首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 31 毫秒
1.
A density-functional theory investigation on the interactions between C2H radical and small gold clusters Au n 0/? (n = 1–4) has been performed. The calculated results predict that C2H radical inclines to interact with small gold clusters Au n 0/? (n = 1–4) as an integrity in the most stable structures of C2HAu n 0/? (n = 1–4). The Au n 0/? (n = 1–4) clusters retain their structural integrity as units in the ground states of C2HAu n 0/? (n = 1–4). The stretching vibrational frequencies of C≡C and C–H in the ground states of C2HAu n ? (n = 1–4) are decreased compared with those of the C2H radical due to the interaction between the Au n 0/? clusters and C2H radical. Smaller red shifts in the C≡C and C–H stretching bands of C2HAu n ? occur with an increase in n. The photoelectron spectra of the most stable structures of C2HAu n ? (n = 1–4) have been simulated to aid their future experimental characterizations. The current study provides further insight into the interaction between C2H radicals and gold clusters, which may lead to exploitation of the high activity of gold nanocrystals.  相似文献   

2.
Extraction of microamounts of cesium by nitrobenzene solutions of ammonium dicarbollylcobaltate (NH4 +B?) and thallium dicarbollylcobaltate (Tl+B?) in the presence of polypropylene glycol PPG 425 (L) has been investigated. The equilibrium data have been explained assuming that the complexes ML+ (M+ = NH 4 + , TI+, Cs+; L = PPG 425) are present in the organic phase. Furthermore, the stability constants of the cationic complex species NH4L+ and TlL+ in nitrobenzene saturated with water have been determined as log β (NH4L org + ) = 4.58 and log β (TlL org + ) = 5.27.  相似文献   

3.
Trinuclear copper(II) and nickel(II) complexes have been prepared by using Schiff base ligands derived from 1,8-[bis(3-formyl-2-hydroxy-5-methyl) benzyl]-4,11-dimethyl-l,4,8,11-tetraazacyclotetradecane, and 1,8-[bis(3-formyl-2-hydroxy-5-bromo)benzyl]-4,11-dimethyl-l,4,8,11-tetraazacyclotetradecane with aliphatic and aromatic diamines. All the complexes were characterized by elemental and spectroscopic analysis. Electrochemical studies of the copper(II) complexes in DMF solution show three irreversible one electron reduction process around E pc  1 = ?0.59 to ?0.80 V, E pc  2 = ?0.89 to ?1.14 V and E pc  3 = ?1.17 to ?1.29 V, and for nickel(II) complexes it is around E pc  1 = ?0.63 to ?0.77 V, E pc  2 = ?1.20 to ?1.35 V and E pc  3 = ?1.60 to ?1.74 V. ESR spectra and magnetic moments of the trinuclear Cu(II) complexes show the presence of antiferromagnetic coupling. Cryomagnetic investigation of the trinuclear copper(II) complexes show that the observed ?2J values are in the range of 116–178 cm?1. The rate constants for hydrolysis of 4-nitrophenylphosphate by the complexes are in the range of 2.68 × 10?2 to 9.81 × 10?2 min?1. The rate constants values for the catecholase activity of the copper(II) complexes fall in the range of 3.03 × 10?2 to 9.32 × 10?2 min?1. All the complexes.  相似文献   

4.
The solvent effect has been studied in this research for the interaction of the $ {\text{VO}}_{2}^{ + } $ VO 2 + cation with trans-1,2-diaminocyclohexane-N, N, N′, N′- tetraacetic acid monohydrate at T = 298 K, I = 0.10 mol·dm?3 sodium perchlorate, and in the range of 0–45 % water + methanol mixtures. UV absorbance data as a function of pH and dissociation constants, obtained from potentiometric titrations, were used for the determination of stability constants. The Kamlet–Abboud–Taft (KAT) model has been investigated for a plausible interpretation and calculation of the linear solvation energy relationship coefficient contribution to the formation of three species VO2H2L, VO2HL? and VO2L2?, which were identified in this work.  相似文献   

5.
The oxygen nonstoichiometry δ of lanthanum cobaltite doped with acceptor impurities (Sr and Ni), La1 ? x SrxCo0.9Ni0.1O3 ? δ (x = 0.1, 0.3), was studied by high-temperature thermogravimetry over the temperature and pressure ranges 723 K ≤ T ≤ 1373 K and 10?3 atm ≤ $p_{O_2 } $ ≤ 1 atm. The partial replacement of cobalt with nickel and lanthanum with strontium increased the oxygen nonstoichiometry δ. The partial molar enthalpies $\Delta \bar H^\circ _O $ and entropies $\Delta \bar S^\circ _O $ of solution of oxygen in the solid phase were calculated. Models of point defect formation were suggested and analyzed. The equilibrium constants of formation and concentrations of predominant point defects, ionized oxygen vacancies V o .. , holes Me Co . (Co Co . and Ni Co . ), and electrons Me Co (Co Co and Ni Co ) localized on 3d transition metals, were determined by nonlinear regression from the experimental and theoretical logp $p_{O_2 } $ ?δ dependences.  相似文献   

6.
The major objective of this study, based on critical review and experimental studies, was to develop a reliable thermodynamic model for the Nd–F system at 25 °C. The SIT model was used to convert concentration constants reported in the literature to constants at zero ionic strengths for cross comparison and selection of reliable values. The critically evaluated thermodynamic constants for the formation of NdF2+ and NdF 2 + were then used to interpret the extensive NdF3(cr) solubility data in NaF and NH4F solutions, ranging in concentrations from extremely low values to as high as 1.0 mol·kg?1, equilibrated for different periods ranging up to as long as 72 days. These efforts have resulted in $ \log_{10} \beta_{n}^{0} $ log 10 β n 0 for the reaction [Nd3+ + nF? ? NdF n 3?n ] of (3.81 ± 0.10), (5.89 ± 0.77), and <12.48 for n values of 1–3, respectively. The $ \log_{10} K_{\text{sp}}^{0} $ log 10 K sp 0 for the solubility of NdF3(cr) (NdF3(cr) ? Nd3+ + 3F?) was determined to be (?20.49 ± 0.37). Because (1) Nd is an excellent analog for trivalent actinides—An(III) (i.e., Pu(III), Am(III), and Cm(III)), and (2) the available data for the An(III)–F system, especially the solubility products of AnF3(cr), are of extremely poor quality, the critical literature review in combination with the experimental Nd–F system data have been used to assign thermodynamic constants for the An(III)–F reactions until good quality specific data for them becomes available.  相似文献   

7.
A new class of surfactant–cobalt(III) complexes of the type trans-[Co(DH)2(OA)X], where DH = dimethylglyoxime, OA = octadecylamine, X = Cl?, Br?, I?, N3 ?, NO2 ?, SCN? or OA, were synthesized and characterized by physicochemical and spectroscopic methods. The critical micelle concentration (CMC) values of these surfactant–cobalt(III) complexes in ethanol solution were obtained by measuring absorption at ~250 nm. Specific conductivity data (at 303–313 K) served for the evaluation of the temperature-dependent CMC and the thermodynamics of micellization (ΔG m 0 , ΔH m 0 and ΔS m 0 ). Steady-state photolysis and cyclic voltammetry of the complexes were studied. The surfactant–cobalt(III) complexes were screened for their antibacterial and antifungal activities against various microorganisms.  相似文献   

8.
The exchange extraction constants corresponding to the general equilibrium C+(aq) + Cs+(nb) ? C+ (nb) + Cs+(aq) occurring in the two-phase water–nitrobenzene system (C+ = protonated α-amino acid methyl ester, 1 = hexaethyl p-tert-butylcalix[6]arene hexaacetate; aq = aqueous phase, nb = nitrobenzene phase) were evaluated on the basis of extraction experiments and γ-activity measurements. Further, the stability constants of the C+ cationic complex species in nitrobenzene saturated with water were calculated; they were found to increase in the following cation order: protonated l-tryptophan methyl ester < protonated l-phenylalanine methyl ester < protonated l-leucine methyl ester < protonated l-methionine methyl ester < protonated l-valine methyl ester.  相似文献   

9.
The complexation kinetics of Mg2+ with CO 3 = and HCO 3 ? has been studied in methanol and water by means of the stopped-flow and temperature-jump methods. Kinetic parameters were obtained in methanol by coupling the magnesium-carbonato reactions with the metal-ion indicator Murexide. Relatively high stability constants were found in methanol (K=1.0×105 liters-mole?1 for Mg2+-Murexide,K=7.0×104 liters-mole?1 for Mg2+?HCO 3 ? , andK=2.0×105 for Mg2+?CO 3 = liters-mole?1). The corresponding, observed formation rate constants were determined to be $$\begin{gathered} k_f = 4.0 \times 10^6 M^{ - 1} - sec^{ - 1} (Mg^{2 + } - Murexide) \hfill \\ k_f = 5.0 \times 10^5 M^{ - 1} - sec^{ - 1} (Mg^{2 + } - HCO_3^ - ) \hfill \\ k_f = 6.8 \times 10^5 M^{ - 1} - sec^{ - 1} (Mg^{2 + } - CO_3^ = ) \hfill \\ \end{gathered} $$ The relaxation times were found to be much shorter (τ≈5–20 μsec) in aqueous solutions, primarily due to the relatively high dissociation rate constants. The data could be interpreted on the basis of a coupled reaction scheme in which the protolytic equilibria are established relatively rapidly, followed by a single relaxation process due to the formation of MgHCO 3 + and MgCO3 between pH 8.7 and 9.3. The observed formation rate constants were determined to be $$\begin{gathered} k_f = 5.0 \times 10^5 M^{ - 1} - sec^{ - 1} (Mg^{2 + } - HCO_3^ - ) \hfill \\ k_f = 1.5 \times 10^6 M^{ - 1} - sec^{ - 1} (Mg^{2 + } - CO_3^ = ) \hfill \\ \end{gathered} $$ These results, in conjunction with NMR solvent exchange rate constants, are analyzed in terms of a dissociative (S N1) mechanism for the rate of complex formation. The significance of these kinetic parameters in understanding the excess sound absorption in seawater is discussed.  相似文献   

10.
The rhenium cluster thiobromide Cs1.95(1)Re6S5.82(3)Br8.19(3), belonging to the solid solution Cs2Re6S6Br8–CsRe6S5Br9, crystallizes in the trigonal system (P31c, = 10.001(5) Å and c = 14.676(5) Å). It is built up from [Re6L 8 i ]Br 6 a cluster units in which sulphur and bromine are randomly distributed on inner position (Li). From the structural refinement performed using single-crystal X-ray diffraction data, the isomers of the [Re6Si 6Br 2 i ] and [Re6S 5 i Br 3 i ] cluster cores present in the structure have been unambiguously determined, due to the non-centro symmetry of the structure. Density functional theory calculations have been performed for all possible di- and tri-substituted isomers in order to confirm experimental analyses. Slight differences between the stability of di-substituted and tri-substituted cluster unit isomers built from Mo6 cluster and Re6 clusters are evidenced.  相似文献   

11.
12.
The molecular structure and conformation of nitrobenzene has been reinvestigated by gas-phase electron diffraction (GED), combined analysis of GED and microwave (MW) spectroscopic data, and quantum chemical calculations. The equilibrium r e structure of nitrobenzene was determined by a joint analysis of the GED data and rotational constants taken from the literature. The necessary anharmonic vibrational corrections to the internuclear distances (r e ? r a) and to rotational constants (B e (i)  ? B 0 (i) ) were calculated from the B3LYP/cc-pVTZ quadratic and cubic force fields. A combined analysis of GED and MW data led to following structural parameters (r e) of planar nitrobenzene (the total estimated uncertainties are in parentheses): r(C–C)av = 1.391(3) Å, r(C–N) = 1.468(4) Å, r(N–O) = 1.223(2) Å, r(C–H)av = 1.071(3) Å, \({\angle}\)C2–C1–C6 = 123.5(6)°, \({\angle}\)C1–C2–C3 = 117.8(3)°, \({\angle}\)C2–C3–C4 = 120.3(3)°, \({\angle}\)C3–C4–C5 = 120.5(6)°, \({\angle}\)C–C–N = 118.2(3)°, \({\angle}\)C–N–O = 117.9(2)°, \({\angle}\)O–N–O = 124.2(4)°, \({\angle}\)(C–C–H)av = 120.6(20)°. These structural parameters reproduce the experimental B 0 (i) values within 0.05 MHz. The experimental results are in good agreement with the theoretical calculations. The barrier height to internal rotation of nitro group, 4.1±1.0 kcal/mol, was estimated from the GED analysis using a dynamic model. The equilibrium structure was also calculated using the experimental rotational constants for nitrobenzene isotopomers and theoretical rotation–vibration interaction constants.  相似文献   

13.
In a previous work the equilibrium geometrical and electronic structures of Xe n + clusters had been established using a non-empirical model hamiltonian. The same model is used to determine the energetic barriers between the nearly degenerate isomers; the movement of the neutral atoms around the Xe 3 + or Xe 4 + ionized linear cores are quite easy (ΔE?0.9 kcal/mole), the changes from a Xe 3 + to a Xe 4 + core are more difficult (ΔE?2.0 kcal/mole). The energetically possible fissions from a vertical photoionization \(Xe_n \xrightarrow{{h v}}Xe_n^{v + } \to Xe_p^ + + Xe_{n - p} \) forn≦19,p=1–9 and 12–14 and mass exchanges Xe p + +Xe q →Xe p+m + +Xe q?m (m=1,2,3) from relaxed Xe p + clusters are given forp+m≦9 and 12–14 andq≦19. Surprisingly the reverse reactions are shown to occur for some values ofp andq. Numerous processes lead to Xe 13 + , which is especially stable.  相似文献   

14.
In this work, the reactions of ?OH, e aq ? , and SO 4 ?? with diethyl phthalate (DEP) were investigated in aqueous solution by pulse radiolysis, and degradation efficiencies of DEP with ?OH and e aq ? were evaluated in water using steady-state radiolysis as well. The absolute rate constants of ?OH, e aq ? , and SO 4 ?? with DEP were determined as 2.3 × 109, 1.0 × 1010, and 1.0 × 108 M?1 s?1, respectively. The degradation efficiencies for the ?OH and e aq ? reactions were 81 and 33 %, respectively. Transient absorption spectra were observed for the intermediate radicals produced by ?OH, e aq ? , and SO 4 ?? reactions. The results suggested that e aq ? transferred to the ester group, resulting in the formation of DEP radical anions. In contrast, ?OH and SO 4 ?? added predominantly to the aromatic ring of DEP, forming the corresponding ?OH adducts. The fundamental mechanistic parameters and degradation efficiencies derived from these results were significant for evaluations and applications of advanced oxidation processes.  相似文献   

15.
From extraction experiments and $ \gamma $ -activity measurements, the extraction constants corresponding to the general equilibrium Eu3+(aq) + 3 A?(aq) + L(nb) $ \Leftrightarrow $ EuL3+(nb) + 3A?(nb) taking place in the two-phase water–nitrobenzene system ( $ {\text{A}}^{ - } = {\text{CF}}_{ 3} {\text{SO}}_{3}^{ - } $ ; L = electroneutral receptors denoted by 1, 2, and 3 – see Scheme 1; aq = aqueous phase, nb = nitrobenzene phase) were evaluated. Further, the stability constants of the EuL3+ complexes in nitrobenzene saturated with water were calculated; they were found to increase in the series of 3 < 2 < 1.
Scheme 1
Structural formulas of N,N,N′,N′,N″,N″-hexacyclohexyl-4,4′,4″-propylidynetris(3-oxabutyramide) (1), bis[(12-crown-4)methyl] dodecylmethylmalonate (2), and bis[(benzo-15-crown-5)-4′-ylmethyl] pimelate (3)  相似文献   

16.
The complex formation reaction of the $ {\text{VO}}_{2}^{ + } $ VO 2 + cation with D-(-)-quinic acid {(1R,3R,4S,5R)-(-)-1,3,4,5-tetrahydroxycyclohexane-1-carboxylic acid} at T = 298 K, I = 0.1 mol·dm?3 of sodium chloride in various aqueous solutions of 1-butyl-3-methylimidazolium tetrafluoroborate, [bmim]BF4, and methanol were studied by using potentiometric and UV spectrophotometric techniques. As far as we know, the calculated stability constants data presented in the current work are the first reported values for [bmim]BF4 and methanol mixed solvents. The Kamlet–Abboud–Taft solvatochromic equation enabled us to interpret the UV data and the stability constants values. The Redlich–Kister equation was applied for the calculation of solvatochromic parameters in the binary water + [bmim]BF4 mixtures. Hydrogen bonding is important for the dissociation constant in both media. In these systems the solvent polarizability and hydrogen-bond donor ability are the main interactions for the stability constants in the aqueous ionic liquid and methanol solutions, respectively.  相似文献   

17.
The stability of multiply charged Pb n m+ -clusters (n ≤ 3;m=0, 1, 2) was studied by solving exactly for the valencep-electrons a many body Hubbard-like Hamiltonian with intra- and interatomic Coulomb interactions. Particularly we obtain that Pb 3 2+ has a metastable ground state, in which Pb 3 2+ has isosceles shape (bond lengthR=3.2 Å, bond angle θ=124°) and a positive binding energyE B =3.4 eV. The activation barrier against dissociation into Pb 2 + + Pb+ is 0.13 eV, yielding a very long lifetime. This is in agreement with recent experiments [1] in which the lifetime of Pb 3 2+ was determined to be at least 10?6 s. Comparison with self consistent Hartree-Fock calculations shows that the metastability of Pb 3 2+ is due to electronic correlations within the paramagnetic ground state.  相似文献   

18.
Extraction of microamounts of europium and americium by a nitrobenzene solution of hydrogen dicarbollylcobaltate (H+B?) in the presence of bis(diphenylphosphino)methane dioxide (DPPMDO, L) has been investigated. The equilibrium data have been explained assuming that the species $ {\text{HL}}^{ + } $ , $ {\text{HL}}_{2}^{ + } $ , $ {\text{ML}}_{2}^{3 + } $ , $ {\text{ML}}_{3}^{3 + } $ and $ {\text{ML}}_{4}^{3 + } $ (M3+ = Eu3+, Am3+) are extracted into the organic phase. The values of extraction and stability constants of the species in nitrobenzene saturated with water have been determined. It was found that the stability constants of the corresponding complexes $ {\text{EuL}}_{n}^{3 + } $ and $ {\text{AmL}}_{n}^{3 + } $ , where n = 2, 3 and L is DPPMDO, in water–saturated nitrobenzene are comparable, whereas in this medium the stability of the cationic species $ {\text{AmL}}_{4}^{3 + } $ (L = DPPMDO) is somewhat higher than that of $ {\text{EuL}}_{4}^{3 + } $ with the same ligand L.  相似文献   

19.
From extraction experiments and $ \gamma $ -activity measurements, the exchange extraction constants corresponding to the general equilibrium M2+(aq) + Sr2+(nb) $ \Leftrightarrow $ M2+(nb) + Sr2+(aq) taking place in the two-phase water–nitrobenzene system (M2+ = Mg2+, Ca2+, Ba2+, Pb2+, Cu2+, Zn2+, Cd2+, $ {\hbox{UO}}_{2}^{2 + } $ , Mn2+, Co2+, Ni2+; 1 = macrocyclic lactam receptor–see Scheme 1; aq = aqueous phase, nb = nitrobenzene phase) were evaluated. Moreover, the stability constants of the M2+ complexes in nitrobenzene saturated with water were calculated; they were found to increase in the following cation order: Mg2+ < Co2+ < Cu2+, Mn2+, Ni2+ < Cd2+ < Ca2+ < Ba2+, Zn2+ < Pb2+ <  $ {\hbox{UO}}_{2}^{2 + } $ .
Scheme 1
Structural formula of 2,18-dichloro-9,10,11,12-tetrahydro-6H, 20H-dibenzo[l,o][1,11,4,8]dioxadiazacyclohexadecine-7,13(8H, 14H)-dione (abbrev. 1)  相似文献   

20.
The oxidation of nanomolar levels of iron(II) with oxygen has been studied in NaCl solutions as a function of temperature (0 to 50?°C), ionic strength (0.7 to 5.6 mol?kg?1), pH (6 to 8) and concentration of added NaHCO3 (0 to 10 mmol?kg?1). The results have been fitted to the overall rate equation: $$\mathrm{d}\mbox{[Fe(II)]}/\mathrm{d}t=-k_{\mathrm{app}}\mbox{[Fe(II)]}[\mbox{O}_{2}]$$ The values of k app have been examined in terms of the Fe(II) complexes with OH? and CO 3 2? . The overall rate constants are given by: $$k_{\mathrm{app}}=\alpha_{\mathrm{Fe}2+}k_{\mathrm{Fe}}+\alpha_{\mathrm{Fe(OH)}+}k_{\mathrm{Fe(OH)}+}+\alpha_{\mathrm{Fe(OH)}2}k_{\mathrm{Fe(OH)}2}+\alpha_{\mathrm{Fe(CO3)}2}k_{\mathrm{Fe(CO3)}2}$$ where α i is the molar fraction and k i is the rate constant of species i. The individual rate constants for the species of Fe(II) interacting with OH? and CO 3 2? have been fitted by equations of the form: $$\begin{array}{l}\ln k_{\mathrm{Fe}2+}=21.0+0.4I^{0.5}-5562/T\\[6pt]\ln k_{\mathrm{FeOH}}=17.1+1.5I^{0.5}-2608/T\\[6pt]\ln k_{\mathrm{Fe(OH)}2}=-6.3-0.6I^{0.5}+6211/T\\[6pt]\ln k_{\mathrm{Fe(CO3)}2}=31.4+5.6I^{0.5}-6698/T\end{array}$$ These individual rate constants can be used to estimate the rates of oxidation of Fe(II) over a large range of temperatures (0 to 50?°C) in NaCl brines (I=0 to 6 mol?kg?1) with different levels of OH? and CO 3 2? .  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号