Hexaaquo complexes

Osmium(II) forms no hexaaquo complex and [Os(NH3)g] +, which may possibly be present in potassium/liquid NH3 solutions, is also unstable. [Os(NH3)5N2] and other dinitrogen complexes are known but only ligands with good 7r-acceptor properties, such as CN, bipy, phen, phosphines and arsines, really stabilize Os , and these form complexes similar to their Ru analogues. 

I6A related phenomenon has been observed in (octahedral) metal complexes, where rates of exchange at the metal centres of hexaaquo-complexes of Ru and Fe(II) and Fe(III) are faster for longer M-OH2 distances (Bernard et al., 1982). Similarly, exchange is faster for the longer bonds at the Ni(II) centres of triamine/aquo-complexes when more nitrogen ligands are present (Schwarzenbach et al., 1983). 

The hexaaquo complex of Fe is only dominant under very acidic conditions. At more neutral pH ranges, various hydroxy-aquo complexes will predominate. We can readily calculate gas phase proton affinities of the different hydroxy-aquo complexes but these will give us only a crude picture of the complex stabilities in aqueous solution when we fail to include the outer sphere solvation. Li et al. (1996) calculated hydrolysis constants but their model of solvation gave poor agreement with experiment. Martin et al. (1998), however, have applied a dielectric continuum model to simulate aqueous solvation of the Fe aquo complex (Fe(H20)6 ) and its hydrolysis products... 

Fe(H20)5(0H), Fe(H20)4(0H)" and Fe(H20)3(0H)2. Their model gave very good results the hydration energy of Fe to give the hexaaquo complex Fe(H20)e was -4277 kJ/mol (experimental values -4349 to -4273 kJ/mol). The predicted free energy change for the first hydrolysis reaction... 

The Ki are the successive equilibrium constants. It shonld be noted that Al(III) in water is best represented as the hexaaquo complex A1(H20) +, and all the species in Equations 9.1 through 9.4 have been adjnsted accordingly (e.g., Eqnation 9.1 — A1(H20)5(0H) +-b H+) however, for simplicity, these... 

The fact that iron(ll) was clearly detected by Mossbauer spectroscopy gives a direct evidence for the iron uptake mechanism of strategy I. As the time of the iron treatment increased, the reductive capacity was decreasing because of the increased amount of iron already taken up by the root [73]. According to the Mossbauer parameters of the Fe(ll), one can see that it formed a hexaaquo complex [52] that might be the primary hydrated product of the ferric chelate reductase enzyme, accumulated in the apoplast and not attached to any of the cell wall components. At the same time, the increase in the Fe(lll)A component, representing iron both attached to the apoplast and taken up inside the cell, could be observed. The ferritin-like component (denoted by Fe(lll)B) was absolutely not detectable, which means this duration of... 

The spectra of Ni(II) and Cr(III) complexes of these ligands are very similar to the spectra of the corresponding hexaaquo complexes except for the wave lengths of ... 

---