Nouvelles recherches sur l'éxistence de cations complexes de structure définie dans les solutions d'électrolytes

Cabaço

J. Phys.: Condens. Matter

et al. 2002

Concentrated aqueous solutions of salts constituted by divalent ions combined with monovalent counter-ions were investigated by x-ray diffraction and Raman spectroscopy at room temperature. The salts studied were strontium, barium, and magnesium chlorides and bromides, and lithium and caesium sulphates. For many of these solutions, intensity maxima were detected in their x-ray diffraction patterns close to 0.6–1 Å−1. Interpretation of these maxima, pre-peaks, is discussed, taking into account the results of previous investigations of the authors on concentrated aqueous solutions of trivalent cations. In these solutions the pre-peaks appear to be narrower and much more intense. In the ionic solutions studied here, a slight contrast between values of the scattering power of two spatial domains is suggested as the origin of the observed pre-peak. One of these comes from an accumulation of scattering power around the ion with the higher electric charge, locally organized into a subtle close packing; the other comes from the holes of this structure. Molecular models of the structure of these electrolytes are used to demonstrate the plausibility of this interpretation.

Section: Both (See Table 2(a)supporting

confidence: 76%

Intermediate-range order in aqueous solutions of salts constituted of divalent ions combined with monovalent counter-ions

Cabaço

J. Phys.: Condens. Matter

et al. 2002

“…The absorption band at 337 cm"1 in this spectrum is assigned to the v(Zn-0) vibration. This is in good agreement with the observations of da Silveira et al 48 and of our group.11…”

Section: (1)supporting

confidence: 94%

Pentacoordinate zinc complexes of imidazole nitrogen donors as structural models for the active site in enzymes: preparation and crystal structures of (.mu.-2,2'-biimidazole)tetrakis(2,2'-biimidazole)dizinc(II) tetraperchlorate trihydrate and bis(2,2'-biimidazole)(formato)zinc(II) perchlorate

Kirchner¹,

Krebs²

1987

Inorg. Chem.

291ChemInform Abstract The reaction of Zn perchlorate with the biimidazole ligand in water gives (I), crystallizing in the space group P212121 with Z=4. (II) is obtained from a hot solution (dioxane/water 1:1) containing Zn perchlorate, the ligand and formic acid, and crystallizes in the space group P21/c with Z=4. In both complexes Zn prefers a stoichiometric composition that enables five-coordination of the metal.Molecular units in (I) and (II) are linked by three-dimensional hydrogen bond networks. The metal environments of the complexes are relevant for the discussion of the active sites in zinc enzymes such as carboxypeptidase A; the importance of trigonal-bipyramidal five-coordinate intermediates for the catalytic action of Zn in enzymes is discussed (no yields given).

“…For example, a wide scattering of n 1 Be-O frequency data between 520 and 539 cm -1 were reported. 19,20,22,23 For this reason, we measured well characterized beryllium salt solutions (Be(ClO 4 ) 2 , BeCl 2 , Be(NO 3 ) 2 and BeSO 4 ) over a broad concentration range by Raman and IR spectroscopy. Specifically, we were interested in the vibrational characterization of the tetraaqua beryllium ion and its ion pairs with anions.…”

Section: Introductionmentioning

confidence: 99%

Hydration of beryllium(ii) in aqueous solutions of common inorganic salts. A combined vibrational spectroscopic and ab initio molecular orbital study

et al. 2009

Raman spectra of aqueous beryllium perchlorate, chloride, nitrate, and sulfate solutions have been measured over a broad concentration (0.098-4.950 mol L(-1)) range. The Raman spectroscopic data suggest that the tetra-aqua beryllium(II) ion is thermodynamically stable in perchlorate, chloride, and nitrate solutions over the concentration range measured. No inner-sphere complexes in these solutions could be detected spectroscopically except in very concentrated beryllium nitrate solutions. Beryllium sulfate solutions however, show a different picture, namely the existence of a thermodynamically stable beryllium sulfato complex most likely monodentate even at very low concentrations. At very high beryllium sulfate concentrations, a small quantity of a bidentate sulfato complex was found. With a temperature increase, the sulfato complex formation increases and this demonstrates the entropically driven sulfato complex formation. Furthermore, with increased temperature the hydrolysis increases, measured by the formation of hydrogen sulfate. Ab initio geometry optimizations and frequency calculations are reported for beryllium-water clusters with only inner sphere waters, clusters with an inner sphere and an incomplete second hydration, and clusters with a higher number of waters in the second hydration sphere. The cluster, [Be(OH2)(12)(2+)] (Be[4 + 8]) with 4 water molecules in the first sphere and 8 water molecules in the second sphere gave sufficiently realistic frequencies for BeO4 skeleton in comparison to the experimental ones. However, the cluster, [Be(OH2)(18)(2+)] (Be[6 + 12]) with 6 water molecules in the inner sphere and 12 water molecules in the outer sphere on an energy minimum gave unrealistically low BeO4 frequencies. This fact demonstrates that a six-fold coordination of Be2+ can be ruled out.