- Dinitrogen coordination and cleavage promoted by a vanadium complex of a σ,π,σ-donor ligand
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The deprotonation of the tripyrrole MeTPH2 [MeTPH2 = 2,5-[(2-pyrrolyl)(C6H5)2C] 2(MeNC4H2)], containing one N-methylated pyrrolyl ring, was carried out with 2 equiv of KH. The corresponding dipotassium salt reacted with VCl3(THF)3 to afford the complex [(MeTP)VCl(THF)]·THF (1). While the two lateral pyrrolide rings are σ-bonded, the central one is perpendicularly oriented in a sort of π-fashion. However, the bond distances clearly indicated that only the quaternized N atom is forming a bonding contact. Subsequent reduction of 1 with Na yielded the corresponding divalent complex [(MeTP)V(THF)]·(C 7H8)0.5 (2) where the central N-methylated ring adopted a more regular π-orientation. When treated with a strong Lewis acid (AlMe3), THF was extracted from the vanadium coordination sphere, forming the dinuclear dinitrogen complex [(MeTP)V(μ-N2)] 2·(C7H8)2.9 (3). Reduction of 3 with potassium graphite gave cleavage of dinitrogen, affording the mixed-valent nitride-bridged complex [(MeTP)V(μ-N)]2·(THF) (4).
- Vidyaratne, Indu,Crewdson, Patrick,Lefebvre, Emeric,Gambarotta, Sandro
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p. 8836 - 8842
(2008/10/09)
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- The dynamical properties of the aromatic hydrogen bond in NH4(C6 H5) 4B from quasielastic neutron s cattering
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N H4 (C6 H5) 4 B represents a prototypical system for understanding aromatic H bonds. In N H4 (C6 H5) 4 B an ammonium cation is trapped in an aromatic cage of four phenyl rings and each phenyl ring serves as a hydrogen bond acceptor for the ammonium ion as donor. Here the dynamical properties of the aromatic hydrogen bond in N H4 (C6 H5) 4 B were studied by quasielastic incoherent neutron scattering in a broad temperature range (20≤T≤350 K). We show that in the temperature range from 67 to 350K the ammonium ions perform rotational jumps around C3 axes. The correl ation time for this motion is the lifetime of the transient H bonds. It varies from 1.5 ps at T=350 K to 150 ps at T=67 K. The activation energy was found to be 3.14 kJmol, which means only 1.05 kJmol per single H bond for reorientations around the C3 symmetry axis of the ammonium group. This result shows that the ammonium ions have to overcome an exceptionally low barrier to rotate and thereby break their H bonds. In addition, at temperatures above 200 K local diffusive reorientational motions ofthe phenyl rings, probably caused by interaction with ammonium-group re orientations, were found within the experimental observation time window. At room temperature a reorientation angle of 8.4°±2° and a correlation time of 22±8 ps were determined for the latter. The aromatic H bonds are extremely short lived due to the low potential barriers allowing for molecular motions with a reorientational character of the donors. The alternating rupture and formation of H bonds causes very strong damping of the librational motion of the acceptors, making the transient H bond appear rather flexible.
- Jalarvo, Niina,Desmedt, Arnaud,Lechner, Ruep E.,Mezei, Ferenc
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- Flame atomic absorption spectrometric determination of trace amounts of cobalt in standard alloys and biological samples after preconcentration of its 1,10-phenanthroline complex on tetraphenylborate - Microcrystalline naphthalene adsorbent
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A rapid, simple and sensitive method has been developed for determination of trace amount of cobalt using flame atomic absorption spectrometry. Cobalt is quantitatively retained as 1,10-phenanthroline-tetraphenylborate ion-associate complex on microcrystalline naphthalene in the pH range 2.6-9.5 from a large volume of its aqueous solutions of various standard alloys and biological samples. After filtration, the solid mass consisting of the cobalt complex and naphthalene is dissolved in 5 mL of dimethylformamide (DMF) and the metal is determined using flame atomic absorption spectrometry by measuring the absorbance at 240.7 nm. Cobalt-1,10-phenanthroline complex can alternatively be quantitatively retained on ammonium tetraphenylborate-naphthalene adsorbent packed in a column at a flow rate of 2 mL/min under the same conditions and determined similarly. In this case, 1.0 μg of cobalt is concentrated in a column from 400 mL of its aqueous sample, where its concentration is as low as 2.5 ppb. Eight replicate determinations of 4.0 ppm cobalt gives a mean absorbance of 0.120 with a relative standard deviation of 1.8%. The sensitivity for 1% absorption is 147 ppb. The conditions have been optimized and utilized for trace determination of cobalt in various standard samples.
- Taher,Puri
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p. 2963 - 2967
(2007/10/03)
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- Synthesis and crystal structure of [U(η-C5Me5) 2(OC4H8) 2][BPh4], the first cationic cyclopentadienyl compound of uranium(III)
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The mixed amide complexes [U(NEt2)2(N{SiMe3}2)2] and [U(η-C8H8)(NEt2)(N{SiMe3}2)] reacted in tetrahydrofuran (THF) with NEt3HBPh4
- Boisson, Christophe,Berthet, Jean Claude,Ephritikhine, Michel,Lance, Monique,Nierlich, Martine
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- The libration-vibration bands of the ammonium ion in ammonium tetraphenylborate: Evidence for nearly free rotation
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The N-H stretching and H-N-H bending regions of the infrared spectrum of the title compound (ATPB) have been examined with care. The stretching bands show rotation-like structure that we attribute to rotational motion of NH 4+ in a very low barrier. The barrier has the symmetry of a tetrahedral molecule in a tetrahedral site and is characterized by the dimensionless parameter β=1. The J=0 and J=1 levels are below the barrier and the J=2 levels are above it. Slow interconversion of nuclear spin species is seen in keeping with the low barrier model. The spectra of the ATPB with some NH3D+, with a high concentration of K+ and with deuterated phenyl groups have been examined, and show spectra in keeping with the model.
- Roberts, Malcolm P.,Clavell-Grunbaum, Dolores,Strauss, Herbert L.
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p. 6393 - 6405
(2007/10/02)
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- The preparation and structure of ammonia and alkylamine addition compounds of phosphine diborane, B2H6·PH3·NR3
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The compound of empirical composition B2H6·PH3·NH3, formed by the reaction of ammonia with H3BPH3, has the structure [NH4] +[H2P(BH3)2]-. The structure is conclusively supported by chemical evidence, by 1H, 11B, and 31P nmr spectra, and by infrared spectra. In terms of a useful analogy relating the isoelectronic BH3 group and an O atom as ligands, the compound [NH4] [H2P(BH3)2] is the BH3 analog of ammonium hypophosphite, [NH4] [H2PO2]. Copyright 1967 by the American Chemical Society.
- Gilje, John W.,Morse, Karen W.,Parry
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p. 1761 - 1765
(2008/10/08)
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