- New sulfate-bridged dinuclear oxidovanadium complexes
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The reaction of oxidovanadium sulfate VOSO4·3H 2O with 4,4′-di-tert-butyl-2,2′-bipyridine (dtb-bpy) in methanol was found to give the complex (VO)2(μ2-SO 4)2(dtb-bpy)2(CH3OH) 2·4CH3OH (1). Single crystal X-ray diffraction reveals that molecule 1 is a centrosymmetric dimer consisting of two {VO(μ2-SO4)(dtb-bpy)(CH3OH)} moieties linked by two bridging sulfate anions. Each vanadium atom is in a distorted octahedral environment formed by two nitrogen and four oxygen atoms. The further reaction of an ethanolic solution of compound 1 with sodium pivalate in CH3CN produces the new dinuclear complex [(VO)2(μ2-O) 2(μ2-SO4)(dtb-bpy)2] ·2CH3CN (2), which does not include pivalate ligands, but contains one bridging sulfate anion and two bridging oxygen atoms. The X-ray study, cyclic voltammetry and magnetic measurements were performed allowing to conclude that both vanadium centers in 2 are in +5 oxidation state. According to ESR studies the dinuclear complex 1 undergoes dissociation upon dissolution in ethanol yielding mononuclear species VO(μ2-SO4)(dtb- bpy)(CH3OH), while solution of 1 in dichloromethane contains dimers exhibiting spin-spin exchange interactions between two paramagnetic monomeric fragments.
- Bazhina, Evgenia S.,Nikiforova, Marina E.,Aleksandrov, Grigory G.,Efimov, Nikolay N.,Ugolkova, Helena A.,Nikitin, Oleg M.,Magdesieva, Tatiana V.,Bogomyakov, Artem S.,Minin, Vadim V.,Sidorov, Aleksei A.,Novotortsev, Vladimir M.,Eremenko, Igor L.
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- A New Family of Ni4 and Ni6 Aggregates from the Self-Assembly of [Ni2] Building Units: Role of Carboxylate and Carbonate Bridges
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Carboxylato (R = tBu and Et) and carbonato bridges have been utilized for nickel(II)-based aggregates [Ni4(μ-H2L)2(μ3-OH)2(μ1,3-O2CBut)2](NO3)2·H2O·2DMF (1·H2O·2DMF), Ni4(μ-hyHL)2(μ3-OMe)2(μ1,1-N3)2(μ1,3-O2CEt)2]·4H2O (2·4H2O), and Ni6(μ4-L)(μ3-L)2(μ6-CO3)(H2O)8](ClO4)·9H2O (3·9H2O). Building blocks [Ni2(μ-H2L)]3+, [Ni2(μ-hyHL)]3+, and [Ni2(μ-L)]+ originating from [Ni2(μ-H2L)]3+ have been trapped in these complexes. The complexes have been characterized by X-ray crystallography, magnetic measurements, and density functional theory (DFT) analysis. In 1, the magnetic interactions are transmitted through the μ3-phenoxido/μ3-hydroxido/syn-syn-tBuCO2-, μ3-phenoxido/μ3- hydroxido, and double μ3-phenoxido/double μ3-hydroxido bridges with J = +11.4 cm-1, J1 = -2.1 cm-1, and J2 = -2.8 cm-1, respectively. In 2, the interactions are ferromagnetic, with J1 = +27.5 cm-1, J2 = +20.62 cm-1, and J3 = +1.52 cm-1 describing the magnetic couplings through the μ-phenoxidoo/μ3-methoxido, μ-azido/μ3-methoxido, and μ3-methoxido/μ3-methoxido exchange pathways, respectively. Complex 3 gives J1 = -3.30 cm-1, J2 = +1.7 cm-1, and J3 = -12.8 cm-1 for exchange pathways mediated by μ-phenoxido/μ-carbonato, μ-alkoxido/μ-alkooxido/μ-syn-syn-carbonato, and the μ-phenoxido/μ-carbonato, respectively. Interestingly, 1 and 3 below 20 K and 35 K, respectively, show an abrupt increase of the χMT product to reach a magnetic-field-dependent maximum, which is associated with a slightly frequency-dependent out-of-phase alternating-current peak. DFT calculations have also been performed on 1-3 to explain the exchange interaction mechanisms and to support the magnitude and sign of the magnetic coupling constants between the NiII ions. (Figure Presented).
- Pait, Moumita,Bauzá, Antonio,Frontera, Antonio,Colacio, Enrique,Ray, Debashis
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- Nitric oxide reacts with methoxide
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(Chemical Equation Presented) Despite over a century of reports to the contrary, sodium methoxide has been found to react with nitric oxide (NO). The reaction, whose final organic product is sodium formate, is postulated to occur via an intermediate O-bound diazeniumdiolate [CH3O-N(O)=NO -] that decomposes to formaldehyde and nitrous oxide. Sodium formate forms from the aldehyde via a Cannizzaro reaction. Carboxylate salts have similarly been obtained by exposing sodium benzylate and sodium neopentoxide to NO in dioxane solution. Accordingly, sodium trimethylsilanoate should be considered as a substitute for sodium methoxide as the base used to accomplish the replacement of active hydrogens by the diazeniumdiolate functional group via the Traube reaction.
- DeRosa, Frank,Keefer, Larry K.,Hrabie, Joseph A.
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p. 1139 - 1142
(2008/09/18)
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- Studies of the Borderline between Concerted and Stepwise Mechanisms of Elimination : E1cB Elimination of Fluoren-9-ylmethyl Carboxylate Esters
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Rates of β-elimination of carboxylate leaving groups from fluoren-9-ylmethyl carboxylate esters in methanolic sodium methoxide at 25 deg C are reported.An E1cB mechanism with rate-determining formation of a carbanion intermediate is assigned on the basis of near identity of measured elimination rates and rates of carbanion formation predicted from a Taft correlation, and the similarity with elimination of 1-(1-acetoxy-1-methylethyl)indene for which the mechanism has been established by Ahlberg and Thibblin.Values of ρ=0.42 and βlg=0.27 measured for substituted benzoate leaving groups are a little larger than expected (ca. 0.24 and 0.18, respectively) and the discrepancy is tentatively ascribed to conformational enhancement of remote substituent effects, rather than to a contribution of E2 elimination.The effects of alkyl and aryl substitution α to the leaving group are discussed, especially in relation to the borderline between concerted and stepwise mechanisms.The measurements fail to confirm an earlier inference that the borderline shows a discontinuity in transition-state structure at the point of mechanistic change.
- O'Ferrall, Rory A. More,Larkin, Finbar,Walsh, Peter
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p. 1573 - 1580
(2007/10/02)
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