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1.
2.
On alkalinization of solutions of the chromiun(III)-aquo ion simple deprotonation takes place first. The degree of hydroxylation n OH however can be brought up to only about 1 (the exact value depending on the total concentration [Cr]t), before the uncharged complex Cr(OH)3(OH2)3 is precipitated. The structure of the very sparingly soluble complex (solubility ~10?7M ) is held together by hydrogen bonds of type I between the molecules, so that its formula may be written as Cr(OH)2H6/2-lattice. The formation of the well ordered structure is extremely fast. On aging, the metallic centers become connected by μ-hydroxo-bridges (type II) and the substances become amorphous and very insoluble. The dinuclear (H2O)4Cr(OH)2Cr(OH2)44+ behaves similar on deprotonation. Concerning the various equilibria constants see Table 1. 相似文献
3.
A new terdentate ligand bis-(diphenylphosphinoethyl)-sulfide (PSP) and a new quadridentate ligand 1, 2-bis-(diphenylphosphinoethylthio)-ethane (PSSP) (structures see page 1928) have been synthesized and their NiII- and PdII-complexes have been studied. There is good evidence that the metal has coordination number five in some of these complexes containing halogen (Cl, Br, J). 相似文献
4.
The complex formation of silver(I) has been studied with the anions of simple mercaptans RSH which have been rendered soluble by replacing some H in the substituent R by OH. All equilibria constants refer to a solvent of ionic strength μ = 0,1 and 20°C. Monothioglycol HO? CH2? CH2? SH (pK = 9.48) forms an amorphous insoluble mercaptide {AgSR} (s), ionic product [Ag+] [SR?] = 10?19.7. The solution in equilibrium with the solid contains the molecule AgSR at a constant concentration of 10?6.7 M which furnishes the formation constant of the 1:1-complex: K1 = 1013. 0. The solid is soluble in excess of mercaptide (AgSR+SR? → Ag(SR)2?: K2 = 104. 8) as well as in an excess of silver ion (AgSR + Ag+ → Ag2SR+K ≈? 106). With the bulky monothiopentaerythrite (HO? CH2? )3C? CH2? SH (pK = 9.89) no precipitation occurs with silver when the mercaptan concentration is below 10?3. 2M. A single polynuclear Ag10(SR)9+ (β10.9 = 10175) is formed in acidic solutions which breaks up with the formation of Ag2SR+ (β2.1 = 1019.0) when an excess of silver ion is added. Below the mononuclear wall ([RS]total < 10?6) Ag2SR+ is formed via the mononuclear AgSR (K1 = 1013). At higher mercaptan concentrations ([RS]tot > 10?3.2) an amorphous precipitate is formed which has almost the same solubility product as silver thioglycolate ([Ag+] [SR?] = 10?19.1). Apparently silver(I) forms with mercaptans always the complexes Ag2SR+, AgSR and Ag(SR)2?. Above the mononuclear wall, these species condense to chain-like polynuclears which are cations Ag(SRAg)n+ in presence of an excess of Ag+, and anions SR (AgSR)n? when the concentration [RS?] is larger than [Ag+]. Usually n becomes rapidly very large as soon as the condensation starts (n → ∞: precipitate). The decanuclear Ag(SRAg)9+ formed with thiopentaerythrit is somewhat more stable than the shorter chains (n < 9) and larger chains (n > 9), because it can tangle up to a ball by coordination of bridging mercapto-sulfur to the terminal silver ions (figure 12, page 2179). This ball seems to be further stabilized by hydrogen bonds between the many alcoholic OH groups of the substituent R = (HO? CH2)3C? CH2? . The stability of the bonds Ag? S, however, is little influenced by the substituent R which carries the mercaptide sulfure. 相似文献
5.
Gerold Wagner 《Discrete and Computational Geometry》1993,9(1):111-129
We use quadrature formulas with equal weights in order to constructN point sets on spheres ind-space (d 3) which are almost optimal with respect to a discrepancy concept, based on distance functions (potentials) and distance functionals (energies). By combining this approach with the probabilistic method, we obtain almost best possible approximations of balls by zonotopes, generated byN segments of equal length.Editors' note: We learned with sadness of Gerold Wagner's untimely death as a result of an avalanche in the Alps shortly after the submission of this paper. When one of the referees, Joram Lindenstrauss, suggested that Wagner's results might be extended to dimensions >6, we invited Professor Lindenstrauss to submit a paper containing that extension which we would publish alongside the Wagner paper. The result is the paper by Bourgain and Lindenstrauss that follows the present one. 相似文献
6.
The structure of GdPS is orthorhombic, space group Pmnb; a = 5.3620(5), b = 5.4079(6), c = 16.742(2)Å, Z = 8. It is a distorted derivative of the tetragonal PbFCl structure (a0, c0) with . The distortions are due to the formation of phosphorus chains. This structure type is found also in other rare-earth sulfopolyphosphides, e.g., with Ln = La···Sm, Tb···Tm, Y. 相似文献
7.
The two hexamines (H2N? CH2? CH2? )2N? (CH2)n? N(? CH2? CH2? NH2)2, «penten» (n = 2) and «ptetraen» (n=3) have been investigated as chelating agents for COIII (preparative Study) and some of the divalent metal ions (potentiometric and calorimetric studies). Both amines function as sexadentate ligands for CoIII, CoII and NiII, but one of the terminal aminogroups is much easier detached from the metal in case of M (penten)v+ than in case of M(ptetraen)v+, thus revealing more strain in the fivemembered chelate rings of the girdle plane of the «penten» complexes. On the other hand, the sixmembered chelate ring in M(ptetraen)v+ is more strained than the five-membered ring comprising the tertiary nitrogen atoms of M(penten)v+ CuII and ZnII coordinate with both ligands only 5 of the 6 basic nitrogen atoms present. Both hexaamines function as sexadentates again with MnII, but the metal is coordinated with a molecule of water in addition to the 6 nitrogen atoms in the «penten» complex in contrast to the «ptetraen» complex. The thermodynamic functions for the protonation of the hexamines and for the addition of metal ions in aqueous solution are understood in almost every detail. The dielectric shielding of the charges of the reactants exerted by the solvent has to be taken into account; it is reduced by electrostriction as well as by an increase in temperature. It is shown that the approach of charges of equal sign often is an exothermic process. 相似文献
8.
Luigi Fabbrizzi Piero Paoletti Markus C. Zobrist Gerold Schwarzenbach 《Helvetica chimica acta》1973,56(2):670-680
The thermodynamic functions of the proton transfer H2tn2++tn → 2 Htn+ (tn = 1,3-diaminopropane) have been determined in aqueous solutions containing different amounts of KCl (0.05 ? μ ? 3.01). The free energy (?ΔG) of the process decreases, whereas the enthalpy (-ΔH) increases with μ. There is reason to believe that the reaction is entirely controlled by the Coulomb forces between the two protonic charges. The electrostatic energy involved can be described in terms of a model incorporating an effective dielectric constant εe, such that δεe/δμ and δ2εe/δμδT are both positive. The polarisation of pure water is produced by orientation of hydrogen-bonded dipole molecules H2O, whereas the electrolyte solution is polarised in addition by dislocation of the ions K+ and Cl?. Our results demonstrate that the former type of polarisation is much more temperature dependent than the latter. 相似文献
9.
The reaction of Be · aq2+ with OH? leeds not only to loss of protons by the metalaquo ion but also to structural changes in the solvation sphere. These can be studied by following the pH variations during the first decisecond after mixing the solutions of metal salt and alkali hydroxide. The equilibrium Be2+ ? BeOH+ is reached within 5 milliseconds if acid free Beryllium solutions are used. If the metal solution is strongly acidic, however, the establishment of the equilibrium needs more time because of the slowness of the process H+ + BeOH+ → Be2+ (k ~ 105 M?1, s?1). The extraction of two protons produces in the first instance an unstable Be(OH) species which transforms into the stable isomer Be(OH)2 (solvatation isomerism) in a first-order reaction of half-life of 7 ms. This isomerisation causes almost complete disappearance of BeOH+ from the equilibrium Be2+ ? BeOH+ ? Be(OH)2. (KAKIHANA & SILLEN state that the relaxed solutions contain only Be2+, Be(OH)2, Be3(OH) and some Be2OH3+.) The formation of the polynuclear species Be3(OH) needs about 30 seconds to go to completion. 相似文献
10.
Purification of astilbin and isoastilbin in the extract of smilax glabra rhizome by high-speed counter-current chromatography 总被引:2,自引:0,他引:2
Purification of astilbin from the rhizome extract of Smilax glabra was conducted using a high-speed counter-current chromatograph equipped with a 700 mL column. In a single operation, 1.5 g of crude sample was separated to yield 105 mg of component astilbin and 48 mg of isoastilbin while the upper phase of the two-phase solvent system composed of n-hexane-n-butanol-water (1:1:2, v/v/v) was used for stationary phase. The chemical structures of the two flavonoid glycosides were confirmed by electrospray ionization ion trap multiple mass spectrometry and nuclear magnetic resonance experiments. 相似文献