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1.
The kinetics of the thermal decomposition of CoOOH powder has been studied isothermally in a temperature range of 260—310°C in air. The reaction was found to proceed by the advance of a two-dimensional reaction interface. The kinetics results indicate that there are two phases in the decomposition in this temperature range: up to 280°C with an activation energy E1 = 34.75 kcal mol −1 and above 280°C with E2 = 18.91 kcal mol −1. A reaction mechanism is proposed to account for these observations. 相似文献
2.
The reaction of HOCl + HCl → Cl 2 + H 2O in the presence of chlorine anion Cl − has been studied using ab initio methods. The overall exothermicity is 15.5 kcal mol −1 and this reaction has been shown to have a high activation barrier of 46.5 kcal mol −1. Cl − is found to catalyze the reaction via the formation of HOCl·Cl −, ClH·HOCl·Cl − and Cl −·H 2) intermediate ion-molecule complexes or by interacting with a concerted four-center transition state of the reaction of HOCl + HCl. 相似文献
3.
The syntheses and structural determination of Nd III and Er III complexes with nitrilotriacetic acid (nta) were reported in this paper. Their crystal and molecular structures and compositions were determined by single-crystal X-ray structure analyses and elemental analyses, respectively. The crystal of K 3[Nd III(nta) 2(H 2O)]·6H 2O complex belongs to monoclinic crystal system and C2/ c space group. The crystal data are as follows: a=1.5490(11) nm, b=1.3028(9) nm, c=2.6237(18) nm, β=96.803(10)°, V=5.257(6) nm 3, Z=8, M=763.89, Dc=1.930 g cm −3, μ=2.535 mm −1 and F(000)=3048. The final R1 and wR1 are 0.0390 and 0.0703 for 4501 ( I>2σ( I)) unique reflections, R2 and wR2 are 0.0758 and 0.0783 for all 10474 reflections, respectively. The Nd IIIN 2O 7 part in the [Nd III(nta) 2(H 2O)] 3− complex anion has a pseudo-monocapped square antiprismatic nine-coordinate structure in which the eight coordinate atoms (two N and six O) are from the two nta ligands and a water molecule coordinate to the central Nd III ion directly. The crystal of the K 3[Er III(nta) 2(H 2O)]·5H 2O complex also belongs to monoclinic crystal system and C2/ c space group. The crystal data are as follows: a=1.5343(5) nm, b=1.2880(4) nm, c=2.6154(8) nm, b=96.033(5)°, V=5.140(3) nm 3, Z=8, M=768.89, Dc=1.987 g cm −3, μ=3.833 mm −1 and F(000)=3032. The final R1 and wR1 are 0.0321 and 0.0671 for 4445 ( I>2σ( I)) unique reflections, R2 and wR2 are 0.0432 and 0.0699 for all 10207 reflections, respectively. The Er IIIN 2O 7 part in the [Er III(nta) 2(H 2O)] 3− complex anion has the same structure as Nd IIIN 2O 7 part in which the eight coordinate atoms (two N and six O) are from the two nta ligands and a water molecule coordinate to the central Nd III ion directly. 相似文献
4.
NH 2 profiles were measured in a discharge flow reactor at ambient temperature by monitoring reactants and products with an electron impact mass spectrometer. At the low pressures used (0.7 and 1.0 mbar) the gas-phase self-reaction is dominated by a ‘bimolecular’ H 2-eliminating exit channel with a rate coefficient of k3b(300 K) = (1.3 ± 0.5) × 10 −12 cm 3 molecule −1 s −1 and leading to N 2H 2 + H 2 or NNH 2 + H 2. Although the wall loss for NH 2 radicals is relatively small ( kw ≈ 6–14 s −1), the contribution to the overall NH 2 decay is important due to the relatively slow gas-phase reaction. The heterogeneous reaction yields N 2H 4 molecules. 相似文献
5.
The macrocyclic compound, [1,2-C 2B 10H 10-1,4-C 6H 4-1,7-C 2B 10H 10-1,4-C 6H 4] 2 (5)—a novel cyclooctaphane, was prepared by condensation of the C,C′-dicopper(I) derivative of meta-carborane with 1,2-bis(4-iodophenyl)- ortho-carborane. The X-ray crystal structure of 5·C 6H 6·6C 6H 12 was determined at 150 K, revealing an extremely loose packing mode. Molecule 5 has a crystallographic Cs and local C2v symmetry; the macrocycle adopts a butterfly (dihedral angle 143°) conformation with the ortho-carborane units at the wingtips and the phenylene ring planes roughly perpendicular to the wing planes. Multinuclear NMR spectra suggest that molecule 5 in solution inverts rapidly via the planar D2h geometry, which (from ab initio HF/6-31G* calculations) is only 1 kcal mol −1 higher in energy than the C2v one. An attempt to prepare an even larger macrocycle, comprising three para-carborane and three ortho-carborane units linked by six para-phenylene units, was unsuccessful. 相似文献
6.
The enthalpy of formation (Δ Hf0), enthalpy of evaporation (Δ Hv0) and enthalpy of atomization (Δ Ha) of permethylcyclosilazanes (Me 2SiNH) n ( n = 3, 4) and 1,1,3,3-tetramethyldisilazane (Me 2SiH) 2NH have been determined. The enthalpies of formation of these compounds were compared with those calculated by the Benson-Buss-Franklin and Tatevskii additive schemes. In higher permethylcyclosilazanes the energy of the endocyclic Si---N bond is 306 ± 2 kJ mol −1 (73 kcal mol −1), that is 12 ± 2 kJ mol −1 (3 kcal mol −1) lower than the energy of the acyclic Si---N bond. The strain energy of the cyclotrisilazane ring is estimated to be 10.5 kJ mol −1 (2.5 kcal mol −1), whereas the energy of the ring Si---N bond is 295 kJ mol −1 (70.5 kcal mol −1). The thermochemical data for permethylcyclosilazanes were compared with the corresponding values for permethylcyclosiloxanes calculated from the results of previously reported studies. 相似文献
7.
The mechanism of the SO 2 + HO 2 reaction was studied theoretically for the first time. Three product channels were revealed, namely, O 2 + HOSO, O 2 + HSO 2, and OH + SO 3. The O 2 + HOSO channel dominates the reaction under combustion conditions. A five-member-ring complex [SO 2–HO 2] exists at the entrance of the reaction. The structure and binding energy ( De and D0) of the SO 2–HO 2 complex have been calculated. In view of D0 = 21.2 ± 2.0 kJ mol −1, the SO 2–HO 2 complex should be stable at low temperature. The infrared spectra and frequency shifts were calculated for both SO 2–HO 2 and SO 2–DO 2, and compared with the available experimental data. 相似文献
8.
Ab initio MO GB theory which includes the continuum model of solvent effect using generalized Born formula has been applied to the dimerization reaction of HCN in aqueous solution which is the starting step in prebiotic synthesis of purine precursors from aqueous hydrogen cyanide. Three steps considered were: (i) the reaction of HCN and H 2O to produce the CN − anion, (ii) the reaction of CN − with HCN to give the NC–CH=N − anion, and (iii) the addition of a proton to the anion to give iminoacetonitrile. The formation of CN − ion from HCN in aqueous solution requires 15.1 kcal/mol (the experimental value estimated from the dissociation constant of HCN in water is 14.8 kcal/mol). The reaction of CN − with HCN requires the activation energy of 32.2 kcal/mol (MP2/6-31++G **//HF/6-31++G **) to give the dimer. This barrier height is reduced to 26.1 kcal/mol when HCN is associated with H 3O +. In the presence of NH 3 in aqueous solution, CN − is produced easily by the reaction of HCN and NH 3 with a low activation energy of 4.3 kcal/mol. It was shown that the formation of CN − becomes easier in ammoniacal solution, and the dimerization occurs efficiently in aqueous solutions which contain NH 3. 相似文献
9.
The new host 1,4,11,14-tetramethoxy-dibenzo[b,n]tetraphenylene forms a 1:1 inclusion compound with pyridine, in which a pair of centrosymmetrically-related guest species are enclosed in the cage surrounded by six host molecules. C 36H 28O 4·C 5H 5N, FW=603.68, triclinic, space group P-1, a=11.796(2), b=16.075(3), c=9.004(2) Å; =98.39(3)°, β=90.01(3)°, γ=108.19(3)°, V=1602.8(5) Å 3, Z=2, F(000)=636, Dc=1.251 g/cm 3, μ=0.080 mm −1. The final R indices [ I>2σ( I)] R1=0.0759, wR2=0.1970 for 5623 MoK observed data. 相似文献
10.
Saddle point geometries and barrier heights have been calculated for the H abstraction reaction HO 2( 2A″)+H( 2S) → H 2( 1Σ +g)+O 2( 3Σ −g) and the concerted H approach-O removing reaction HO 2 ( 2A″)+H( 2S) → H 2O( 1A 1)+O( 3P) by using SDCI wavefunctions with a valence double-zeta plus polarization basis set. The saddle points are found to be of C s symmetry and the barrier heights are respectively 5.3 and 19.8 kcal by including size consistent correction. Moreoever kinetic parameters have been evaluated within the framework of the TST theory. So activation energies and the rate constants are estimated to be respectively 2.3 kcal and 0.4×10 9 ℓ mol −1 s −1 for the first reaction, 20.0 kcal and 5.4.10 −5 ℓ mol −1 s −1 for the second. Comparison of these results with experimental determinations shows that hydrogen abstraction on HO 2 is an efficient mechanism for the formation of H 2 + O 2, while the concerted mechanism envisaged for the formation of H 2O + O is highly unlikely. 相似文献
11.
The vibrational frequencies of the N–H stretching modes of aniline after forming a strong doubly H-bonded complex with tetrahydrofuran (THF) are measured with infrared depletion spectroscopy that uses cluster-size-selective resonance-enhanced multiphoton ionization (REMPI) time-of-flight mass spectrometry. Two strong infrared absorption features observed at 3355 and 3488 cm −1 are assigned to the symmetric and antisymmetric N–H stretching vibrations of the 1:2 aniline–THF complex, respectively. The red-shifts of the N–H stretching vibrations of aniline agree with the ab initio calculated (MP2/6-31G**) aniline-(THF) 2 structure in which both aniline N–H bonds interact with the oxygen atom of THF through two hydrogen bonds. The calculated binding energy is found to be 29.6 kJ mol −1 after corrections for basis set superposition error (BSSE) and zero-point energy. The calculated structure revealed that the angle between the N–H bonds in the NH 2 group increased to 112.5° in the aniline–(THF) 2 complex from that of 109.8° in the aniline. The electronic 0–0 band origin for the S1 ← S0 transition is observed at 32,900 cm −1 in the aniline–(THF) 2 complex, giving a red-shift of 1129 cm −1 from that of the aniline molecule. 相似文献
12.
The bimetallic [Pt(NH 3) 4] 2[W(CN) 8][NO 3]·2H 2O is characterised by single-crystal X-ray diffraction [S.G. P2 1/ m(11), a=8.0418(7), b=19.122(2), c=9.0812(6) Å, Z=2]. All platinum centres have the square-plane D4h geometry with average dimensions Pt(1)–N 2.042(2) and Pt(2)–N 2.037(10) Å. The octacyanotungstate anion has the square-antiprismatic D4d configuration with average dimensions W(1)–C 2.164(13), C–N 1.140(12), W(1)–N 3.303(5) Å. The structure exhibits two different mutual orientations of Pt versus W units resulting in Pt(2)–W(1), W(1) * separations of 4.77(2), 4.55(2) * and Pt(1)–W(1) of 6.331(8) Å. A centrosymmetric structure reveals groups of two distinct columns: the first is formed by intercalated NO 3− between parallel [Pt(1)(NH 3) 4] 2+ planes and the second consists of [W(CN) 8] 3− interlayered by, parallel to square faces of W-antiprisms, [Pt(2)(NH 3) 4] 2+. The structure is stabilised through a three-dimensional hydrogen bond network via nitrogen atoms of cyanide ligands, hydrogen atoms of NH 3 ligands, water molecules and oxygen atoms of NO 3− counteranions. The vibrational pattern and the range of ν(CN) frequencies attributable to the electronic environment of W(V) and W(IV) are consistent with the ground state Pt(II)↔W(V) charge transfer. 相似文献
13.
The geometries and vibrational frequencies of the adducts ClCO 2, ClCOS and ClCS 2 were derived at the Hartree-Fock (HF) 3-21G ( *) level. The Ca, structure of ClCO 2 corresponds to one C-O bond and one C=O bond. Similarly, Ca, ClCS 2 has one C-S and one C=S bond, and ClCOS has one C-S and one C-O bond. Single-point spin-projected fourth-order Møller-Plesset (MP4) 3-21G ( *) calculations at these geometries were used in bond-separation reactions to derive Δ Ho0 for adduct formation, which is calculated to be about 39 kJ mol −1 exothermic for ClCOS and ClCS 2, but about 39 kJ mol −1 endothermic for ClCO 2. The C2v structures for ClCO 2 and ClCS 2 were also characterized. The geometry of ClCS 2 has not been determined experimentally; comparison with an available measured entropy for ClCS 2 suggests that the C2v structure is the one formed by addition of Cl to CS 2, although the energy relative to the Ca form is not reliably calculated because of instability in the HF wavefunction. 相似文献
14.
Excess molar enthalpies HE and excess molar volumes VE have been measured, as a function of mole fraction x1, at 298.15 K and atmospheric pressure for the five liquid mixtures ( x11,4-C 6H 4F 2 + x2n-C lH 2l+2), l = 7, 8, 10, 12 and 16. In addition, HE and excess molar heat capacities CPE at constant pressure have been determined for the two liquid mixtures ( x1C 6F 6 + x2n-C lH 2l+2), l = 7 and 14, at the same temperature and pressure. The instruments used were flow microcalorimeters of the Picker design (the HE version was equipped with separators) and a vibrating-tube densimeter, respectively. The excess enthalpies of the five difluorobenzene mixtures are all positive and quite large; they increase with increasing chain length l of the n-alkane from HE(x1 = 0.5)/(J mol−1) = 1050 for l = 7 to 1359 for l = 16. The corresponding excess volumes VE are all positive and also increase with increasing l: VE(x1 = 0.5)/(cm3 mol−1) = 0.650 for l = 7 and 1.080 for l = 16. Interestingly, the excess enthalphies of the corresponding mixtures with hexafluorobenzene are only about 5% larger, whereas the excess volumes of (x1C6F6 + x2n-ClH2l+2) are roughly twice as large as those of their counterparts in the series containing 1,4-C6H4F2. Specifically, at 298.15 K HE(x1 = 0.5)/(J mol−1) = 1119 for (x1C6F6 + x2n-C7H16) and 1324 for (x1C6F6 + x2n-C14H30), and for the same mixtures VE(x1 = 0.5)/(cm3 mol−1) = 1.882 and 2.093, respectively. The excess heat capacities for both systems are negative and of about the same magnitude as the excess heat capacities of mixtures of fluorobenzene with the same n-alkanes (Roux et al., 1984): CPE(x1 = 0.5)/(J K−1 mol−1) = −1.18 for (x1C6F6 + x2n-C7H16), and −2.25 for (x1C6F6 + x2n-C14H30). The curve CPE vs. (x1 for x1C6F6 + x2n-C14H30) shows a sort of “hump” for x1 0.5, which is presumed to indicate emerging W-shape composition dependence at lower temperatures. 相似文献
15.
Infrared and Raman spectra of the polycrystalline complex cyanide acids H 3M III(CN) 6 (M=Fe,Co) and their deutero analogues were investigated at 300 and 90K in the region 4000-100 cm −1. The spectra indicate clearly that the site symmetry of the M(CN) 63− ion is C3v for M=Fe and D3d for M=Co. These conclusions are consistent with an asymmetric N-H·N bond in H 3Fe(CN) 6 and with a symmetric one in H 3Co(CN) 6. The N-H stretching frequencies are assigned as ca. 1100 cm −1 (Fe) and as 560 cm −1 (Co), the shift being related to the difference in the hydrogen bonding strength, 2.665 Å (Fe) and 2.582 Å (Co). The spectroscopic behaviour of these very short N-H·N bonds appears to be similar to that of the strong O-H·O bonds in type A (for M=Co) or type pseudo-A compounds (for M=Fe). 相似文献
16.
The gas-phase rapid ion-molecule reaction Si + ( 2P) + NH 3→ SiNH 2+ + H is theoretically investigated by the ab initio molecular orbital methods. Several possible pathways (A, B, C) on its potential energy surface have been examined, discussed and compared. Theoretical calculations indicate that pathway A is favourable in energy and that the reaction begins by forming a collision complex of the ion-dipole molecule Si-NH +3, which forms with no barrier into the first energy well of the reaction coordinate. Migration of an H atom from an N atom to a Si atom forms the intermediate HSi-NH +2, which corresponds to the second energy well and can fragment to the observed product SiNH +2 by losing an H atom from the Si atom. The barriers for migration and fragmentation are 52.5 and 38.6 kcal mol −1 respectively. Pathway A has a negative activation energy of −42.1 kcal mol −1. 相似文献
17.
Non-empirical molecular orbital calculations have been performed on the seven possible [C 2H 6N] + isomers at different levels of sophisitcation. The results suggest that the ions possessing a resonance contribution with a filled octet are the most stable ones. Barriers to CH 3 — and NH 3 —rotation have also been computed and are generally quite low ( 5 kJ mol −1). 相似文献
18.
The activation barrier for the CH 4 + H → CH 3 + H 2 reaction was evaluated with traditional ab initio and Density Functional Theory (DFT) methods. None of the applied ab initio and DFT methods was able to reproduce the experimental activation barrier of 11.0-12.0 kcal/mol. All ab initio methods (HF, MP2, MP3, MP4, QCISD, QCISD(T), G1, G2, and G2MP2) overestimated the activation energy. The best results were obtained with the G2 and G2MP2 ab initio computational approaches. The zero-point corrected energy was 14.4 kcal mol −1. Some of the exchange DFT methods (HFB) computed energies which were similar to the highly accurate ab initio methods, while the B3LYP hybrid DFT methods underestimated the activation barrier by 3 kcal mol −1. Gradient-corrected DFT methods underestimated the barrier even more. The gradient-corrected DFT method that incorporated the PW91 correlational functional even generated a negative reaction barrier. The suitability of some computational methods for accurately predicting the potential energy surface for this hydrogen radical abstraction reaction was discussed. 相似文献
19.
At 25°C, I = 1.0 M (CF 3SO 3−Li ++CF 3SO 3H), [H +] = 0.034–0.274 M and λ = 453 nm, the rate equation for the oxidation of Ti(H 2O), 63+ by bromine was found to be: −d/[Br 2] T/d t= kK/[Br 2][Ti III]/[H +]+ K+ kK/[Br 3−][Ti III]/[H ++ K, where k = 9.2 × 10 −3 M −1 s −1 and K = 4.5 × 10 −3 M. At [H +] = 1.0 M, [Br −] = 0.05–0.4 M, the apparent second-order rate constant decreases as [Br −] increases. The pH-dependence of the oxidation of TiIII-edta by bromine is interpreted in terms of the change in identity of the TiIII-edta species as the pH of the reaction medium changes. The second-order rate constants were fitted using a non-linear least-square computer program with (1/k0edta)2 weighting into an equation of the form: k0edta =k1+k2K1[H+]−1+k3K1K2[H+]−2/1+K1[H+[H+−1+K1K2[H+]−2, with K1 and K2 fixed as earlier determined at 9.55 × 10−3 and 2.29 × 10−9 M, respectively, for the oxidation of bromine. k1=k2=(3.1±0.32)×103M−1s−1 k3=(2.3±0.45)×106N−1s−1. It is proposed that these electron transfer reactions proceed by univalent changes with the production of Br2.− as a transient intermediate. An outer-sphere mechanism is proposed for these reactions. The homonuclear exchange rate for TiIII-edta+TiIV-edta is estimated at 32 M−1 s−1. 相似文献
20.
A new family of heteropolytungstate complexes (NH 4) 21[Ln(H 2O) 5{Ni(H 2O)} 2As 4W 40O 140]· xH 2O(Ln=Y, Ce, Pr, Nd, Sm, Eu, Gd) were prepared by the reaction of Na 27[NaAs 4W 40O 140]·60H 2O with NiCl 2·6H 2O and Ln(NO 3) 3· xH 2O at pH≈4.5. The crystal structures of (NH 4) 21[Gd(H 2O) 5{Ni(H 2O)} 2As 4W 40O 140]·51H 2O was determined by X-ray diffraction analysis and element analysis. The compound crystallizes in the monoclinic space group P2 1/ n with a=19.754(3), b=24.298(4), c=39.350(6) Å, β=100.612(3)°, V=18564(5) Å 3, Z=2, R1( wR2)=0.0544(0.0691). The central site S1 and two opposite sites S2 of the big cyclic ligand [As 4W 40O 140] 28− are occupied by one Ln 3+and two Ni 2+, respectively, each site supply four O d coordinating to metal ion, another one water molecule and other five water molecules coordinate, respectively, to Ni 2+and Ln 3+. Polyanion [Ln(H 2O) 5{Ni(H 2O)} 2As 4W 40O 140] 21− has C2v symmetry. IR and UV–vis spectra of [NaAs 4W 40O 140] 27− of the title compounds are discussed. 相似文献
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