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1.
《Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy》1993,49(7):897-901
Single crystal EPR studies of Mn(II)-doped magnesium potassium Tutton's salt, MgK2(SO4)2.6H2O, was studied at room temperature. The spin-Hamiltonian parameters obtained are: g=2.0036(3), A = −96(3), D = 350(5), a = 14(2) and F = −5(1) (A, D, a and F are in units of 10−4 cm−1). The tetragonal distortion axis corresponds to one of the MgO bond directions. The zero-field splitting parameter (D) shows a linear dependence in the temperature range 77–370 K. The percentage of covalency of the MnO bond has been estimated to be 8 per cent. 相似文献
2.
《Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy》1989,45(2):285-291
Single crystal e.s.r. spectra at room temperature and Q-band frequencies on [PPh4]2 [(Mo/V)O(qdt=2] (qdt = quinoxaline-2,3-dithiolate) containing ca 3% vanadium gave the spin-Hamiltonian parameters g1 = 1.977 ± 0.001, g2 = 1.985 ± 0.001, g3 = 1.987 ± 0.001, A1 = (−38.5 ± 0.3) × 10−4, A2 = (−45.1 ± 0.3) × 10−4, A3 = (−133.2 ± 0.3) × 10−4 cm−1, and Q′ = −(0.15±0.05) × 10−4 cm−1. The g and A tensor axes are not coincident. The principal values of the g and A tensors have been analysed via an angular overlap treatment. Proton spin-flip transitions were observed in the spectra at X-band frequencies. Single crystal e.s.r. spectra of undiluted [PPh4]2 [VO(qdt)2] at both X- and Q-band frequencies are interpreted in terms of a two-dimensional weak exchange model with J0 = −48 ± 2G (ferromagnetic). 相似文献
3.
Mitsuo Sawamoto 《Macromolecular Symposia》1994,85(1):33-43
The objective of this paper is to discuss: (i) the general approaches to living cationic polymerizations; (ii) the nature of the growing species thus generated. For the first, it is concluded that three general methods are currently available which involve the nucleophilic stabilization of the growing carbocations by (a) a suitable counteranion, (b) an added Lewis base, or (c) an added neutral salt. According to this view, a variety of initiating systems are classified. For the second, findings are presented for the recently developed living cationic polymerization of vinyl ethers by the HCl/SnCl4 initiating system in the presence of an added salt (nBu4N+Cl−). The nature of the growing species therein is discussed on the basis of the steric structure of the living polymers, relative to nonliving counterparts, and the in-situ 13C NMR spectroscopic analysis of model reactions where the interaction of the growing end model [CH3CH(OR)Cl] with SnCl4 and the added salt is analyzed. 相似文献
4.
It has previously been proposed (Ref. 1) that in the cationic vinyl polymerizations, proceeding with termination due to the collapse of ion pairs, addition of bases increases “livingness”, because of the fast convertion of the otherwise dead (within the time of polymerization) covalent species into the onium ions; these, in turn, fast convert into carbenium ions, the actually propagating species. Equilibria between carbenium ions (CH3OCH2+A− has been used as a model) and their onium counterparts ((CH3)2O taken as a model base) as well as between covalent species (CH3OCH2OSO2CF3) and the corresponding oxonium ion (with a (CH3)2O ligand) have been studied by dynamic 1H and 19F NMR. Total ionization of methoxymethyl triflate (CH3OCH2OSO2CF3) has been shown to increase indeed from 104 (-10°C) to 106 (-70°C) times when 1,0 mol·L−1 of (CH3)2O is added. Although this model system better describes polymerization of cyclic acetals than that of vinyl ethers, it shows at least qualitatively the importance of bases in ionization of covalent species, which may be responsible for reinitiation in the cationic polymerization of vinyl ethers. 相似文献
5.
Robson F. Storey Kelly A. Shoemake 《Journal of polymer science. Part A, Polymer chemistry》1999,37(11):1629-1641
Multiarm star‐branched polymers based on poly(styrene‐b‐isobutylene) (PS‐PIB) block copolymer arms were synthesized under controlled/living cationic polymerization conditions using the 2‐chloro‐2‐propylbenzene (CCl)/TiCl4/pyridine (Py) initiating system and divinylbenzene (DVB) as gel‐core‐forming comonomer. To optimize the timing of isobutylene (IB) addition to living PS⊕, the kinetics of styrene (St) polymerization at −80°C were measured in both 60 : 40 (v : v) methyl cyclohexane (MCHx) : MeCl and 60 : 40 hexane : MeCl cosolvents. For either cosolvent system, it was found that the polymerizations followed first‐order kinetics with respect to the monomer and the number of actively growing chains remained invariant. The rate of polymerization was slower in MCHx : MeCl (kapp = 2.5 × 10−3 s−1) compared with hexane : MeCl (kapp = 5.6 × 10−3 s−1) ([CCl]o = [TiCl4]/15 = 3.64 × 10−3M; [Py] = 4 × 10−3M; [St]o = 0.35M). Intermolecular alkylation reactions were observed at [St]o = 0.93M but could be suppressed by avoiding very high St conversion and by setting [St]o ≤ 0.35M. For St polymerization, kapp = 1.1 × 10−3 s−1 ([CCl]o = [TiCl4]/15 = 1.82 × 10−3M; [Py] = 4 × 10−3M; [St]o = 0.35M); this was significantly higher than that observed for IB polymerization (kapp = 3.0 × 10−4 s−1; [CCl]o = [Py] = [TiCl4]/15 = 1.86 × 10−3M; [IB]o = 1.0M). Blocking efficiencies were higher in hexane : MeCl compared with MCHx : MeCl cosolvent system. Star formation was faster with PS‐PIB arms compared with PIB homopolymer arms under similar conditions. Using [DVB] = 5.6 × 10−2M = 10 times chain end concentration, 92% of PS‐PIB arms (Mn,PS = 2600 and Mn,PIB = 13,400 g/mol) were linked within 1 h at −80°C with negligible star–star coupling. It was difficult to achieve complete linking of all the arms prior to the onset of star–star coupling. Apparently, the presence of the St block allows the PS‐PIB block copolymer arms to be incorporated into growing star polymers by an additional mechanism, namely, electrophilic aromatic substitution (EAS), which leads to increased rates of star formation and greater tendency toward star–star coupling. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1629–1641, 1999 相似文献
6.
A kinetic study of the anionic polymerization of hexamethylcyclotrisiloxane ((CH3)2SiO)3 (D3) was carried out in toluene with the cryptate Li+ + [211] as a counterion. The kinetic order with respect to the living end concentration was found to be equal to 1, and the propagation rate constant relative to cryptated ion pairs was determined at several temperatures between −20 and +20°C. The corresponding activation parameters were calculated : Ep = 9.8 kcal.mol−1 and Δ S°t = −20 cal.mol.−1K−1. The reaction of 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetra-siloxane ((CH3)(CH2=CH)SiO)4 (D4*) was studied under the same conditions, the reactivity towards silanolate active centers was shown to be very close to that of D3. The rate constants of propagation and depropagation of D4* and of larger cycles D5* and D6* were determined from polymerization experiments on D4*. The propagation rate constants were found to be nearly the same for D4* and D5* : 1.2–1.31.mol−1. s−1, D6* being the less reactive monomer : 0.41.mol−1. s−1. The differences observed in equilibrium constants of the cycles are essentially due to the rate constants of their formation which were found to be 0.42, 0.23, and 0.006 s−1 for D4*, D5* and D6*, respectively. 相似文献
7.
M. G. Evans M. Santappa N. Uri 《Journal of polymer science. Part A, Polymer chemistry》1951,7(2-3):243-260
A new method for the photochemical initiation of polymerization of vinyl compounds in aqueous solution is described. The photochemically active species is an ion pair complex of the formula Fe3+X−(X− = OH−, CI−, N−3, etc.). The light absorption by the ion pair leads to an electron transfer causing reduction of the cation and oxidation of the anion to an atom or free radical X. The latter leads to the initiation of polymerization in accordance with X + CH2CHR→XCH2 CHR . The kinetics of the reaction were studied by the measurement of: (a) ferrous ion formed (colorimetrically), (b) monomer disappearance (by titration and by weighting the polymer), (c) the chain length of the polymer (in the case of methyl methacrylate). The dependence of the quantum yield on the light intensity, light absorption fraction, and the concentration of vinyl monomer and ferrous ion added initially was investigated. A complete mechanism, both with regard to the formation of free radicals and the polymerization reaction, was put forward involving: (1) light absorption, (2) a primary dark back reaction, (3) dissociation of the primary product, (4) a secondary dark back reaction, (5) initiation of polymerization by free radicals, (6) propagation of polymerization, and (7) termination by recombination of active polymer endings. The mechanism was verified by the experimental results and some constant ratios were estimated quantitatively. 相似文献
8.
Thomas C. Schäfer Jonathan Becker Marcel T. Seuffert Dominik Heuler Alexander E. Sedykh Prof. Dr. Klaus Müller-Buschbaum 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(23):e202104171
Eight cationic, two-dimensional metal-organic frameworks (MOFs) were synthesized in reactions of the group 13 metal halides AlBr3, AlI3, GaBr3, InBr3 and InI3 with the dipyridyl ligands 1,2-di(4-pyridyl)ethylene (bpe), 1,2-di(4-pyridyl)ethane (bpa) and 4,4’-bipyridine (bipy). Seven of them follow the general formula 2∞[MX2(L)2]A, M=Al, In, X=Br, I, A−=[MX4]−, I−, I3−, L=bipy, bpa, bpe. Thereby, the porosity of the cationic frameworks can be utilized to take up the heavy molecule iodine in gas-phase chemisorption vital for the capture of iodine radioisotopes. This is achieved by switching between I− and the polyiodide I3− in the cavities at room temperature, including single-crystal-to-single-crystal transformation. The MOFs are 2D networks that exhibit (4,4)-topology in general or (6,3)-topology for 2∞[(GaBr2)2(bpa)5][GaBr4]2⋅bpa. The two-dimensional networks can either be arranged to an inclined interpenetration of the cationic two-dimensional networks, or to stacked networks without interpenetration. Interpenetration is accompanied by polycatenation. Due to the cationic character, the MOFs require the counter ions [MX4]−, I− or I3− counter ions in their pores. Whereas the [MX4]−, ions are immobile, iodide allows for chemisorption. Furthermore, eight additional coordination polymers and complexes were identified and isolated that elaborate the reaction space of the herein reported syntheses. 相似文献
9.
《Chemical physics letters》1985,122(4):361-364
Reaction rate constants of SiH2(X̄1A1) have been directly measured for the first time using the laser photolysis—laser-induced fluorescence method. The preparation of SiH2 radical in the laser photolysis (193 nm) of phenylsilane and the concentration of the radical is demonstrated by a dye laser at 580.1 nm (X̄1A1-Ā1B1). The reaction rate constants of SiH2(X̄1A1) with H2, CH4, C2H4, SiH4 and Si2H6, are 0.001, 0.01, 0.97, 1.1 and 5.7×10−10 cm3 molecule−1 s−1, respectively. For SiH2(Ā1B1(0.2,0)), the collision-free lifetime is 0.6 μs and the quenching rate constant for He is 3.8×10−10 cm3 molecule−1 s−1. 相似文献
10.
Rate constants have been determined for the reactions of Cl atoms with the halogenated ethers CF3CH2OCHF2, CF3CHClOCHF2, and CF3CH2OCClF2 using a relative‐rate technique. Chlorine atoms were generated by continuous photolysis of Cl2 in a mixture containing the ether and CD4. Changes in the concentrations of these two species were measured via changes in their infrared absorption spectra observed with a Fourier transform infrared (FTIR) spectrometer. Relative‐rate constants were converted to absolute values using the previously measured rate constants for the reaction, Cl + CD4 → DCl + CD3. Experiments were carried out at 295, 323, and 363 K, yielding the following Arrhenius expressions for the rate constants within this range of temperature:Cl + CF3CH2OCHF2: k = (5.15 ± 0.7) × 10−12 exp(−1830 ± 410 K/T) cm3 molecule−1 s−1 Cl + CF3CHClOCHF2: k = (1.6 ± 0.2) × 10−11 exp(−2450 ± 250 K/T) cm3 molecule−1 s−1 Cl + CF3CH2OCClF2: k = (9.6 ± 0.4) × 10−12 exp(−2390 ± 190 K/T) cm3 molecule−1 s−1 The results are compared with those obtained previously for the reactions of Cl atoms with other halogenated methyl ethyl ethers. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 165–172, 2001 相似文献
11.
《Journal of Inorganic and Nuclear Chemistry》1981,43(7):1517-1520
Cu(II) complexes have been prepared with 2-n-propylaminopyridine N-oxide (nP) employing the perchlorate, tetrafluoroborate, nitrate, chloride and bromide salts. Preparative molar ratios of 4:1 and 2:1 ligand to Cu(II) salt yielded the following unique salts: Cu(nP)4X2(X=ClO4−, BF4−, NO3staggeredt-) and Cu(nP)2X2)(X=NO3−, Cl−, Br−). Characterization has been accomplished primarily by IR, electronic and electron spin resonance measurements of the solid state. nP binds as a monodentate ligand via its N-oxide oxygen in the complexes prepared from the Cu(II) salts of polyatomic anions and as a bidentate ligand in the halogen solids. Anion coordination occurs in the halogen complexes as well as in Cu(nP)2(NO3)2. 相似文献
12.
《Journal of fluorine chemistry》1986,31(1):75-88
Octafluorobiphenylene was made by heating 1,2-diiodotetrafluorobenzene in a sealed, evacuated tube with either copper, lead or bismuth. The crystal used for the diffraction studies was grown from hexane. Crystal data: C12F8, Mr = 296.116, monoclinic, A2/a, a = 21.140(2), b = 6.430(6), c = 36.340(3) ÅA, β = 123.76(3)°, U = 4106.73 ÅA3, Z = 16, Dm = 1.884 g cm−3, Dx = 1.907 g cm−3, λ(Cuka) = 1.5418 ÅA, μ = 1.810 mm−1, F(000) = 2304, measurement temperature = 293K, R = 0.059 for 2230 reflections with I > 3σ(I). 相似文献
13.
《Journal of Inorganic and Nuclear Chemistry》1978,40(3):559-566
The rate of extraction of Ti(IV) from aqueous sulphuric acid solution into benzene with HDEHP [HDEHP = H2A2 = bis-(2-ethyl hexyl)-phosphoric acid] and back extraction of the Ti(IV)-DEHP chelate from the benzene phase to an aqueous phase have been studied under various conditions. The distribution equilibria have also been investigated. The structure of the extracted species has been investigated by IR spectral data, molecular weight determination and phosphorous-titanium atom ratio determination. The extracted species has been shown to be [TiOA2]3. From the extraction equilibrium studies, the reaction for the extraction of Ti(IV) has been proposed and the extraction equilibrium constant has been evaluated.The rate of forward extraction is proportional to [(TiO)+2]3, [H2A2](org)+3 and [H2SO4]−3, whereas the rate of backward extraction is proportional to [TiOA2](org)+1, [H2A2](org)−1 and [H2SO4]−1. The rate determining step in the forward extraction involves the reaction of 3 atoms of titanium in a stable chain or ring with 3 molecules of HDEHP dimer molecules. The rate of backward extraction studies indicate that the rate determining step of the backward extraction involves the reaction of [TiOA2] molecule with one molecule of H2SO4. The values of the equilibrium constants obtained from the equilibrium study and rate study are 10(3.646±0.16) and 10(10.604±0.194) respectively. The cause of this discrepancy has been explained. 相似文献
14.
《Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy》1988,44(9):889-897
From the reaction of Pb with metastable oxygen O2(1Δg) in a Broida type oven we have analysed at high resolution some vibrational levels of the X0+, a1, A0+ and B1 states of the 208PbO molecule. The rotational parameters determined allowed us to recalculate the position of the various isotope lines to within 0.01 cm−1. We have found a negative value of ωeχe (−0.123 (25) cm−1) in A0+, contrary to previous observations. The Ω type doubling in a1 varies from +1.8 × 10−4 cm−1 (υ′ = 2) to +2.3 × 10−4 cm−1 (υ′ = 9) and in B1 from −1.17 × 10−4 cm−1 (υ′ = 0) to −0.97 × 10−4 cm−1 (υ′ = 2). 相似文献
15.
《Journal of mass spectrometry : JMS》2017,52(3):144-151
To improve our understanding of the electrospray ionization (ESI) process, we have subjected equimolar mixtures of salts A+X− (A+ = Li+, NBu4+; X− = Br−, ClO4−, BF4−, BPh4−) in different solvents (CH3CN, tetrahydrofuran, CH3OH, H2O) to negative‐ion mode ESI and analyzed the relative ESI activity of the different anionic model analytes. The ESI activity of the large and hydrophobic BPh4− ion greatly exceeds that of the smaller and more hydrophilic anions Br−, ClO4− and BF4−, which we ascribe to its higher surface activity. Moreover, the ESI activity of the anions is modulated by the action of the counter‐ions and their different tendency toward ion pairing. The tendency toward ion pairing can be reduced by the addition of the chelating ligands 12‐crown‐4 and 2.2.1 cryptand and is, although to a smaller degree, further influenced by the variation of the solvent. Complementary electrical conductivity measurements afford additional information on the interactions of the ionic constituents of the sample solutions. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献
16.
《Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy》1994,50(7):1309-1315
The ESR spectra of the kainite (KMgClSO4.3H2O) crystal revealed an intense isotropic (g = 2.004) peak C attributed to the SO−3 radical and two pairs of lines (A1, A2) and (B1, B2) bearing intensity ratio 5:3. The intensity and linewidth variation of peak C suggested that the signal contains an unresolved shf structure. The power saturation studies on SO−3 indicate that its ESR line is homogeneously broadened and its line shape is Lorentzian. The spin—lattice and spin—spin relaxation times (T1 and T2) of SO−3 have been estimated to be 0.44 s and 656 μs, respectively. The analysis of the anisotropic pairs of lines show that they constitute two sets A and B and are due to two chemically inequivalent SO−4 radical species in the lattice. The ESR spectra of the polycrystalline samples recorded at 300 and 77 K confirm the isotropic behaviour of SO−3 and chemical inequivalence of two types of SO−4 radicals. The principal g-values of the SO−4 radical were evaluated to be: g1 = 2.007, g2 = 2.011, g3 = 2.014 for species A and g1 = 2.008, g2 = 2.012, g3 = 2.015 for species B. The low microsymmetry of the SO2−4 ion in the lattice seems to promote the radiation damage. 相似文献
17.
《Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy》1982,38(6):621-625
A series of CuLX2, CuL2X2, CuLYZ and AgCuL2Z3 {X− = Cl−, Br−, NO−3; Y− = OAc−; Z− = NO−3 or ClO−4; L = 1,4-diaza-7-thiaoctane [2,2-NNS(Me)] or 1,5-diaza-8-thianonane [3,2-NNS(Me)]} have been prepared and characterized by means of elementary analysis, i.r. and electronic spectroscopy. All 1 : 1 complexes containing polyanions (NO−3, OAc−, ClO−4) are five-coordinated species with the meridionally arranged thiadiamine acting as a tridentate. The remaining coordination positions are occupied by an asymmetric bidentate nitrate or acetate group. In contrast, in the 1 : 2 complexes, the thiadiamines are incompletely coordinated leaving one or even two sulphur donors free. These free sulphide-groups readily coordinate with the Ag(I) ions to form mixed-metal AgCuL2Z3-compounds. 相似文献
18.
Tadeusz Biedron Ryszard Szymanski Przemyslaw Kubisa Stanislaw Penczek 《Macromolecular Symposia》1990,32(1):155-168
Polymerization of cyclic ethers by activated monomer mechanism involves consecutive additions of protonated monomer molecules to the growing macromolecules fitted with hydroxyl groups at their ends. For oxirane itself and symmetrically substituted oxiranes there is only one kind of hydroxyl groups and one, unique way of ring-opening. Unsymmetrically substituted oxiranes provide however two sites of attack and two different hydroxyls, resulting from these ring-openings. Kinetics of polymerization of epichlorohydrin (chloromethyloxirane) has been studied and all four rate constants determined, namely rate constants of the primary and secondary alcoholate chain ends with a protonated monomer, opening in result of the attack on substituted or unsubstituted carbon atom. These rate constants are (in mol−1·1·s−1 at 25°C, in CH2Cl2 solvent): k11 = 0.055, k12 = = 0.41, k22 = 0.135, and k21 = 0.0011 (e.g. k12 is the rate of reaction of the primary alcohol producing the secondary alcohol). Thus, polymerization proceeds almost exclusively on the secondary alcoholate groups, reproducing themselves (k22). 相似文献
19.
Julian Teichmann Chantal Kunkel Isabelle Georg Dr. Maximilian Moxter Tobias Santowski Dr. Michael Bolte Dr. Hans-Wolfram Lerner Dr. Stefan Bade Prof. Dr. Matthias Wagner 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(11):2740-2744
Trichlorosilylated tetrelides [(Cl3Si)3E]− have been prepared by adding 1 equiv of a soluble Cl− salt to (Cl3Si)4Si (E=Si) or 4 Si2Cl6/GeCl4 (E=Ge). To assess their donor qualities, the anions [(Cl3Si)3E]− (E=C, Si, Ge) have been treated with BCl3, AlCl3, and GaCl3. Both BCl3 and GaCl3 give 1:1 adducts with the anionic centers. AlCl3 leads to Cl− abstraction from [(Cl3Si)3E]− with formation of (Cl3Si)4E (E=Si or Ge). (Cl3Si)4Ge is cleanly converted to the perhydrogenated (H3Si)4Ge by use of Li[AlH4]. Another case of Cl− abstraction was observed for [(Cl3Si)3Ge ⋅ GaCl3]−, which reacts with GaCl3 to afford the neutral dimer [(Cl3Si)3Ge−GaCl2]2. 相似文献
20.
Following earlier suggestions the values for the rate coefficient of chain termination kt in the bulk polymerization of styrene at 25°C were formally calculated (a) from the second moment of the chainlength distribution (CLD) and (b) from the rate equation for laser-initiated pseudostationary polymerization (both expressions originally derived for chain-length independent termination) by inserting the appropriate experimental data including the rate constant of chain propagation kp. These values were treated as average values, k and k , respectively. They exhibited good mutual agreement, even the predicted gradation (k < k by about 20%) was recovered. The log-log plot of kt vs. the number-average degree of polymerization of the chains at the moment of their termination yielded exponents b of 0.16–0.18 in the power-law kt = A · Pn −b, A ranging from 2.3 × 108 to 2.7 × 108 L · mol−1 · s−1. These data are only slightly affected if termination is not assumed to occur by recombination only and a small contribution of disproportionation is allowed for. 相似文献