Bond distances aquo complexes

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 values of the radii of the aquo complexes are assumed to be 132 pm larger than the M-0 bond lengths to account for the contribution of the water molecules to the overall radius. The distance factor in equation (7.8.26) is... 

The comparison of the C-Co distances determined by EXAFS and X-ray crystallography of the Costa model (R = CH2CF3, CH2COOMe) has been made. By EXAFS, it was found that the Co-C bond distance increased with the decrease in the R cr-donating ability, in marked contrast to the results obtained with the crystallographic data of the aquo complexes (R = Me, Et, CH2Ph, f-Pr). Randaccio< /<7/. thus proposed that the EXAFS conclusions should be refuted. 

Crystals of uranyl perchlorate, U02(C10[13093-00-0] have been obtained with six and seven hydration water molecules. The uranyl ion is coordinated with five water molecules (4) in the equatorial plane with a U—O(aquo) distance of 245 nm (2.45 E). The perchlorate anion does not complex the uranyl center. The unit cells contain two [0104] and one or two molecules of hydration water held together by hydrogen bonding (164). 

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