New potential-energy functions for Cu, Ag and Au solids and their applications to computer simulations on metallic surfaces

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Investigation of electrochemical reactions in the solid state cell Cu/RbCu4Cl3I2/C

Using experimental potential values for a vitreous carbon electrode in contact with the RbCu₄Cl₃I₂ solid electrolyte, the concentration of Cu²⁺ ions in the electrolyte was determined. At 0.5 V, the concentration of Cu²⁺ was 1.25×10¹⁸ cm^–3. The estimated values of the Cu²⁺ ion concentration in RbCu₄Cl₃I₂ (0.8%) and the potential of the vitreous carbon electrode after electrochemical decomposition of RbCu₄Cl₃I₂ (0.606 V) correspond to experimental values of 2% and 0.58 V, respectively. This demonstrates the adequacy of the model describing the electrode potential of Cu²⁺ as a function of the concentration in RbCu₄Cl₃I₂. When the C/RbCu₄Cl₃I₂ interface was polarized, the diffusion coefficient of Cu²⁺ was 1.5×10^–8 cm² s^–1. Investigations of the interface between the copper electrode and RbCu₄Cl₃I₂ were carried out by galvanostatic and potentiostatic methods. A 1-μm layer of cuprous oxide, Cu₂O, was discovered on the interface of the copper electrode with RbCu₄Cl₃I₂. This layer blocks the course of the electrochemical reaction Cu⁰–e^–⇌Cu⁺ with participation of copper metal. The copper electrode behaves as an inert redox electrode at low overvoltages. In this case, at the Cu₂O/RbCu₄Cl₃I₂ interface an electrochemical reaction with Cu²⁺ ion participation, Cu⁺–e^–⇌Cu²⁺, takes place. The results suggest that the reaction rate is limited by slowing the Cu²⁺ diffusion in RbCu₄Cl₃I₂. The initial Cu²⁺ ion concentration in the electrolyte near this interface is about 1.4×10¹⁷ cm^–3. The exchange current density is about (4±2)×10^–6 A cm^–2. At potentials ϕ>8–10 mV, an electrical breakdown of the Cu₂O layer takes place, allowing copper metal to ionize to Cu⁺. We suggest that at 10 mV<ϕ<100 mV the rate of this reaction is limited by the formation and growth of copper nuclei and at ϕ>120 mV the reaction rate is limited by charge transfer. Electronic Publication     

MLCT state structure and dynamics of a copper(I) diimine complex characterized by pump-probe X-ray and laser spectroscopies and DFT calculations

The molecular structure and dynamics of the photoexcited metal-to-ligand-charge-transfer (MLCT) state of [Cu(I)(dmp)(2)](+), where dmp is 2,9-dimethyl-1,10-phenanthroline, in acetonitrile have been investigated by time-domain pump-probe X-ray absorption spectroscopy, femtosecond optical transient spectroscopy, and density functional theory (DFT). The time resolution for the excited state structural determination was 100 ps, provided by single X-ray pulses from a third generation synchrotron source. The copper ion in the thermally equilibrated MLCT state has the same oxidation state as the corresponding copper(II) complex in the ground state and was found to be penta-coordinate with an average nearest neighbor Cu-N distance 0.04 A shorter than that of the ground state [Cu(I)(dmp)(2)](+). The results confirm the previously proposed "exciplex" structure of the MLCT state in Lewis basic solvents. The evolution from the photoexcited Franck-Condon MLCT state to the thermally equilibrated MLCT state was followed by femtosecond optical transient spectroscopy, revealing three time constants of 500-700 fs, 10-20 ps, and 1.6-1.7 ns, likely related to the kinetics for the formation of the triplet MLCT state, structural relaxation, and the MLCT excited-state decay to the ground state, respectively. DFT calculations are used to interpret the spectral shift on structural relaxation and to predict the geometries of the ground state, the tetracoordinate excited state, and the exciplex. The DFT calculations also indicate that the amount of charge transferred from copper to the dmp ligand upon photoexcitation is similar to the charge difference at the copper center between the ground-state copper(I) and copper(II) complexes.     

Synthesis and structure of 1,4:3,6-dianhydro-2-O-p-tosyl-D-mannitol

1,4:3,6-Dianhydro-2-O-p-tosyl-D-mannitol (3) has been isolated from the reaction of 1,4:3,6-dianhydro-D-mannitol (2) andp-toluenesulfonyl chloride (1:2 mole ratio) in pyridine in 19% yield after fractional crystallization. It crystallizes in the orthorhombic space groupP2₁2₁2₁ (Z=4) witha=6.064(2),b=8.347(1) andc=26.455(16) Å. Disorder associated with the unsubstituted furanose ring provides two arrangements, rings B and C, with two sets of sites for both the hydroxyl group and a ring carbon atoms: the relative occupancy of ring B: ring C=0.53(1):0.4791). Distinct H-bonding situations (both intra-and inter-molecular) are associated with the two arrangement. The conformations of the unsubstituted furanose ring with the weaker intramolecular H-bonding (ring B) and the tosyl-substituted ring (ring A) are very similars, being 1:2 mixtures of envelope [³ E] and twist forms [³ T ₄]: the stronger H-bonding in ring C results instead in a conformation made up from a 30:70 mixture ofE ₀ and⁴ T ₀ forms. The¹H-NMR spectrum for3 indicates that the average solution conformation is also a mixture of envelope and twist forms and is similar to that of the A/B solid-state arrangement.     

Chromatographic,spectroscopic, topographic,and X-ray crystallographic studies of the solid solution formed by racemic 3-carboxy-2,2,5,5-tetramethyl-1-pyrrolidinyloxy (3-carboxy-proxyl)

The solid solution formed by the title compound, C₉H₁₆NO₃, has been examined by a variety of techniques and shown to be an equi-molecular mixture of the two enantiomers. Refinement of the disordered structure was based on the orthorhombic space groupPnma witha=8.023(2),b=10.030(3), andc=12.352(2)Å, finalR=0.055. The oxygens of the carboxyl group are disordered and both enantiomers can occupy the same, rather than alternate, crystallographic sites. Results from studies involving IR, GC-MS, and chiral chromatography are also presented. In addition we report on the use of synchrotron X-ray topography to investigate strain in crystals of the solid solution.     

Crystal and molecular structure of 2-(2′-chloro-5′-nitrostyryl)benzoselenazole

The title compound C₁₅H₉ClN₂O₂Se (nsbse) is orthorhombic, witha=6.823(2),b=7.860(2),c=26.349(5) Å,Z=4,D _x =1.709,(MoK)=28.3 cm^–1,F(000)=720,T=298K in space groupP2₁2₁2₁. The structure was solved by heavy atom and Fourier methods and refined toR=0.045 for 1095 unique observed reflections. The molecule is almost planar, with a dihedral angle of 4.8(2)° between the benzoselenazole and phenyl rings. The C-Se-C angle in the selenazole ring is very small, 84.6(4)°, while the C-N-C angle in that ring is 113.7(7)°.     

(Aroxymethyl)triphenyltin compounds: Crystal and molecular structure of triphenyl(p-toloxymethyl)tin

Compounds, Ph₃SnCH₂OAr, are available from Ph₃SnCH₂I and NaOAr in EtOH. The crystal and molecular structure of Ph₃SnCH₂OC₆H₄Me-p (II) has been determined by X-ray crystallography. The molecule in the crystal contains a slightly distorted tetrahedral tin atom [C-Sn-C valency angles varying from 106.9(5) to 114.1(6)°] with an intramolecular Sn---O distance of 2.900(11) Å. NMR spectral data for (II) and for Ph₃SnCH₂OC₆H₃Br₂-2,4 are reported.     

Crystal structures of two thienyl analogs of benzil – 1,2-dithien-2-ylethanedione (2,2′-thenil) and 1,2-dithien-3-ylethanedione (3,3′-thenil)

2,2-Thenil crystallizes in P2₁/c with a = 7.2501(12) Å, b = 4.7846(8) Å, c = 13.9867(23) Å, = 96.897(3), V = 481.67(14) ų, and Z = 2. The molecule resides on an inversion center and is planar. 3,3-Thenil also crystallizes in P2₁/c with a = 3.9904(8) Å, b = 21.310(4) Å, c = 11.618(2) Å, = 101.83(3), V = 966.9(3) ų, and Z = 4. Refinement of 3,3-thenil data indicated that 10.3(2)% of both thienyl rings are flip-disordered in this nonplanar molecule. A brief discussion of disorder in molecules containing terminal, unsubstituted 2- and 3-thienyl rings is presented.     

Crystal structures of baclofen analogs: 3-thienyl- and 3-furylaminobutyric acids

X-ray crystal structures of 4-amino-3-(2-thienyl) butyric acid (compound1), 4-amino-3-(4-bromo-2-thienyl) butyric acid (compound2), and 4-amino-3-(5-methyl-2-furyl) butyric acid (compound3) are reported. Space groups and unit/cell parameters are: compound1, monoclinic,P2₁ c,a=13.288(3),b=5.231(1),c=12.388(2)Å,=92.3(1)°; compound2, monoclinic,P2₁/c,a=12.610(7),b=5.156(1),c=15.814(8)Å,=101.8(1)°; compound3, orthorhombic, Pccn,a=11.461(1),b=25.284(2),c=6.977(1)Å. FinalR indices are: compound1, 0.057; compound2, 0.069; compound3, 0.060. Conformations of their -aminobutyric chains are compared with the one of -amino--(p-chlorophenyl)-butyric acid (baclofen, compound4). Two different types of conformations are observed, i.e., conformations (i) with folding (compound3) or (ii) without folding (compounds1,2, and4) of the ammonium group toward the heteroaromatic or aromatic ring. However, distances between ionized groups are constant.     

Structure of 2-(2′-bromo-5′-nitrostyryl)benzothiazole

The title compound C₁₅H₉BrN₂O₂S (brnsb) is monoclinic, witha=7.730(2),b=26.847(5),c=7.773(2) Å,=117.48(1)°,V=1431(1) ų,Z=4,D _x=1.677,(MoK)=29.9 cm^–1,F(000)=720,T=298K in space groupP2₁/c. The structure was solved by heavy atom and Fourier methods and refined toR=0.034 for 1776 unique observed reflections. The molecule is nearly planar, with a dihedral angle of only 3.8(1.1)° between the benzothiazole and phenyl rings. The C-S-C angle in the thiazole ring is 89.0°, while the C-N-C angle in that ring is 111.5(3)°.