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1990 Volume 6 Issue 6
1990, 6(06): 641-644
doi: 10.3866/PKU.WHXB19900601
Abstract:
The Fenske-Hall molecular orbital calculations were performed on the model cluster Cu_3O_(12)~(17-). The calculated results revealed that the valence levels are mainly composed of Cu d and O p components, and the levels near E_f are predominately of O p nature. Oxidation removes the antibonding electrons from the Cu (1) d_(z~2-y~2) MO and strengthens the chain Cu(1)—O(1) and Cu(1)—O(4) bonds so that they have slightly larger overlap population than the plane Cu(2)—O(2) and Cu(2)—O(3) bonds. The oxidation beyond the Cu~(2+) state does not lead to Cu~(3+) but to O~- state so that the O(1) as well as O(4) ions have slightly smaller electron charge than the O(2) and O(3) ions. The holes introduced by doping reside primarily on the Cu—O chain with dominantly sigma O(4) 2p_z character.
The Fenske-Hall molecular orbital calculations were performed on the model cluster Cu_3O_(12)~(17-). The calculated results revealed that the valence levels are mainly composed of Cu d and O p components, and the levels near E_f are predominately of O p nature. Oxidation removes the antibonding electrons from the Cu (1) d_(z~2-y~2) MO and strengthens the chain Cu(1)—O(1) and Cu(1)—O(4) bonds so that they have slightly larger overlap population than the plane Cu(2)—O(2) and Cu(2)—O(3) bonds. The oxidation beyond the Cu~(2+) state does not lead to Cu~(3+) but to O~- state so that the O(1) as well as O(4) ions have slightly smaller electron charge than the O(2) and O(3) ions. The holes introduced by doping reside primarily on the Cu—O chain with dominantly sigma O(4) 2p_z character.
1990, 6(06): 645-647
doi: 10.3866/PKU.WHXB19900602
Abstract:
It was found that Li-Nd-Zn-Mg oxide has an extremely high activity for the oxidative coupling of methane to C_2 hydrocarbons. For example, Li-Nd-Zn-Mg oxide catalyst gave a conversion for methane 53.5%, yield for C_2 hydrocarbons 30.8%(ethene yield 19.0%, ethane yield 11.8%), selectivity for C_2 hydrocarbons 57.6% at 770 ℃, flow-rate of methane and oxygen 2000 ml·h~(-1), 1000 ml·h~(-1) respectively.
It was found that Li-Nd-Zn-Mg oxide has an extremely high activity for the oxidative coupling of methane to C_2 hydrocarbons. For example, Li-Nd-Zn-Mg oxide catalyst gave a conversion for methane 53.5%, yield for C_2 hydrocarbons 30.8%(ethene yield 19.0%, ethane yield 11.8%), selectivity for C_2 hydrocarbons 57.6% at 770 ℃, flow-rate of methane and oxygen 2000 ml·h~(-1), 1000 ml·h~(-1) respectively.
1990, 6(06): 648-650
doi: 10.3866/PKU.WHXB19900603
Abstract:
A mag1c angle spinning system for sealed samples has been achieved with a speed from 1.5 to 4.2 kHz. Using this system, high-resolution ~1H spectra are obtained for H_2S and alcohols adsorbed on charcoal in sealed ampoules. For high coverage of alcohols, the spectral lines are resolved very well, but for low coverage, the spectral lines cannot be separated completely. The details are discussed and the solution is anticipated.
A mag1c angle spinning system for sealed samples has been achieved with a speed from 1.5 to 4.2 kHz. Using this system, high-resolution ~1H spectra are obtained for H_2S and alcohols adsorbed on charcoal in sealed ampoules. For high coverage of alcohols, the spectral lines are resolved very well, but for low coverage, the spectral lines cannot be separated completely. The details are discussed and the solution is anticipated.
1990, 6(06): 651-653
doi: 10.3866/PKU.WHXB19900604
Abstract:
The influences of the reaction temperature, contact time and methane/oxygen on the oxidative coupling of methane were studied over Li-Nd-Mg oxide. A conversion of methane: 62.3%, yield of C_2 hydrocarbons: 31.3% (ethene yield: 20.3% and ethane yield: 11.0%) selectivity of C_2 hydrocarbons: 50.3% were obtained under the following conditions: T=730 ℃, CH_4/O_2=1.5 and space velocity of methane and oxygenis 5000 ml·h~(-1)·g~(-1).
The influences of the reaction temperature, contact time and methane/oxygen on the oxidative coupling of methane were studied over Li-Nd-Mg oxide. A conversion of methane: 62.3%, yield of C_2 hydrocarbons: 31.3% (ethene yield: 20.3% and ethane yield: 11.0%) selectivity of C_2 hydrocarbons: 50.3% were obtained under the following conditions: T=730 ℃, CH_4/O_2=1.5 and space velocity of methane and oxygenis 5000 ml·h~(-1)·g~(-1).
1990, 6(06): 654-659
doi: 10.3866/PKU.WHXB19900605
Abstract:
The supersonic molecular beam technique is used to study the dynamics of laser-induced surface reactions of Ta surface with chlorine at three different wavelengths (355, 560, 1064 nm). The mass and velocity distributions of the reaction products are determined by the time-resolved mass spectrometry. The observed time-of-flight(TOF) spectra of the products show that the main products are TaCl, TaCl_2, TaCl_3 and TaCl_4 and there is no TaCl_5 observed. Their TOF spectra can be fitted with Maxwell-Boltz-mann distributions at translational temperatures in the range of 500-1500 K. The effect of translational energy of incident Cl_2 molecules and laser fluences on the laserinduced Cl_2-Ta surface reactions at different wavelengths are presented. Finally, the possible reaction mechanism is discussed based on the experimental observations.
The supersonic molecular beam technique is used to study the dynamics of laser-induced surface reactions of Ta surface with chlorine at three different wavelengths (355, 560, 1064 nm). The mass and velocity distributions of the reaction products are determined by the time-resolved mass spectrometry. The observed time-of-flight(TOF) spectra of the products show that the main products are TaCl, TaCl_2, TaCl_3 and TaCl_4 and there is no TaCl_5 observed. Their TOF spectra can be fitted with Maxwell-Boltz-mann distributions at translational temperatures in the range of 500-1500 K. The effect of translational energy of incident Cl_2 molecules and laser fluences on the laserinduced Cl_2-Ta surface reactions at different wavelengths are presented. Finally, the possible reaction mechanism is discussed based on the experimental observations.
1990, 6(06): 660-665
doi: 10.3866/PKU.WHXB19900606
Abstract:
The measurement of rate constant of reaction O~3(P) + SiH_4 with discharge flow-chemiluminescence technique is presented. The Arrhenius form of the rate constant over temperature range 293--413 K is
k=(1.05±0.36)×10~(-10)exp[(-3.06±0.10)kcal·mol~(-1)/RT]cm~3·molecule~(-1)·s~(-1)
Using transition-state theory, the result was extrapolated to temperature range of 200--2000 K. The calculated dependence of the rate constant on temperature with three parameters is
k=7.67×10~(-19)T~(2.59)exp (-720 cal·mol~(-1)/RT)cm~3·molecule~(-1)·s~(-1).
The measurement of rate constant of reaction O~3(P) + SiH_4 with discharge flow-chemiluminescence technique is presented. The Arrhenius form of the rate constant over temperature range 293--413 K is
k=(1.05±0.36)×10~(-10)exp[(-3.06±0.10)kcal·mol~(-1)/RT]cm~3·molecule~(-1)·s~(-1)
Using transition-state theory, the result was extrapolated to temperature range of 200--2000 K. The calculated dependence of the rate constant on temperature with three parameters is
k=7.67×10~(-19)T~(2.59)exp (-720 cal·mol~(-1)/RT)cm~3·molecule~(-1)·s~(-1).
1990, 6(06): 666-672
doi: 10.3866/PKU.WHXB19900607
Abstract:
Initial adsorption heat of benzene on NaHY of different Na:H ratios have been determined in the temperature range of 250--300 ℃ by gas chromatographic pulse method. It was found that the adsorption heat decreases stepwisely with the decrease of Na content in NaHY: It is 62.4 kJ·mol~(-1) for Na:H<0.6, 60.3 kJ·mol~(-1) for 0.14<? Na /><Na:H<0.6, discussed. are zeolites NaHY in cation Na~+ of location the and strength adsorption sites, property results, above-mentioned on Based NaHY. sites H~+ benzene between interactions distinguish to used be could pairs two These cm~(-1). 1975 1832 at appears pair another HY while cm~(-1), 1948 1848 bands a displays NaY adsorbed that show data IR The interaction types three there means This HY. for Na:H<0.14 kJ·mol~(-1) 54.6></Na:H<0.6,>
1990, 6(06): 673-680
doi: 10.3866/PKU.WHXB19900608
Abstract:
The kinetics of a-FeO(OH) formation in weak acidic medium was studied. The effects of initial concentration, temperature, pH value, partial presure of oxygen, air flow rate and agitating intensity on the oxidation rate of Fe(OH)_2 suspensions have been investigated. It is confirmed that reaction order for Fe(Ⅱ) is zero at the stage of a-FeO(OH) seeds formation, and around 0.5 at the stage of the seeds growth, and in both processes of the partial pressure of oxygen appears to be first order. The activation energy is determined respectively. Dissolution-oxidation equilibrium existing in the process of seeds formation has been assumed, by which the zero order reaction for Fe(II) and plateau in the pH-t curve may be explained. Physical process is the rate-determining step of the heterogeneous reaction. The studies of the dinetics of α-FeO(OH) formation may provide some fundamental information for the reactor design, the engineering scale-up and the optimizing control for the industrial process.
The kinetics of a-FeO(OH) formation in weak acidic medium was studied. The effects of initial concentration, temperature, pH value, partial presure of oxygen, air flow rate and agitating intensity on the oxidation rate of Fe(OH)_2 suspensions have been investigated. It is confirmed that reaction order for Fe(Ⅱ) is zero at the stage of a-FeO(OH) seeds formation, and around 0.5 at the stage of the seeds growth, and in both processes of the partial pressure of oxygen appears to be first order. The activation energy is determined respectively. Dissolution-oxidation equilibrium existing in the process of seeds formation has been assumed, by which the zero order reaction for Fe(II) and plateau in the pH-t curve may be explained. Physical process is the rate-determining step of the heterogeneous reaction. The studies of the dinetics of α-FeO(OH) formation may provide some fundamental information for the reactor design, the engineering scale-up and the optimizing control for the industrial process.
1990, 6(06): 681-685
doi: 10.3866/PKU.WHXB19900609
Abstract:
The corrosion behaviour of titanium substance and the XPS characterization of Ti surface in the H_2C_2O_4 solution have been first studied by X-ray photoelectron spec-troscopy. The experimental results show that there are only Ti~0 and Ti~(2+) on sample surface in 10% H_2C_2O_4 solution for two hours corrosion at 80 ℃, but if corrosion is extended to 4 hours, the surface composition is mainly TiO_2 with a small amount of Ti~(2+).
This result corresponds to the structure of TiH_(1.942) composion in sample surface found by XRD analysis. Since both TiO_2 and the surface coating RuO_2 are of Gald-Redstone structure, therefore electrode materials of Ti-Ru are stable in chemical industry.
The corrosion behaviour of titanium substance and the XPS characterization of Ti surface in the H_2C_2O_4 solution have been first studied by X-ray photoelectron spec-troscopy. The experimental results show that there are only Ti~0 and Ti~(2+) on sample surface in 10% H_2C_2O_4 solution for two hours corrosion at 80 ℃, but if corrosion is extended to 4 hours, the surface composition is mainly TiO_2 with a small amount of Ti~(2+).
This result corresponds to the structure of TiH_(1.942) composion in sample surface found by XRD analysis. Since both TiO_2 and the surface coating RuO_2 are of Gald-Redstone structure, therefore electrode materials of Ti-Ru are stable in chemical industry.
1990, 6(06): 686-692
doi: 10.3866/PKU.WHXB19900610
Abstract:
A comprehensive analysis method of prediction of protein's secondary structure is presented. It combines several commonly used secondary structure prediction me-thods (Chou-Fasman method, Cohen method, Garnier method, hydrophobicity method). With taking the advantages of every method, the different results obtained from different prodiction methods were analyzed comprehensively. Through this treatment, the accuracy of prediction is about 7% higher than that of every individual method.
A comprehensive analysis method of prediction of protein's secondary structure is presented. It combines several commonly used secondary structure prediction me-thods (Chou-Fasman method, Cohen method, Garnier method, hydrophobicity method). With taking the advantages of every method, the different results obtained from different prodiction methods were analyzed comprehensively. Through this treatment, the accuracy of prediction is about 7% higher than that of every individual method.
1990, 6(06): 693-698
doi: 10.3866/PKU.WHXB19900611
Abstract:
The thermodynamics of micellization for polystyrene-b-poly(ethylene/propylene) two-block copolymer(SEP) in the mixtures of n-octane and benzene with different proportions have been studied in this paper. The critical micelle concentrations(CMC) of micelle solutions at various temperatures were measured by low angle laser light scattering photometer(LALLS). The results show that the micellization process of nonpolar copolymer SEP in hydrocarbon solvents are exothermal, and the entropy change is negative. In contrast, for ordinary surfactants in water, it is the enthalpy contribution to the energy change which is responsible for micellization.
The thermodynamics of micellization for polystyrene-b-poly(ethylene/propylene) two-block copolymer(SEP) in the mixtures of n-octane and benzene with different proportions have been studied in this paper. The critical micelle concentrations(CMC) of micelle solutions at various temperatures were measured by low angle laser light scattering photometer(LALLS). The results show that the micellization process of nonpolar copolymer SEP in hydrocarbon solvents are exothermal, and the entropy change is negative. In contrast, for ordinary surfactants in water, it is the enthalpy contribution to the energy change which is responsible for micellization.
1990, 6(06): 699-705
doi: 10.3866/PKU.WHXB19900612
Abstract:
A kinetic study of the Mannich reaction of 3-thiolcoumarin with diphenylamine was studied. It was found that the mechanism of this reaction is different from the classical mechanism of Mannich reaction. 3-Thiolcoumarin first condenses with form-aldehyde to produce 3-hydroxy-methylthiocoumarin which then reacts with diphenyl-amine with the formation of the a-aminomethylated thioether. The reaction appears to be third order at low concentrations (below 0.2 mol·L~(-1)) and first order at higher concentrations (above 0.35 mol·L~(-1)) of the acetic acid used in the acid catalysis.
A kinetic study of the Mannich reaction of 3-thiolcoumarin with diphenylamine was studied. It was found that the mechanism of this reaction is different from the classical mechanism of Mannich reaction. 3-Thiolcoumarin first condenses with form-aldehyde to produce 3-hydroxy-methylthiocoumarin which then reacts with diphenyl-amine with the formation of the a-aminomethylated thioether. The reaction appears to be third order at low concentrations (below 0.2 mol·L~(-1)) and first order at higher concentrations (above 0.35 mol·L~(-1)) of the acetic acid used in the acid catalysis.
1990, 6(06): 706-709
doi: 10.3866/PKU.WHXB19900613
Abstract:
A series of NiZSM-5 zeolites with different sodium content have been prepared, and their acidity, adsorbability and catalytic activity for the conversion of toluene have been studied. The results show that the NiZSM-5 zeolite exchanged with Na~+ ions not only modulates the properties of acid-base of zeolite, but also results in the increase of adsorption of toluene molecule. The Na~+ ions as the adsorbed sites of toluene molecule promote both the metallic and acid-base functions for toluene conver-sion. The promoting effect of Na~+ ion was observed.
A series of NiZSM-5 zeolites with different sodium content have been prepared, and their acidity, adsorbability and catalytic activity for the conversion of toluene have been studied. The results show that the NiZSM-5 zeolite exchanged with Na~+ ions not only modulates the properties of acid-base of zeolite, but also results in the increase of adsorption of toluene molecule. The Na~+ ions as the adsorbed sites of toluene molecule promote both the metallic and acid-base functions for toluene conver-sion. The promoting effect of Na~+ ion was observed.
1990, 6(06): 710-715
doi: 10.3866/PKU.WHXB19900614
Abstract:
Surface structure of the glassy carbon surface modified with cobalt tetraphenyl-porphyrin (CoTPP) by thermal-treatment has been studied by XPS, DTA and TG. During the thermal treatment a bond can be formed between the glassy carbon sur-face and TPP. Therefore the stability of electrode for the catalysis of dioxygen redu-ction is improved. Upon thermal treatment at 600 ℃, FWHM of Co(2p_(3/2)) is broa-dened, the reason is due to overlapping of peaks of multiple states; the spin orbit separation between Co(2p_(1/2)) and Co(2p_(3/2)) increases to 15.5—16.3 eV, which indicates a change from low spin divalent to high spin divalent states; the kinetic energy of Co L_3VV Auger line and Auger parameter also increase. These changes of central cobalt ion provide a suitable redox potential for Co(III)/Co(II) which is related to the activity for catalysis of dioxygen reduction.
Surface structure of the glassy carbon surface modified with cobalt tetraphenyl-porphyrin (CoTPP) by thermal-treatment has been studied by XPS, DTA and TG. During the thermal treatment a bond can be formed between the glassy carbon sur-face and TPP. Therefore the stability of electrode for the catalysis of dioxygen redu-ction is improved. Upon thermal treatment at 600 ℃, FWHM of Co(2p_(3/2)) is broa-dened, the reason is due to overlapping of peaks of multiple states; the spin orbit separation between Co(2p_(1/2)) and Co(2p_(3/2)) increases to 15.5—16.3 eV, which indicates a change from low spin divalent to high spin divalent states; the kinetic energy of Co L_3VV Auger line and Auger parameter also increase. These changes of central cobalt ion provide a suitable redox potential for Co(III)/Co(II) which is related to the activity for catalysis of dioxygen reduction.
1990, 6(06): 716-719
doi: 10.3866/PKU.WHXB19900615
Abstract:
Liquid-crystal system consists of egg yolk phospho-liqid (PC) and little water was studied by means of the small angle X-ray scatter (SAXS), in methanol, ethanol or isobutynol. Experments show thet layer distance decreases as the alcohol content increases in the system studied (5% H_2O-PC-alcohol) and as the hydrocarbon chain or branched chain increased in these alcohols, the layer distance is decreased. We consider that these changes might be in consequnce of the changes of molecule or force in the system. For this reason, it might be plausible that drinking a lot of alcohol would distroy the structure of biological liquid-crystal in the humanb boby and make human boby poisoning.
Liquid-crystal system consists of egg yolk phospho-liqid (PC) and little water was studied by means of the small angle X-ray scatter (SAXS), in methanol, ethanol or isobutynol. Experments show thet layer distance decreases as the alcohol content increases in the system studied (5% H_2O-PC-alcohol) and as the hydrocarbon chain or branched chain increased in these alcohols, the layer distance is decreased. We consider that these changes might be in consequnce of the changes of molecule or force in the system. For this reason, it might be plausible that drinking a lot of alcohol would distroy the structure of biological liquid-crystal in the humanb boby and make human boby poisoning.
1990, 6(06): 720-724
doi: 10.3866/PKU.WHXB19900616
Abstract:
The resonance Raman spectra of the cationic radicals of p-phenylenediamine and its N-substituted derivatives (N-methyl, N,N-dimethyl, N,N-diethyl and N,N'-dimethyl) are reported. The spectra reveal that the radicals have a half-quinoid structure with obvious C=C and C=N double bond characteristics. The resonance Raman bands at about 1635 cm~(-1) and 1410 cm~(-1) which are caused respectively by the C=C and C=N double bonds shift to lower frequencies when methyls or ethyls are bonded to the N atom as the substituting groups are bonded directly is lost in the radicals and a partial C=N double bond is formed between this N atom and the ring C atom as the π electrons are attracted by the positive charge. The two visible absorption bands are assigned based on the changes of the resonance Ranman spectra with the alternation of the wavelength of the excitation.
The resonance Raman spectra of the cationic radicals of p-phenylenediamine and its N-substituted derivatives (N-methyl, N,N-dimethyl, N,N-diethyl and N,N'-dimethyl) are reported. The spectra reveal that the radicals have a half-quinoid structure with obvious C=C and C=N double bond characteristics. The resonance Raman bands at about 1635 cm~(-1) and 1410 cm~(-1) which are caused respectively by the C=C and C=N double bonds shift to lower frequencies when methyls or ethyls are bonded to the N atom as the substituting groups are bonded directly is lost in the radicals and a partial C=N double bond is formed between this N atom and the ring C atom as the π electrons are attracted by the positive charge. The two visible absorption bands are assigned based on the changes of the resonance Ranman spectra with the alternation of the wavelength of the excitation.
1990, 6(06): 725-729
doi: 10.3866/PKU.WHXB19900617
Abstract:
Four aromatic naphthalenediazonium salts have been synthesised with the formula as: p-RC_(10)H_6N_2BF_4 (R=—H(Ⅰ), —NO_2(Ⅱ), —Br (Ⅲ), —N=N—C_6H_5(Ⅳ)). The thermal stability of the four diazonium salts is higher at room temperature and/or between certain temperature range, however they decomposed in the temperature range of 100-145 ℃. The thermal stability of the four diazonium salts correlated to their substituents is discussed. The possible mechanism of their thermal decomposition is presented. The order of the thermal stability of the four diazonium salts is: —NO_2(II)>—Br(III)>—N=N—C_6H_5(IV)>—H(I), and it is in consistent with the electron-withdrawing capability of the substituents. Some kinetic parameters of this reaction are determined also in this work. When diazonium salts (I), (II) and (III) react with NaBH_4, Then CIDNP signals have been detected with an improved NMR device. It shows that free radical processed play an important rote in thermal reductions of these diazonium salts with sodium borohydride.
From our experiment results the possibitity of diazonium salts (I)、(II) and (III) used as thermal sensitive materials may be promised.
Four aromatic naphthalenediazonium salts have been synthesised with the formula as: p-RC_(10)H_6N_2BF_4 (R=—H(Ⅰ), —NO_2(Ⅱ), —Br (Ⅲ), —N=N—C_6H_5(Ⅳ)). The thermal stability of the four diazonium salts is higher at room temperature and/or between certain temperature range, however they decomposed in the temperature range of 100-145 ℃. The thermal stability of the four diazonium salts correlated to their substituents is discussed. The possible mechanism of their thermal decomposition is presented. The order of the thermal stability of the four diazonium salts is: —NO_2(II)>—Br(III)>—N=N—C_6H_5(IV)>—H(I), and it is in consistent with the electron-withdrawing capability of the substituents. Some kinetic parameters of this reaction are determined also in this work. When diazonium salts (I), (II) and (III) react with NaBH_4, Then CIDNP signals have been detected with an improved NMR device. It shows that free radical processed play an important rote in thermal reductions of these diazonium salts with sodium borohydride.
From our experiment results the possibitity of diazonium salts (I)、(II) and (III) used as thermal sensitive materials may be promised.
1990, 6(06): 730-734
doi: 10.3866/PKU.WHXB19900618
Abstract:
The title compound Fe_3(CO)_8 (P(SC_6H_5) Cl_2) (μ_3′-S)_2 was synthesised by reacting Fe_3(CO)_9 (μ_3-S)_2 with P (SC_6H_5) Cl_2.
The crystal and molecular structure of the title compound has been determined by single crystal diffraction method. Crystal data: triclinic, space group P1, with a=0.7571(1), b=0.9097(1), c=1.7706(2) nm, α=95.03(1), β=101.79(1), γ=105.73(1)°, V =1.1359 nm, Z=2, Dc=1.935 g·cm~(-3). The structure was solved by direct method and difference Fourier synthesis, and refined by full-matrix least-squares with anisotropic thermal paramaters for non-hydrogen atoms, using 3724 observed reflections withI≥3σ(I). The final residual factor R=0.025, R_W=0.028.
Fe_(CO)_8(P(SC_6H_5)Cl_2)(μ_3-s)_2 has a face-bridged 4e donors and the monosubstituted ligand is on the apical Fe atom.
The title compound Fe_3(CO)_8 (P(SC_6H_5) Cl_2) (μ_3′-S)_2 was synthesised by reacting Fe_3(CO)_9 (μ_3-S)_2 with P (SC_6H_5) Cl_2.
The crystal and molecular structure of the title compound has been determined by single crystal diffraction method. Crystal data: triclinic, space group P1, with a=0.7571(1), b=0.9097(1), c=1.7706(2) nm, α=95.03(1), β=101.79(1), γ=105.73(1)°, V =1.1359 nm, Z=2, Dc=1.935 g·cm~(-3). The structure was solved by direct method and difference Fourier synthesis, and refined by full-matrix least-squares with anisotropic thermal paramaters for non-hydrogen atoms, using 3724 observed reflections withI≥3σ(I). The final residual factor R=0.025, R_W=0.028.
Fe_(CO)_8(P(SC_6H_5)Cl_2)(μ_3-s)_2 has a face-bridged 4e donors and the monosubstituted ligand is on the apical Fe atom.
1990, 6(06): 735-738
doi: 10.3866/PKU.WHXB19900619
Abstract:
The electrochemical reduction processes of [Fe(H_2O)_3(NCS)_3] (18-C-6) have been studied in nonaqueous media by method of cyclic voltammetry and spectroelec-trochemistry at an optical transparent thin layer electrode. The formal potential, E°′, electron transfer number, n, diffusion cofficient, D_O, formal heterogeneous electron transfer rate constant, k_S′, and electrochemical transfer coefficient, a, are deter-minated. Significant effect of solvents on the electrochemical behaviors has been observed. The higher the β, the higher the thermodynamic and kinetic stabilities of the coordination compound resulted.
The electrochemical reduction processes of [Fe(H_2O)_3(NCS)_3] (18-C-6) have been studied in nonaqueous media by method of cyclic voltammetry and spectroelec-trochemistry at an optical transparent thin layer electrode. The formal potential, E°′, electron transfer number, n, diffusion cofficient, D_O, formal heterogeneous electron transfer rate constant, k_S′, and electrochemical transfer coefficient, a, are deter-minated. Significant effect of solvents on the electrochemical behaviors has been observed. The higher the β, the higher the thermodynamic and kinetic stabilities of the coordination compound resulted.
1990, 6(06): 739-742
doi: 10.3866/PKU.WHXB19900620
Abstract:
From superacid POSA (perfluorooctanesulfonic acid) catalyzed esterification of p-substituted benzoic acids with ethanol, we t not only the rate canstants k, the energy of activation ΔE, the entropy of activation ΔS~≠, and the enthalpy of acti-vation ΔH~≠; but also a od Hammett linear Free energy relationship (LFE Rela-tionship). This is the first report of applying LFE relationship to superacid catalysis. Finally, the reaction intermediate, the reaction constant ρ, and the mechanism of the reaction were also discussed. It is deduced by this paper that the mechanism of POSA catalyzed esterification is basically identical with those of normal strong acids catalysis, and the reaction is a process of general acid catalysis.
From superacid POSA (perfluorooctanesulfonic acid) catalyzed esterification of p-substituted benzoic acids with ethanol, we t not only the rate canstants k, the energy of activation ΔE, the entropy of activation ΔS~≠, and the enthalpy of acti-vation ΔH~≠; but also a od Hammett linear Free energy relationship (LFE Rela-tionship). This is the first report of applying LFE relationship to superacid catalysis. Finally, the reaction intermediate, the reaction constant ρ, and the mechanism of the reaction were also discussed. It is deduced by this paper that the mechanism of POSA catalyzed esterification is basically identical with those of normal strong acids catalysis, and the reaction is a process of general acid catalysis.
1990, 6(06): 743-746
doi: 10.3866/PKU.WHXB19900621
Abstract:
A binuclear tin complex [Sn_2Cl_6(μ-OH)_2(DMF)_2]·4DMF has been synthesized through direct reaction of SnCl_4·5H_2O with DMF. Its molecular and crystal structure has been determined by single X-ray diffraction technique. The crystal is triclinic with space group P1. The unit cell parameters are a=0.9153(2), b=1.0722(3), c=1.2192(3) nm, α=63.07(2), β=93.26(2), γ=65.75 (2), V=0.92821(36) nm, D_c=1.649 g·cm~(-3), Z=1, The tin atom in the complex takes six-coordinated distorted octahedral configuration with sp~3 d~2 hybrid. The two tin atoms are connected through hydroxyl bridge to form a plane at the molecular center. The four noncoordinated DMF molecules distribute symmetrically around the dimer. The whole complex has an inversion center which coincides with the gravity center of the parallelogram.
A binuclear tin complex [Sn_2Cl_6(μ-OH)_2(DMF)_2]·4DMF has been synthesized through direct reaction of SnCl_4·5H_2O with DMF. Its molecular and crystal structure has been determined by single X-ray diffraction technique. The crystal is triclinic with space group P1. The unit cell parameters are a=0.9153(2), b=1.0722(3), c=1.2192(3) nm, α=63.07(2), β=93.26(2), γ=65.75 (2), V=0.92821(36) nm, D_c=1.649 g·cm~(-3), Z=1, The tin atom in the complex takes six-coordinated distorted octahedral configuration with sp~3 d~2 hybrid. The two tin atoms are connected through hydroxyl bridge to form a plane at the molecular center. The four noncoordinated DMF molecules distribute symmetrically around the dimer. The whole complex has an inversion center which coincides with the gravity center of the parallelogram.
1990, 6(06): 747-750
doi: 10.3866/PKU.WHXB19900622
Abstract:
A voltage-regulated coulometry on RDE is described. It shows that the electric quantity due to the reaction of soluble intermediate Ms, Q_(Ms), is proportional to the inverse square root of the rotation speed, ω~(-1/2). And the slope of the Q_(Ms)-ω~(-1/2) plot is proportional to the surface concentration of the soluble intermediate Ms. However, the qantity Q_(Mad), the electric quantity due to the reaction of adsorbed inter-mediate Mad is independent of the angular velocity of rotation of the electrode.
A voltage-regulated coulometry on RDE is described. It shows that the electric quantity due to the reaction of soluble intermediate Ms, Q_(Ms), is proportional to the inverse square root of the rotation speed, ω~(-1/2). And the slope of the Q_(Ms)-ω~(-1/2) plot is proportional to the surface concentration of the soluble intermediate Ms. However, the qantity Q_(Mad), the electric quantity due to the reaction of adsorbed inter-mediate Mad is independent of the angular velocity of rotation of the electrode.
