Researchers worldwide have identified a large number of compounds with high hydrogen capacity that can fulfill these gravimetric and volumetric requirements.Unfortunately, the majority of these compounds fail to fulfill the thermodynamic and kinetic requirements for on-board storage systems. Alane has the gravimetric (10.1 mass% H 2 ) and the volumetric (149 kg H 2 /m 3 ) density needed to meet the 2010 DOE goals. In addition, rapid hydrogen release from alane can be achieved using only the waste heat from a fuel cell or a hydrogen internal combustion engine. 9 The main drawback to using alane in hydrogen storage applications is unfavorable hydriding thermodynamics. The direct hydrogenation of aluminium to alane requires over 10 5 bars of hydrogen pressure at room temperature as shown in equation(1). This impractically of using high hydriding pressure has precluded alane from being considered as a reversible hydrogen storage material. The other possible electrochemical reaction is having AlH -4 ion react with the aluminium anode to form alane. In this reaction route, the evolution of hydrogen is suppressed and the reaction is expected to consume the Al electrode as in equation (5) Experimental observations confirm that the anode is indeed consumed as shown in voltage experiments were performed. During these experiments, the current was steady and increased slightly with time. The electrochemical production of alane is not slowed by the formation of AlH 3 . In contrast to previous reports, no perception of alane is observed and the alane produced by our method is completely dissolved in solution as a THF adduct. 17During electrolysis, dendritic material was deposited on the platinum counter electrode.This material was collected and determined to be Na 3 AlH 6 from XRD data.Experiments were conducted to determine the feasibility of plating sodium at the platinum cathode as an alternative to NaH formation in the fueling cycle. The platinum cathode and aluminium anode potentials were -2.89 V and -1.31 V respectively. Plating of Na metal was observed at the cathode while alane was produced at the aluminium anode.Reacting sodium with aluminium from used alane under pressurized hydrogen will regenerate the starting material NaAlH 4 leading to a reversible cycle.In addition to determining the electrochemical processes for producing AlH 3 , recovering AlH 3 from the solution is a major step of this cycle. The separation of alane from AlH 3 •Et 2 O is well established and affords pure AlH 3 . [10][11][12] However, separation of the AlH 3 •THF adduct is more complicated because it decomposes when heated under vacuum.Therefore, adducts such as triethylamine (TEA) were added to the reaction product to stabilize the alane during purification. Adduct free alane is recovered by heating the neat liquid AlH 3 •TEA en vacuo.Alane recovered from the electrochemical cells was characterized by powder X-ray diffraction, Raman spectroscopy, and thermal gravimetric analyzer (TGA). Powder X-ray diffraction patterns data for two different...
The synthesis of the m-terphenyl isocyanide ligand CNAr (Mes2) (Mes = 2,4,6-Me 3C 6H 2) is described. Isocyanide CNAr (Mes2) readily functions as a sterically encumbering supporting unit for several Cu(I) halide and pseudo halide fragments, fostering in some cases rare structural motifs. Combination of equimolar quantities of CNAr (Mes2) and CuX (X = Cl, Br and I) in tetrahydrofuran (THF) solution results in the formation of the bridging halide complexes (mu-X) 2[Cu(THF)(CNAr (Mes2))] 2. Addition of CNAr (Mes2) to cuprous chloride in a 2:1 molar ratio generates the complex ClCu(CNAr (Mes2)) 2 in a straightforward manner. Single-crystal X-ray diffraction has revealed ClCu(CNAr (Mes2)) 2 to exist as a three-coordinate monomer in the solid state. As determined by solution (1)H NMR and FTIR spectroscopic studies, monomer ClCu(CNAr (Mes2)) 2 resists tight binding of a third CNAr (Mes2) unit, resulting in rapid isocyanide exchange. Contrastingly, addition of 3 equiv of CNAr (Mes2) to cuprous iodide readily affords the tris-isocyanide species, ICu(CNAr (Mes2)) 3, as determined by X-ray diffraction. Similar coordination behavior is observed in the tris-isocyanide salt [(THF)Cu(CNAr (Mes2)) 3]OTf (OTf = O 3SCF 3), which is generated upon treatment of (C 6H 6)[Cu(OTf)] 2 with 6 equiv of CNAr (Mes2) in THF. The disparate coordination behavior of the [CuCl] fragment relative to both [CuI] and [CuOTf] is rationalized in terms of structure and Lewis acidity of the Cu-containing fragments. The putative triflate species [Cu(CNAr (Mes2)) 3]OTf itself serves as a good Lewis acid and is found to weakly bind C 6H 6 in an eta (1)- C manner in the solid-state. Density Functional Theory is used to describe the bonding and energetics of the eta (1)- C Cu-C 6H 6 interaction.
Reaction of the azidoborate salt [N(n-Bu)(4)][(C(6)F(5))(3)B(N(3))] ([N(n-Bu)(4)][1]) with the uranium(III) tris(anilide) complex (THF)U(N[t-Bu]Ar)(3) (2; THF = tetrahydrofuran; Ar = 3,5-Me(2)C(6)H(3)) results in formation of the paramagnetic uranium(V) nitridoborate complex [N(n-Bu)(4)][(C(6)F(5))(3)BNU(N[t-Bu]Ar)(3)] ([N(n-Bu)(4)][3]). Chemical oxidation of [N(n-Bu)(4)][3] is facile and provides the diamagnetic uranium(VI) nitridoborate complex (C(6)F(5))(3)BNU(N[t-Bu]Ar)(3) (3). [N(n-Bu)(4)][3] and 3 are the first nitridoborate complexes of uranium and were characterized by multinuclear NMR spectroscopy, single crystal X-ray diffraction methods, and elemental analysis. The X-ray crystal structures of [N(n-Bu)(4)][3] and 3 reveal extremely short UN(nitrido) distances (1.916(4) A and 1.880(4) A, respectively). Density functional theory was used to calculate the optimized structure of the truncated model (C(6)F(5))(3)BNU(N[Me]Ph)(3); the procedure was carried out similarly for several other relevant complexes featuring UN multiple bonds. Bond multiplicities based on Nalewajski-Mrozek valence indices were calculated, the results of which suggest that the UN(nitrido) interaction in 3 is close to a full triple bond.
Reaction of the uranium(III) tris(anilide) complex (THF)U(N[t-Bu]Ar)(3) (1, THF = tetrahydrofuran; Ar = 3,5-Me(2)C(6)H(3)) with MN(3) (M = Na, [N(n-Bu)(4)]) results in the formation of the bimetallic diuranium(IV/IV) complexes M[(mu-N)(U(N[t-Bu]Ar)(3))(2)] (M[3]), which feature a single nitride ligand engaged as a linear, symmetric bridge between two uranium centers. The stability of the U=N=U core across multiple charge states is illustrated by stepwise chemical oxidation of Na[3] to the diuranium(IV/V) complex (mu-N)(U(N[t-Bu]Ar)(3))(2) (3) and the diuranium(V/V) complex [(mu-N)(U(N[t-Bu]Ar)(3))(2)][B(Ar(F))(4)] {[3][B(Ar(F))(4)]; Ar(F) = 3,5-(CF(3))(2)C(6)H(3)}. M[3], 3, and [3][B(Ar(F))(4)] were characterized by NMR spectroscopy, single-crystal X-ray diffraction, and elemental analysis. The cyclic voltammogram of 3 reveals two clean, reversible one-electron electrochemical events at E(1/2) = -1.69 and -0.67 V, assigned to the [3](-)/3 and 3/[3](+) redox couples, respectively. The X-ray crystal structures of [N(n-Bu)(4)][3], 3, and [3][B(Ar(F))(4)] reveal a linear U=N=U core that contracts by only approximately 0.03 A across the [3](n) (n = -1, 0, +1) series, an effect that is rationalized as being primarily electrostatic in origin. [3][B(Ar(F))(4)] reacts with NaCN, eliminating Na[B(Ar(F))(4)] and forming the known diuranium(IV/IV) cyanoimide complex (mu-NCN)(U(N[t-Bu]Ar)(3))(2), suggesting that the U=N=U core has metallonitrene-like character.
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