Number of water molecules coordinated

For instance, Lowe et al. showed that the relaxivity of a series of macro-cyclic Gd(III) complexes bearing (3-arylsulfonamide groups is markedly pH-dependent (Fig. 15) on passing from about 8 s mM at pH < 4 to ca. 2.2 s mM at pH > 8 in one selected case (Chart 12, ligand 2) (130). It has been demonstrated that the observed decrease (about 4-fold) of ri is the result of a switch in the number of water molecules coordinated to the Gd(III) ion from 2 (at low pH values) to 0 (at basic pHs). This corresponds to a change in the coordination ability of the p-arylsulfonamide arm that binds the metal ion only when it is in the deprotonated form (Fig. 15). 

The results show that the metal ion binding ability increases with increasing size of the alkyl group on the copolymer chains. The number of water molecules coordinated to the Tb(III) in polycarboxylates such as PAA and MA-E was found to be 3.5. On the other hand in the monomeric carboxylates such as propionate and 2,3-dimethylsuccinate this number was 5.8 to 6.0 41). 

A good understanding of the way or paths of deexcitation of lanthanide ion excited states in complexes with simple ligands like water can throw light on the coordination sphere of the lanthanide ion. Techniques based on this principle have been used in the determination of the number of water molecules coordinated to the lanthanide ion [121]. 

For the water-propanediol system, the number of water molecules coordinated to chromium (III) in each species cannot be taken as six minus the number of coordinated molecules of glycol. This quantity has been determined by considering the dependence of the species concentration upon the solvent composition. The extents of formation of the two species containing one glycol molecule can be expected to show... 

So = organic solvent component w = number of water molecules coordinated to metal n = number of organic solvent molecules coordinated to metal (g) = gas... 

The interatomic distances and the hydration number of Li" " were determined by a least-squares fitting procedure applied to the r -weighed GLi(r). Characteristic Li-0 and Li-D distances are 2.02 0.05 A and 2.61 0.05 A respectively, independent of temperature. The number of water molecules coordinated to Li is 4 1 at the temperatures down to 213 K, but decreases to 3 1 at 173 K when the second hydration shell is established. 

With the exception of the dien complex there is a fair correlation between the number of water molecules coordinated to nickel and the rate constant. Such a statistical factor would be reasonable if the inner sphere can rotate rather freely relative to an ammonia molecule outside the inner sphere. 

An increase in the number of water molecules coordinated to cobalt(III) is accompanied by an increase in the first add dissodation constant and this is attributed to proton repulsion by clustering of the proton-donor groups. In such cases, the complex geometry may be important since a cis-arrangement of X-H ligands in an octahedral complex may give rise to more effective proton repulsion than a fr/ms-arrangement (vide infra). 

Hoirocks and co-workers took advantage of this and derived an empirical equation, which allows the determination of the number of water molecules coordinated to Eu(Ill) and Tb(lII) by comparing emission lifetimes in water and deuterated water. This will be further discussed in Chapter 2 [76,77]. 

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