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1.
It is argued that the use of the Avrami theorem, S(t) = 1−e−Sx(t), is in principle not allowed when applied to overlapping diffusion zones or, more generally, in all cases where the phantom nuclei overtake the front of their parent nuclei. Via computer simulations the overtake effect is shown to exist and is found to be surprisingly small. The use of a modified Avrami equation, S(t) = FSx(t)·[1 −e−Sx(t)], is suggested for such cases and the function F[Sx(t)] pertaining to diffusion-controlled growth is reported.  相似文献   

2.
Quasielastic light scattering measurements are reported for experiments performed on mixtures of gelatin and glutaraldehyde (GA) in the aqueous phase, where the gelatin concentration was fixed at 5 (w/v) and the GA concentration was varied from 1×10−5 to 1×10−3 (w/v). The dynamic structure factor, S(q,t), was deduced from the measured intensity autocorrelation function, g 2(τ), with appropriate allowance for heterodyning detection in the gel phase. The S(q,t) data could be fitted to S(q,t)=Aexp(−D f q 2 t)+Bexp(−tc)β, both in the sol (50 and 60 C) and gel states (25 and 40 C). The fast-mode diffusion coefficient, D f showed almost negligible dependence on the concentration of the crosslinker GA; however, the resultant mesh size, ξ, of the crosslinked network exhibited strong temperature dependence, ξ∼(0.5−χ)1/5exp(−A/RT) implying shrinkage of the network as the gel phase was approached. The slow-mode relaxation was characterized by the stretched exponential factor exp(−tc)β. β was found to be independent of GA concentration but strongly dependent on the temperature as β=β01 T2 T 2. The slow-mode relaxation time, τc, exhibited a maximum GA concentration dependence in the gel phase and at a given temperature we found τc(c)=τ01 c2 c 2. Our results agree with the predictions of the Zimm model in the gel case but differ significantly for the sol state. Received: 25 May 1999 /Accepted in revised form: 27 July 1999  相似文献   

3.
The two complexes, [RE(Gly)4(Im)(H2O)](ClO4)3(s)(RE = Eu, Sm), have been synthesized and characterized. The standard molar enthalpies of reaction for the following reactions, RECl3·6H2O(s)+4Gly(s)+Im(s)+3NaClO4(s) = =[RE(Gly)4(Im)(H2O)](ClO4)3(s)+3NaCl(s)+5H2O(l), were determined by solution-reaction colorimetry. The standard molar enthalpies of formation of the two complexes at T = 298.15 K were derived as Δf H mΘ {Eu(Gly)4(Im)(H2O)}(ClO4)3(s)} = = −(3396.6±2.3) kJ mol−1 and Δf H mΘ {Sm(Gly)4(Im)(H2O)}(ClO4)3(s)} = −(3472.7±2.3) kJ mol−1, respectively.  相似文献   

4.
Extraction of polymer (1), formed in the reaction of CoCl2 with KOOCBut, with boiling hexane gives crystals of hexamer Co63-OH)2(OOCBu1)10(HOOCBu1)4 (2). According to data of X-ray study, four Co11 atoms in the hexanuclear molecule2 have an octahedral ligand environment and two Co11 atoms have a tetrahedral one. Dissolution of polymer1 in EtOH results in its splitting into Co43-OH)2(OOCBu1)6(HOEt)6 tetramers (3). In molecule3, two asymmetric dimeric (η2-OOCBut)(EtOH)Co(μ-OOCBut)Co(HOEt)2 fragments are bound by two tridentate bridging OH groups. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1773–1778, September, 1999.  相似文献   

5.
We introduce and discuss a generalized electron-pair radial density function G(q; a) that represents the probability density for the electron-pair radius |r 1+ar 2| to be q, where a is a real-valued parameter. The density function G(q; a) is a projection of the two-electron radial density D 2(r 1, r 2) along lines r 1ar 2 ± q = 0 in the r 1 r 2 plane onto a point in the qa plane, and connects three densities S(s), D(r), and T(t), defined independently in the literature, as a smooth function of a: For an N-electron (N ≥ 2) system, S(s) = G(s; + 1), D(r) = 2G(r; 0)/(N − 1), and T(t) = G(|t|;−1)/2, where S(s) and T(t) are the electron-pair radial sum and difference densities, respectively, and D(r) is the single-electron radial density. Simple illustrations are given for the helium atom in the ground 1s2 and the first excited 1s2s 3S states.  相似文献   

6.
The octahedral complex, [CoIII(HL)]·9H2O (H4L = (1,8)-bis(2-hydroxybenzamido)-3,6-diazaoctane) incorporating bis carboxamido-N-, bis sec-NH, phenolate, and phenol coordination has been synthesized and characterized by analytical, NMR (1H, 13C), e.s.i.-Mass, UV–vis, i.r., and Raman spectroscopy. The formation of the complex has also been confirmed by its single crystal X-ray structure. The cyclic voltammetry of the sample in DMF ([TEAP] = 0.1 mol dm−3, TEAP = tetraethylammonium perchlorate) displayed irreversible redox processes, [CoIII(HL)] → [CoIV(HL)]+ and [CoIII(HL)] → [CoII(HL)] at 0.41 and −1.09 V (versus SCE), respectively. A slow and H+ mediated isomerisation was observed for the protonated complex, [CoIII(H2L)]+ (pK = 3.5, 25 °C, I = 0.5 mol dm−3). H2Asc was an efficient reductant for the complex and the reaction involved outer sphere mechanism; the propensity of different species for intra molecular reduction followed the sequence: [{[CoIII(HL)],(H2Asc)}–H] <<< {[CoIII(H2L)],(H2Asc)}+ < {[CoIII(HL)],(H2Asc)}. A low value (ca. 3.7 × 10−10 dm3 mol−1 s−1, 25 °C, I = 0.5 mol dm−3) for the self exchange rate constant of the couple [CoIII(HL)]/[CoII(HL)] indicated that the ligand HL3− with amido (N-) donor offers substantial stability to the CoIII state. HSO3 and [CoIII(HL)] formed an outer sphere complex {[CoIII(HL)],(HSO3)}, which was slowly transformed to an inner sphere S-bonded sulfito complex, [CoIII(H2L)(HSO3)] and the latter was inert to reduction by external sulfite but underwent intramolecular SIV → CoIII electron transfer very slowly. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.  相似文献   

7.
Homogeneous MnIn2S4 single crystals ∼14 mm in diameter and ∼40 mm long were grown by directional solidification of melt. For these MnIn2S4 single crystals, the composition was determined by electron probe microanalysis, structure by X-ray diffraction, and melting temperature by differential thermal analysis. Transmission spectra were studied in these single crystals, in the region of the intrinsic absorption edge within 10–300 K. The transmission spectra were used to determine the bandgap width, and it was plotted as a function of temperature. The thermal expansion of MnIn2S4 single crystals was studied dilatometrically in the range 80–700 K, and the thermal expansion coefficient was determined.  相似文献   

8.
Novel Synthesis of a Lanthanide Trialkyl – Characterization and Crystal Structure of Yb(CH2 t Bu)3(thf)2 The solvated ytterbium alkyl Yb(CH2tBu)3(thf)2 ( 1 ) was obtained in moderate yield from the reaction of ytterbium metal with neopentyl iodide. Ruby‐red air‐sensitive crystals of 1 were characterized by melting point, elemental analysis, IR, NMR, and UV/Vis spectroscopy and by X‐ray crystallography. In the solid state the ytterbium atom shows a trigonal bipyramidal coordination with the neopentyl groups and the THF ligands occupying equatorial and axial positions, respectively.  相似文献   

9.
Two novel oxamidato-bridged Mn[Cu(PMoxd)]3(ClO4)2 (1) Ni[Cu(PMoxd)]3(ClO4)2 (2) tetranuclear complexes were prepared and characterized by i.r., e.p.r., electronic spectra, cyclic voltammograms, and magnetic properties. The magnetic analysis was carried out by means of the theoretical expression of the magnetic susceptibility deduced from the spin Hamiltonian H=−2JSM(SCu1+ SCu2 + SCu3) (M=Mn, Ni), leading to J=−20.4 cm−1; −121.1 cm−1 for complexes (1) and (2) respectively. Magnetic measurements indicate that the overall magnetic behavior of the tetranuclear species are antiferromagnetic.  相似文献   

10.
The change in the valence state of nanocluster can induce remarkable changes in the properties and structure. However, achieving the valence state changes in nanoclusters is still a challenge. In this work, we use Cu2+ as dopant to “oxidize” [Ag62S12(SBut)32]2+ (4 free electrons) to obtain the new nanocluster: [Ag62−xCuxS12(SBut)32]4+ with 2 free electrons. As revealed by its structure, the [Ag62−xCuxS12(SBut)32]4+ (x=10∼21) has a similar structure to that of [Ag62S12(SBut)32]2+ precursor and all the Cu atoms occupy the surface site of nanocluster. It′s worth noting that with the Cu atoms doping, the [Ag62−xCuxS12(SBut)32]4+ nanocluster is more stable than [Ag62S12(SBut)32]2+ at higher temperature and in electrochemical cycle. This result has laid a foundation for the subsequent application and exploration. Overall, this work reveals crystals structure of a new Ag−Cu nanocluster and offers a new insight into the electron reduction/oxidation of nanocluster.  相似文献   

11.
[Ni(dien)2]3[W4S4(CN)12]·20H2O and [Cu(dien)(Hdien)]2[W4S4(CN)12]·8H2O were obtained by evaporating water-ammonia solutions containing K6[W4S4(CN)12]·2H2O·2CH3OH, diethylene triamine, and NiCl2·6H2O or CuCl2·6H2O. The crystals of the complex compounds were obtained within 3 days. The complex compounds were characterized by IR spectroscopy and by XRD and elemental analysis. XRD data for the complex [Ni(dien)2]3[W4S4(CN)12]·20H2O are: triclinic system, , a = 14.671(2) Å, b = 16.448(3) Å, c = 19.814(3) Å, α = 67.841(3)°, β = 68.996(3)°, γ = 67.527(3)°, V = 3961.6(11) Å3, Z = 2; for the complex [Cu(dien)(Hdien)]2[W4S4(CN)12]·8H2O: monoclinic system, C2/c, a = 37.4290(1) Å, b = 17.7370(1) Å, c = 25.7370(2) Å, β = 105.3840(2)°, V = 16474.02(16) Å3, Z = 12. Original Russian Text Copyright ? 2005 by I. V. Kalinina, D. G. Samsonenko, Z. A. Starikova, A. A. Korlyukov, J. Lipkowski, V. P. Fedin, and M. Yu. Antipin __________ Translated from Zhurnal Strukturnoi Khimii, Vol. 46, No. 1, pp. 139–148, January–February, 2005.  相似文献   

12.
The reaction of [PtMe3(bpy)(Me2CO)](BF4) (2) (prepared from [PtMe3I(bpy)] (1) plus Ag(BF4)) with MeSSMe resulted in the formation of [PtMe3(bpy)(MeSSMe-κS)](BF4) (3). A single-crystal X-ray diffraction analysis revealed in the octahedral Pt(IV) complex (configuration index: OC-6-33), a conformation of the monodentately κS bound MeSSMe ligand (C–S–S–C 92.7(4)°) being very close to that in non-coordinated MeSSMe, thus allowing some hyperconjugative interaction stabilizing the S–S bond. The reaction of [K(18C6)][(PtMe3)2(μ-I)(μ-pz)2] (4; 18C6 = 18-crown-6, Hpz = pyrazole) with Ag(BF4) and MeSSMe resulted in the formation of dinuclear complexes [(PtMe3)2(μ-pz)2(μ-MeSSMe)] existing at room temperature in acetone solution as different fast interconverting isomers. At –40 °C, two isomers with a μ-1κS:2κS (5a) and a μ-1κS:2κS′ (5b) coordinated MeSSMe ligand in the ratio 2:1 could be identified 1H NMR spectroscopically. DFT calculations of type 5 complexes revealed the existence of two conformers with a μ-MeSSMe-1κS:2κS ligand, which differ mainly in the C–S–S–C dihedral angle (66.4 vs. 180.0° 6a/6a′). They have essentially the same energy and a very low activation barrier in acetone as solvent (1.3 kcal/mol) for their mutual interconversion. A further equilibrium structure was identified to be an isomer having a μ-MeSSMe-1κS:2κS′ ligand (6b) that proved to be only 1.9 kcal/mol higher in energy than 6a/6a′.  相似文献   

13.
Three new chalcogen-bridged mercury–iron clusters with 7, 14, and 39 mercury centers were obtained from the reaction of tBuSSiMe3 with [Fe(CO)4(HgX)2] (X= Cl, Br). The compounds were isolated in the form of orange crystals that were characterized by X-ray crystallography. The picture on the right shows the structure of the heavy-atom skeleton of [Hg14Fe12{Fe(CO)4}6S6(StBu)8Br18] (Hg, Fe, Br, and S are black, diagonally striped, white, and horizontally striped, respectively).  相似文献   

14.
The object of the paper is an investigation of the glasses of the (As2S3)x(AsSe0.5Te0.5I)100-x. type for 65≤;x≤;95, using methods of thermomechanical analysis. Values of the thermal coefficients of linear expansion in solid and visco-plastic phase were determined. it was shown that introducing arsenic-sulfide in glass-matrix AsChI, i.e. (AsSe0.5Te0.5I), leads to an increasing stability of these glasses. The characteristic temperatures of softening Tg and the temperature of the beginning of deformation tw increase by increasing content of As2S3. The analytical forms of dependence of four significant physical values αg, αl, Tg, Tw, as a function of As2S3 content in the structure of glasses were fitted. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

15.
The changes of enthalpy for the reactions
  1. Sn(c)+2I2(c)+4165 CS2(l)=[SnI4; 4165 CS2] (sol.),
  2. SnI4(c)+4223 CS2(l)=[SnI4; 4223 CS2] (sol.)
At 298,15 K have been found by solution calorimetry to be ΔH 1=(?46.7±0.3) and ΔH 2=(+3.2±0.1) kcal Mol?1, resp. Neglecting the heat of dilution which is approximately zero these values give ΔH f o (SnI4; c; 298 K)=9?49.9±0.4) kcal Mol?1 for the enthalpy of formation of SnI4. From existing literature data the standard entropy is calculated to beS o(SnI4; c; 298 K)=69,7 cal Mol?1 K?1 giving ΔG f o (SnI4; c; 298 K)=?50,5 kcal Mol?1 for the corresponding change in theGibbs free energy.  相似文献   

16.
An efficient procedure was developed for the asymmetric synthesis ofS-alkyl derivatives of (R)-cysteine by nucleophilic addition of alkanethiols (BunSH, ButSH, ortert-C5H11SH) to the C=C bond of the dehydroalanine fragment in the NiII complex of the Schiff's base of Δ-Ala with (S)-2-N-(N-benzylprolyl)aminobenzophenone [(S)-BPB-Δ-Ala]NiII. Under conditions of thermodynamic control of the reaction, the diastereomeric excess of the complexes with the (S.R)-configuration was 88–96%. After decomposition of the complexes,(R)-S-butylcysteine,(R)-S-tert-butylcysteine, and(R)-S-tert-pentylcysteine were isolated with an enantiomeric purity of >97%. Published inIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1467–1470, August, 2000.  相似文献   

17.
From extraction experiments and γ-activity measurements, the extraction constant corresponding to the equilibrium 2Li+(aq)+SrL2 2+(nb) 2LiL+(nb)+Sr2+(aq) taking place in the two-phase water-nitrobenzene system (L=15-crown-5; aq=aqueous phase, nb=nitrobenzene phase) was evaluated as logK ex (2Li+;SrL2 2+)=−3.7. Further, the stability constant of the 15-crown-5—lithium complex in nitrobenzene saturated with water was calculated: log βnh(LiL+)=7.0.  相似文献   

18.
Summary From extraction experiments and γ-activity measurements, the extraction constant corresponding to the equilibrium Li+(aq)+NaL+(nb) ↔LiL+(nb)+Na+(aq) taking place in the two-phase water-nitrobenzene system (L = valinomycin; aq = aqueous phase, nb = nitrobenzene phase) was evaluated as logKex(Li+,NaL+)=-1.1. Further, the stability constant of the valinomycin-lithium complex species in nitrobenzene saturated with water was calculated: logβnb(LiL+)=6.3.  相似文献   

19.
The redox reactions of thiosulfate with four iron(III) complexes having phenolate-amide-amine coordination, FeIII(L){L = 1,2-bis(2-hydroxybenzamido)ethane, L1; 1,3-bis(2-hydroxybenzamido)propane, L2; 1,5-bis(2-hydroxybenzamido)3-azapentane, L3; and 1,8-bis(2-hydroxybenzamido)3,6-diazaoctane, L4} have been investigated in 10% v/v MeOH + H2O and I = 0.3 mol dm−3. At constant pH (~ 4.8) and under pseudo-first order conditions of [S2O 3 2− ] the reaction obeyed the rate law : − d[FeIII(L)]/dt = k obs [FeIII(L)] + k obs where k obs denotes the observed rate constant of thiosulfate decomposition; k obs = a[S2O 3 2− ] + b[S2O 3 2− ] T 2 is valid for all the complexes, particularly at pH < 6, while k obs = [H+][S2O 3 2− ] T 2 is consistent with the rate law for thiosulfate decomposition proposed earlier. The rate data (k obs) were analysed on the basis of the reactivities of various species of FeIII(L) generated by the equilibrium protonation of the sec-NH of dien and trien spacer units resulting in the ring opening (for [FeIII(L3/L4)]), and acid base equilibrium of the aqua ligand bound to the iron(III) centre ([FeIII(L)(OH2) n ]). The redox activities, both for second and third order paths, show the ligand dependencies : L4<L3<L1<L2 conforming to the fact that the complexes tend to be less susceptible to electron transfer from S2O 3 2− with (i) the increase of the number of chelate rings, (ii) the decrease of overall charge, and (iii) the decrease of ring size offered by the amine moiety (from six membered to five membered one as for [FeIII(L1/L2)(OH2)2]+. There was no evidence for the formation of inner sphere thiosulfato complex, the possibility of the formation of the outer sphere ion-pairs, [Fe(L/HL)(OH2)n +/2+, S2O 3 2− ] with low equilibrium constant value may not be excluded. In view of this, the outer sphere electron transfer (ET) mechanism is the most likely possibility.  相似文献   

20.
Niobium(V) chloride aryloxides [NbCl3(OAr)2] and [NbCl2(OAr)3] (Oar = —OC6H4Bu t -4 and —OC6H4OMe-4) have been prepared by reacting NbCl5 with two and three equivalents of the respective phenol in CCl4. The complexes have been characterized by elemental analysis, molecular weight determination, i.r., 1H-n.m.r., u.v.–vis. and MS techniques. Thermal behaviour (t.g.–d.t.) of the complexes has also been studied and decomposition schemes proposed. The kinetic and thermodynamic parameters namely, the activation energy 'E *', the frequency factor 'A', entropy of activation 'S' and specific rate constant 'kr' etc. have been calculated employing the Coats–Redfern equation. The non-isothermal t.g. data has also been utilized to determine the most probable mechanism and corresponding activation energy for the decomposition of niobium(V) complexes by testing seven different theoretically possible decomposition mechanisms.  相似文献   

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