the PDMS structure, enabling independent flow characterization.     

Synthesis and Crystal Structures of Two Novel Anionic Aluminophosphates: A One-Dimensional Chain, UT-7 ([Al(3)P(5)O(20)H](5-)[C(7)H(13)NH(3)(+)](5)), and a Layer Containing Two Cyclic Amines, UT-8 ([Al(3)P(4)O(16)](3-)[C(4)H(7)NH(3)(+)](2)[C(5)H(10)NH(2)(+)])

UT-7 and UT-8 (University of Toronto, structure numbers 7 and 8) are two novel aluminophosphate materials prepared under non-aqueous conditions. Their structures, extended in one and two dimensions, respectively, have been solved by single-crystal X-ray diffraction and characterized by a variety of methods including powder X-ray diffraction (PXRD), insitu high-temperature PXRD, thermogravimetric analysis (TGA), energy dispersive X-ray analysis (EDX), and scanning electron microscopy (SEM). UT-7 ([Al(3)P(5)O(20)H](5)(-)[C(7)H(13)NH(3)(+)](5), triclinic space group P&onemacr;, Z = 2, a = 10.118(3) ?, b = 15.691(4) ?, c = 18.117(3) ?, alpha = 72.91(2) degrees, beta = 85.18(2) degrees, gamma = 79.49(2) degrees ) is built of polymeric one-dimensional chain units, hydrogen-bonded into anionic layers that are charge-compensated by interlamellar cycloheptylammonium cations. UT-7 is isostructural to our previously discovered UT-3 chain structure, isolated in the analogous cyclopentylamine system. UT-8 ([Al(3)P(4)O(16)](3-)[C(4)H(7)NH(3)(+)](2)[C(5)H(10)NH(2)(+)], monoclinic space group P2(1), Z = 2, a = 8.993(4) ?, b = 14.884(8) ?, c = 9.799(9) ?, beta = 103.52(3) degrees ) is a two-dimensional net isostructural to several previously reported [Al(3)P(4)O(16)](3)(-) layers. The interlayer region of UT-8 is occupied by two different cyclic organic amine species, namely piperidinium and cyclobutylammonium. To our knowledge, this is the first report of the crystal structure of an aluminophosphate material containing cyclobutylammonium or a mixture of cyclic amines. Interestingly, UT-7 is observed to thermally transform in the solid state to an as yet unknown layered material that can be independently synthesized in a similar synthetic system. In the same way as UT-3 transforms to the UT-4 layered phase, we believe UT-7 transforms to a layered material by means of a chain to layer transformation.     

The two-step chemical vapor deposition of Pd(allyl)Cp as an atom-efficient route to synthesize highly dispersed palladium nanoparticles on carbon nanofibers

Highly dispersed palladium nanoparticles supported on carbon nanofibers, which show high catalytic activity and stability in the hydrogenation of cyclooctene, were synthesized by the two-step metal organic chemical vapor deposition (MOCVD) of allylcyclopentadienylpalladium (Pd(allyl)Cp) as precursor at atmospheric pressure.     

Recent advances toward sustainable flow photochemistry

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First experiments on transmutation studies of129I and237Np using relativistic protons of 3.7 GeV

First experiments on the transmutation of long-lived¹²⁹I and²³⁷Np using relativistic protons of 3.7 GeV are described. Relativistic protons generate in extended Pb-targets substancial neutron fluences. These neutrons get moderated in paraffin and are used for transmutation as follows:¹²⁹I(n,)¹³⁰I and²³⁷Np(n,)²³⁸Np. The isotopes¹³⁰I (T _1/2-12.36 h) and²³⁸Np (T _1/2=2.117 d) were identified radiochemically. One can estimate the transmutation cross-section (n,) in the given neutron field as (¹²⁹I(n,))=(10±2)b and (²³⁷Np(n,))=(140±30)b The experiments were carried out in November 1996 at the Synchrophasotron, LHE, Dubna, Russia. The investigation has been performed at the Laboratory of High Energies, JINR, Dubna.     

Synthesis and spectroscopic characterization of a new family of Ni(4) spin clusters

A new family of tetranuclear Ni complexes [Ni(4)(ROH)(4)L(4)] (H(2)L = salicylidene-2-ethanolamine; R = Me (1) or Et (2)) has been synthesized and studied. Complexes 1 and 2 possess a [Ni(4)O(4)] core comprising a distorted cubane arrangement. Magnetic susceptibility and inelastic neutron scattering studies indicate a combination of ferromagnetic and antiferromagnetic pairwise exchange interactions between the four Ni(II) centers, resulting in an S = 4 spin ground state. Magnetization measurements reveal an easy-axis-type magnetic anisotropy with D approximately -0.93 cm(-)(1) for both complexes. Despite the large magnetic anisotropy, no slow relaxation of the magnetization is observed down to 40 mK. To determine the origin of the low-temperature magnetic behavior, the magnetic anisotropy of complex 1 was probed in detail using inelastic neutron scattering and frequency domain magnetic resonance spectroscopy. The spectroscopic studies confirm the easy-axis-type anisotropy and indicate strong transverse interactions. These lead to rapid quantum tunneling of the magnetization, explaining the unexpected absence of slow magnetization relaxation for complex 1.     

Microwave-assisted ring-closing metathesis revisited. On the question of the nonthermal microwave effect

The ring-closing metathesis reactions (RCM) of six standard diene substrates leading to five-, six-, or seven-membered carbo- or heterocycles were investigated under controlled microwave irradiation. RCM protocols were performed with standard Grubbs type II and a cationic ruthenium allenylidene catalyst in neat and ionic liquid-doped methylene chloride under sealed vessel conditions. Very rapid conversions (15 s) were achieved utilizing 0.5 mol % Grubbs II catalyst under microwave conditions. Careful comparison studies indicate that the observed rate enhancements are not the result of a nonthermal microwave effect.