Hexaquo complexes

Figure 10. Comparison of isotopic fractionations determined between Fe(II)aq and Fe carbonates relative to mole fraction of Fe from predictions based on spectroscopic data (Polyakov and Mineev 2000 Schauble et al. 2001), natural samples (Johnson et al. 2003), DIR (Johnson et al. 2004a), and abiotic formation of siderite under equilibrium conditions (Wiesli et al. 2004). Fe(II)aq exists as the hexaquo complex in the study of Wiesli et al. (2004) hexaquo Fe(II) is assumed for the other studies. Total cations normalized to unity, so that end-member siderite is plotted at Xpe = 1.0. Error bars shown reflect reported uncertainties analytical errors for data reported by Johnson et al. (2004a) and Wiesli et al. (2004) are smaller than the size of the symbol. Fractionations measured on bulk carbonate produced by DIR are interpreted to reflect kinetic isotope fractionations, whereas those estimated from partial dissolutions are interpreted to lie closer to those of equilibrium values because they reflect the outer layers of the crystals. Also shown are data for a Ca-bearing DIR experiment, where the bulk solid has a composition of q)proximately Cao.i5Feo.85C03, high-Ca and low-Ca refer to the range measured during partial dissolution studies (Johnson et al. 2004a). Adapted from Johnson et al. (2004a).

Their conclusion is that in the hydrated Cu Y zeolite the copper ions are present mainly as the hexaquo complexes. Spectra reported by Holmes and McClure (19) for six-coordinated Cu in the CuS0 5H20 lattice are also very similar, although two of the ligands are sulfate oxygens and not water molecules. The near infrared band has been resolved into 10500 cm-, 13000 cm-, and 14500 cm- components with a total half-width of 5500 cm-. The hydrated Cu Y bands in Fig. 5 show components at 11200 cm-, ... 

Knudsen, J.E. Mossbauer spectroscopic studies of ferric hexaquo complex in amorphous frozen solutions at weak applied magnetic fields. J. Phys. Chem. Solids 1980, 41(6), 545-550. 

The Effect of Adsorbed Molecules on the Spectrum of the Cu Cations in Zeolites. Figure 5 shows the change in the spectrum corresponding to the transitions between d-electron levels of Cu during dehydration of the zeolite. The spectrum of completely hydrated zeolite revealed a broad absorption band with a maximum at 12,100 cm" Thermal treatment of the zeolite at 100 °C resulted in the appearance of a new absorption band at approximately 15,500 cm" After vacuum treatment at high temperatures, there appeared in the spectrum an absorption band at 11,200 cm" The position of the absorption band due to Cu " in the spectrum of completely hydrated zeolite is close to that of the [Cu(H20)e] complex (12,600 cm" ) (2). This indicates that Cu " enters the hydrated zeolite structure as an octahedral hexaquo-complex. The same conclusion has been reached by other investigators 4, 18, 20) on the basis of e.s.r. spectroscopic measurements of the Cu " cations in completely hydrated zeolites. 

The spectrum of the hydrated Co (II) A sieve after ion exchange was identical with that of the hexaquo-complexes of divalent cobalt, which is a situation completely analogous to that in the Ni(II)A sieves (4). 

Remarkably, one of the simplest conceivable H2 complexes, [Ru(H20)s(H2)]2+, can be formed by displacement of an aquo ligand from the hexaquo complex by pressurized H2.14 It seems astonishing that interaction of a bonding electron pair could be on a par with that for a lone pair. What is unique about the three-center bonding in M-H2 and other bond complexes that stabilizes them and sets them apart from species such as carbocations is BD, i.e., donation of electrons from a filled metal d orbital to the a orbital of the H-H bond, similar to metal donation to n orbitals in the Dewar-Chatt-Duncanson model for olefin coordination. 

As an example, we consider the equilibrium in aqueous solution between iron hexaquo complex cations and thiocyanate anions on the one hand and the blood red iron thiocyanate complex on the other which can be described in the following simplified manner ... 

According to Beck et al [Ra 76], this catalytic effect can be explained in that the carbonato or nitrito complex of chromium is formed without splitting of the inert Cr—O bond in the hexaquo complex (in effect, in an oxygen-exchange reaction). 

Coprecipitation takes place by condensation of hexaquo complexes in solution, forming brucite-like layers where both cations are homogeneously distributed, and with the anions (and water molecules) hosted between the layers. Observation of recently precipitated particles and powder X-ray diffraction (PXRD) studies show that formation of the layers and of the interlayer domains is immediate, without previous delamination of the brucite-like layers [54]. 

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